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What is a solar water heater?

A solar water heater is a device that can be used to capture sunlight in order to heat the water in your pipes to be used for baths, showers, etc.

It consists mainly of:

  • a thermal panel (solar collector) installed on the roof;
  • a tank to store hot water;
  • accessories, such as a circulating pump to carry the solar energy from the collector to the tank, and a thermal regulator.

However, a back-up heating system is required for times when there is insufficient luminosity.

Unlimited clean energy to heat your water

A solar water heater is a device that uses sunlight (rather than the heat of the sun) to heat water. It enables substantial energy savings, as the sun shining on 1m² of roof replaces 100 l of heating oil or 100 m³ of natural gas (approximately 1 000 kWh) a year. Generally speaking, it is possible to heat 50 to 70 % of the water used in the kitchen and the bathroom in this way.

Supplying a washing machine or dishwasher with this hot water also cuts out the electricity used by these appliances to heat the water and shortens the washing cycles.

A basic solar water heater costs on average € 5,500, including VAT and installation. To help you with this investment, the Brussels Region gives you an energy grant (link in French, which is supplemented by certain communes.

How does a solar water heater work?

Solar water heater

The solar water heater absorbs light by means of a collector placed on the roof and converts it into heat. It passes this heat to a water tank by means of a circulating pump. This exchange is triggered by the thermal regulator, but only when the collector is hotter than the water in the tank. This prevents the circulating pumps using electricity needlessly. Conversely, it also prevents overheating.

The efficiency of the collectors is at its highest at midday, in summer, when the sky is cloudless, and when the collectors face south. However, the collectors also work well in other seasons, when the sky is cloudy, for a good part of the day, even if they face east or west. Likewise, the efficiency is best at a gradient of 35° to the horizon, but good results can be achieved with collectors fitted vertically to a façade.

When there is insufficient sunlight, the water is preheated and a back-up system takes over to bring the water to the required temperature. This system can therefore be used to produce hot water at a constant temperature throughout the year without emitting any CO2.

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