Although I agree with most of your post I believe this is wrong.
Quote:
Originally Posted by osolemio
If you have a need of 140F and your solar panel peaks at 110F, the energy produced - in reality - is zero.
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if your water started below 110F then any heating the panels managed to do is energy produced. Yes you will still require an additional source of heating to get the desired temperature but that source will not need as much energy.
In my case my desired final temperature is 105-110 F My starting temperature is 45-50 F. Any rise that the solar panels accomplish is energy saved that the electric hotwater heater doesn't need to achieve the final temperature.
I agree about the larger tank sizes but there is some sort of ratio between collector size/efficiency and tank size. If you make your tank the size of a swimming pool, 50 sqft of collector isn't going to be able to heat the tank to a useful temperature. if your tank is the size of a garbage can the panels will quickly heat it beyond the desired temperature so you will stagnate the panels instead. My tank is roughly 160 gallons. This should be a fine size for DHW heating but is probably too small to be really useful for space heating. I'm guessing I'd draw the available energy out rather quickly running it through a couple of radiators.