[QUOTE=Xringer;5360]This simple technology (DC heating of water using PV panels)
has been tested for a few years by the government.
BFRL: Solar Photovoltaic Hot Water System
it just might be cheaper to skip all the plumbing hardware and just wire some PV to a heating element in your HW tank.?.
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On a trip this spring on the park side of Gatlinburg, Tenn. I saw a Photovoltaic Array
Ref:
fire.nist.gov/bfrlpubs/build02/PDF/b02162.pdf
That solar photovoltaic water heating system had been installed at the Great Smoky Mountains National Park (Sugarland) Visitors Center in the 90's. The solar was out behind the restroom/vending area. I had asked the Park Ranger about it and he pull out a reference info book, out of their office and told me a little about it. He said it was for hot water.
That's what got me thinking about Solar Hot Water (Electric Resistance Water Heater)
OK here's what I'm a thinking ……….
"Using electric resistance heat, it takes 0.171 kWh to raise a gallon of 50 degree water to 120 degrees".
Ref:
http://http://www.greenbuildingadvis...r-thermal-deadSolar Thermal is Dead | GreenBuildingAdvisor.com
And my PV System does 320-326 kWh per panel, per year.
So I generate about 1 kWh per day per panel at this location. Lets say I build a stand alone system and use 4 panels and a inverter transfer device…
4/0.171 = 23.4 gallons of 120 degree hat water. (only two of us here)
My cost would be around est. of $1250 for all the parts (I know a guy that knows a guy and so on)
My savings would be 1460 x $0.0954 (kw rate now) = $139.28 per year (or (8.98) years for payback, but with the 30% tax credit it comes to 6.28 years)
I plan on using the bottom element (electric resistance heat) for this on my two element electric water heater.
This might be Pie in the Sky, as the costs will only go up the more I dig into this. But it's what I'm thinking for now.
So far I plan on separate either 2,3,4 panels but will start with 2 and see how that would work.
Can't tie in to the grid as that's AC (get paid base $0.10 plus $0.12 over per kw) and my contract is set, to open it up would lower the over rate to $0.09 or even lower.
http://http://tackyted.com/solar/
(I'll have to read up on the code for this DC stuff)
The new 2 panels would feed about 50 VDC down to a fused interface (
working on it!) and then to the tanks lower heat element. The thermostat on the lower element on the tank would dictate the on/off.
The upper element would run on the normal AC power, but set at a lower temp. As heat rises (well really cold falls) the upper element would stay off most of the time, cause the lower is keeping it warm.
My big problem is finding a type of MPPT controler in the USA. I've seen the immerSUN & EMMA from the UK but these are for AC and I just want to do the DC.
If y'all see any problems with my line of though or know of a control link please post, Thanks