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What is a solar water heater?

A solar water heater is a device that captures sunlight to heat water. It can be an economical way to generate hot water for your family (for shower and bath).

A solar heater not only enables substantial energy savings as solar power is free in contrast to natural gas or fuel oil. Moreover, it is a way to produce hot water for sanitary use throughout the year without emitting any CO2

1m² of roof = 100m³ of natural gas/year

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

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, as long as certain precautionary measures are taken.

Hot water all year round

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.

An investment of € 4,500 to € 6,000

A basic solar water heater (i.e. for a family of 4 people, demanding 200 to 300 litres, with 3 to 5 m2 of solar collectors) costs on average € 4,500 to € 6,000, including VAT and installation. To help you with this investment, the Brussels Region gives you an RENOLUTION-grant, which is supplemented by certain communes.

Wondering whether your roof suitable for a solar water heater? 

Depending on the region of residence, you will find different solar mapping tools on the suitability of your roof.

  • Evaluate the solar potential of your rooftop situated in the Brussels-Capital Region
  • Do you live in Flanders? Then the solar map (online ‘zonnekaart’) will give you all the feedback you need
  • In Wallonia you will find more info on the site of l’APERe, the association for the promotion of renewable energy.

How does a solar water heater work?


1. Light is absorbed by solar collector

The solar water heater absorbs light by means of a collector placed on the roof and converts it into heat.

2. Heat transferred to water tank

The heat is then passed to a water tank by means of a circulating pump. This exchange is triggered by the thermal regulator, but exclusively when the collector is hotter than the water in the tank. This not only prevents the circulating pumps from needlessly using electricity but conversely, also avoids overheating.

3. Insufficient sunlight? Back-up heating system

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 at a constant temperature throughout the year.

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