Conference unifix::sailing

The greatest power output from a solar panel is obtained when the plane
of the solar cells is perpendicular to the sun's rays. I haven't seen
any data on how rapidly solar cell output decreases with increasing
angle of incidence, but it probably falls off at something faster than
the cosine of the angle (the angle of incidence is zero when the sun's
rays are perpendicular to the plane of the cell). Thus at 45 degrees,
the output of the panel would be only about 70% of maximum. Haze, fog,
and clouds would reduce output also. The total amp-hrs per day is much 
less than peak output current x hours of daylight. I don't know how much 
less, but 50% less would not be unlikely. First guess: a 42 watt (peak) 
panel will give about 15 amp-hrs per day (10 hours of sunlight). That's 
not all that much. My masthead tricolor light uses maybe 25 amp-hr per 
night and my Autohelm probably 10 to 20 amp-hr per 24 hours (which is 
one reason we have a windvane). 

A 42 watt Arco panel is something 13"x42.5". Finding that much space on
your deck (you shouldn't walk on the panel) is not so easy. I'm still 
looking for a place. 

My feeling is that a solar panel is good for recharging batteries when 
you're not aboard (most of us only sail two days a week or less), 
running a bilge pump (assuming your boat doesn't leak all that much),
and as a backup to the engine alternator. To use solar panels as the
only method of battery charging means either many panels (current price
of a 42 watt Arco is about $350) occupying much hard-to-find deck space
(mounting on top of a dodger is an option if you have a dodger -- we
don't) or living on very, very little electrical consumption (which is
hard to do). 

A simpler, more effective, and no more costly backup to the engine
alternator is one of those little gasoline-powered generators (which 
would fit in a 18" or so square deck box. 

Of course, if you have a trimaran, you could mount many, many panels on 
the beams connecting the hull to the amas. Expensive, though.

Alan

RE:.1 by MSCSSE::BERENS "Alan Berens" 


> First guess: a 42 watt (peak) panel will give about 15 amp-hrs per day 
> (10 hours of sunlight). That's not all that much. 

West Marine's estimate for Arco's 44 Watt panel is 16 to 26 Amp-Hour per day.


Phil

re .2:

>> West Marine's estimate for Arco's 44 Watt panel is 16 to 26 Amp-Hour per day.

Maybe. 26 amp-hr per day is about 7.5 hours at peak output. This might 
be possible if you made a mounting that allowed keeping the panel 
perpendicular to the sun. I'm a little dubious about this much output on 
a regular basis. One's latitude has a big influence, also. I tend to 
think in terms of sailing north of 42 degrees (since I've only sailed 
south of this once). Output per day would certainly be higher nearer the 
equator. 

RE:.3 by MSCSSE::BERENS "Alan Berens"

> Maybe. 26 amp-hr per day is about 7.5 hours at peak output. This might 
> be possible if you made a mounting that allowed keeping the panel 
> perpendicular to the sun. I'm a little dubious about this much output on 
> a regular basis. 

If one was above the Arctic circle,  and followed the sun,  24 hours of peak
output would be available for a short time.  At any place in spring or summer,  
there will be 12 or more hours of sun (ignoring details like clouds).

On a long passage,  adjusting the solar cells on every watch change (4 hours)
wouldn't be unreasonable,  and would keep output near peak.


Phil

re .4:

At high latitudes, sunlight is much less intense than near the equator 
(which is why the Artic and Antartica are so chilly). I don't know how 
solar panel makers determine peak output, but I'm sure you won't get 
anywhere near peak output at high latitudes. 

It will take a two-axis mounting to keep a panel always perpendicular to 
the sun's rays since a boat can sail on any compass course. A two-axis 
mounting would be rather difficult to implement. A single-axis tilting 
mount is certainly feasible. 

RE:.5 by MSCSSE::BERENS "Alan Berens"

> At high latitudes, sunlight is much less intense than near the equator 
> (which is why the Artic and Antartica are so chilly). 

