Hi, welcome. The best way to heat your water with PV would be to net meter, that way all the surplus in the summer builds up credit with the utility. To hook electric elements directly to PV would not work very well because the load needs to be varied to match the solar conditions. This company claims to be addressing that with an MPPT (maximum power point tracking) box:http://www.presolarnet.com/products/liberty_box.htm
Then of course there are also the hot water type of collectors which are for exactly that, we don't handle those.