The fothermo solar heating element is a powerful heating element for hot water preparation. It reduces the load on your heating system. An integrated excess function also makes surplus electricity usable.
Reduce the strain on your heating system. Save money.
Reduce the strain on your heating system. Save money.
BUY NOWPowerful. Economical. Simple.
Save more money with less effort. The 1,000-watt solar heating element pushes the boundaries of photovoltaic power utilization.
Application
Households of 1-4 persons: The solar heating element is ideally suited for smaller households.
Switch off the heating system: The solar heating element supports the heating system (gas, oil, pellet or heat pump) in hot water production. During the summer months, the heating can thus be almost completely switched off.
Up to 500 liter volume: The heating element is particularly suitable in combination with hot water storage tanks with a volume of up to 500 liters.
Advantages
Lower hot water costs: Up to 75% of the hot water is supplied via the solar heating element throughout the year.
Short payback period: Easy installation. High annual savings. No ongoing costs.
No electrician required: The heating element operates at a very low voltage (max. 50 volts). The photovoltaic modules are connected directly to the solar heating element.
Web calculator - calculate your savings!
What our customers say
The solar heating element exceeded my expectations. I switched off my heat pump from April until the end of September.
Fantastic customer service and a product that delivers on its promises. Easy connection. Quick setup.
The costs for gas heating were high. Now, during the summer months, it is completely switched off in the two-person household.
Excellent quality and unbeatable value for money. Would buy again anytime.
Made in Germany. The heating element lives up to its promises. I use it with four photovoltaic modules and am more than satisfied.
Finally, a simple system. This will allow me to reduce my hot water costs cost-effectively.
function
3,000 watts of connected load: Up to 3,000 watts of photovoltaic power can be connected to the solar heating element. This corresponds to approximately 6 to 7 photovoltaic modules. This allows for the production of a large amount of hot water even on cloudy days.
Stepless power control: The heating element's output is continuously adjustable up to its maximum power. The heating process starts with a minimum photovoltaic output of just 6.5 watts.
Patented MPP tracker: The solar heating element features a patented MPP tracker with 99% efficiency. It ensures that the photovoltaic modules are always operated at their optimal operating point (MPP).
Intelligent surplus function: Excess electricity can be fed into a second solar heating element or into the home's electrical grid using a micro-PV inverter. This helps reduce hot water and electricity costs.
Maximum water temperature: 85 °C: The maximum water temperature is 65 °C in drinking water systems and 85 °C in descaled heating systems.
Independence: The solar heating element does not require a 230-volt power connection. It also works during a power outage.
Technical specifications
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plug & play
Simple plug-in system. Uncomplicated assembly. Quick commissioning.
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1.5 inch connection
Easy retrofitting: The 1.5 inch (6/4 inch) thread allows for easy retrofitting of the solar heating element into existing hot water storage tanks and heating systems.
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Quality
Specifically designed for all types of hot water storage tanks - stainless steel, enamel, steel.
Maximum quality - Made in Germany.
How does the solar heating element work? Everything explained in the video!
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Surplus utilization
A cascade connection of several solar heating elements or feeding into a micro PV inverter is possible.
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Simply
Off-grid system without registration. No bureaucracy! No registration of the photovoltaic system is necessary.
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Economically
Quick and easy reduction of heating system energy costs.
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Made in Germany
The development and production of the solar heating elements takes place in Ulm, Germany.
Reference projects
Heating element with heat pump
In the older building, a 1,000-watt solar heating element powered by four PV modules relieves the heat pump. The heat pump was switched off from March until the end of September.
Download the test report
2-person household with gas heating
The gas heating system now runs significantly less. The photovoltaic modules generate enough hot water for the two-person household. [Test report to follow - page under construction]
Intelligent surplus function
Excess solar power can be fed into the home's own grid (grid feed-in) or forwarded to a second solar heating element (cascade circuit).
Intuitive operation
Simple operation with two buttons ensures easy use. A variety of different values can be read on the heating element's display. These are:
- Water temperature
- Photovoltaic power
- Photovoltaic voltage
- Photovoltaic energy used for hot water and surplus feed-in
- Software version etc.
