Ron Purvis wrote:

I think you are off on your figures. According to
http://www.fsec.ucf.edu/solar/apps/sdhw/dhwsave.htm the typical home uses
20 gallons of hot water per day for the first two persons and 15 gallons
of hot water for each additional person. That would be 25,550 gallons of
hot water per year for a family of four.

OK, I'll accept those numbers. Anyone got a better figure on the average
cost of heating water? My numbers for heat required are, if anything, on
the low side, but at $25/million BTU, and only 25,000 gallons per year,
you're talking $250/year (somebody else said $20/month, so same ballpark).
Still plenty to make a commercial solar water heater pay off.

--
derek