Conference 7.286::home_work

    Is anyone familiar with what happened to all the companies who use
    to sell active solar systems after the energy tax credits expired?
    
    Does anyone still buy these things given the price of gas and oil
    today?
    
    Did these companies lower their prices since tax credits were no
    longer available?
    
    Any of you HOME_WORKers have any stories regarding the purchase/use
    of active solar (hot water) systems?
    
    -al

    In a word, the answer to your question is "YES".
    
    Solar powered systems have never been economically competitive in
    New England provided you lived in an area with easy access to other
    power sources. After fixed costs for installation (less tax credits
    while they were applicable) you wind up with a system that will lower
    the marketability of your property -- and consequently the price.
    Further, the systems have a questionable level of reliability and,
    unless you take the responsibility for maintaining the thing, you
    have a good chance of buying from a contractor who will no longer
    be there when you need them to fix the system.
    
    It's really too bad. We ought to decrease our reliance on fossil
    fuels (including biomass - wood, peat, etc.). But it doesn't make
    any financial sense today. 

    Well, wood, etc., aren't quite in the same boat with fossil fuels,
    being at least to some degree renewable as used if we plan properly.
    
    Nor are all solar installations created (or not created) equal.
    
    It still makes sense to combine passive solar collection with the
    aesthetics of a nice view when you happen to have one (and a clear
    shot to the South), and this at least relieves some of the heating
    burden at no cost (or more of the burden with little additional
    cost if you make other adjustments to increase its effectiveness).
    
    Even in partly cloudy New England, a South-facing window with no
    provision for night-time insulation is a net energy gainer if its
    R value is over about 2 (the current "heat mirror", etc., double
    pane variants run R3 to R4+).  The only thing to watch out for is
    having too much glazing area:  if you over-heat, you'll have to
    throw some away in the afternoons, decreasing the overall efficiency
    (that's where properly distributed "thermal mass" comes in...).
    
    And a Trombe wall can make sense if you can slide in an insulating
    panel between the glass and the wall during the off-hours:  collection
    plus mass in one fell swoop.
    
    Another variant is similar to the system developed by what's-his-name
    in Weston (grand old man of solar design - I think he's got some
    patents and charges modest license fees...):  lots of glass-bottled
    water spread out in the attic, and South-facing roof windows with
    night-time insulating shutters.  Water is the most effective commonly-
    available heat retention compound that exists (over twice as effective
    per unit volume as concrete, around 7 times as effective per unit
    weight, which means that if you cover your attic floor to an average
    of about 40 pounds/square foot with bottled water it's equivalent
    to a concrete slab about two feet thick...):  assuming the roof
    over everything is VERY well insulated (say to R40 or more), you
    get significant amounts of storage, some distribution down through
    the ceilings, and no moving parts save for the insulating shutters;
    then add a few fans and ducts for other distribution needs.
    
    Which brings up the final point:  not all "active" systems are
    created equal, either.  The weak points don't tend to be fans,
    pumps, etc.:  after all, most other systems also rely upon these,
    and offer no relative advantage there.
    
    Where things get messy is areas relating to the quest for efficiency.
    Water is a better collecting/distributing medium than air in this
    respect, but brings with it a host of problems:  collector glazing
    fogging and moisture deterioration if the water flows openly (e.g.,
    Thomason-type corrugated collectors), collector corrosion/deposits
    if it's confined, freezing issues.  Use something else, like Freon,
    and other specialized problems crop up.
    
    But if you stick with direct collection supplemented by some air
    collection and distribution, and design carefully to avoid the major
    inefficiencies that using air as a medium can create, then your
    largely-passive system should over the long haul be significantly
    more maintenance-free than any conventional system other than
    resistance heating (though you'll always need SOME kind of back-up).
    
    It's true, though, that for retro-fits (rather than new designs),
    such largely passive approaches are far more difficult than a neatly-
    packaged active supplement - and in those cases, it's pretty difficult
    to justify the expense and potential headaches.
    
    		- Bill
    

    (Minor brain-fade:  Should have said that water is about THREE times
     as effective in heat storage as an equivalent volume of concrete...)

    I hope that solar isn't dead.  One of the first things I noticed
    about my house when I saw it was that it faced south.  Though the
    two large windows in the south wall do collect a good amount of
    energy, I'd like to consider collecting more.
    
    As for experience... My father has a active solar hot water system
    on hs roof.  I believe it has been there about 5 years.  He has
    replaced the water/anti-freeze mixture once (2 years ago).  It has
    worked perfectly since it was installed.  He gets the largest benefit
    in the summer when it allows him to shutdown his boiler - the sole
    source of hot water becomes the 120 gallon tank in the basement.
    In the cooler months the system is used in an assist mode - the
    potential hot water first get heated by the solar, then goes through
    the boiler before being distributed through the house.  The only
    complaint that I/my father could voice about it is that because
    he chose to have the panels mounted flush with roof (installed 3
    instead of 2 to make up for decreased collection) the snow doesn't
    always slide off, so we occassionally have to get out the ladder
    and broom and sweep them off.
    
    Rich

    I had an active solar hot water system put in last year (two 4 X 10 
    panels, 120 gal. tank), and I've been tickled ever since. This week with
    the cold but clear days I've been getting 165 degree water out of
    the tank. My furnace (backup system) was turned off in April, and
    except for a couple of cloudy stretches, wasn't turned on again
    until late Sept. (used about 15 gals. of oil in that time, compared
    to a full tank in previous summers). 
    
    Cost effective? Even without tax credits it'll be paid for in 7-10
    years. Not a bad return, and then there's the intangibles. Like
    not caring how long the kids (or myself for that matter) are in
    the shower, and doing my part to put the Arabs out of business,
    and a cooler basement in the summer, and ...
    
    DEcreased property value? First time I've ever heard that one. My
    neighborhood is quite upbeat, and has several solar systems on rooves
    (or is it roofs, roofes, etc.). Our values were up about 40% last
    year.
    
    Maintenance? What maintenance? This is an area where not all systems
    are created equal. My neighbor came over last spring and offerred
    me a coupon to have my system cleaned and refilled. I thanked them,
    but then explained that my system used an antifreeze guaranteed
    to last AT LEAST 10 years, with thermodynamic properties better
    than water's. Snow falls right off since they are up at 50 degrees.
    That alignment also lengthens the 'solar season' - it is a little
    less efficient in the summer (when the sun is more direct anyway),
    but more efficient in spring and fall. And it was installed by a
    reputable dealer for a national top-notch solar manufacturer, both
    of which (whom?) will be around for a long time. I like it!

    Re: .-1
    
    What brand did you buy and how much was it?
    
    -al

    The panels and antifreeze are made by Novan, the tank (with built
    in heat exchanger at the BOTTOM of the tank) is stone lined and
    made by Sepco (10-15 year warranty if I remember right). It was put in
    by Advanced Energy Systems in Sterling (1-800-322-3818), and they
    also carry other energy saving goodies. The president of the company
    has several years of solar engineering under his belt, and was very
    helpful and forthright in answering technical questions about different
    approaches. The system cost was about $5500, but I got a grant from
    the State for $1000 to reduce the cost. I'm not sure if the grants
    are available again this year or not, but contact People's Energy
    Resource Cooperative (872-4853) for more info. on the program.

    As a clarification (open mouth before inserting foot), my comments
    claiming solar is dead related only to active solar heating (space
    and water) systems, not passive ones.
    
    On real estate values, all properties have gone up in the NE in
    the past 3 years. A house with large solar panels and an active
    solar heating system (water or space) appeals to a much smaller
    market. Remember, the value of your house is how much you can actually
    get for it when you put it on the market. The smaller the number
    of people to whom active solar systems appeal, the smaller the market
    into which you will sell your house. If, in selling your house,
    you have an unlimited amount of time to sell, you will get just
    as much, maybe more, for a solar heated property than an equivalent
    unequipped house. But in the real world, we rarely have the luxury
    of keeping our houses on the market for an unlimited amount of time.
    And the additional equipment reduces the marketability of a house,
    meaning, unless you get lucky, solar (active) will cost you when
    you sell.
    
    A straight line 7 to 10 year payout is, after you factor in inflation
    and calculate the 'net present value' of the savings, more like
    a 10 to 15 year payout, something into which I wouldn't put my money.
    Different strokes for different folks. My wife would pay dearly
    for a totally self sufficient house but, fortunately, we don't have
    the assets to waste in that fashion.
    
    Passive solar is great! If done right, it increases the marketability
    of your house. Active? That's great too, if you're into trading
    off the costs and risks against the personal satisfaction the system
    might give you. But I don't believe it's economically justified.
    (Repeat those words to me during the next energy crisis...I'll eat
    crow then.)
    

    RE .-1
    
    I don't quite understand your logic.  I have a solar hot water system
    installed when fossil fuels were expensive and tax credits were
    high.  I would think it wouldn't affect a potential buyer anymore
    than, say, if it were gas instead of oil. The solar panels don't
    detract from the appearance of the house any more than skylights
    do, and the system isn't any trouble from a maintenance point of
    view either.
    
    I wouldn't do it again because the economics have changed, but I
    sure don't see how it shrinks the potential buyer population.
    
    Jim
    

    
    Does anyone have information about solar electric installations.
    I have a passive solar house.  It would be a great benifit to make
    my own electricity.
    ed

Solar electric cells are available.  You could probably pay some high-school 
kids $5.00 and hour to pedal-power generators and get your electricity cheaper, 
though.  I have thought that it would be nice to have just enough solar 
electricity to run the solar collectors (by definition, if you have enough heat
to move, you have enough electricity to move it), but you could still buy a 
gasoline generator and enough gas to run it for every power outage for the next 
20 years for what it would cost for the solar cells.

Paul

    Well the base note seems to have disappeared but this has got to
    be the right place for this.
    
    My wife and I just heard a sales pitch for what is actually a heat
    pump using large flat collector panels and freon.  Of course the
    panels are black and designed to heat up in sunshine, but since
    freon boils at -20F they will pick up heat just from the air passing
    by.  One of the claims is that the only thing they spent their
    engineering effort on was the panels, the rest of the system
    (compressor, heat exchanger, thermostats, etc.) is off-the-shelf
    refrigerator technology.
    
    They claim they can heat your whole house with this system with
    only very occaisonal resorts to your old heat generator when the
    weather gets very cold and cloudy (not a likely combination).  I
    don't remember how much heat the system stored if any.
    
    To their credit they did not offer us any microwaves or real simulated
    35mm cameras.  And the sell was not a 'hard sell'.  They offer a
    'different' financing deal where you pay them the savings the system
    gained for you until it is paid off.  The rate was 12% and they
    had some kind of formula for what the savings would be.  The bottom
    line was it wouldn't cost you anything and no money down.
    
    According to the salesman they are new to this part of the country.
    Has anyone heard of this kind of a system?  Had any experience with
    it?  As with anything that sounds too good to be true, it probably
    is.
    
    The name in New Hampshire and Massachusetts is Renewable Energy
    Systems.  It was known formerly in other parts of the country as
    the Lampf (?) System.

    re .2	Hmmmm, interesting algorithm for paying it off, lessee:
    
    	I'll sell you a  "Widget"  for, say $10K.
    
    	I will accept payments equal to whatever it saves you per year.
    
    	I will charge you 12% interest on the outstanding balance, lets
    make it simple and just say 1% per month.  You have to pay me the
    interest regardless of what the energy savings actually are.
    