At high lattitudes,  sunlight is as intense as at the equator,  but the sun
never gets high in the sky.  At the pole,  the sun never gets more than about
20 degrees above the horizon,  and only that for a short time.  If the sun
is shining and you track the sun,  you will get better (about twice!) output 
at the pole than at the equator.  Also,  solar cells are temperature dependant,
the colder the better!

Phil

re .last:

Sorry, I think that I am correct and you are not, for two reasons. 
First, near the equator, the sun is very high in the sky (nearly 
overhead), and the distance through the earth's atmosphere that the 
sunlight must travel is at a minimum. Less light is absorbed and 
scattered and more reaches the earth's surface. 

Second, and much more importantly: Take a small flashlight and hold it
directly above and close to a large piece of paper (the sun near the
equator). The flashlight illuminates a small circular area on the paper.
Now tip the paper so that the light strikes it at a shallow angle (the
flashlight beam is nearly parallel to the paper). You will see that a
very large area of the paper is illuminated. The total light from the
flashlight (sun) hasn't changed, but the light is now spread over a very
much larger area (the Artic in northern summer). The light intensity per
unit area is much less when the light is at a shallow angle. It is light
intensity that results in solar panel output and local heating from
sunlight. Both are much lower in the polar regions than in tropical
regions. This is also why the output from solar panels is much less in
the early morning and late afternoon even if the panel directly faces
the sun. 

Besides, if your argument were correct, the polar icecaps would melt,
and we sailors would have much more ocean to sail upon. Of course, we'd
have to buy new charts. 

RE:.7 by THRUST::BERENS "Alan Berens"

> The total light from the flashlight (sun) hasn't changed, but the light 
> is now spread over a very much larger area (the Artic in northern summer). 
> The light intensity per unit area is much less when the light is at a 
> shallow angle. It is light intensity that results in solar panel output 
> and local heating from sunlight. 

Assuming that the solar panel is flat on the ground,  you are correct.  If 
you noticed,  however,  I stated a tracking solar cell.  It's interesting
to note that for about a month out of the year,  the poles get more heat from 
the sun than anywhere else on earth.


> This {passing through more atmosphere} is also why the output from solar 
> panels is much less in the early morning and late afternoon even if the panel 
> directly faces the sun. 

The main scattering and absorbing parts of the atmosphere are dust and water
vapor.  Dust and water are much less common near the poles than near the 
equator.  Ever notice that,  on humid days,  you can look directly at the sun
as it rises or sets,  and on dry days,  you can't?  The clear air at the poles
might add to their advantage!


> Besides, if your argument were correct, the polar icecaps would melt,
> and we sailors would have much more ocean to sail upon. Of course, we'd
> have to buy new charts. 

Hmmm.  Ever hear of global warming or "the greenhouse effect"?  "See this
foul bottom notation on the chart?  That's where my house used to be!"  
:-) or :-(


Phil

    I have seen films of circumnavigation boats using Solar cells on deck -
    flat.
    
     Anyone know for what purpose they are used?
    
     I thought that the output of photoelectric cells were a function of
    frequency and not intensity? 
    
    Gregg

re .8:

> Assuming that the solar panel is flat on the ground,  you are correct.  If 
> you noticed,  however,  I stated a tracking solar cell.  

Uh, facing the solar panel toward the sun maximizes the panel's output. 
That outout is low because the intensity of the sunlight is low due to 
the low angle of the sun in the sky.

> It's interesting
> to note that for about a month out of the year,  the poles get more heat from 
> the sun than anywhere else on earth.

Hmm, are you sure? Heat depends on sunlight intensity.

>> This {passing through more atmosphere} is also why the output from solar 
>> panels is much less in the early morning and late afternoon even if 
>> the panel directly faces the sun. 

I was referring to the spreading of the sunlight over a larger area at 
dawn and dusk (the sun is low in the sky), not to atmospheric 
absorption.

