In this post, I will talk about how free energy from your solar panels relates to what you use in electrical heating.

The answer here is not a simple one and depends greatly on the size of your solar panels as this will correlate directly with how much electricity they will produce. It also relates to the size of your heating system and how you use it.

Firstly, there are 2 types of solar system. One is owned by the householder  who will have the use of any electricity generated and will gain the FIT subsidy

The other type is owned by a 3rd party who collect the FIT subsidy and the property owner gets the use of the electricity generated.

Domestic systems usually have a maximum generation size of 4kw in peak conditions, so when the sun is shining you can run for example 2x 2kw radiators. Which is enough to heat 2-4 rooms if you have the maximum size array of solar panels, meaning you will pay nothing for the energy the heaters are using (not taking into account any loss in export tariff).

The problem is that when the solar panels are at their peak performance is usually the time when you don’t have such high heating demand i.e mid summer. Similarly when you need it most i.e mid winter, the solar array will probably be working at a reduced capacity (due to lack of sunshine) or not at all. So for example a full size 4kwp array may only be able to run 1x 2kw radiator or less and then only for the short period.

Electricity cannot be stored so there are 2 solutions,

If you get the FIT subsidy you could save the money you are awarded in the summer and then put it toward the energy bill where you import extra energy in winter for heating etc.
OR you could get a bigger solar array where the Kwp capacity is a minimum of twice the size of your heating load, and then only use it during daylight.

The later one is generally unsuitable for domestic customers but can suit commercial customers that have a large system on the roof where the building is occupied during the day. It is more common that these systems are owned by a 3rd party so all the building user gets is the generated electricity. If the solar system is very large, a lot of electricity will be generated.

For example I recently fitted 15kw of  Elkatherm electric radiator heating to a large hall that was only used during the day and evening as a supplement to their gas system. The roof had a 50kwp solar array and even on a cloudy march day generated excess 100 units of electricity. I designed a control system that switched the heating system on when the sun came up (which varies throughout the year) and off when the sun went down. In this scenario most of the heat was free and if the sun wasn’t up the gas system took the load. They estimated recouping the cost of the install off their gas bill in under 2 years.

By Simon Scholes, BSC (Hons) Senior qualified electrician

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