variants
The photovoltaic hybrid boiler reduces your hot water costs by up to 100%. Use primarily the energy of the sun. On cloudy days, additional heating can be provided automatically via the socket.
Characteristics
75% energy saving
A 2-4 person household can use an 80 liter photovoltaic boiler to obtain around 75% of the energy required for hot water preparation from the photovoltaic modules. The remaining energy is drawn from the grid, especially in the winter months. With particularly economical hot water consumption, up to 100% of the requirement can be covered by the photovoltaic modules.
1,500 W electric post-heater
The powerful electric after-heating via the 230 V power network enables sufficient hot water to be produced even on the darkest days. Once the boiler has completely cooled down or been emptied, the water temperature can be heated back up to a high temperature within a short time.
Digital display on the boiler
An LC display provides information about the system, such as: B. the water temperature, the power and the energy already used!
Plug and play
The photovoltaic modules are simply connected using MC4 plug connections. Since the entire system works in safety extra-low voltage, no electrician is required for assembly/commissioning.
Direct current use
Direct use of the direct current from the photovoltaic modules to heat water. No inverter or battery is required for operation. This enables very easy commissioning and reduces costs and complexity.
Warranty 3 year manufacturer's warranty
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Up to 100% hot water supply
You can cover up to 100% of your hot water needs using photovoltaics.
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550W + 1,500W
550 W photovoltaic output and 1,500 W automatic after-heating via 230 V mains power on sunny days.
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plug & play
Easy installation. The photovoltaic modules are simply plugged into the boiler.
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safety extra-low voltage
Due to the low voltage level of less than 50 V, no electrician is required for installation.
Photovoltaic hybrid boiler at a glance
The photovoltaic hybrid boiler is the ideal solution for a cost-effective and sustainable hot water supply in your home. Hot water usually accounts for around 20 - 40% of the energy consumption in a household. fothermo boilers are the easiest way to use the sun's energy directly.
With up to 550 W, the photovoltaic hybrid boiler heats the water using photovoltaic power. In order to have sufficient water available even on cloudy days, up to 2,000 Wp of photovoltaic power can be connected and/or the intelligent 230 V auxiliary heating can be used.
The boilers are available in 30 litre and 80 litre sizes. The boiler is mounted on a load-bearing wall using two screws. A corresponding mounting device is already mounted on each boiler.
A pressure relief and check valve is also included in the delivery. The water connection is made via two 1/2 inch connections with external thread.
1,500 W afterheating & assembly
If the sun does not provide enough energy to heat the water for a longer period of time, the boiler can be automatically reheated using the 230 V reheating system. To activate the reheating system, the boiler's thermostat is set to a minimum temperature. For example, 35°C. As soon as the water temperature falls below the set minimum temperature, the water is reheated using 1,500 W electricity from the mains. The reheating process ends automatically as soon as the water has reached the set minimum temperature again.
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.
The solar hybrid boiler explained in the video:
How does the fothermo photovoltaic hybrid boiler work? What connections does it have, and how do I replace my existing electric boiler with the solar hybrid boiler?
Calculate savings
Use the interactive energy savings calculator to calculate your annual savings with the fothermo hybrid boiler.
Information to download
Technical specifications
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Easy construction
Plug & Play: The photovoltaic modules are simply plugged into the solar hybrid boiler. The heating process starts immediately. Here is an image for illustration.
Installation: The boiler is hung in the boiler mounting device using two screws screwed into the wall. -
1/2 inch thread
Easy water connection: The 0.5 inch (1/2 inch) thread allows for easy connection of the solar hybrid boiler to the existing water pipe.
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Accesories
Check valve & pressure relief valve : The safety valve protects the boiler from possible overpressure.
230 V power cable : The power cable (Schuko plug) for the socket ensures easy connection to the 230 V power grid.
Both are included in the scope of delivery.
Hybrid boiler without grid feed-in
In the connection plan shown, 3 photovoltaic modules (optionally more or fewer possible) are simply connected to the photovoltaic hybrid 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.
Hybrid boiler with 800 W mains feed
In this example, excess photovoltaic power is fed into the house grid via an 800 W micro PV inverter. The fothermo switching device is required as an energy manager for this.
The switching device detects when the photovoltaic hybrid boiler has finished heating or when more photovoltaic power is available than the boiler can convert into heat. In these cases, excess energy is fed into the house network.
On particularly sunny days, the switching device starts feeding in partial surplus power from 1 - 2 modules early in the morning. This ensures that the house's basic electrical load is covered in the morning hours.
This means you save not only on hot water costs but also on electricity costs.
More information about the photovoltaic hybrid boiler
Calculate heating times
Use our interactive tool to calculate the heating times of the hybrid boiler using solar power or mains power.
digital display
A variety of different values can be read on the hybrid boiler's display. These are:
- current water temperature in °C
- current photovoltaic output in watts
- current photovoltaic voltage in volts
- Total photovoltaic energy used in kWh
The maximum water temperature (10 °C to 65 °C in 5 °C increments) can also be set using the two buttons on the right edge of the display.