    	It sort of looks like I would rather you had no energy savings,
    i.e. I'd rather have ~$100 a month from you for ever.
    
    
    	R
    
    PS  I could probably manufacture such a widget real cheap.
    

    FWIW, there is 0% interest loans available in Mass. for renewable
    energy expenses.
    
    RE: Freon solar collectors.
    
    I saw an article on this type of system in Popular Science a number
    of years back when the energy crunch was on. Apparently it had a
    COP in actual use of around 8 which would be quite economical. One
    drawback that I could see would be that, contrary to popular opinion,
    Mass. doesn't really lend itself to a soalr application [not much
    yearly insolation available].
    
    Charlie

    Re:  .3
    
    You are quite right, but they thought of that.  They use what I
    consider a bookeeping trick:  they let you pay off some of the balance
    at the beginning when you 'should' be paying the interest and several
    years down the road when the principal is down some you slow down
    the principal payments and start paying off the 'accrued' (their
    term) interest.
    
    Why don't they just use a payment book like normal creditors?  I
    believe (or guess) that they count on increasing energy costs for
    a substantial part of your savings.  I didn't question closely on
    that because it makes a lot more sense to use a home equity loan
    (about 10% now from DCU) on which the interest is tax deductible.

    I forgot the price:  $8800.  One size fits all.  Three 'mounting'
    options (my term):  roof, rack (like a listing rack), tower (same
    config as a Cray!).
    
    They are supposed to have some sort of electricity generator available
    in 3-4 months.

    re: .4
    
    Mass isn't great for solar, but it isn't all that awful. For about
    $320 a year in backup (propane) I get heat and hot water for my
    2400 square foot house in NH. I have an active solar system - 8
    collectors and 750 gallons of toasty warm water in a tank in the
    basement.
    
    							Trace

    The way I understood how they worked, the system should be sealed,
    so liquid should not leave. The only way I now of separating the
    H from the O2 is by electrolysis. You would need to pressure test
    the system to see if there really is a leak. One possible area that
    wouldn't show up visibly is the heat exchanger within the how water
    heater. The explaination you got doesn't sound right.
    
    Eric

< Note 3074.1 by NSSG::FEINSMITH "I'm the NRA" >

>    One possible area that
>    wouldn't show up visibly is the heat exchanger within the how water
>    heater. The explaination you got doesn't sound right.
    
    Thanks, Eric.
    
    If the system was leaking into the HWH, would I know it ?  ie Would
    the water have the look/taste/feel/smell/color of antifreeze ?  Maybe 
    I just need to keep pumping liquid into the system until all the air gets
    purged from the piping ?  BTW, when I just added some stuff you could put
    your finger on one of the air valves and feel the air coming out.

	Again, thanks.
	
	Any more tips ?
	
	Scott.

    It would depend on how much is being lost and the design of the
    heat exchange. I would expect that you could taste any of the fluid
    if it got into potable water, but you usually don't drink water
    from the hot tap. So if it was leaking, you may not taste it. Also,
    in some part of the country (depending on local code), the exchange
    had to be double isolated, so if the solar side sprung a leak, it
    couldn't get into the potable water. So again, the leak would not
    be obvious.
    
    How much liquid are you actually loosing/unit time? A small leak
    may be able to evaporate without leaving a puddle. The air that
    came out of the bleeder valve when you refilled the system was probably
    normal (being displaced by fluid).
    
    I'm not well enough versed on how to pressure test a solar system,
    but if you could locate a solar contractor, they might be able to
    help you. Good luck.
    
    Eric
    

    I love it -- "the hydrogen and oxygen are separating and leaking out".
    Some day I am going to write a book about all the "explanations" that
    repair people come up with to cover up the fact that they don't have a
    clue about something they are supposed to know about.  'Course some of
    'em do it on purpose -- when I worked in a TV shop my boss used to
    tell people all kinds of things to justify the $20.00 fuses he sold
    'em.  Even when you boil water and turn it into steam, which is a gas,
    it is still H2O.  You can even heat steam up to very high temperatures
    and it still won't come apart.  It takes the heat of a nuclear reaction
    to make compounds come apart.  This isn't the problem you are
    experiencing.
    
    I agree with .? who said that electrolysis is the only way to separate
    H2O into its component elements.  That is not what is happening to you.
    The only reasonable explanation I can think of is that there is a leak
    somewhere, and it is just a matter of locating it.  One thing you said
    is that you could hear the air coming out of a valve when you added
    water.
    
    Do you have to do anything to the valve to allow the air to come out,
    or does it just come out all by itself?  If it just come out by itself,
    what is there to prevent fluid from coming out the same way?  Is it
    perhaps a special valve that allows only air to escape?
    
    if it is a valve that looks like a tire valve and you have to push the
    little stem in the middle to let the air out, then that seems OK.  You
    just push in the stem until fluid instead of air comes out -- that's
    how to bleed air out of the system.
    
    Most solar water systems have some sort of provision for preventing
    overheating in the collectors.  Some of them can drain all the fluid
    out of the collectors when the system has had enough heat and the
    temperature in the collectors exceeds a certain level.  There may be
    other ways to limit collector fluid temp besides drain down.  The
    problem is that a good collector can actually boil the water in it on a
    good hot sunny day when then water heater has had enough and the
    collector water is not circulating any more.  If the collector water
    boils it will probably punch a hole somewhere in the system (at the
    weakest point) because of the sharp increase in pressure.
    
    Another possible cause of forced leakage (from high pressure) could be
    a loss of air cushion in an expansion tank.  Normally the water in any
    such system expands and contracts considerably as it changes
    temperature.  In order for an expansion tank to absorb the changes in
    fluid volume, the tank has to have a lot of air in it to allow the
    water to compress into it without the pressure going up too much.  If
    the air has all leaked out of a pressure tank, or if it has all
    dissolved into the fluid because the pressure tank diaphragm has a leak
    or because there isn't a diaphragm (to separate air from fluid), then
    when the fluid expands it will simply force a leak somewhere because
    the fluid is just not compressible like air is.
    
    Leaking fluid usually leaves some sign of its having been there, even
    if it has evaporated.  There is usually some whiteish or greenish or
    something-ish color stain where the fluid ran down pipes or dripped
    onto the floor or something.  If you can't find any sign of leaking fluid 
    anywhere, then it must be leaking where you can't see it (Murphy says
    this is most likely anyway).
    
    Before taking everything apart, though, I would check for leaks and for
    an airless expansion tank first.  If the expansion tank has a valve on
    it then you can add air using a bicycle pump, otherwise you'll have to
    figure out how to empty all the water out of it.  Then look for leaks
    and fix them.  Actually any such system should incorporate a safety
    pressure release valve that will allow fluid to escape if the pressure
    exceeds a preset limit.  That prevents the tank or collectors from
    blowing up as a result of expansion.  Unless the safety valve is
    defective, leakage there is OK, but means that something else is wrong.
    
    Hope this barrage of random thoughts does some good.

I have and still use a solar hot water system.  The previous owner
installed it (it would not be cost-effective to install it today).

Like yours, mine circulates antifreeze through a heat exchanger with
electric backup.  But we don't use the electric backup in the
winter (when there isn't much sun anyway) since the outlet of the
solar tank can be sent through the tankless on our oil burner.

But to answer your question:  If the pressure drops, you have a leak.

I have had my system recharged twice now (once to maintain the
warranty, once to do some work on the roof).  Never has the pressure
dropped since it has been filled.  It varies because it is hot,
and also because the pump is running.  It usually is at about 25 PSI
when cold.

Another possibility is that your expansion tank is full, and the
expansion of the fluid forces some of it out the pressure relief
valve.  In any case, you should be able to see a visible trace of
a leak, since antifreeze doesn't dry up clean.  My expansion tank has
an air bladder so it can't fill (and can be pressurized with air).

Your system must differ from mine, since it sounds like you can add
more fluid easily.  Mine requires a pump to do that, which I don't
own and have to call the local solar folks to recharge.  I guess I'm
glad I don't have a leak.  Also, I don't have any "air thingies".
There are manual bleeders on the roof (just like for FHW) but they
don't let naything out unless you open them up.

Another (horrible) possibility is a leak in your heat exchanger,
which would put your fluid pressure at the same as your house pressure.
This doesn't sound like the case since you seem to have a monotonic
decrease in pressure.

Good luck... feel free to call if I can be of more help.
          --tom   DTN 223-4694

Well guys, since the writing of the base note (which was the day after
the solar was recharged) the pressure has yet to drop -- which really
begs the question:

Is it possible that the plumber merely seriously underestimated the
amount of fluid to put in initially and the amount of air that needed
to be displaced ?

Also to the previous:

- I do need a pump to recharge - wondering if its worth the $60 bucks
  to buy one.
 
- The air bleeders are automatic and there are some special valves that
  let only the air out -- Haven't looked at the one on the roof but the
  one in the utility room looks like its never leaked fluid.
  
I'm waiting to see if the pressure drops again.  Like the previous replyers,
I didn't install my solar stuff either but since its there, and I get LOTS
of sun all year round, might as well use it.  With an 82 gallon hot water
tank it sure helps.

We'll keep everybody posted...and thanks.
Scott.

    I also have a solar H/W system. I had it recharged last fall due
    to a leak in the exchange collar which I fixed. The system was 
    charged to 35-40 lbs and after a few weeks I noticed the pressure
    starting to drop. I hate getting up on the roof but convinced myself
    to do just that. I discovered (at least for my system) the weak
    link. They run copper tubing up to the roof and used short pieces
    of heavy duty neoprene to mate to the exchanger. Close examination
    revealed that two of four of these unions were leaking ever so
    slightly. I tightened the clamps and the system has been stable
    ever since. I may also invest in a pump as the recharge procedure
    is very simple on my system.
    
    
       bob

>	Anybody out there still using a solar water heater ?
	
I want to be!!!  I have a Sunmaster System (Corning New York).
It worked fine until this past summer when the water heater started
to leak.

I got a local outfit (Walsh Solar) to replace the water heater.
I now have an electric hot water heater.  The pumps aren't sending
water to the solar panel.

Anyone recommend someone "good" that can fix a Sunmaster System?

Gardner, Mass.

    Mathew McDonald at 508 365-4691
    
    My installer out of business and I thought I needed a 'recharge' to
    mine. I dont have  his address with me, but I think he is in Clinton,
    Ma. (I live in Merrimack,NH so he would go to Gardner.)
    He was quick, real reasonable $$$ and came in the evening!!! so I didnt
    have to take time off. Mention my name. He seemed excellant.
    		Regards jack-- Call if you want more details DTN 264-9108

    The house we bought last fall used to be heated with a solar-heated
    water system.  Apparently, everything was repossessed except the
    4 (4 x 8 ?) panels on the roof.  According to the company that removed
    the equipment this system would heat the entire 3-level (2800 ft)
    house all winter except during the coldest days.  The wood stove
    should help keep the house warm then.   The location is the west
    side of Pikes Peak at 8500' which is usually mild and sunny.
    
    The solar company said that they could re-install the original
    equipment for $3000-4000 and I've been told that I could probably
    round up my own used equipment and install it myself for $1500.
    
    This system, if I understand the solar man, uses plain water that
    is pumped up into the panels.  When this is heated it is drained
    into a storage tank that transfers the heat to the hot water/electric
    water lines.  This heated water is pumped through the radiators
    to heat the house.  More water is pumped up to the panels to be heated
    to start another cycle.  When the sun sets the system drains the
    panels and stores the water below to protect it from freezing.
    
