Hi,
You might want to consider a home made solar thermal panel instead of a PV panel.
PV panels are selling for about $1 per peak watt -- maybe a bit less if you can order a lot of them (plus shipping).
A good homemade solar thermal water heating panel runs about $5 per sqft.
On a comparable peak watt basis, it delivers about (1 sqft)(1 sqm/10.76 sqft)(1000 watts/sm)(0.6 efic) = 56 peak watts per sqft, or $5/56watts = 9 cents a peak watt -- so, the homemade thermal panel is about 10X more cost effective than the PV panel (roughly).
Since the PV panels are about 15% efficient and the water heating panels are about 60% efficient, it only takes about 1/4 of the roof space for the same heat output panel from a thermal collector.
You could basically use a system like this:
http://www.builditsolar.com/Experimental/PEXColDHW/Overview.htmbut, just leave the insulation out of the storage tank so that it can lose its heat more rapidly to the room.
If you wanted to take it a step further, you could also use the same system for some cooling in the summer by using a scheme like this:
http://www.builditsolar.com/Experimental/RadiationCool/EvaproRad.htmIt achieves quite good cooling rates in my climate, but may not work as well in cloudy more humid climates.
You would want to be careful to monitor for condensation on the tank if you use it for cooling -- all depends on your climate.
If you use the PV approach, I'm not sure if you need some kind of matching between the heating element and the PV panels to get good efficiency out of your PV panel. Most PV systems now have inverters that keep the PV panel at the point on its power curve where it generates the most power (MPPT) -- would something like that be needed between the PV panel and the heating element?
How much heat storage would a 200 gallon tank give you?200 gallons of water cooled from 130F down to 80F gives you (200 gallons)*(8.3 lb/gal)(130F - 80F)(1 BTU/lb-F) = 83000 BTU -- about equivalent to a gallon of propane burned in an efficient furnace.
Would the tank be able to get rid of the heat fast enough between collection periods?If the tank walls were about R1 and the tank wall area was 80 sqft, then when the tank temperature was 110F and the room temperature 70F, then the tank would deliver about (80 sqft)(110F - 70F)/R1 = 3200 BTU/hr, or about (24)(3200) = 77K BTU/day -- so, its not such a bad match to the amount of heat it stores. A tank that is made thinner and longer would have more radiator area, and would get the heat out faster.
How much collector do you need to heat up a 200 gallon tank on a sunny day?The rule of thumb is about 1.5 to 2 gallons of water per 1 sqft of solar thermal collector area, so the 200 gallon tank could handle about 100 sqft of solar thermal collector.
Gary