I intend to add a grid tied PV system. Just in the deciding what size phase, atm. My interest in solar water heat is primarily to heat a pool. If i was able to add btu's to my winter storage, so much the better. I'm sure I'll get some output from flat plate collectors in the winter but I want to be sure I was getting the best bang for my buck.
Since I can fab the flat plate collectors, those will likely brovide the best yield for my investment. Loss of credit will diminish that a bit, however.
I've been working on a method that would allow people to estimate how much collector area is needed for a solar water heating system that will get an 80% solar fraction for various US climates. I'm using the free retscreen simulation software to do this. It takes into account climate, hot water demand, hot water temp, collector orientation, ground water temp, storage size and a few other things.
For my effort to simplify things, I'm assuming: 48 gallons/day demand, collector pointed south and tilted at the cities latitude, 120F hot water, cities ground water temp, 2.5 gallons storage per sf of collector, typical flat plat collector efficiency curve.
My aim is to put this up on my website when its done, but since it comes up in this discussion, thought I would pass along some results so far.
This is collector area required for an 80% solar fraction for 15 cities given the assumptions above:
Pheonix 22 sf
Miami 31 sf
LA 34 sf
Denver 37 sf
San Fran 40 sf
Salt Lake 48 sf
Topeka 48 sf
Boston 57 sf
Madison 60 sf
Bozeman, MT 68 sf
Bangor 78 sf
Buffalo 80 sf
Portland, OR 100 sf
Seattle 125 sf
Anchorage 195 sf
I would not take these as gospel, but retscreen is used by a very wide audience and they do validate their results against other simulations.
One interesting thing is that the areas vary over such a wide range.
In the end, the stuff I'm planing to put up covers things like cost (DIY), payback, IRR, solar fraction, carbon emissions, ...
If you look at the data above, you might think that Pheonix would be the hands down winner on payback, but several of the cities do better, with Denver the best (2.9 years). A good part of the reason for this appears to be the high ground water temp in the south -- it means that there is not as much money to be saved by heating it with solar, so you save a bit on system cost with the smaller collector and storage, but this is more than offset by the smaller savings -- did not expect that.
Just looking at the numbers, the east coast locations don't look that bad to me. I picked Buffalo because it has reputation for very cloudy winters, and its really not a whole lot worse than Bozeman (where I am).
Anyway, thought this might be of interest.
Any thoughts on the method would be appreciated.
By the way, you can download retscreen and run it yourself if you want to see other conditions -- it also can do solar heating systems. There is a bit of a learning curve, but not awful.
http://www.retscreen.net/ its based in CA, but used worldwide -- some areas require a retscreen analysis to get rebates.
Gary