"Roger Long" wrote in
:

Come to think of it, I don't want any permanent connection between the
battery banks to complicate things when I am using my dual charger on
shore power with the master switch off so I probably need two separate
solar panels.



I'm not sure how many watts/sq meter you get in Main, Roger, but I'm sure
it's very low in comparison to SC. Let's analyze your loads:

Multiply 13.8V x the amp load of everything that will be running on the
boat....such as anchor light, 13.8V x 1.2A = 16.56W x 12 hours = 198.72
watt-hours each night. (Your spare anchor light bulb may say how many
watts it is, so just multiply that by 12 hours (or more as it gets dark
early in Maine and the sun comes up late).

Do this for every load you can think of. Add up all the Watt-Hours to
get a total. The current usage of the electronics is in the
specifications page of the manual. Do NOT rate them conservatively to
try to get the number down. We're going to ADD more to your answer to
get a relatively "worst case scenario" for our purpose.

Now, I found this Maine Solar House on:
http://www.solarhouse.com/index2.htm
Click on SOLAR DATA on the left panel to get what power they generated
with a whole roof of solar panels, 4,200 watts of them!

In July of 1998, this 4,200 watt, perfectly placed array generated 467KWH
of real power. Let's scale that down to two 80W panels of a perfectly-
placed, unobstructed boat. 80/4200 x 467 = about 8.9KWH in Coastal Maine
in July, about the hottest month when the sun is most North it gets.

Your boat solar cells are never going to make 8.9 KWH for a lot of
reasons.....
1 - The boat moves around on the hook every 6 hours. If we tilt the
panels for best exposure, half the day they're going to be pointed away
from the sun. If we lay them flat, that takes care of that, but the sun
is at an obtuse, inefficient angle, which reduces cell output
accordingly.
2 - The damned rigging shades the panels. Panel output drops like a rock
if anything makes a shadow across the panels. Everything on a sailboat
makes a shadow across the panels at SOME time during a day.

There are many other reasons we can probably identify, including keeping
the salt off the panels which reduces the solar radiation making it
through the glass or plastic cover....

Ok, so it's not going to be easy to figure out how much power you're
going to get from two 80W panels, in reality, but let's work on 5 KWH per
MONTH...not per day. This is 166 watt-hours per day from two 80W panels
on a sailboat. Being most generous, let's say 200 WH per day.

Do you think the anchor light will use it all? The house looks like it's
on a hill, even though it's close to the coast. His air is THINNER than
yours, and he has a lot LESS fog/haze/etc. on his panel roof beast.

So, what happens? The panels don't produce enough power and the
batteries quickly lose the battle going dead, REALLY dead.

I hope this has given you some kind of idea who inefficient solar power
on a sailboat really is...especially that far North. Sure glad I found
that solar house on the Maine Coast. Look how STEEP the panels are set
trying to get perpendicular to those solar rays. Snow won't be much of a
problem...

An 80 watt panel is about 22" x 48" on:
http://www.wholesalesolar.com/products.folder/module-
folder/bp/bp380U.html
When you go to the boat, take a 2x4' sheet of plywood you can't bend with
you. Make believe it's 1-2" thick. Try to find TWO places for TWO
panels on a 32' boat. If you stow the panels up for sailing, you make NO
POWER for the electronics and house batteries underway...making the watt-
hour deficiency even worse.

At noon on their best day, each panel makes a little less than 5A of
power for the few hours in the middle of the day. Bubba would tell you,
"Thait ain't 'nuf, Bo!" Plan on running the engine a few hours to
recharge. Remember we must recharge SLOWLY, not in 10 minutes at
500A....at least not YET given our current lead-acid batteries.

Two panels are $1000, good for 20 years.

All is not lost, however. Maine is WINDY! WIND is our FRIEND, in more
ways than one. Let's compa
http://www.emarineinc.com/products/w...irxmarine.html
I'm not endorsing ANY wind generator product. AirX was the first marine
unit Google found, and is representative of their capabilities.

In a 28 mph breeze, an AirX makes 400 watts of DC. Look at:
http://www.emarineinc.com/products/w...es/airxoutput1
..jpg
Everytime the wind is 13 mph, the AirX puts out as much power as the
solar panel does pointing at the sun, at noon, on its best day....

Question....Are there more windy days on the Maine coast than totally
sunny days...at anchor, swinging in the tide?

The wind genny makes power whichever way the wind is blowing. It cares
less where the boat is pointing or which way the tide is running. It
simply spins around into the wind at an optimal angle for maximum power
generation with NO INPUT ON YOUR PART, which I find very important.
Remember when the solar beasts were stored getting underway? The wind
genny output GOES WAY UP when you add APPARENT WIND to it! Sailboats and
Wind gennys LOVE apparent wind...(c; When we're whipping along with all
the lights and electronic gadgets buzzing away, leaned over on the
handrail, EVEN AT MIDNIGHT, the wind genny sees an apparent wind of 25
mph! Hell, according to this graph, we may have to turn on more than the
running lights! We're making 25A x 14V = 350 watts...AT MIDNIGHT!

I hope you can see the practicality of wind power on your wind-powered
boat over this solar nonsense with the dead batteries and flashlights.
Running the fore-aft-mast running lights all night...that solar panel,
even if you permanently mounted it, is USELESS on the midwatch when the
batteries are going flat. The wind gennys now have special loading
circuits on them so when the batteries get up to full charge, and they
will, the genny's own computer will load the genny to prevent overspeed
and turn excess power into heat.....well, at least until we get BIGGER
house batteries to store it all...(c;

Wind genny is half what two measily solar panels cost. Are you going to
own this boat for 20 years to worry about how long the wind genny will
last? I thought not.

Larry
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