wrote in message ups.com...
[...]
Have you provided a figure to rebut mine with?

Yes.

Did I miss it? What is your figure for the annual saving of a typical
commercial DSHW system, and how do you arrive at that figure?


OK. Since I caused the confusion, let me explain why I thought that the cost (or savings; sorry for the misunderstanding) was
extremely low :

Here is a 'saving' calculator for DHW :
http://www.infinitepower.org/calc_waterheating.htm

I have a 1-family home, using a 50 gallon tank with about 65% overall efficiency, using about 60 gallons HW per day. Gas-powered.
Northern California natural gas price (retail) is around $1.50 / therm.
So, I see DHW cost of about $350/year. That seems right extrapolating my summer gas bills (when I use gas only for HW).

Now, expected savings using solar DHW should be beteen 50% and 80% of DHW usage (seen this at various web-sites).
So I should save between $175 to $280/year.
And note that I an on the low-end of the consumption scale, using nat gas for DHW in a small household, using front-loader European
washer, and water-saving shower heads and such. Most people use a lot more than me, and many use electric DHW heaters, which
essentially double the cost.

So, once again : how did you get to savings of just £20 / year ?

Rob