Installation and commissioning
1. Drain the water : Empty the water from the water tank down to below the thread for the solar heating element.
2. Seal the solar heating element: Seal the thread of the solar heating element with suitable material.
3. Remove threaded sleeve : Remove the 6/4 inch threaded sleeve screwed into the water tank.
4. Screw in the solar heating element
5. Refill with water: Refill the water tank with water.
6. Connect the photovoltaic modules: Connect the photovoltaic modules in parallel to the solar heating element. The heating process starts immediately.
Technical drawing and dimensions
Dimensions : Length: 468 mm, Height: 97 mm, Width: 154 mm
Unheated area : The first 4 cm of the solar heating element are unheated.
How much hot water is produced per year?
How many liters of hot water and how much heat energy per year can be generated with a specific number of photovoltaic modules (power output per module approx. 450 W)? These values serve as practical guidelines based on average solar irradiance conditions.
Even with just 2 PV modules, around 14,000 liters of hot water or about 900 kWh of heat energy can be generated annually – ideal for smaller households or seasonal use.
With 3 to 4 PV modules, the annual production increases to approximately 20,000 to 26,000 liters of hot water or 1,300 to 1,600 kWh of heat energy – perfect for the daily hot water needs of single-person to multi-person households.
Those who install 5 to 7 PV modules can generate approximately 30,000 to 34,000 liters of hot water or 1,900 to 2,200 kWh of heat energy annually – sufficient for high hot water demands or the parallel operation of several taps.
This overview will help you choose the optimal number of photovoltaic modules in combination with our solar heating element – for maximum efficiency, independence and cost savings.
Heating times
The heating time of a hot water storage tank depends on the power of the heating element and the tank volume. The smaller the tank and the higher the power, the faster the water temperature rises.
The following table shows the theoretical temperature increase per hour (°C/h) for different storage tank sizes using a solar heating element with a power output of 500 watts and 1,000 watts. The values are based on an idealized calculation without heat losses.
Practical advice:
In reality, heating rates can vary slightly due to heat losses, weather conditions, and temperature stratification within the storage tank. However, these values provide a good guideline for sizing your solar thermal system and selecting the appropriate hot water storage tank.
The right photovoltaic modules
The maximum heating output of the fothermo solar heating element depends directly on the voltage of the connected photovoltaic modules.
- At low module voltages, only reduced power is available (e.g., at 11 V max. 65 W).
- As the module voltage increases, the heating power increases continuously until the maximum value of 1,000 watts is reached.
- From a module voltage of approximately 43 V, the maximum heating power of 1000 W is reached and kept constant.
For optimal energy yield, we recommend photovoltaic modules with an MPP voltage of 38–43 Vmpp , as specified in the respective module datasheet. Note: Under strong sunlight and high photovoltaic power output, the module voltage increases. Therefore, even with a voltage of 38 Vmpp, high heating outputs of nearly 1,000 watts can be achieved.
Downloads
Download important documents and files here.
operation manual
Frequently Asked Questions (FAQ)
At least one photovoltaic module is required.
Up to 3,000 watts of photovoltaic module power (approx. 6-7 modules) can be connected to the solar heating element. Excess energy is regulated.
Recommendation:
The connection of 3 to 6 photovoltaic modules is recommended.
Yes, but with limitations:
- Solar power decreases in bad weather and low sunlight.
- However, hot water is still produced in principle.
Good to know: The heating process starts with as little as 7 watts of solar power.
No , because the maximum voltage of the system is very low (less than 50 volts).
Yes, if the memory has a 1.5 inch standard thread (6/4 inch) .
Notes :
- Please check the thread and immersion depth before purchasing.
- A 5/4 inch thread in the hot water storage tank is not compatible with the 6/4 inch thread of the solar heating element.
No. The system does not feed power into the grid. The PV modules are operated directly by the heating element (off-grid operation). Therefore, registration with the grid operator is not required.
Exception: If excess electricity is fed into a micro-PV inverter, then registration is required, similar to a balcony power plant.
The heating element limits the power drawn to 1,000 W. Excess module power is simply not used .
The payback period is typically 2 to 5 years. This depends on the cost of the energy saved (e.g., oil, gas, pellets, electricity).
Due to the low installation costs and low module prices, the solar heating element becomes economical very quickly.
Feel free to use the profitability calculator linked on the website.
Yes, the solar heating element is suitable for use in drinking water. It was specifically designed for this purpose.
To keep losses in the solar cables as low as possible, we recommend a maximum distance of 25 meters between the photovoltaic modules and the solar heating element.