    I'd like to install the system myself and save some money as long
    as it was certain that it would be worthwhile.  If I started to look
    for bargain equipment now it could be operating before next winter.
    
    Parts List:
    	electrically controlled water valves
    	electric water pumps
    	water pressure sensors
    	water and air temperators sensors
    	water storage tank--for storing cool system water overnight
    	heat exchanging tank
    	room radiators
    	computer to control system
    	PVC pipe
    
    Could the old-style steam radiators work for heating rooms?
    
    
    I'd like to hear from anyone that has an opinion on solar systems
    of this type or has any knowledge or ideas on this subject.
    
    Thanks, Charlie

    re: .0  No Solarites out there?
    
    How 'bout this question then:
    
    I want to install a duct to run from the ceiling in the
    basement, above the area where the woodstove is and where
    the radiator will be, to the top floor.  It will branch
    off into two for the bedrooms here.  We have a fan which
    measures about 10" that can be mounted inside this duct.
    In the top floor's bathroom I want to run a cold-air
    return duct from the floor back down to the laundry room
    in the basement.  The forced warm air going to the top
    floor should help move the cold air out of the bathroom.
    
    My question is:  Where is the most effective location in
    the duct for the fan--in the basement or in the top floor?
    (Push or pull the warm air?)
    
    PS--This fan has a variable speed POT so can be run very slow.
    
    Charlie

    Given a duct with a fixed intake and exhaust, the location of the fan
    is immaterial (assuming constant cross section). More important would
    be a solid mounting location for noise and vibration concerns and a
    location accessible to control and power wires. - Chris

    
    re: older radiators
    
    	I don't think you should use them. You might have problems with
    corrosion.
    
    re: parts 
    
    	You should contact: 
    
    		Solar Components Corp. in Manchester NH.
    
    		603-668-8186
    
    	They have a very complete line of solar parts.

    re: last 2
    
    Thanks for the input.
    
    BTW, the fan for the warm air duct measures 8" and I found that
    it is mounted in a short "duct" that will press into another
    piece.  A real easy installation--especially if it stays in 
    the basement where it is now.
    
    re: old radiators/corrosion
    
    I hadn't thought of having a problem with corrosion.  This
    system would be a "closed" system so wouldn't normally pollute
    the good water.  Is there a potential problem using old steam
    radiators in this type of system?
    
    Charlie

      I don't heat my house with solar but I do heat our water with it.
    I've got two of the slightly larger than 4x8 panels on my roof. Here
    in New England where the weather is at best not optimal year round for
    SHW. This time of year after several cloudy days one sunny day brings
    and 82 gallon hot water tank up to around 155 degrees. Back to back
    days and the system approaches the 190 degree cutout point. I've hit 
    that point twice. My system has two separate fluids and the heat
    transfer takes place just above the hot water tank..
    
       With your application in Pikes Peak you'd probably be able to heat
    the house and then some. Does the system you plan to rebuild have a
    large storage tank??
    
       Bob

    My dad was visiting and doing the talking to the solar man
    while I was at work and I haven't been able to see the
    equipment yet.  Seems that he told my dad there was an 85
    gallon storage tank.  Maybe this is where the heat exchanging
    takes place.  It is probably the highest $$ part too.  I'm
    hoping that most of this can be found used at low prices.
    
    It sounds like yours puts out good heat even with clouding
    days.  After going home to a cold house (and burning 12
    cords of firewood) last winter we are ready to put this
    system together.
    
    Charlie

    
    re: corrosion
    
    	Corrosion will happen in any system with more than one metal type.
    If you have some copper pipe, and some steel, then there will be some
    corrosion. It might not be quick, but it will be there. (I got this
    from a solar book I read once.)
    
    	There is probably a plenum someplace above the tank, with a 
    large radiator type beast - wait - did you say this was FHA or FHW?
    I remember you said there was a blower in a duct, but you're also
    talking about old radiators. 
    
    	Sounds like you're still making plans. Is it worth going to
    FHA & adding an Air Conditioning System? 
    
    bld
    

    >	Corrosion will happen in any system with more than one metal type.
    >If you have some copper pipe, and some steel, then there will be some
    >corrosion. It might not be quick, but it will be there. (I got this
    >from a solar book I read once.)
    
    The only solar parts that are still installed are the 4 roof panels,
    the 2 copper water lines that run down the roof, and several wires
    that must go to valves and/or temperature sensors on the panels.
    
    I thought that the ol' style steam radiators would be easy to find
    at a bargain price.  Aren't these cast iron?  I don't know if that
    would cause corrosion problems with the copper lines.
    
    
    >	There is probably a plenum someplace above the tank, with a 
    >large radiator type beast - wait - did you say this was FHA or FHW?
    >I remember you said there was a blower in a duct, but you're also
    >talking about old radiators. 
    
    The blower is an 8" fan that is mounted in a short piece of duct
    that must have been designed to slip into an air-duct line.  Now it's
    simply nailed into the basement ceiling, above the wood stove, to
    force warm air into the living room upstairs.  What I want to do
    is install a duct to force warm air up to the 3rd floor and would
    have to move the fan a few feet to do this.
    
    The house uses an electric water heater and has baseboard heat
    will we will never use.  Electricity rates are out of sight in our
    rural area.  Until the solar is re-installed the only heat is from
    the wood stove.
    
    
    >	Sounds like you're still making plans. Is it worth going to
    >FHA & adding an Air Conditioning System? 
    
    >bld
    
    We considered installing propane but decided to try the wood stove
    first.  It is fine so far except that it's an old style that is
    unefficient and the house is cold by the time we get home at night.
    The solar should keep the house warm all day (for free minus any
    maintenance costs) and then the stove can be started during the
    colder nights.
    
    Charlie

   Charlie,

   If you do decide to go with the old steam radiators, there's a
   place in Union Sq., Somerville, MA (I think on Prospect St.)
   that sells them for about $10 (at least the last time I asked).

   -Amy

    Thanks for the pointer Amy.
    
    That's a bargain, especially if they'll deliver free.
    I'm in Colorado.  8*O
    
    Hopefully they'll be easy to find locally.
    
    Charlie

Before you get too excited about space heat with solar I'd recommend 
doing a few calculations first. I know Colorado is real sunny but it also get
 mighty cold in the mountains.

Have you done a heat loss calculation for your building. I'm sure someone else in
this notes file has gone through this in more detail but just quickly:

Exterior surface area of your house(in sq ft) * 1/R values of insulation of 
walls and windows etc. 
6" fiberglass is R19, most double pane windows are R3, 10" celulose(in my Roof)
 is R30.

Take all these loss factors and multiply by the temperature differential inside
 vs outside you'd like to maintain, and that your houses heat loss in BTUs. On
a cold day say -10F and interior of 60F that temperature that's a 70 degree 
differential! 

If your hose is 30'*30' foundation, 20' high with 360' of windows, your heat
 loss on that -10 deg day would be 17,640 btu/hr(ignoring the basement). 

Your 80 gal tank of heat
 storage water would drop 28 degrees in 1 hour of maintaining your house. When
 it drops to 120 even the most efficient radiators stop doing much, so you'll
 get mabe 3 hours of storage there more likely 1 or 2.

Get the manufacturers value for your panels output and compare that to your heat
loss numbers, remember the panels put out only 6 hrs a day or so while the house
loses heat 24 hrs a day. The number 2000 btu/hr sticks in my mind for a typical
flat plate 4*8 panel, but I'm not sure. If it's right your system would be good
for 36,000 btu hrs from a good days sun. That'll heat the place for only 2hrs!

My guess is that you've got a hot water system there, space heat is unlikely
without 10 panels or so.

About those cast iron steam radiators, corrosion is the least of your problems,
their efficiency is terrible, not much surface area. They're ok for steam
because it's over 212F (depends on pressure of course) but your system is water
and would need to operate in the 140-200 degree range. They'll do just about
 nothing at all at that range.

BTW I've had a drain down system myself, the principle is simpler than you
think, no valves on the roof, just a temperature sensor. When the temp in the
 panels is so many degrees above your storage tank, the pump turns on. While
 the pump is running, water keeps flowing to the panels, when the pump stops,
 the water drains down into a reservoir. The trick here is that all the pipes
are tilted so the water just runs down hill to the tank unless the pump pushes
 it up hill. No valves at all!

Good luck!

Roger

  I live in a development in southern NH, some folks have solar hot water (3
panels, 80 or so gal. tank sounds about right). Others have solar heat/hot
water. We have the latter system, including a 750 gal tank in the basement.
We're only heating 1600 sq. ft. and dip into the integrated propane backup
system from time to time during the winter. House is pretty well insulated
(R19 walls, R38 roof with lots of south-facing glass). Granted, you probably get
more sun than we do, but I'd have a really tough time convincing myself you
could heat that size house on the amount of water it takes to fill a couple of
bathtubs.

						Trace

    re: last 2
    
    Thanks for the good info and comments.  I'll have to play with the
    numbers but I think that you might be over-estimating the winters
    here.  Last winter we rarely came home to a house that was colder
    than 60 deg. (and that was about 6-7:00 and dark already)  The only
    heat was a wood stove in the basement that probably quit putting
    out heat by noon and the heat created by the sun during the middle
    of the day.  It's almost always sunny and warm near the south windows.
    So, the solar would only have to add maybe 5-10 deg more heat--until
    the wood stove is fired up at night.
    
    A solar catalog, from a company listed in these notes, arrived yesterday
    that showed 2 water-to-air radiators that were priced $170 and $200.
    Seems that the Btu/hr were around 40k-60k?  They also listed some
    heat exchanger tanks which ran into some money. One was made by
    Ford that was a 120gal tank which was stone-lined and could be ordered
    with an electric heating element. I guess that was to replace the
    normal water heater used as a backup.  The price on this was $850.
    There were other heat exchanger units for more money but were only
    about half the size.  The drawings showed that the units for more
    money also had a much larger heat exchanger.  I don't know if that's
    really the case tho.  Another idea is using the wood stove to also
    heat water as a back up.
    
    Charlie 

    
    
    I just don't understand how you could use cast iron radiators 
    designed  for steam heat.  Maybe I'm misunderstanding you.  
    They don't work with hot water, just steam.
    
    -th�r�se
    

    It sounds like the steam radiators wouldn't put out enough
    heat to make them practical.  My idea was to simply run
    hot water through them as you would with a modern radiator.
    I've never used them for heat before so don't have a good
    idea as to how they're made.
    
    I've found that the modern radiators designed for water-to-
    air heat transfer are priced right (<$200 new) and should
    do the job much better.
    
    Charlie
    

    As far as I know, the only difference between a steam radiator
    and a hot water radiator is a pipe plug.  The steam radiator
    has one inlet and a steam vent; a hot water radiator has an
    inlet and an outlet and no steam vent.  Various holes are
    plugged or not, as appropriate.  

    Someone mentioned that steam radiators don't have enough surface
    area when used with hot water.

    Re: .17
    I've got 'em in my house...used with hot water...they work fine.
    Now, we're talking about 180-degree water out of the boiler, and
    you probably won't get that with solar, although I suppose it's 
    possible.

    > I've got 'em in my house...used with hot water...they work fine.
    > Now, we're talking about 180-degree water out of the boiler, and
    > you probably won't get that with solar, although I suppose it's 
    > possible.
    
