Fothermo has developed packages of one to four photovoltaic modules plus a direct current heat supply that allow small systems for apartments or small houses to pay for themselves more quickly. It can also be interesting for a camping holiday with a caravan. According to the founder, the system can be assembled completely by yourself.
Many people are currently considering purchasing a photovoltaic system in order to reduce their electricity costs in the long term. But the technical and bureaucratic effort is rather high and waiting times can be long, and not everyone has their own roof. So what do you do if you want a quick solution and also have low power consumption? “In Germany, around 70 percent of households have one or two people living in them,” says Manuel Masenko, founder of Fothermo. They often only consume 1,000 to 2,000 kilowatt hours of electricity per year. Savings from investing in a photovoltaic system including storage usually only pay off after more than 15 years, as Masenko explains.
Therefore, back in 2020, Fothermo developed a solution to these needs with its photovoltaic boiler, available this year with new products. The boilers are available with plug-and-play photovoltaic systems with up to four modules, i.e. up to 1.6 kilowatts of power. The highlight: The power generated can be divided into heat and electricity supply via an energy management system. To generate heat, the direct current is used directly to heat water. Using microinverters, excess solar power of up to 600 watts is fed into the grid, as Masenko describes the principle of the Fothermo solution. This means that it can be used in the home network for your own supply. If you want to continue using an existing boiler, you can also get the package with a photovoltaic heating element. Masenko goes so far that he sees the solution as a paradigm shift, a big solution on a small scale.
Fothermo offers different sizes. It starts with a ten-liter water boiler, which is intended more for outdoor applications such as caravans or tiny houses. The 30 liter boiler is then enough for a one-person household. Two-person households are also well served from 80 liters. The photovoltaic boilers with 200 or 300 liters are sufficient to supply households with up to five people.
Masenko calculates that the costs for the 80 liter boiler solution from Fothermo with four solar modules with a total output of up to 1.6 kilowatts, a heating element, a switching device and a microinverter amount to around 1,600 euros. If an existing boiler is retrofitted with a heating element and solar modules, the costs would be just under 1,500 euros.
Due to the high rate of self-consumption, Masenko sees the payback period at around three to five years. Storing energy in heat is five to ten times cheaper than in battery storage, he says. In addition, it is easy to assemble by yourself within just a few minutes. There were also no costs for an electrician. “Everyone is allowed to put the photovoltaic system into operation themselves, as the entire system works on safety extra-low voltage,” explains Masenko.
And that's not all he sees as an advantage of the solution developed in-house. Fothermo has a patent for its boilers, as well as for the inexpensive MPP tracker. “The price advantage comes from the fact that we can use the direct current generated directly. This makes the power electronics more cost-effective,” says the Fothermo founder.
The start-up focuses on the market for solar modules that can be installed on balconies. An important aspect of their technology is that it integrates the production of hot water. This means that a significant portion of solar power is used directly to heat water without first having to be converted to AC power. According to Fothermo, this immediate consumption helps to increase self-consumption and significantly shorten the payback period of the solar modules. This is particularly useful if you have an electric instantaneous water heater for heating hot water. The photovoltaic boiler that you then install can also be reheated electrically if there is not enough solar power available.
Both the price and the wide range of possible applications - from caravans to garden sheds to multi-person households - also convinced the pv magazine jury to award the concept a spotlight. With spotlights, pv magazine highlights products and concepts that the jurors believe are worth taking a closer look at and are based on convincing ideas.
Fothermo does not limit itself to the market for new systems. Existing plug-in solar devices can also be retrofitted with a boiler, as there are no special requirements for the combination. If households already have a buffer storage tank in the basement, they could usually retrofit their system with the photovoltaic heating element from Fothermo. “There only needs to be a prefabricated 1.5 degree thread in the buffer storage,” explains Masenko.
Replacing a boiler isn't rocket science either. In addition, the photovoltaic boiler can be connected to an existing gas heater via an integrated heat exchanger, for example, which then ensures that the water is reheated if there is not enough solar power.
Fothermo sold around 7,000 of its photovoltaic boilers in the first few years of its existence. Thanks to fresh investor money, production capacities have just been significantly expanded in order to be able to meet increasing demand. “This year we plan to sell another 10,000 boilers,” says Masenko.
In view of the currently heated debates about heat pumps, he makes it clear: “The photovoltaic boiler cannot replace heating.” Nevertheless, hot water production links the electricity and heat sectors. If the sun doesn't shine but warm water is still needed, the temperature in the boiler can also be reheated using mains power or via an integrated heat exchanger, i.e. an existing oil or gas heater or an instantaneous water heater.
Masenko is currently personally testing how well his system works. In the summer of 2022, the 300-liter hot water buffer tank in his apartment building, in which five people live, broke after around 25 years and was heated by a gas boiler via a heat exchanger. The system was almost completely replaced by a photovoltaic 200 liter boiler, says Masenko. He also connected seven solar modules with 325 watts of power to the boiler, four of which are installed on a roof overhang and three more on the garage. “Since the end of March, we have been getting our hot water almost exclusively from the photovoltaic boiler. The gas boiler only starts again during long periods of bad weather, when the water temperature in the boiler falls below 40 degrees Celsius,” says Masenko. And in addition, the photovoltaic system falls under the plug-in solar regulation and therefore only a small registration with the network operator was required.
