Solar PV water heat

Joseph, for some reason, the site would not allow me to reply to your post, so I am posting my reply in this manner.  I have been using solar PV water heat for several years now with excellent results and no problems.  I am using 50vdc from 4 solar panels in series through a 120v/1200W lower element in a standard 30 gallon electric water heater.  The element has a resistance of 10 ohms, which passes 5 amps of current from 50vdc.  This is 250 watts of heating power.  (The upper element is still available for AC usage for emergency heat should the DC heat fail.)  I use a relay operated by the standard thermostat in the water heater to switch the 50vdc in and out of the heating element.   You cannot use the thermostat for directly switching DC power to the heater element because the DC will ionize the thermostat gap and will burn the thermostat contacts.  Thus the use of a switching relay to buffer the thermostat.  Any further questions, feel free to contact me at  JonChristenson @ msn.com   :-)