No point in making H2 from the PV electricity to then burn. Just heat from the electricity directly. Unless you are storing the H2 to allow for seasonal variations.
exactly, no point heating water during the day while you're at work, once it reaches a certain temp it won't heat further, so all that sunlight is going to waste..
also, you can get a more instant heat if you store the gas, and can shower when it's dark..
hydrogen is the cleanest burning gas.. all you get as a byroduct is water..
you could also use the hydrogen in fuel cells to produce electricity at night and during dull days..