Convert hot water from solar thermal system to photovoltaic system?

Hello Forianer,

I currently have a solar system on the roof that heats water when the sun is shining, designed for 6 people.

In a few weeks, the photovoltaic system (11.3 kWp) is to be installed. The solar system is over 20 years old and will be removed. In the future, the photovoltaic system will also be used for water heating.

A 300l water tank is already available. It is equipped for the solar system.

Now my question is how can the water tank be converted so that the photovoltaic system takes over the function of the solar system?

In my opinion, you need a controller and a heating element for that.

Many thanks for your help.

Greetings from hanghaus2023

What kind of heating do you use?

I still have a gas condensing boiler.

If this continues like this for a longer time, one could first add a domestic hot water heat pump. It is significantly more efficient than an electric heating element.

How much does a domestic hot water heat pump cost compared to the heating element?

300 L are completely oversized for 6 people and definitely a blatant waste of money.

If the people do not shower for hours, half of that is more than enough. I have a 500 L hot water tank for my 9 apartments, and the heating engineer wanted to go down to 300 L. Mind you, for 9 tenants.

I have an 80 liter electric hot water boiler for 3 people. It is simply plugged into the outlet. Before that, I connected an analog small timer switch for 1.99 euros, so to speak as a control. The hot water boiler is heated daily between 10 am and 3 pm.

Thus, the photovoltaic system heats my hot water from March to October. November to February only partially, unfortunately. But the 80 L require about 3 kWh of electricity per day to heat up to 70 degrees. It almost never cools down. If I calculate 40 cents electricity price, I need 120 days from the grid, so 1.20 euros daily. So I come to annual hot water costs of about 150 euros. With very low investment costs. I also do not need a circulation or recirculation pump.

Of course, you can also install a heat pump, but the investment costs are significantly higher there.