    
    I've been told that the solar *will* put out 180 deg water but
    won't really know until we try.  BTW, 180 deg water isn't that
    far from boiling at our elevation (8500') and trying to get it
    any hotter would probably not be wise.
    
    Maybe the thing to do would be to first set up the system to
    just heat our hot water supply and then hook up 1 radiator to
    see if it can handle the extra heat drain.  A radiator (either
    old steam type or new one) could be located only about 8' from
    the heat exchanger and would be in a central location in the
    basement.  The cost to experiment shouldn't be bad at all.
    
    Charlie

The cast iron radiators will put out some heat of course, but not as good as the 
stuff designed to do it, and especially if you can't do any better than 180F.

The fan driven units probably are the best for extracting lots of heat out of
not so hot water.

You should be careful about mixing heating, sometimes called hydrionic systems,
 with domestic hot water (the stuff you wash with). Pumps, radiators, etc. are
 NOT all acceptable for runing water in which you want to wash clothes in later.
Especially stuff like cast iron radiators, rust you know...

The difference is that hydrionic systems are basically closed loops and
 therefore the oxygen that is initially disolved in your water is purged out and
gotten rid of. If you're running new water through all the time as in a domestic
 hot water system, there will be more of a corrosion problem.

Btw I have one of the FORD 120 gal tanks, it's just fine but heavy, decide where
 you want it and don't plan on moving it!

Heating with the wood stove works well, a small circulator on a controller(from
that catalog) should be hooked to one of the exchangers in the base of the
 ford tank. Just make sure you get a big enough exchanger inside the wood stove,
they have plates which can bolt inside your stove and act as a heat exchanger. I
used a single loop (plumber called it a trombone) and don't get all that much
heat.

I still worry about even a 120 gal tank being enough storage to do the job.

Roger

>You should be careful about mixing heating, sometimes called hydrionic systems,
>with domestic hot water (the stuff you wash with). Pumps, radiators, etc. are
>NOT all acceptable for runing water in which you want to wash clothes in later.
>Especially stuff like cast iron radiators, rust you know...
    
    Oooops, I forgot which pipe was what.  The hot water that runs through
    the heaters would definitely not work in the washer, etc.
    
>I still worry about even a 120 gal tank being enough storage to do the job.

>Roger
    
    What do you use your Ford unit for?  Just for your hot water supply?
    Do you use a backup water heater?  What area do you live in and how
    many collectors do you use?
    
    Charlie
    

    I sort of hate to pop into an old note and throw a peaceful topic
    into activity.... but I couldn't resist.  Earlier in this note a
    bunch of people poo-poohed breaking water into its elemental parts,
    mentioning even as steam it was still water.  True.  And since the
    molecules of water in steam are very very small (I'd have to read
    Gore-Tex propeganda to find out how small), wouldn't steam pass
    out an air bleeder valve fairly easily? A few replies back there
    was some talk about the fluid expanding.... I wouldn't bet the farm
    or anything, but I thought fluids don't have a particularly big
    thermal expansion coefficient.  I know water isn't compressable
    to any real degree.  That's why water pressure is actually created
    by something else; gravity, compressed air, etc, not the compressed
    water trying to expand.  That's what makes hydraulics such a useful
    thing.  
    
    Anyway, it's been my understanding that any air in a solar collector
    is what's expanding, necessitating the expansion tanks.  Ideally
    in an active system you want as little air as possible, as the pumps
    move the liquid, and the liquid carries the heat, and the air is
    a pain.
    
    Eric _who may be all wet... but curious!

        I may be all wet too but here goes anyway :-)))
    
       My solar HW system kept losing it's charge. I'd charge it to
    20 PSI and during really sunny days the pressure would exceed
    40 psi. It turned out that expansion tank had lost it's charge 
    and the expanding water caused leaks to develop at some joints.
    Since recharging the air bladder with 20PSI the water pressure has
    been constant at about 15PSI. 
       My system holds about 5 gallons in the exchanger loop and
    without the air bladder reached 40psi. An automobile radiator
    when it reaches operating temperature is typically 8-12psi almost
    100% water as I believe the pressure caps release most of the air??
    
         Bob

    For those interested in sources of Solar energy supplies
    and services in the New England area, the
    New Hampshire Governor's Energy Office publishes a
    solar directory containing extensive lists of sources
    of materials and services, classified by type of
    materials and services available.
    
    To obtain this catalog call New Hampshire Governor's
    Energy Office at
    271-2711 or (806)-852-3466
    
    Ask for the New Hampshire Solar Directory.  It's
    free.

>   To obtain this catalog call New Hampshire Governor's
    Energy Office at
    271-2711 or (806)-852-3466
                   ^
    
    (806)?  That's Texas!  Did you mean (800)?
    
    -Bob

    Re .1
    Yup, that 806 should have been 800

    I'm in the UK and looking for solar cells which put out 12V DC.
    
    I've checked with a few companies in the US and have been given the name
    of Hoksan (sp?) as probably the most popular (cheap?).  I believe this
    is either Japanese or Singaporean.
    
    Given that cells seem the cheapest in the USA, before I dive in and go
    through the hassles and expense of importing them I'd like to see if
    they're available in Britain.  If anyone can tell me the origin of
    Hoksan (and the spelling) I could perhaps track if there is a British
    importer through the Japanese, Singaporean or whatever Trade Office.
    
    Similarly, the most popular charge controller is the 30 Amp C30A made
    by Trace (again, sp?).  Does anyone know the origin of this company?
    
    Thanks, Richard.

    Also posted in ENERGY_CONSERVATION

    Does anyone have experience with a parabolic dish solar heating system?
    
    I live in Madrid Spain where we have a lot of cheap sun, but expensive
    oil, gas, and electric ultilities.  Therefore to save money and have
    fun with a new project, I want to try the following:
    
    I have a surplus satellite T.V. parabolic dish with horizon to horizon
    motor driven mount.  I am planning to build a sun sensor, chrome plate
    the dish, build a copper tube heat exchanger at the focus point, and
    connect it to a heat exchanger hot water storage tank.
    
    The sun sensor will drive the motor to keep the parabolic dish pointing
    to the sun.  I will need sensors to detent overheating and drive the
    dish off if necessary.  Also sensors will stop the pump on the heat
    exchanger to prevent cooling the storage tank when there is not enough
    heat generated by the sun to have a positive exchange.  It will have to
    be driven over to the east at night to be ready to track the sun in the
    morning.
    
    How does this sound?  Where are the problems?  Will it be efficient
    with a 4 foot chrome plated dish?  Any experience or ideas would be
    appreciated.
    
    Ken

    Re .0:
    
>   Does anyone have experience with a parabolic dish solar heating system?
    
    This certainly looks like an interesting project.  I went the other
    way, flat plates and no moving parts (other than the circulating pump). 
    Overheat protection is built into the collectors (a valve opens to
    allow hot fluid to enter a finned radiator loop).  My system has been
    in operation with no problems for nine years.
    
    The other common variety in this part of the world uses reflectors that
    are parabolic in cross-section to reflect sunlight on a tubular black
    collector.  These don't seem to have aged as well, perhaps in part
    because of hard New England winters.
    
    If you're intent on using you satellite tracking equipment to track the
    sun, don't forget that the sun ISN'T parked over the equator, so you'll
    have to track it North-South in addition to East-West.  Good luck.

    Sounds like a neat project.  But will you be getting enought
    output for the system to "pay for itself"?  
    Something to think about:  The less moving parts, the better.
    Your tracking system sounds like it might get the most out of
    the sun but with all thoes eyes watching, whats the $ figure.
    You might want to set it up using a gear motor to rotate the
    collector to follow the suns path.  Or, have it move a few
    degrees at a time.
    
    If memory is correct.  Somewhere's in the US, there is a power
    station that used banks of fixed mirrors to reflect the suns 
    heat on a series of pipes filled with oil (700' worth), heats 
    water and then runs a steam turbine.
    
    Good luck!
    JD
     

    Isn't there an enormous solar furnace somewhere in the mountains in 
    Spain?  I think I read somewhere that keeping the mirrors clean was the
    biggest chore.
    
    I don't think you need that level of complexity.  My (rented) house is
    fitted with three static flat panels consisting of copper tube soldered
    to flat black backplate (no fins).  This generates more than enough hot
    water for a family of three in the New Hampshire summer.  It also cuts
    down gas consumption in spring and autumn by raising the water
    temperature so that it takes less gas to bring it to a usable
    temperature. This system is requires so little maintenance and
    servicing that I'll probably fit a similar system in the house that I
    have recently purchased. 
    
    
    I have stayed in many houses in Greece that rely totally on solar
    energy for water heating and these were also never short of hot water. 
    They all used static panels - some of which were based on a giveaway
    low-tech design that was created by British Petroleum.  (It used to be
    that you could get the data from BP in Uxbridge,  UK.  but that was a
    few years ago.)  As you have roughly the same climate as Greece, a
    similar system would probably work as well for you.
    
    Regards,
    
    Colin
    
    [By the way, if you do build your own heat collector, you will need a
    sensor to ensure that cool water does not hit the hot collector.  For
    example, if there has been a power cut to the circulating pumps and the
    collector is very hot, the circulating water will be relatively cool.
    The rapid contraction will most likely damage the collector.  In the
    system I use, such an event would cause the coils to strip their
    soldered connection to the collector backplate.]
    
    
    
    
    
    
    

    Thanks for the inputs so far. I am still looking for information on the
    parabolic dish method.
    
    I know that with moving parts it will be more likely to break down but
    I have chosen this for several reasons:
    
    1.  Challenge... I want to try something new that requires some
    engineering, and explore some unknowns.  (I am also thinking about a 
    hot air system to heat the house using beer cans as a collector and
    rocks to store the heat until needed at night.)
    
    2.  Cost...  Sence I already have the satellite dish, it is cheaper to go
    this way.  To crome plate will cost about $200.  The electronic sun
    sensor will cost about $20 plus parts I have in my shop.  The pump and
    storage tank is the same as for a flat panel system.  I already have
    the addition motor to drive the elevation angle.  
    
    Even to build flat solar panels, it will cost more.  Flat radiators
    cost about about $100/sq meter, and the glass, frame, installation,
    support  will cost about another $100/sq meter.  As most systems here
    has about 6 sq meters, the material will cost about $1200 for the
    panels.  To buy factory built panels it will cost about $3000. 
    
    3. Ease... It would take much longer to build the flat panels than to set
    up the dish.  Temperature control is easier to control by pointing the
    dish.
    
    4. Weight & size...  This system can be mounted in a corner on any balcony 
    or on any wall facing south.
    
    5. Other uses...  A larger dish may be able to supply enough energy to 
    heat my swimming pool in the spring & fall, and help heat my home in 
    the winter, in addition to hot water supply.  
    
    
    I have heard a rule of thumb that I would like to confirm.  The sun
    provides about 3 kw of energy per sq. meter of surface perpendicular to
    the sun's rays.  Is that about right? I was hopeing for more. What
    would the efficiency of my system? 
    
    ref .2
    I have also been told that oil would be a better heat transfer agent than
    water.  In addition it would not freeze in winter.  What kind of oil
    is best and safe in case of a leak in the storage tank?
    
