Now that the principle of the ‘meter running backwards’ no longer applies in Brussels, it is all the more interesting for owners of photovoltaic panels to consume as much self-generated electricity as possible rather than feeding it back into the grid.

But what should you do with the excess electricity if you have no machines to run or no electric vehicle to recharge? You can store it in a home battery if you have one, but this is still an expensive solution. Another solution is to store it in the form of hot water with a PV heater.

How do you convert solar power into hot water?

In practice, the PV heater is usually a box placed between your photovoltaic system and your electric boiler.

The PV heater constantly compares the energy produced by your photovoltaic installation and the consumption of your household in real time:

• Do your panels produce more than you consume? Then the excess electricity is sent to your boiler to produce hot water.
• When your panels produce less electricity or are not working (at night for example), electricity from the grid is used to heat your domestic water.

How much does it cost?

Currently, this installation costs €400 to €1500. Several suppliers in Europe offer PV heater solutions. However, on the Belgian market, PV heaters are not very common yet.

Do not hesitate to ask your heating technician or the installer of your PV panels for advice.

PV heater or domestic battery?

Given that the purchase of a domestic battery is still relatively expensive, investing in a PV heater could be an efficient and economical solution.
According to a study conducted by ULB in 2017, a PV heater allows you to cover up to 70% of your annual electricity consumption. Without a PV heater, you can only cover an average of 40%. To achieve this result with a battery, you would need to invest up to €15,000.

PV heater, solar water heater or heat pump?

In practice, a PV heater works like a solar water heater. However, it offers other advantages.
For example:

• it offers you more flexibility since you can alternate between electricity and heat production according to your needs;
• it is less expensive to purchase;
• it works better during the least sunny months of the year;
• it is easier to install.

For a detailed comparison of the different solutions, consult this article on the Renouvelle.be website.

Another recent analysis by Renouvelle.be shows that it is currently more interesting to combine photovoltaic panels with a PV heater rather than investing in a heat pump. This is mainly because heat pumps are expensive to buy and consequently more difficult to make profitable.

Moreover, a heat pump takes up space on the roof. Using this space for photovoltaic panels is more profitable. The savings generated can even cover the installation of a PV heater.

Convert solar power into heat, without a PV heater

If you do not want to invest in a PV heater yet, an intermediate solution is to program the hot water production of your boiler when your photovoltaic panels are at their most productive.
Obviously, this is not a smart system that can adapt to real-time production, but it's a good start!