Note : The solar boiler's display will only turn on AFTER the photovoltaic modules are connected. If only 230-volt mains power is used, the display will remain off.
Technical information
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33 mm insulation
33mm insulating foam: All solar hybrid boilers have good thermal insulation. When the maximum water temperature of 65°C is reached in the evening, the 80-liter boiler loses only about 7°C by the next morning without reheating.
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100% Independent
Operation without mains connection : The solar hybrid boiler can also be operated without a 230 V mains connection. In this case, hot water is produced 100% using photovoltaic power.
Calculation of profitability:
The classic 80-liter electric boiler is usually the largest consumer of electrical energy in the household. It generally consumes around 3.5 kWh of electricity per day. This corresponds to around 1,277 kWh of electricity per year. With average electricity prices of €0.31/kWh, the annual cost of producing hot water is €396.02.
The photovoltaic boiler gets its energy primarily from the sun. For example, if three photovoltaic modules with 430 Wp each (1.29 kWp total photovoltaic output) are connected to a boiler, these photovoltaic modules generate around 1,200 kWh per year. A large part of the electricity generated can be stored in the hot water.
On cloudy days, electricity must be drawn from the grid to heat the water.
The photovoltaic hybrid boiler can generally reduce hot water costs by around 75%. This corresponds to around €300 per year.
fothermo photovoltaic hybrid boiler - generate hot water with photovoltaics and save costs
This video explains how the photovoltaic boiler works, how it is connected to the photovoltaic modules and how much money it saves.
Frequently Asked Questions (FAQ)
The number depends on the storage volume and the hot water demand.
- We recommend 2 PV modules for the 30-liter hybrid boiler.
- For the 80 liter hybrid boiler, 3 to 4 PV modules are required .
- Photovoltaic modules with a power output of up to 2000 W can be connected to the hybrid boiler. This corresponds to approximately 4 modules.
- Modules are connected in parallel to keep the voltage below 50 V DC (SELV) .
👉 The hybrid boiler can also reheat at any time via 230 V AC .
Yes, but with limitations:
- Summer half-year (March–October): In many cases, the solar power output is sufficient to cover 100% of the hot water demand.
- Winter (November–February): Solar yield is lower. However, the boiler can be supplemented with an integrated or external 230V auxiliary heater or the existing heating system.
Advantage: The system is hybrid-capable – no one is left without hot water.
- PV connection (DC): No – the solar input runs via SELV < 50 V DC with MC4 connectors.
- AC connection (230 V): No – the mains connection is made via a standard Schuko plug. Connection by an electrician is not required.
- Due to the small boiler volume , no Legionella bacteria can form.
- Once the water reaches a temperature of 60 °C, potential Legionella bacteria are reliably killed .
👉 In practice, the formation of Legionella bacteria is not a problem.
- Short amortization period of 3-5 years , as it is simpler than solar thermal energy and cheaper than the running costs of an electric boiler.
- The hybrid boiler is virtually maintenance-free.
👉 Example: 80-liter hybrid boiler
Usable solar yield with 4 PV modules: approx. 900 kWh/a
Savings: approx. €315 (at €0.35/kWh)
Payback period: 3-5 years
- This depends on the volume, irradiance, and number of modules.
- Example: 80 L storage → 60 °C in 4–6 hours on sunny summer days.
- Fewer modules or cloud cover → longer heating time.
👉 Advantage of hybrid: The AC reheating kicks in automatically when needed.
👉 Click here to go to Heating time calculator . Calculate the duration of the heating process yourself.
- The solar boiler uses a maximum of 550 W of power .
- When more power is available, the innovative electronics (MPP tracker) regulate the excess power.
👉 To ensure sufficient hot water supply even in spring, autumn and winter and on cloudy days, connecting more than one photovoltaic module to the solar boiler is recommended.
No, registration is not required.
- PV connection (DC): No registration is required, as the hybrid boiler does not feed electricity into the grid. It operates as a so-called off-grid system. (Regulations for Germany)
- AC connection (230 V): No registration is required for mains-powered supplementary heating. The solar boiler is an electrical appliance, like a kettle, stove, or hairdryer.
👉 Important: The hybrid boiler does not feed into the grid and is not considered a feed-in system.
- We recommend the 80-liter boiler.
- When the storage tank has reached the maximum temperature of 65 °C, you can use approximately 150 L - 200 L of hot water for showering.
- The 30L boiler provides you with up to 75L of hot water (35 degrees Celsius).
- The display is powered by photovoltaic electricity.
- If only 230V mains power is connected to the boiler, the display remains off. However, a minimum temperature for the mains backup heating can still be set using the thermostat. The mains backup heating will still function.
👉 Solution : For the display on the hybrid boiler to turn on, at least one photovoltaic module must be connected.