    The heat collector at the focus point present a problem in design. 
    Should I try for the maximum temperature leaving this collector by
    restricting flow and placing it at the focus point, or should I try
    for maximum heat transfer with high flow rate and defocusing to spread
    the sun over a larger collector area?  Remember this is a close loop 
    system therefore the effect is accumulating.  Which approch would be the 
    most efficient transfer of heat in both the collector and storage tank
    and/or easier to build?  Should I use a flat coil tube solder on the
    back of black copper sun focus plate, or a round flat container at the
    focus point that the cooling liquid passes through, or a cylinder shape 
    coil of tubing that the sun focus into (like a waveguide)?
    
    ref .1
    I do have an additional motor to track the elevation of the sun, in
    addition to the motor to track the hour angle.
    
    ref .3
    I think that the large solar furnace is in southern France.
    I plan to have a over heat sensor on the collector to drive the dish 
    off the sun if it is too hot.
    
    Ken.
    
    

    I strongly suspect that if you focus the parabolic dish on a point,
    you will quickly melt whatever is at that spot.  At the very least,
    I think you're going to have to worry a lot about boiling whatever
    transfer liquid you use.  Getting water up to 180 degrees with a plain
    old flat plate collector is no big deal on a nice sunny day, and
    you're going to multiply that heat by a factor of X, where X is going
    to be pretty big, if you use a parabolic reflector.

    
>    5. Other uses...  A larger dish may be able to supply enough energy to 
>    heat my swimming pool in the spring & fall, and help heat my home in 
>    the winter, in addition to hot water supply.  
 
I have been intrigued by your project.  I wonder if you can aim a focused
sun beam at your pool to heat the water.

I understand (from a trivia book I have that "in 214 B.C., a powerful Roman
force attacked the city of Syracuse, the home of Archimedes, the great
mathemetician and astronomer.  To hold off the Roman legions, the Greek 
inventor devised one ingenious weapon after another.  Among these weapons 
was the catapult, which sent a ton of stones flying as far as 600 feet.

  "But Archimedes' most ingenious contraption was an arrangement of mirrors 
that directed the concentrated rays of the sun on the Roman ships and set 
them ablaze."

Now I do not suggest you use your project as a weapon, but the concept for
focusing the sun's rays is about 2200 years old, according to this trivia
book.

Please report here how your project goes!

    
    	
    
    	Well, I have seen small hand-held parobolic mirror 'cigarette'
    lighters.  I also have heard of something called a parabolic mirror
    furnace that attained VERY high temperatures.  
    
    
    	Try an experiment first by making a small model(lined with Al.
    Foil) and make some Temp measurements.   I wouldn't be suprised that
    if focused to a small point, temperatures in excess of 212 deg F. would
    be easy for a 6-8 ft parabolic mirror.

    re: .6
    
    	Ummm, I hope no one will be swimming in the pool when the sun beam
    is focused on it. Talk about sun burn!  
    
    	BTW I believe Archimedes used many warriors holding polished
    shields. They aimed the sun at the enemy ships and *set them on fire*.
    
    	I think that you will find that the temperature at the focal point of
    even a small parabolic reflector can easily excede a quite a few
    hundred degrees. After all you can light cigarettes with one. (What is
    the combustion point of tobacco, wood or paper?)
    
    	I think that the author of the base note will find that the
    temperature of his focal point will be too hot for practical use.
    Remember it isn't temperature that you are after, it's BTU's of heat. I
    can light a candle and develop higher temperatures than say, a radiator,
    but the radiator will probably heat the room much faster.
    

    Oh yeah I remember hearing another story (possibly a shaggy dog story)
    that occurred in South America.
    
    	It seems that a soccer promoter printed up programs with a
    reflective surface on the back cover. The idea was to use these to
    harass the opposing side by reflecting the sun into the opposing player
    eyes.
    
    	Unfortunately at one point in the game a referee made a bad call.
    Thousands of fans decided at the same instant to reflect the sun on
    him... and he was incinerated!

    �(What is the combustion point of tobacco, wood or paper?)
    
    The temperature at which paper burns is 451�F.

    I mention tobacco because there are some parabolic cigarette lighters on
    the market. I also know from experience that it is possible to use
    focused sunlight through a magnifing lens to ignite paper and wood. If
    I am not mistaken there are even large parabolic reflectors that can
    melt metal.
    
    	Since the principle of a magnifing lens is similar to a parabolic
    reflector the temps generated would be similar. The larger the
    lens/reflector the higher the temperatures at the focal point. 
               

    About 15 years ago I was project manager for  design & development of a
    high concentration (1000x) tracking solar collector system. Although we
    decided not to commercialize it, we built a working system on a rooftop
    in Cambridge, MA. The system comprised a number of mirror stations
    controlled by a central computer, with full instrumentation to monitor
    performance: output was electricity, hot water and hot air (the system
    was in an a-frame which itself was a large collector.) Each mirror
    station included a Cassegrainian mirror set, tracking motors, solar
    cell mounted on a heat exchanger, pedestal, plumbing and wiring. Each
    solar cell had four independent segments that were used for tracking
    correction as well as generation: a system sun sensor was used for overall
    tracking decisions.
    
    Concentrating, tracking systems are used primarily for generating high
    temperatures and high light intensities. They offer little advantage
    for domestic hot water or hot air.  Remember that the amount of energy
    impinging per unit area is the same regardless of the type of
    collector. Although the tracking reduces cosine losses, the higher
    temperatures, poorer heat transfer and tracking energy loss means that
    they will rarely be more efficient than flat plate or passive systems if
    the primary goal is domestic heat.  A simple parabolic collector will
    have additional losses from the shadow of the plumbing and heat
    exchanger. The biggest improvement from tracking  comes early and late
    in the day, when insolation is too low to matter. Your idea of using a
    small dish to replace a large fixed system is a fantasy--you will need
    a similar collection area either way.
    
    We monitored insolation for two years. The textbook value is 1kw/sq
    meter; however, we rarely saw that figure. For New England in winter,
    I'd use 900 watts as more typical, and that only on clear days for a
    couple of hours around solar noon. Under such conditions, your 4-foot 
    dish will collect less than 1kw in full sun. Although you live in a
    sunnier clime, I don't believe maximum insolation is higher, just the
    number of available hours.
    
    We encountered numerous interesting problems. The plumbing connections
    had to withstand tracking motions. The pipe insulation often caught
    fire from stray reflections off the edges of the mirrors: we instituted
    a rule against wearing dark clothing after a few scary incidents. You
    might consider what will happen if you lose coolant or
    circulation--even modest concentrations of sunlight can generate
    dangerous temperatures. We lost numerous solar cells because of heat
    damage. There is the very real possibility of being blinded by a stray
    reflection, and we frequently got burned.
    
    I'll admit to having forgotten more than I ever knew about solar energy
    in the intervening years, but part of my job was to evaluate various
    methods of collection, since the company for which I worked was in the
    business of acquiring such technologies. I examined many types of
    systems, none of which turned out to be cost effective or even
    particularly efficient compared to flat plates. Unless you need to
    generate high temperatures for heat pumps, steam or other industrial
    uses, or high intensities for electrical generation, a tracking system
    should be considered an interesting, potentially dangerous time-waster.
    

    
    Not wanting to be a Jonah, but.....
    
    I've got this nagging suspicion that the physics is all wrong.
    The heat generated at the focal point will be high, but the focal
    point will be small -- heat will be too quickly dissipated by the
    metal of the boiler acting as a heat sink. That's why these commercial
    solar furnaces have such a huge reflective surface area relative to the
    heat collector.
    
    There must be a physicist in the notesfile.....
    
    Colin
    
    
    
    

    re .13
    
    	Right the temperature at the focal point is high and the focal
    point is small. What you are doing is *concentrating* the sunlight
    falling on the reflector into a very small area. Negating the losses
    from the reflective surface we can say that a square meter of reflector
    focused to a point will deliver 1 Kw to that point. If the metal of
    whatever is in the focal point can withstand that energy input and
    carry it off efficiently we have goodness. If not we will melt whatever
    is at the focal point, (or set it on fire). The trick is to take this
    concentrated energy and do something useful with it. 
    
    	The trick with most "engines" that run on any king of thermal power
    is to find a working medium that has a boiling point at the temperature
    that you are able to generate. You can then use the pressure generated
    by the phase change of this medium to generate mechanical energy.
    However if all you want to do is generate heat you just need a means of
    transferring the heat from the collector/generator to where it is
    needed. In this kind of system very high temperatures may be more of a
    liability than an asset.
    
    	BTW to the base noter - I hope we don't discourage your
    inventiveness. Your idea is really interesting even though the
    application *may* be wrong.
    
    				regards,
    				Mark

It is theoretically possible for the focal point to get as hot as the sun's
surface.  The focal point in this case will be quite small with a reasonable
sized mirror.

To prevent overheating a point on the target, you should ensure the light is
out of focus at the target enough so the whole area is illuminated, but not out
of focus enough to spill light past it.  This prevents a small point from being
overheated. 

-Mike

I remember reading once about a huge collecter - I don't remember where it was
built or exactly what technology it used.  But it covered a very large area 
(like an entire small valley or something), and focused the sunlight into a 4" 
diameter beam.

The one thing I vividly remember about it was that it could bore a 4" hole in
1/4" steel plate in something under 10 seconds.

Paul

    I beleive the collector was built in New Mexico,
    
    also I think it was a lot thicker piece of steel then 1/4 plate.
    
    Skip

    Re .4:
    
>   Thanks for the inputs so far. I am still looking for information on the
>   parabolic dish method.
>             
>   I know that with moving parts it will be more likely to break down but
>   I have chosen this for several reasons:
>   
>   1.  Challenge... I want to try something new that requires some
>   engineering, and explore some unknowns.  (I am also thinking about a 
>   hot air system to heat the house using beer cans as a collector and
>   rocks to store the heat until needed at night.)
    
    It should be ineresting.  Just don't be disappointed if the finished
    product isn't very useful.

>   2.  Cost...  Sence I already have the satellite dish, it is cheaper to go
>   this way.  To crome plate will cost about $200.  The electronic sun
>   sensor will cost about $20 plus parts I have in my shop.  The pump and
>   storage tank is the same as for a flat panel system.  I already have
>   the addition motor to drive the elevation angle.  
>   
>   Even to build flat solar panels, it will cost more.  Flat radiators
>   cost about about $100/sq meter, and the glass, frame, installation,
>   support  will cost about another $100/sq meter.  As most systems here
>   has about 6 sq meters, the material will cost about $1200 for the
>   panels.  To buy factory built panels it will cost about $3000. 
>   
>   3. Ease... It would take much longer to build the flat panels than to set
>   up the dish.  Temperature control is easier to control by pointing the
>   dish.

    True.  You could also vary the distance from the collector to the dish
    in order to focus/defocus the image.
    
>   4. Weight & size...  This system can be mounted in a corner on any balcony 
>   or on any wall facing south.
>   
>   5. Other uses...  A larger dish may be able to supply enough energy to 
>   heat my swimming pool in the spring & fall, and help heat my home in 
>   the winter, in addition to hot water supply.  

    A parabolic reflector can certainly pack a lot of energy into a small
    area (resulting in impressively high temperatures), but it's not at all
    clear that the efficiency of your reflector is enough greater than that
    of a flat black plate to compensate for the smaller area involved.  (I
    get as much hot water as I can use from about 6m� of collector area.)

>   ref .2
>   I have also been told that oil would be a better heat transfer agent than
>   water.  In addition it would not freeze in winter.  What kind of oil
>   is best and safe in case of a leak in the storage tank?
    
