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Photovoltaic off-grid boilers

Inexpensive, simple and CO2-free hot water generation


Photovoltaic off-grid boiler

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

safety extra-low voltage:
Due to the low voltage level of less than 50 V, no
Electrician required.

DC electricity direct use: Direct use of the direct current of the photovoltaic modules for water heating. No inverter or battery is needed.

Digital display on the boiler An LC display provides information about the system, e.g. B. the water temperature and the incoming solar power!

Warranty 3 year manufacturer's warranty

Cost-saving hot water thanks to almost free photovoltaic electricity. High profitability due to low initial investment costs and almost no operating 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.

Whether in your own home, garden or holiday home, warm water is now available everywhere with the help of solar energy. Simply mount the boiler, connect it to a water supply and plug in the solar supply, done. From now on you can get hot water wherever you need it.

The water heaters are available in the sizes 10 l, 30 l and 80 l. It is easy to mount on a wall. A pressure relief and non-return valve is also included. The water connection is made to two 1/2 inch connections with external thread. The solar connection is made via the MC4 connector system.

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


  • plug & play

    Easy installation. The photovoltaic modules are simply plugged into the boiler.

  • Off-grid / island system

    Hot water supply independent of the 230V mains power. Photovoltaic Energy
    can also be used without a 230V connection.

  • safety extra-low voltage

    Due to the low voltage level of less than 50 V, no electrician is required for installation.

  • Innovative MPP tracker

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

Data sheet German
Datasheet English
operation manual
Which and how many photovoltaic modules?

possible applications

Water preheating - instantaneous water heater / gas boiler

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

Read here how Mr. Barzen was able to save 7,000 liters of hot water from gas heating in one year.

island system

Generate your own hot water in places without electricity. The photovoltaic off-grid boiler is used in mountain huts, garden houses or even for long-term camping.


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.

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.