i am getting one 500 pma and if everything will work fine i will insatall another before winter starts, but my question is what volume of battery bank i should have in order to run 4000 power inverter to run the water heater ? i live on a higher elevation and 80% of the time the wind is above 15 mph. Any suggestion will be greatly appreciated. And where do i get such inverter? ( off grid inverter). thanks, Greg.