Home / Photovoltaic off-grid boilers - solar boiler with balcony power plant


Off-grid capable hot water independent of the power grid and without registration of the photovoltaic system.

Warranty 3 years manufacturer warranty

Cost-saving hot water thanks to almost free photovoltaic power. Highly economical due to low initial investment costs and almost no running costs!

Plug and Play The photovoltaic modules are simply connected using MC4 connectors.

Environmentally friendly energy from the power of the sun! 100% renewable and sustainable! Save CO2 every day and actively contribute to climate protection.

  • Drinking water preheating

    Ideally suited in combination with an electric instantaneous water heater.

  • reduce costs

    Reduce your energy costs by using the free energy of the sun.

  • Commissioning without an electrician

    Simply connect the photovoltaic modules to the solar boiler. The heating process begins immediately.

  • Innovative MPP tracker

    50% higher yield thanks to the innovative MPP tracker, which always ensures the maximum yield of the PV modules.

Photovoltaic off-grid boiler at a glance

Whether in your own home, garden or holiday home, warm water is now available everywhere with the help of solar energy. Simply install the boiler, connect it to a water supply and plug in the solar power supply, and you're done. From now on you will have warm water wherever you need it.

The water boilers are available in sizes 10 l, 30 l and 80 l. They are easily mounted on a wall. A pressure relief and non-return valve is also included in the delivery. The water connection is made to two 1/2 inch connections with external thread.

The photovoltaic off-grid boiler heats the water with up to 550 W. In order to have sufficient water available even on cloudy days, up to 2,000 Wp of photovoltaic power can be connected.

65 °C water temperature

The maximum water temperature of the boiler is 65°C. When the 30-litre boiler is fully heated, around 72 litres of 34-degree water can be taken from it, for example for showering. The 80-litre boiler delivers around 180 litres of 34-degree hot water.

The installation of the photovoltaic modules is very easy thanks to plug & play connections. The modules are connected directly to the boiler via plug contacts (MC4). An extension cable can optionally be used to bridge longer distances between the photovoltaic modules and the boiler.

possible applications

Connection plan "Offgrid / island system"

In the connection plan shown, 2 photovoltaic modules (optionally more or fewer possible) are simply connected to the photovoltaic off-grid boiler.

The heating process begins immediately after the photovoltaic modules are connected. Two or more photovoltaic modules are connected in parallel using photovoltaic parallel plugs . Anextension cable connects the photovoltaic modules to the boiler.

If the output of the photovoltaic modules exceeds the output of the boiler, the boiler regulates the maximum output of the modules down.

Since the entire system operates at protective extra-low voltage, no electrician is required for installation.

Excess photovoltaic power can optionally be easily fed into the home grid via a 600 W / 800 W Micro PV inverter using the fothermo switching device.

Read here how you can reduce about 75% of your hot water costs with the photovoltaic boiler.

Connection plan for water preheating - instantaneous water heater / gas boiler

Install the photovoltaic off-grid boiler in front of your existing instantaneous water heater or heating system. The water in the boiler is preheated by the energy from the photovoltaic modules. This means that the water only needs to be heated a little or not at all via the instantaneous water heater.

Excess photovoltaic power can optionally be easily fed into the house grid via a 600 W / 800 W micro PV inverter with the help of the fothermo switching device .

Read here how you can reduce about 75% of your hot water costs with the photovoltaic boiler.

Further information on the photovoltaic off-grid boiler

3 years payback period

The conventional electric boiler is often the largest consumer of electricity in the home. It normally requires around 3.5 kWh of electricity per day, which equates to around 1,277 kWh per year. With an average electricity price of €0.31/kWh, this results in annual costs of €396.02 for hot water production.

A photovoltaic boiler, on the other hand, primarily uses solar energy. For example, if three photovoltaic modules with 430 Wp each (1.29 kWp in total) are connected to a boiler, these modules generate around 1,200 kWh per year. A large part of this electricity can be used to heat water. On cloudy days, however, additional electricity must be drawn from the grid to heat the water. With a photovoltaic off-grid boiler, you can usually save around 75% of hot water costs, which corresponds to around €300 per year.

What happens when the boiler is full and the sun is still shining?

The boiler simply switches off the PV modules. Or you can feed excess electricity into your home electrical network with the fothermo switching device and a standard micro PV inverter

You no longer lose energy.

It also makes sense to oversize the connected photovoltaic module output of the boiler to up to 1,600 Wp, since you can feed excess electricity up to 600 W into the power grid. Best of all: The photovoltaic system still counts as a balcony power plant. Only a very simplified registration of the photovoltaic system is necessary.


I installed the boiler in August 2022 and now after 10 months I would like to give very positive feedback. The combination with 2 modules and the 30 liter fothermo boiler is really perfect.

fothermo 30 liter boiler is a 100% purchase recommendation (there is nothing comparable for the average consumer). Since the installation, we have saved all the energy that the dishwasher needs.

Even with visitors at the weekend, 4 people took a warm shower. The gas heating has been completely out of order since March.

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