This is basically how solar hot water heaters work today (I have one). They are superheated during the day (75C/170F) with a mixing valve to produce warm, but n

This is basically how solar hot water heaters work today (I have one). They are superheated during the day (75C/170F) with a mixing valve to produce warm, but not scalding, water to the tap. The tanks are also oversized with a backup electric heater for the top half of the tank. It works pretty well for my climate. I wonder how it compares to PV panels driving an electric heater though. Neither is going to work very well during the winter but the hydronic based system probably needs to get above some base level of solar input to meaningfully heat the water. Whereas PV will always produce some electricity in the winter which can always be converted to heat.