Convert hot water from solar thermal system to photovoltaic system?

300 L are completely oversized for 6 people and already a huge waste of money. If the people don’t shower for hours, half is more than enough.

LOL - rarely seen such a clueless nonsense Greetings. 150 liters for six people – that’s 25 liters of shower water per person. Only works if you shower cold. Or if you disregard the 125 liters of the bathtub. 10 minutes of showering means a water consumption of about 120-150 liters. At normal temperature, about three minutes per person should be enough with 150 liters. When my three girls shower after a day at the stable and have to wash their long hair, the temperature in the 300-liter tank drops from 52 degrees to just above 30 degrees. The parents can then only shower lukewarm. With 150 liters as a family in practice without a bathtub, this is not feasible. With a bathtub, even less so. Unless fixed times are set so that the hot water tank can reheat.

But it does not heat up to normal temperatures (70°C).

As already mentioned, you actually have two options: heating element or heat pump.

With the control system, you then have to see how your gas boiler manages this and add the necessary components, or remove the unnecessary ones.

I would install a 3 kW heating element. Is that enough in the summer to heat the water in the 300 l tank to 70 degrees? In winter, heating will be done as usual with gas as soon as too little electricity is supplied by the photovoltaic system.

The gas boiler is programmable and the hot water is controlled separately. So as usual in combination with the solar system. For the heating element I only need a control unit that, for example, switches off at 70 degrees. What is the perfect temperature?

Regarding the sizing of the 300 liters. We have always managed with it. Very rarely had to take a lukewarm shower (when the kids washed their long hair). However, with a setting of 60 degrees. Bathtub only by arrangement.

I was also recommended Shelly for the control. Does anyone have experience with it?

I have now set up the solar collectors in the garden. I will connect them soon. Now I just need to find a craftsman to lay the cables.