A few years ago, investing in a solar water heater was not that interesting. Energy prices were much lower than today, so you earned back your investment very slowly. Is a solar boiler for hot water really worth it today? How does it work? How much do you save with it? And for whom is it interesting?
“In short: with a solar boiler you make hot water. To do this, you have so-called solar collectors placed on your roof, in which a freeze-resistant liquid flows. When the sun’s rays fall on it, the liquid heats up a boiler tank with water. So with free solar energy,” says Wim Persoons, chairman of Belsolar, the sector association for solar water heaters.
How much does such an installation yield?
That is the question, of course. “Well, you have to count on about 500 kWh per m² of solar collectors per year. On average, such an installation is about four to five square meters in size, which produces about 2,000 to 2,500 kWh each year. Enough to heat up about 60 percent of the water that a family of four to five people uses on average.”
A solar water heater works better in periods when the sun shines more, so especially in the months of April to October. “But it doesn’t necessarily have to be warm,” Wim Persoons notes. “If it freezes -2 to -3 °C, but there are no clouds, you already achieve a good return. Then such a solar collector can work at 40 to 50 °C.”
“In the summer months, the solar boiler can cover your entire consumption of hot water. In the rest of the year you have to combine the solar water heater with another solution. But that can be your existing hot water installation. You can easily combine a solar water heater with this. Regardless of whether you have a gas boiler, an oil boiler or already have a heat pump.”
How many euros do you save?
“Suppose you have an electric boiler for hot water and combine it with a solar boiler that generates an average of 2,000 kWh. At the current electricity price, which is about half a euro per kWh, you save a thousand euros a year. Do you currently heat your water with natural gas? Then you save around 300 euros per year with an additional solar water heater.”
How quickly will you earn back your investment? Wim Persoons: “On average, a solar water heater costs 6,000 euros. You get about 40 percent subsidies for that. This leaves 3,600 euros that you have to pay yourself. If you use an electric boiler for the rest, you will earn back your solar boiler in less than four years. If you heat with gas, then the installation – at current gas prices – pays for itself in ten years.”
“It seems like a distant past, but the price for natural gas was once low, at 0.07 euros per kWh. Then you only saved 150 euros per year with a solar water heater, so the investment was difficult to defend. But with the current evolution of energy prices, the situation is completely reversed.”
When is it better to choose or not?
More and more households are opting for a solar water heater today. “In 2022, we saw an increase of more than 60 percent on the Belgian market, with the majority of solar boilers being sold in Flanders,” explains Wim Persoons.
“A solar boiler is certainly interesting if you heat water with an electric or gas boiler, because of the savings I mentioned earlier. Do you already heat with a heat pump, but don’t have solar panels yet? Then you will only save a few hundred euros extra with a solar water heater, so it is better to invest in solar panels first. Do you already have a heat pump and solar panels, and do you want to save even more energy? Then a solar water heater is an interesting option.”
Time to clear up a misunderstanding. “Those who heat with an electric boiler often have the reflex: I have to generate cheap electricity with solar panels. But it is better to save on electricity by heating your water without using electricity with a solar boiler. This also leaves more energy from your solar panels for your other electricity consumption. You sell too much solar energy back to the grid.”
And what about who today only heats with natural gas? “In that case, you cannot heat your sanitary water with electricity, so solar panels are not a solution for that anyway. Or you can place a heat pump boiler in combination with solar panels for your hot water, but that brings the total price tag to more than 10,000 euros. It is therefore best to combine a gas boiler with a solar boiler to save money.”
Do you have to be patient?
If you order a solar water heater today, you will have to wait about three to four months for the installation. “From the summer of 2023, that waiting time should decrease, since manufacturers will probably be able to produce faster from then on,” says Wim Persoons. “The cost price – an average of 6,000 euros – is 20 percent higher than two years ago, because it takes more energy to produce solar boilers. But you also save more because energy prices have risen.”
