The fothermo 200 liter photovoltaic standalone boiler produces enough hot water for 5 people for most of the year with 7x 325 Wp photovoltaic modules (total output 2,275 WP). At the same time, photovoltaic surpluses are fed into the power grid via a balcony power inverter. Last year, almost 450 kWh of excess electricity was fed into the power grid.

The following experience report provides an insight into the structure, operation and benefits of the 200 liter photovoltaic stand-alone boiler from fothermo.

You can see the cold water inlet at the bottom of the freestanding boiler. The photovoltaic modules are connected directly to three MPP trackers in the gray box shown. The water is heated by three direct current heating elements in the boiler.

The integrated heat exchanger for connecting an existing oil, gas or pellet heating system is shown above. The hot water drain is in the upper area of ​​the boiler. In addition, two magnesium sacrificial anodes ensure special protection for the enameled steel tank.

In summary, it can be said that the photovoltaic boiler works like a normal storage tank but also offers the option of photovoltaic hot water preparation.

4x photovoltaic modules are connected to the fothermo switching device. The first output of the switching device supplies the photovoltaic boiler. The second and third output feeds excess power into a 600 W / 800 W micro PV inverter.

Two further photovoltaic modules were each connected to another input of the photovoltaic storage system.

If the energy from the photovoltaic modules is not sufficient, the water is automatically reheated via a gas boiler connected to the heat exchanger of the storage tank.

The photovoltaic modules with an output of 2,275 Wp generate around 2,400 kWh of electricity per year. Over the course of the year, around 70% of the electricity or 1680 kWh of hot water could be stored in the photovoltaic boiler.

For comparison:
1,680 kWh corresponds to around 168 liters of heating oil.
The energy used heats 28,000 liters of water from 15 °C to 65 °C. With this amount of hot water, you can have free hot showers around 1,120 times a year if 25 liters of hot water are needed per shower. In practice it turned out that from April to October there was hardly any need for additional heating using the gas heater. In 7 months of the year, hot water could be provided free of charge via the sun. During the transitional periods in spring and autumn, the majority of the required hot water could be provided on sunny days.

Conclusion:
The photovoltaic standalone boiler produces more than enough hot water for a 5-person household most of the year. Connecting the photovoltaic modules is very cost-effective as no electrician is required for commissioning. And since no electricity is fed into the grid, the photovoltaic system is also registration-free. Since no mechanical components are necessary to operate the boiler, the photovoltaic boiler is also almost maintenance-free.
At the end of the day, it just feels good to know that the hot water used for showering is renewable and sustainably produced. This makes showering twice as much fun.

If you already have an existing heating system that does not need to be replaced, you can use a photovoltaic heating element. This will be screwed into most hot water tanks using a standard 1.5 inch thread. This makes it very easy to retrofit an existing system. With photovoltaic heating elements, the photovoltaic modules are also plugged in directly. In addition, excess electricity can be fed into your own home network via a micro PV inverter.