> Hmmm.  Ever hear of global warming or "the greenhouse effect"?  "See this
> foul bottom notation on the chart?  That's where my house used to be!"  

Greenhouse effect is another matter entirely. It increases the warming 
of the entire planet. 

re .last:

Yes, the photoelectric effect is a function of frequency in that a more 
energetic photon (higher frequency) is more likely to result in a larger 
effect. But intensity (number photons) is also important. The more 
sunlight photons falling on a solar panel, the more output from the 
panel. Enough panels will provide a significant amount of battery 
charging. When way offshore, one's electrical requirements tend to be 
less -- not as much use of cabin lights and navigation electronics don't 
need to run continuously.

RE:.10 by MSCSSE::BERENS "Alan Berens"

> Uh, facing the solar panel toward the sun maximizes the panel's output. 
> That outout is low because the intensity of the sunlight is low due to 
> the low angle of the sun in the sky.

Think about your flashlight again.  If the surface is at a small angle to
the light,  the light will spread over a large area,  so over that area,
the intensity PER UNIT AREA is reduced.  A surface at right angles to the
light will always have the intensity of the source.


Phil

    I wish I knew some of you guys better so that I could gauge just
    how far the various tongues are poked in the various cheeks !
        
    It makes me somewhat envious that you could consider solar power
    as anything other than a minor source as I am sure that there would
    be very little value to Solar Power here.  I do not know what
    the Atmospheric Environment Service advertises as the annual amount
    of Sunlight for Newfoundland, however what we get is very sporadic
    and I suspect that the amount is probably around 50-75% of say the
    Boston area.  It is not uncommon here to have several days, even
    weeks of RDF - (Rain Drizzle and Fog) - and if summer will put together
    two sunny days on a weekend most Newfoundlanders go from fishbelly
    white to lobster red (Ouch!).
        
    My point is that while perhaps some of the more southerly climes
    might provide the kind of sunlight required, I have a very difficult
    time believing that Solar Power would ever be of value here.  The
    only uses of Solar Power that I see around here is for those small
    Mushroom vents that some people mount on their cabin tops.
        
    Now a wind powered generator mounted somewhere on the boat which
    did not involve a constant thrumming that would work very well here
    ....
        

    -.1: Quite right. I just got back from Halifax and it was foggy nearly
    all the time! Wind is a nice alternative to solar energy in those
    climes.
    
    On the topic of the amount of sunlight on a panel at the pole. Alan,
    think about the inverse-square law. The difference between the distance
    from the sun at the equator and the distance from the sun at a pole is
    negligible. That means that if a panel is directly facing the
    sun, and the sun is not obscured (ie. setting or rising), then the only
    factor affecting the intensity of sunlight on the panel is the
    atmospheric attenution, which can often be less at a pole than at the
    equator.
    
    You are arguing that the ground is cooler than at the equator, but that
    is mainly because the ground is tilted away from the perpendicular,
    therefore receiving less photons per unit area.
    
    But this is really academic. Use the right system for the right
    conditions.
    
    Ray

    Check out the latest Scientfic American--there's a story (p. 103)
    about Sanyo's lightweight, flexible solar cells.  An airplane
    with wings covered with this stuff flew San Diego to Kitty Hawk.
    57 foot wingspan, 2000 watt output.
    
    Doug.

see also note 1514.63

    
    .We got 85% of sunshine a year, that means 300 days of sunshine; 
    
    .I sail on Paranoa's lake, Brasilia-Brazil, on a 24' sloop;
    
    .I have a 70Amp battery, eletric pump shower, cabin ligths,
     running-ligths (4 lamps), stereo, VHF, autohelm-800, etc...
    
    .I use the boat only during the weekends, including two 24 hour
     race a year and about 15 overnigths on full moon;
    
    .All I use to charge the battery is a Arco 5 watt solar panel and
     the battery never went bellow 12 v (I have no diesel to start or
     other heavy use).