In article ,
says...

"Glenn Ashmore" wrote

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com


I like the idea of diverting to the water heater, but most of us do not have
the option to add a second 12V element to our existing heaters.

One thought, would be to add a second heater in an external loop around the
water heater - something like the add-on heaters that are sold for cars in
lieu of a block heater. This site has the elements:

http://www.realgoods.com/renew/shop/...204/ts/1025078

But, if the solar panels put out, say 150 watts for 8 hours, what happens
when the water becomes too hot? With a small boat type water heater say 6 or
10 gal, this could happen quite quickly. Maybe then we throw the towel?

According to this handy calculator:

http://chuck-wright.com/calculators/watts.html

Heating 6 gallons of water by 100F will require about 240 Watts
for 6 hours. You're not likely to boil the water in in
the heater with that amount of input. With losses, 6 hours
at 150Watts is probably just enough for a hot shower. OTOH,
on a day sunny enough to give you 150 Watts for 6 hours,
you probably don't need a HOT shower. ;-)

Mark Borgerson