ᐅ Convert solar thermal system for hot water to photovoltaic system?

Ytong2023 schrieb:

300 liters (79 gallons) is completely oversized for 6 people and clearly a waste of money.

If the people don’t shower for hours, half that amount is more than enough.

LOL – rarely have I seen such unrealistic nonsense. Regards. 150 liters (40 gallons) for six people – that’s only 25 liters (6.6 gallons) of shower water per person. That only works if you shower cold, or if you ignore the 125 liters (33 gallons) used by the bathtub.
A 10-minute shower uses about 120–150 liters (32–40 gallons) of water. At normal temperature, 150 liters (40 gallons) means about three minutes of showering per person.

When my three girls shower after a day at the stable and wash their long hair, the temperature in the 300-liter (79-gallon) tank drops from 52°C (126°F) to just above 30°C (86°F). After that, the parents can only shower lukewarm. For a family, 150 liters (40 gallons) without a bathtub is not practical in real life. With a bathtub, even less so—unless you set fixed shower times to allow the hot water tank to reheat.

However, it also does not heat up to normal temperatures (70°C (158°F)).

@hanghaus2023

As already mentioned, you basically have two options: an electric heating element or a heat pump.

With the control system, you need to check how your gas boiler manages this and then add the necessary components or remove any that are no longer needed.

I would install a 3 kW heating element. Is that sufficient to heat the water in the 300 l (79 gallons) tank to 70°C (158°F) during summer? In winter, heating will be done with gas as usual when there is not enough electricity from the photovoltaic system.

The gas boiler is programmable, and the hot water is controlled separately, as usual in combination with the solar system. For the electric heating element, I only need a controller that, for example, switches off at 70°C (158°F). What is the ideal temperature?

Regarding the sizing of the 300 liters (79 gallons), we have always managed well with it. Only very rarely did we have to take lukewarm showers (when the kids washed their long hair). This was with a 60°C (140°F) setting. The bathtub use was only by arrangement.

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

I have now installed the solar collectors in the garden. I will connect them soon. Now I just need to find a tradesperson to install the wiring.