    My domestic system uses propylene glycol (anti-freeze, but potable). 
    My system is not supposed to exceed about 90�C, so this medium works
    quite well.  I'd suggest a visit to the CRC book for such data as
    specific heat and boiling points.

>   The heat collector at the focus point present a problem in design. 
>   Should I try for the maximum temperature leaving this collector by
>   restricting flow and placing it at the focus point, or should I try
>   for maximum heat transfer with high flow rate and defocusing to spread
>   the sun over a larger collector area?  Remember this is a close loop 
>   system therefore the effect is accumulating.  Which approch would be the 
>   most efficient transfer of heat in both the collector and storage tank
>   and/or easier to build?  Should I use a flat coil tube solder on the
>   back of black copper sun focus plate, or a round flat container at the
>   focus point that the cooling liquid passes through, or a cylinder shape 
>   coil of tubing that the sun focus into (like a waveguide)?
    
    I think I'd go for the flat (or convex) coil tube at something less
    than the focal length from the reflector.  There should be NOTHING at
    the actual focal point (which could disasterous in the event the dish
    stops tracking at some point).
    
    Good luck!

    re image size
    
    The size of the focussed spot is not related to the size(diameter) of
    the mirror, but its focal length.  A mirror with a 4 ft focal length
    would produce a focussed image of the sun about 0.4 inches in diameter.
    An 8 ft focal length would be twice that, etc.
    
    Any of you who have touched an overloaded 1/2 watt resister (about the
    same size) can appreciate just how hot 1 KILOwatt of power in such a
    small area will get.
    
    Bob

    re: .19
    Wouldn't the focal point always be (in theory) a point, regardless
    of focal length?  Mathematically, a parabola always has a focal point 
    that is a point, regardless of its curvature.
    
    If you're talking about a spherical mirror, on the other hand, you
    may be right - I don't know what would happen in that case.

    
    A point source would produce a point at the focal point (so to speak);
    the sun, being somewhat larger, will produce a slightly larger image
    (but it will be in focus :-)
    

If your goal is to do something interesting with a parabolic dish, how
about making a photovoltaic system, rather than a water heater?  As other
replies have noted, unfocussed sunlight is hot enough to to provide hot
water.  Tipping the flat plate to face the sun is cheap and cost effective, 
but a parabolic dish really isn't necessary.  

However, that isn't the case for photovoltaic.  Electrticity can be
generated *much* more efficiently if the sunlight is focussed, because
the voltage produced is higher.  Also, reducing the area of silicon 
required for the collector is a major cost savings.

	Enjoy,
	Larry

PS -- From what I've heard, the major application for the solar furnaces
described in previous notes is creation of high quality alloys that have
high melting points.  The problem with a regular furnace is that it is
dirty -- impurities are generated by the process of creating heat, and
the higher the temperature required, the more the impurities.  That isn't 
a problem for making steel or most other things, but in some specialty
cases it is a major problem.  A solar furnace, however, gets its heat 
with absolutely no impurities beyond what's floating in the air.  

    re: .21
    
    Not for a parabolic reflector, I don't believe.  This isn't like 
    a lens in, say, a camera.  Parallel rays coming into a parabolic 
    reflector all converge to a point, and rays from the sun, because 
    it's so far away, are essentially parallel.  
    (Not that it is of much more an academic interest anyway, I
    expect; the temperature at the focal point will be extremely
    high in any case, even if it's spread out a little.)

re .23:

The rays from the sun aren't exactly parallel.  While the sun is extremely
far away, it is also extremely large, which is why it is visible as a disk
and not a point of light like (other) stars.

This can be seen during an eclipse of the moon, part of the moon becomes darker
as light from part of the sun is blocked by the earth.  If the rays were
parallel, any part of the moon would go from full brightness to total darkness
instead of getting darker and darker.

-Mike

    Wild Bill and Mike have it right.  The sun is not a point source of
    light so it will not focus to a point no matter what the focal length
    of the mirror (or lens).  In fact (if I remember correctly) the sun's
    disk is about 1/2 of a degree wide as viewed from Earth.
    
    Bob

    I don't have a ruler that'll measure a point (except my typographer's
    rule, but I digress) anyway, but I'll bet it makes one heck of a hot
    little spot.
    
    ed

    I am going to look at a house for sale that is billed as a "solar 
    contemporary."  From what I have read here in this Notes file on 
    SOLAR, my guess would be that it's an "active" solar heating system 
    (since, under Heat in the listing sheet, it says solar).
    
    I know zero, zilch, nada about solar heating, but the price on this
    house is right (just dropped 15K, which makes me wonder if some of
    these previous replies on resale value are indeed true...).
    
    Anyway, what should I be looking for?   My hopefully (good) sense 
    tells me that if the house is "solar", I should expect to find it
    well insulated (walls and roof), good windows, etc.  But what else?
    
    Here's a few questions right off the bat?
    
    	o  should the house have a backup heating system?
    	o  is there some kind of ratio of solar panels to
           square feet?
    	o  what about tank size?
    	o  are there "brands" of solar heating equipment,
    	   and if so, which are the better ones?
    	o  is a solar system expensive to maintain?
    	o  other questions?
    
    A couple more things -- I'm the kind of person that NEVER warms up
    in the winter, no matter how many layers.  Can a solar home get as
    toasty warm as a "fossil fuel" home -- i.e., can you just turn the
    thermostat up?, or is there a limit on heat, say, on a stint of
    cloudy days?  Is there where a backup system comes in?
    
    Lastly,  I'll re-ask this question five years later -- IS SOLAR
    DEAD?  Should I maybe stay away from this house no matter what 
    the price, because it IS solar, or should I get adventurous and
    learn more about it?  
    
    Thanks.
    
    Carol

Why shy away?  The worst that could happen is that you decide you have
to install a replacement heating system -- and if the house is a good
enough deal to cover that cost, then it's a good deal.

It all depends on what the solar system is, and how it affects your
life in the house.  And on just why the house is being offered for $15K.  
It's hard for me to believe that solar could drop the price of a
reasonable house to that level, no matter where it is.

By the way, you don't mention what part of the country you are in
(and I can't find you in ELF).  It makes a *big* differences.  
It's tough to make solar pay in New England, because it's it gets
very cold and very cloudy.  But it is a lot easier in other areas.

	Enjoy,
	Larry

	    I'd guess that the house was built during the Carter Admin.,
	when people were allowed tax breaks for Solar and other forms of
	energy saving devices.  I think I was in grammar school at the 	
	time.
	    The house is probably set up with passive and active solar
	heating systems.  Passive would be thoughtful tricks like having
	big (hopefully double pane) windows facing south.  To increase
	their usefuleness, the sun should shine on something with a high
	heat retention, such as brick.  Passive is great because it has 
	no moving parts and should just about last forever.
	    I've heard that active solar, especially circa 1970, was not
	all that dependable.  Unfortunately, it was too short lived and
	not enough research went into it's development.  As I understand
	it, repair of most active solar heating systems could be difficult
	as well as costly.  Many companies that developed/installed these
	systems went belly up after the rush for these alternatives went
	away.  (The "Energy Crisis" disappeared)
	    I don't mean to sound so pessimistic.  I would love to have a
	practical solar house, but that's not an easy thing to come by in 
	New England.  How handy are you and how much are you willing to
	learn about solar heating as it pertains to your house?  If you
	like the house and think it's a good deal, I think you'll have to
	do some research and come up with a lot of your own answers.
	    Sorry I can't be more helpful.

					Tim

    Re .13, sorry to mislead -- the house dropped 15K, but not TO 15K.
    The house is in Groton -- I'm going to look at it tonight.  It is
    11 years old -- I will check out what "active" and "passive" solar
    I see in the house and hopefully provide more info here tomorrow.
    
    Carol

    It is gawd-awful difficult to make a comfortable 100% solar heated
    house.  It is pretty easy to make a comfortable 50% solar heated 
    house, and not all that hard to get 75%.  The last 25% is the killer.
    (More or less. I'm just making these numbers up, but the point is
    that the first bit is easy, and the last bit is really hard.)
    
    You do need a backup of some kind, in New England, due to the general
    perversity of nature and also to take care of that last x% of heat that
    determines how comfortable you are on any random day.
    
    I would certainly not avoid a solar house, especially if it's passive
    solar.  If active solar I might worry a bit about maintenance.
    Nevertheless, the chance to save 50% (or more) of my heating bill, 
    year after year, has a great deal of appeal.
    
    Get more details about just what is involved.  There may be a certain
    amount of lifestyle change required to make it work really well.  For
    instance, you may need to be sure to close special curtains at night
    and open them during the day, etc.  
    
    The "solar house" business might turn out to be mostly realtor puffery,
    once you check into it.  There may be a perfectly fine conventional
    heating system which, upon direct questioning, "was on 75% of the time
    last year, but that's because we were spending so much time away from
    the house and couldn't monitor the solar system properly" or whatever.
    
    Let us know what develops.

Ah!  So much for my late night note comprehension.

I'd say that a house dropping $15K is nothing special in this house selling 
climate.  Also, I believe that's a lot more than it would cost to install
a FHW system from scratch, given the new chimney-less systems.  

I would love to have a solar house -- provided that it had a reliable backup.
Remember the week before Christmas a couple of winters ago?  Where I live
(on a low hill in centeral Mass) the high was below 10 deg F for over a 
week straight -- and it got as low as 19 below one awful night.  My FHW
furnace ran continuously and still the house didn't get as warm as I
wanted.  It's an old house that needs more insulation... but I wouldn't
have wanted to be in a solar house without a full backup system that week!

From what I've read, the reason Solar is moribund has nothing to do with
whether it works -- it is because it isn't the most cost effective solution.
Energy conservation never really happens unless energy prices are high.  If
we paid the same price for gas and oil as they pay in Europe, solar would
look very attractive in much of this country.

	Luck,
	Larry

PS -- If you decide that you want to research solar heating, there's a
mail order company that sells a "Home Energy Sourcebook" for $15, which
lists lots of places that sell that equipment and which gives lots of
information for evaluating the systems.  I understand that it is very
good -- and you get a refund if you order from them.  There also used to 
be an Energy_Conservation notes file, but the node it is on disappeared 
in early January and I haven't been able to find the node or moderator.  LS

    Thanks for the replies -- as a result, some of my fears have been
    allayed, at least until I get there tonight.  Now I know to look
    for a backup system -- I had imagined having no source of heat
    other than good ole Mr/Ms Sun, and while it sounds lovely, I too
    was worried about what happens on those frigid days.
    
    I used to live on Plum Island in Newburyport and had a cistern to
    collect rain(water) -- or water from Lawrence that was delivered
    in a MAC truck when the skies didn't contribute their part.  I am
    not afraid of relying on Mother Nature, but I've learned that she
    isn't always as consistent as we have come to depend on her to be.
    
    So I'll check out this house with an inquisitive spirit and then
    see how I feel after.  If I'm interested, I'd probably be interested
    in having the system checked out by a professional.  
    
    More later.  Again, thanks.
    
    Carol
    

	Keeping with the question "Is Solar Dead?", and being more specific,
I'd appreciate hearing any recent stories on successes/failures with solar
water heating. I have a large roof area which would be perfect for this;
southwest facing, in the back of the house off to the side. We plan to be
there for awhile...

	I've often thought that when our current water heater (propane
gas) goes, I'd look into it.

	Has the technology improved over the past few years?
	Has the technology cost decreased?
	Any immanent breakthroughs being talked about?

