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From: (no name) (no email)
Date: Thu Feb 07 2008 - 20:19:37 EST
>From recent posts it appears that many listees are starting down the slippery
slope of solar power. Solar power for battery maintenance is one thing. Solar
power to run all ship systems is another. The limiting factor, other than
your pocket book, is the amount of unshaded level surface you have available.
Noon sunlight delivers about 1000 watts of power per square meter. Good
commercial solar cells are about 15% efficient so you can extract approximately 150
watts per square meter. I estimate that an average trawler in the 40' range has
about 4 square meters atop the pilothouse and possibly 6 square meters on the
aft cabin roof for a total of 10 square meters. That assumes that you don't
carry a dinghy on the roof.
With 10 square meters of area you have space available for 1500 watts. In
full sun, you will be able to generate full power for 5 hours a day or about 7500
watt hours. Add another 1000 watt hours for the morning and evening periods
and you have 8500 to 9000 watt hours per sunny day. Averaged over a 24 hour
day, you would be able to support about 400 watts of continuous electrical load.
It may be enough to run a small refrigerator, a TV and laptop, modest internal
lights, keep the battery charged, and run a bilge pump but not much else. You
would certainly not be able to operate an air conditioner or an electric
cooktop.
But you probably do keep a dinghy on the back deck. That means you have only
about 4 square meters of unshaded surface on the pilothouse. That reduces the
solar generating capacity to 600 watts, 3000 to 4000 watt hours per full day,
or about 150 watt hours of load averaged over 24 hours. It would be possible
to run a small refrigerator for a few hours during the day, then use the solar
power from early and late hours to keep up the battery and run the bilge pump.
To fully power a well equipped trawler, refrigerator, air conditioner, TV,
microwave, etc. would probably require about 20,000 watt hours over a 24 hour
period. That might require 26 square meters of solar cells, about three times as
much flat space as most of us have available. And, of course, you would have
to keep a backup generator for those days when the sun doesn't shine. I know
that passagemaking sailboats sometimes use solar panels to generate all their
electricity but sailors have learned to drink warm beer.
The current cost of solar power, using good commercial equipment, is about
$0.60 per kilowatt hour. The is about twice as costly as power derived from a
diesel genset even with $4 per gallon fuel.
The best bet for most trawler owners is to install enough solar power for
battery maintenance and bilge pumping. Alternatively cover the entire roof, and
have some surplus power for a few other things. But unless you want to build an
extension to your deck for additional panels, forget about fully meeting your
electrical needs. But then boating isn't a rational exercise, is it?
Larry Z
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