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Solar hot water
Thought that all may like to read the reply.
The element in a hot water unit, be it solar or otherwise, will corrode quickly when supplied with dc as opposed to normal 50 hz (or 60Hz for our USA viewers !) energy. They are not designed for operation on dc, even thought the rating may well be the same and the resistance is suitable. This assumes you have a 240 v dc battery bank.
Our hot water is solar heated, and the backup is the wood stove, with a backup-backup that switches the 3.6 kw element to the 240 v from the inverter either through a manual switch, or when the battery's are fully charged, via a relay from one of the PL60 regulators. It also helps to have 20 kw of installed solar, at 48 volts, a 2,500 amp hr submarine battery bank, plus a 5 kw continuously rated inverter/charger. Yes, that's over 400 amps dc at 48 volts and takes 3 regulators all communicating with each other to keep it under control. The panels are angled to take advantage of different sun angles during the day, so the peak power is around 300 amps in summer in full sun.
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