	It seems to me that this has always been the area where solar
could take hold. If someone could come up with a relatively cheap system
which didn't massively tower over the architecture of the house, they
could make a lot of money.

							Mark

I saw a nice solar saltbox in RI.  One roof face (the longer one) was all 
the collectors (flat to the roof so it looked OK from outside).  In the 
basement it had a huge cinderblock arrangement that took up a fair percent 
(30% say?) of the floor area.  This was the heat sink to provide heat over-
night and on cloudy days.  This house was designed and built as a solar house 
(not a DYI project by a guy named Rube Goldberg) so the system was well 
integrated into the house.  As I recall, this house cost about $15K more 
than a similar house.  This was in the early 1980s so my memory may be a 
little foggy.

Stan

    Re .17
    
    As an aside re gas prices in Europe: it depends what kind of gas you
    are talking about. Gas that powers your car (i.e. gasoline) is 3-4
    times more expensive in Europe than here in the US. But gas that heats
    your house (natural gas) isn't more expensive in Europe.
    According to my last Dutch natural gas bill from about a year ago 
    natural gas in the Netherlands costs about $0.77 per therm (after
    conversion of Dfl to US$, m3 to ccf and hPa to psi). ComGas here in MA
    charges $0.9637 for the first 50 therms, and $0.67 thereafter. So it
    doesn't make much difference.
    So in Europe too Solar doesn't make economic sense.
    
    /Date

    
    
    
    I would say that that depends were in the U.S. you reside....
    
    My bill for the period of Jan 13 thru Feb 11 is  for $70.65
    
    Base rate/ccf at .3532300 plus a customer charge of $5.30
    
    
    
    Ben,
    

    Well, just to serve as an update -- I looked at the solar house
    and didn't like it.  Besides just not caring for the interior 
    of the house, it was VERY cool when we walked in (instant turn-
    off), and I saw no signs of what looked like a backup system to
    me, unless it was right on the tank somewhere.
    
    Thanks for all the replies.  
    
    Now onto foundation questions....
    
    Carol

    
>    So in Europe too Solar doesn't make economic sense.
    
    This is the exact mentality that MUST change in order to reduce the US
    dependence on fossil fuels.  Besides the out-of-pocket cost of energy, 
    there is a hidden ecological cost of the energy we use.  Unfortunetly,
    90% of people think only in terms of the out-of-pocket costs.  
    
    It baffles me as to how solar can NOT make economic sense?   Granted,
    based on current cost of fossil fuels, the cost for instalation and 
    maintenance of a solar system may never be re-couped, however, this 
    way of looking at the issue of energy cost is pretty short-sighted.  
    When the US and other energy hungry nations wake up and realize the 
    hidden costs of our energy usage (read Greenhouse effect, polution and 
    associated health problems, gulf war costs etc.) and place the cost
    where it belongs, on the energy itself, the price of fossil fuels 
    will ski-rocket.   A lot of good could come out of an effective energy
    program, unfortunetly, the present administration doesn't seem to be 
    interested in making it happen (only canidate I've heard mention it is 
    Gerry Brown).
    
    If solar is truely DEAD as this note questions, I hope and pray
    it will be resurrected soon.  Once I get my new roof done, my panels
    are going up, and with any luck, President Brown will ensure I get a 
    tax credit for my effort.  
    
    /Jeff
    

I'm of the opinion that waste disposal and other environmental costs should
be made explicit in the cost of *all* products.

For "ordinary" garbage, the way to achieve this is to drastically raise the
tippage fees.  This is in fact already happening, and is what has made it
cost effective to separate out some recyclables.  You have to pay to get
them to take your newsprint, but you pay less than you have to pay for
general garbage.

For motor oil, appliances, etc., there should be a disposal fee included
in the purchase price.  There are various ways it could work, but the main
point is that when you buy a car, say, you are also paying the price for
its disposal.  Then all of a sudden there is an economic incentive to make
cars so that they can be more effectively recycled!  Motivation on the
part of the consumer to buy only those weed killers they need.  And, of
greatest importance, items that are costly to dispose of properly will be
less often dumped by the side of the road, since the cost of proper
disposal will have already been paid.

The application to solar energy is obvious -- fossil fuels have a serious
environmental impact that the users of the fuels are not at present paying.
Instead, we are largely borrowing the money from our descendents, who will
have to pay the cleanup price.  Sort of like the people of the former USSR 
who are now suffering with the cost of paying for 70 years of communism,
except worldwide and more extreme.

HOWEVER, there are still problems with solar.  Keep in mind that it takes
a lot of energy to make a solar cell, and since a roof is such a hostile
environment, they don't last as long as other types of energy facility.
In an area like New England, solar electric power has a very bad payback.

Solar heating, though, is relatively cheap -- it should be possible to
get a reasonable payback on that, even now, when we aren't paying the real 
costs of using fossil fuels.  

	Enjoy,
	Larry

    "Economic sense" is based on cold mathematical figuring of the costs of
    different alternatives, in this case of heating a home. The cheapest
    solution that achieves the desired result makes "economic sense". It
    may not make "common sense" though. 
    
    So if you install solar panels because you care for the environment,
    you have a lot of common sense, but your solution doesn't make
    economic sense because you could get the same result cheaper. Fossil
    fuels need to become a lot more expensive, or solar technology needs
    to make a technical break-through before solar also makes economic
    sense.
    
    Yes, it's too bad a lot of people feel economic sense and common sense
    are identical.
    
    Good luck with your solar project!
    
    /Date

	    Solar cells are getting more efficient and cheaper to build
	but it's been slow in coming.  There isn't all that much research
	into their development; there's not a big enough market to warrant
	the costs.  Consumers aren't looking to buy solar because it's not
	practical nor affordable.  Manufacturers aren't investing so much
	into research and development because they're not marketable. 
	    If you could make them affordable, durable and a little bit 
	flexible, you could presumably shingle your house with them.  A
	company could make a killing and the oil companies would take a
	major loss.  To compensate, the price of fossil fuels would go up.
	The demand for alternative energies, ie. solar, would likewise
	increase which would further threatedn the profits of the oil
	conglomorates, ad infinitum (extinction?)...
	    What a wonderful world it would be.

					Tim

Just my humble opinion, (but I *AM* the moderator) 8^)

    This note is close to heading down a rathole. Please, let's keep the 
discussion on the cost/advantages/disadvantages/etc of solar. Making your 
points by discussing ways to add the cost of disposal into products is 
nearly off the subject and political views should be taken to SOAPBOX or 
similar files.....

    Thanks,

    Vic H

      Unfortunately,  the  high  cost and relatively short life of solar
      cells makes photovoltaic a poor economic  choice  in  most  cases.
      Notable  exceptions are locations that have no or little potential
      for hydro or wind power, and are  many  miles  from  the  existing
      grid.

      On  the  other hand I believe that SOME solar *DOES* make economic
      sense/cents.  For example,  the  simples  form  of  passive  solar
      requires only two things:  (1) Make sure that the long axis of the
      building runs within 10-15 degrees of east-west. (2) Put 2/3rds to
      3/4ths  of  the  glass  area  in  the  south  wall.  Both of these
      represent *NO* cost increase during initial construction. Together
      they should save $500-1000/per year in heating/cooling costs.

      (Assumptions:   a) You aren't heating with free wood from your own
      wood lot.  b) Your house is tight and well insulated.)

      Some active systems can also make sense. For example, systems that
      help with heating domestic hot water can often pay for  themselves
      (in cost savings) over a relatively few years.

      What  is  not  cost  effective  under current economic conditions,
      assuming  reasonable  access  to  electricity  and  oil   or   gas
      deliveries, is TOTAL dependence on solar for heat.  Well, maybe in
      some locations, but most places need  backup  systems  capable  of
      picking up the load during long cold/cloudy spells.
      
 ==============================================================================
      
      Now  I  find  it very hard to understand why people will buy homes
      that don't even do the no-cost things that can be done to increase
      overall efficiency of energy use.

    
    Steve's reply hits the key point - it's the maintenance of these
    systems that is the problem now.  I rented a contemporary energy
    efficient condo in Nashua NH for a year - moved last October to a
    standard garrison.  The solar was great from April to September it
    eliminated the need to use natural gas water heating.  The house was
    always warm in winter and reasonably cheap to aircondition in summer. 
    water heating bills in summer came to around $10 per month, and
    it cost about an extra $13 to run the pump.
    
    However, as an 8-year old active system it broke down twice in the
    year. On both occasions it was repaired by eastern Solar services from
    Mass, at about $100 per visit.  The service engineer remarked that he
    was getting his spares from cannibalised systems and did not know how
    much longer he could service this particular model.
    
    I tracked down the manufacturer of the system, who was still in business
    in (guess where) Nashua NH! they were able to supply me with a list
    of the standard parts & suppliers, but there will still many custom
    moving parts that were not obtainable.
    
    If you do buy (or build) a system, I would recommend that you get a
    solar heating engineer to check it out, quote for maintenance etc.
    Also, try to ensure that it's built from off-the-shelf parts -
    particularly pumps, motors and temperature controls.  make sure there
    is a BIG storage tank and it's well insulated.
    
    One important thing to check from an efficiency standpoint here in the
    North is the roof panel pitch & orientation.  When solar was
    benefitting from tax breaks, a lot people had panels installed by
    simply laying them flat on the south side of the existing roof
    (sometimes ignoring any tree shade). You can greatly increase
    efficiency by mounting the panels on a support using the correct pitch
    tables (degree of tilt minus roof pitch) for whatever latitude you are
    in the USA (42deg in Mass).
    
    If you're happy that the system can be maintained, I would go for it.
    
    Rgeards,
    
    Colin
    

I have active solar/forced hot air. The solar unit has an automatic backup to a
high-efficiency propane hot-water heater (~$300/year for propane in Southern NH).
In fact, my unit was probably made by the same company as .30's. It does have
some custom-made parts and I didn't want to get "left out in the cold" so to
speak, so a few years ago when adding central air, I included a propane furnace.
No fancy tie-ins to the solar: if I want to use it I have to shuffle a couple of
duct panels around. I still use only the solar unit, but if it ever zonks out in
the dead of winter, I'll still be warm and toasty.

Would I do it again? Probably not without a tax credit. It added $10K to the cost
of the house (just a mere coincidence that that's also the max allowed under the
60% tax credit, I'm sure :-). I've helped mop up a neighbor's flooded basement,
and there's nothing like getting up in January to a waterfall off your roof after
something's gone wrong, your collectors got ice and broke as the water has
nowhere to go. Too hard to get enough winter sun up here - a ground source heat
pump with photovoltaics to drive it might be neat next time around.

						Trace

  I am in the process of building a solar air collector. In the available
drawings that I've gotten from the libraries, some say that there is a 
hard board type insulation that goes behind the collector plate.
  I'm not shure if it's a hard fiberglass board or -isocyannorate (sp)board.
I'd like to use a selective surface coating on the plate and definately cannot
use the 'iso'. Selective surfaces are hot!
  Anyone know of a hard-board insulation that can handle temps up to 700 F
degrees. Or for that matter high-temp insulation that has a high flammability
rating without outgassing?

  The old alternative energy notes file doesn't exist anymore... So I have to
ask it here... Any ideas?


Regards,

  John D'Errico

    
    
    John,
    
    I dont believe (in respect to any designs of S.A.C.s' I know of)
    you'd reach that high a temp in the collection area seeing the
    movement rate of air would keep your temp down and the consentration
    would be over a relitively large area, not at some focal point.
    Correct me if i'm wrong here???
    
