Based on the numbers I have provided for the best days a day (of which I might get 50 a year) we can get 9% more output, but over a year that is maybe a few percent. If the pump needs replacing on typical pump periods of 5-10 years that will cost more than I would gain as each is going to be £200 (100 replacement and 100 for the pump) and that alone is more than a few percent of the system. If it drops the life of the panels to 20 years or requires one maintenance on the roof all the savings disappear instantly. Also if the panels cost more than 3% more than the electrical gains aren't worth it alone.

The problem is the gains are just too small and the risks and extra costs far too high.

Its not really fair because what you would do is flow this hot water into a water cylinder and get ~6KWh of water heating out of it a day. It will produce a lot more heat than that, you get nearly 4x as much heating as you do electricity but i can't use it, I don't need 120Kwh of heated water for showers and in the winter its not going to be enough to heat the house. That is fairly substantial amounts of extra power but I don't need that amount of panels of water heating I likely only need 1 solar heater, the rest is going to be wasted and not help in cooling the panels.

Who ever its for its not for people like me.