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Hot water as a battery: increase your solar self-consumption by up to 80% without a large investment
With the gradual disappearance of the reverse-running meter in Belgium, solar self-consumption is becoming the new keyword for owners of photovoltaic panels. A home battery may be the next step, but what if it is full or if the investment seems too significant? The solution may not necessarily be in your electrical box, but in your water heater. By converting the surplus solar electricity from your photovoltaic panels into hot water, you can increase your self-consumption by up to 80% and take your boiler out of service for several months. We spoke with Émilien Feron from Soliseco and Roel Defrancq from my-PV.
Solar self-consumption: have you reached the limit?
According to the latest figures, the total capacity of photovoltaic installations in Wallonia has reached nearly 3 gigawatts peak. This represents a huge amount of solar electricity produced by photovoltaic panels and available for self-consumption. However, more and more households are reaching the limit of their electrical self-consumption. You can certainly run the washing machine or dishwasher during the day, but this consumption remains relatively limited. In a household, the real significant energy demands are hot water production and heating with gas or oil.
Use solar surplus: convert electricity into hot water
This is precisely the point where Soliseco and my-PV focus. The two companies offer affordable solutions to increase solar self-consumption in homes equipped with photovoltaic panels. Their principle is simple: recover the surplus solar electricity to produce domestic hot water.
Émilien Feron from Soliseco explains: "Instead of injecting your solar energy into the grid for a fraction of its value, you use it to heat water in your boiler. This way, you replace expensive fossil fuels with your own free solar electricity. You immediately become less dependent on geopolitical situations and fluctuations in energy prices."
How does a thermal battery work?
The technology is surprisingly simple: a smart controller uses the smart meter to measure the amount of excess electricity generated by your solar panels. This surplus solar energy is then sent to an electric heating element in your water tank. “A 10- to 15-kWh home battery can easily cost several thousand euros,” explains Roel Defrancq of my-PV. “A water tank actually functions as a thermal battery that you likely already have in your home. Whether you heat with oil, gas, pellets, or a heat pump, this solution works in almost every case. For those who already own a home battery, it’s also an ideal complement. The battery is often fully charged by around 11 a.m. For the rest of the day, you can store solar energy in your water tank.”
Impact on energy bills: up to 80% self-consumption
According to experts, the impact on solar self-consumption can be significant. Without intelligent energy management, the self-consumption of an average household is around 30%. With a home battery, it can reach 50 to 55%. With thermal storage using hot water as a battery, self-consumption can rise to 70%, even 80%, with or without a home battery. Feron: "We even see customers who, in February and March, achieve self-consumption of 85% to 90%. All the energy produced by their solar panels is directly used in the home to heat water." In this way, investing in solar panels takes on a whole new dimension.
Eight months a year without gas or oil
Throughout the year, many households can do without gas or oil for hot water production for about eight months a year. "This represents a reduction of about 50% of your consumption," says Feron. In the other months, the system can operate in a hybrid mode. "If there is enough sunlight, the box heats the water up to 65 °C, for example. If the temperature drops below 45 °C, the existing boiler automatically takes over. This way, you maintain all the necessary comfort with minimal fossil fuel consumption."
Installation and costs: a quick return on investment
One of the major advantages of this solution for solar self-consumption is its low entry threshold. There are generally no major works required, and the installation remains relatively affordable. Defrancq: "If you already have a boiler, expect to pay around 1,500 euros, installation included. If this allows you to eliminate your consumption of oil, pellets, or gas for half the year, you will have recouped your investment in less than two years."
Feron: "For us, the complete solution, including installation, costs about 1,000 to 3,000 euros, depending on the complexity. Compared to an electric battery, thermal storage is 2 to 5 times cheaper per kWh of installed storage capacity."
Advice from the Livios editorial team: "A home battery quickly costs between 5,000 and 10,000 euros. An intelligent control system for your electric water heater is often available from 1,000 euros. For an average family equipped with solar panels, the payback time for this "water battery" is therefore much shorter than that of a conventional battery."
Compatible with all boilers
The system works with almost all existing installations: old oil boilers, gas condensing boilers, or modern heat pumps. Defrancq: "my-PV solutions can be integrated into almost any installation, with or without a home battery and with or without a smart meter. They are also compatible with the EMS systems and with the home automation. Additionally, our products can operate with dynamic tariffs, which allows for making fossil heating more sustainable even without photovoltaic panels."
Heat pump and electric resistance: a smart combination
Even in a house equipped with a heat pump, an electric resistance can be useful to utilize the solar surplus. "A heat pump is very efficient, but the compressor does not like to have to turn on and off constantly with every passing cloud," explains Defrancq. "An electric resistance can absorb these small fluctuations in solar production without any problem."
Smart priorities: electric car, battery, or hot water
If you have a charging station or a home battery, the different systems can work together. The controls are "smart" and generally intervene last in line. "The Soliseco box continuously analyzes the surplus solar electricity on the smart meter," explains Feron.
"You come home and plug in the electric car? The surplus disappears and the water heating stops immediately. The car or the battery remains a priority. The hot water simply uses the remaining solar energy."
Conclusion: who is this interesting for?
Thermal storage for solar self-consumption is particularly interesting for:
- Families equipped with a smart meter who want to reduce injection into the grid.
- Homes heated with gas, oil, or pellets that want to avoid using their boiler in the summer.
- Owners of large photovoltaic installations who regularly have a solar surplus.
"It’s an affordable intermediate step in the energy transition," concludes Defrancq. "Not everyone can immediately invest 20,000 euros in a complete renovation with a heat pump. But for about 1,500 euros, you can already significantly reduce your fossil fuel consumption."