    JD

  I think that it's only for safety reasons. If the power were to go out
and the temperature stagnates without any airflow, it's possible that you
could reach temperatures that high. That's without any mechanical devices
to vent out the hot air. There are a couple of devices that you can add
to a collector to do that.
  I think that most air collectors on the market are "warm air" collectors.
They (I think) run in the low-hundreds as far as temperature goes. This is 
without a selective surface on the collector plate. You can correct me if 
I'm wrong on any of this! I could be overly cautious too... But I want to 
get it right the first time...


/John

One of the disadvantages of notes files is the age of the
information provided.

The phone number for Matthew McDonald, which was so
graciously provided in .9, is no longer correct.  The 
person who answered sounded like he hears this regularly.

Anyone who knows of another solar repairman in Central
Mass, please feel free to update this note...

tim

    
    Check your yellow pages for Eastern Solar services
    in Wayland Mass.  Very good service.
    
    Regards,
    
    Colin
      

Thanks Colin,

I have one of those Novan systems that was raved about in
here, albeit about six years ago...it's not working.

How can I tell?  Thermometer in the storage tank never
goes above 50 degrees (how do you do those little o's?)
Antifreeze circulator pressure gauge never goes above
0 psi...probably out of antifreeze, or just alot of air
in the line...

tim

>goes above 50 degrees (how do you do those little o's?)

	[Compose Character] 0 ^  =  �

	[Compose Character] - +  =  �

					 Tim

Thanks Tim,

I had my Novan system repaired, thanks to Eastern Solar Service.  In case
anyone else is interested, here's the scoop...

It took about eight gallons of propylene glycol antifreeze - the system
was completely empty.  This stuff is non-toxic, but EXPENSIVE: $15.50/gal.
It's cheaper if you buy it directly from that outfit in Manchester, N.H.,
though.  The Taco circulator for the solar panels was burnt out, thanks
to being operated by the previous owner without any antifreeze to 
circulate, for perhaps a year prior to my moving in. With 2 hours of 
labor ($45/hr), the bill checked in at about $335.

The good news is that in the first three days of operation, the temperature
in the storage tank rose 10 degrees per day - despite the fact that the
outside air temperature never got above freezing.  The unit is already
having an impact on the amount of available hot water in the house, and
I'm hopeful that by summer we'll be using little or no electrical water
heating...  Hopeful, anyway.

tim

    That's a lot of money. Have you considered a claim against the previous
    owner? Will the repair shop testify for you? 

>   That's a lot of money. Have you considered a claim against the previous
>    owner? Will the repair shop testify for you? 

Umm...I agree, it is.  I don't need them to testify, though.  You see,
the house was a foreclosure/bankruptcy disaster for the seller, and they
have no money...but I'm looking into private alternatives to recover
some of the loss.

I'll figure something out - don't worry...;-) ;-)

tim

    	I know this is an old topic but figured I'd ask anyway. Does anyone
    in here know how you'd go about making a parabolic dish. It doesn't
    have to be "real" efficient, just something that basically works.
    Someone in here mentioned making one using aluminum foil ?
    
    	Also, how are these used ? I'm familiar with using a magnifying
    glass to focus the sun to a point in back of the lens. Does a parabolic
    dish basically do the same thing to a point in front of the dish ? Does
    it focus the point in a similar way (i.e. move it closer/further away) ? 
    
    	I would imagine that the parabolic dish is more cost effective when
    you're talking about a larger scale project due to the cost in grinding
    an equivilant sized lens. Is this true or are the other reasons for a
    parabolic dish over a lens or vice-versa ?
    
    	Ray

   Well, I don't have any details, but I do have some comments... from
   what I remember of dishes, there is a single focus point that is
   somewhere above the center of the dish.  The location of that "hot
   spot" is dependant on the size and shape of the dish.  If you recall,
   there have been demos over the years where people would make small
   dishes (maybe 12-18" across) that they could use to cook hot dogs.

   You might want to look at a catalog from Edmund Scientific (sorry, I
   don't have their number).  I seem to recall that they had all sorts of
   stuff along those lines.  I don't know if they had anything big enough
   for your application, but it might give you some good ideas on what
   they look like and all.
   
   Regards,
   
   - Tom
   

    	What I was going to try (on a very small scale) was to see if I
    could generate steam using a traditional solar panel to get the water 
    as close as possible to the boiling point, and then a parabolic dish 
    focused on a heat sink to get it to boil.
    
    	Anyone ever try this with any sort of success ? What I wanted to do
    was to see if I could use this to drive a small model steam engine.
    
    	Ray

    It might be easier (but less efficient) to make a parabolic trough,
    rather than a hemispheric shape.  The trough would be a piece of
    polished aluminum bent into a U shape; then a (glass? black?) tube
    would run down the length of the reflector at the focal point (actually
    the focal "line".  I don't know if this style collector will
    concentrate enough to create steam; maybe if it were big enough.  
    
    You could buy a sattelite dish and coat that with aluminum foil.
    
    Carl

    Oh, yeah, I've seen science projects that use kid's snow saucers.
    
    Carl

    
    I saw an article on this recently where the engineers were
    using silvered mylar to create a reflector.  It's used for candy-bar
    wrappers, And a lot of my windsurfer sails are mylar because it
    stretches uniformly.
    
    The stuff is thin, light and much more reflective than aluminum.  It
    can be shaped on a frame, or made into light optical lenses by
    vacuum-forming or simply by electrostatic charge.  (the application was
    for broadcast dish antennae). Varying the vacuum/charge focuses the
    lens.
    
    I guess you could experiment by sealing some across a drum and pumping
    out the air so the mylar is formed into a parabola. (Get your steam
    engine to drive the airpump, and you have a nice closed loop solar
    system!)
    
    If you want to try a real small-scale experiment, an old CDROM can be
    formed into a crude parabolic lens by heating it pressed between two
    cereal bowls.   Use the "no parallax" technique to establish the
    approx focal length.
    
    Regards,
    
    Colin
     
    
    

    
    As a kid of 15 or so I managed to spend some time with a friend
    of my parents who was the quintessential backyard mad scientist.
    
    Among his many experiments was a 6' diameter parabolic dish made
    much the same way as the previous note describes. He created a 
    round hollow frame by laminating large circles together until he
    had about a 8" depth. He then glued round sheets of mylar to the
    front and back and sucked out much of the air with a pump... 
    streching the mylar on both sides into perfect, shallow parabolas.
    
    These dishes were obviously limited by the fact that they wouldn't
    hold their "vaccuum" for more than a few hours... but we had great
    fun with them. The focal point was also well out front due to their
    shallowness. I remember the first experiment startling us both when 
    he used a 2x4 to find the focal point and the thing burst into flames
    so fast we jumped!
    
    The real plan (which he only built in miniature) was an array of dishes
    mounted around each other in a sort of shallow parabola aimed at 
    sterling engine mounted at their combined focal points. The whole
    assembly was mounted on a sun tracking frame.
    
    								- Mac
    

       	Can you just use a sheet of paper to show you where the focal point
    is (i.e. look at where the light hits the paper) ? Also, does the 
    parabolic dish have to track the sun or can it remain stationary and 
    still work ? Is the focal point of a parabolic dish similar in
    intensity to the focal point of a lens (i.e. will burn through paper in
    a few seconds in bright sunlight) ?

    	Regarding the kids saucer, I was thinking the same thing. Not sure
    if the aluminum ones would be shiny enough. Perhaps combining two ideas 
    by bonding mylar to a kids saucer using a spray adhesive and a vacuum 
    cleaner might work better. Does anyone know if the amount of concaveness 
    would affect anything other than the focal point ?
    
    	Ray

    	Looks like the previous note answered a lot of my questions. Better
    use a 2x4 vs. a piece of paper to find the focal point though ;-)
    Would a 6' dish be twice as intense as a 3' dish ?
    
    	Ray

    Nope, the intensity is directly proportional to the surface area of the
    reflector, which can be approximated as a circle (it's actually a bit
    larger than a circle), which is proportional to the radius squared.
    A 6' dish would thus be 4 times as intense as a 3' dish.  Note also
    that to be most effective, the dish must be a true parabola, which
    would focus the sun's rays all at a single point.  If you don't get the
    parabolic shape quite right, you will get a "focal column" rather than
    a point.
    
    One thing I've seen for those who like lenses rather than dishes, is a
    large fresnel lense.  It's flat, which is very convenient.  I've seen
    one a couple of feet square which very quickly burned a hole in a
    blacktop driveway.
    
    Paul

    	How big was the fresnel lens you were using in the previous note and
    where could I get one ? Are they expensive ?
    
    	After thinking about it, I would think the lens would be a little
    easier and safer to use for my application. By using a lens, the focal 
    point is in back and down rather than up and in front. The focal point 
    of light can then more easily be enclosed without anything in the way to 
    block the suns rays. 
    
    	A little off the subject but does anyone know approx. how hot you can 
    get water using a passive solar water heater ? I was planning on using
    one of these to raise the temp as much as possible, and then use a lens
    focused on a heat sink with a pipe running through it to generate
    steam. I know attics can easily reach 140 degrees, so I suspect passive 
    solar panels would be at least in the 180-200 degree range (if not
    higher.)
    
    	Ray

    The lens was around 2 x 3 feet.  I believe it came from Edmund
    Scientific Co.  I don't know the price, since I didn't buy it...
    
    Paul

    
    The solar system in the last place I rented was about 140, but that was
    the temparature in the secondary coil of the heat exchanger.  It would be
    higher in the primary coil.  If you plan to draw from the primary coil
    the system will never reach the full potential temperature, as it
    will be constantly topping up with cold water.  If you opt for a
    heat exchanger, you'll lose some heat in the exchange, but the system
    will work more efficiently.
    
    Some older theatre spotlights use multi-element fresnel lenses for
    focusing.  For something like a follow spot, these are only about 6" to
    8" in diameter and it was pretty expensive to replace even one element. 
    They are also very heavy!  What you probably need is an army surplus
    searchlight or a pensioned off lighthouse lamp, which will need quite a
    bit of support.
    
    (This made me think - what if you could use a diffraction lens - like
    the field-of-view expander use on a bus rear windshield.)

Re: .39

�The solar system in the last place I rented...

I didn't know you could rent a solar system.  How many planets can you get, and
are options such as comets and asteroids available?

Couldn't resist...

								-- Chuck Newman

    
    :-)  Another one for my anbiguous sentence collection.
    
    Colin

    The limit on temperature is something like 4000 degrees C - there is a
    Scientific American article that explains why - a thermodynamic limit
    based on our distance from the sun, and the sun's surface temperature
    of about 6600 C.
    
    There's a solar furnace in France that routinely gets to 3500 C, using
    an array of parabolic reflectors that track the sun. Its used for
    smelting high purity metals and ceramics.
    
    Reflectors are more efficient than refractors, becuase all the energy
    in a reflector can be focused at one point - refractors have different
    focal points for different wavelengths of light. Also, for a refractor,
    there is not the transmission loss.
    
    A friend of mine used to work at a hospital at Wilcannia - they have
    (or had, at least, courtesy of CSIRO) a solar array that provides steam 
    at 200 C, 1.7 bar for the hospital. The water is preheated, though, by
    the diesel generator that provides the electricity. The solar array is
    a series of channel collectors that track the sun.
    
    regards,
    Michael Watts.