Linking solar PV and the immersion heater

UPDATE: The Feed-In Tariff is now closed for new applications. To find out about the new scheme designed to replace it, click here.

Immersion heaters powered by Solar PV

Solar PV panels produce electricity from the sun; these panels can be coupled with the immersion heater on the hot water tank to produce free hot water using a device known as a power diverter or Solar PV optimiser.

The solar power diverter works by constantly measuring the electricity being produced by the solar PV on the roof and how much energy is being used in the home. As soon as there is an excess of electricity being produced, these units divert the excess electricity to the immersion unit on the hot water tank providing the household with free electricity.

What about the Solar PV export tariff?

Remember that almost all solar PV systems installed in the UK are grid-tied systems, that means that the electricity you produce can either be used by you in the home or the electricity gets exported – very few people have electricity storage capability.

When you have solar PV installed, you benefit from the Government’s feed-in tariff which pays you for every unit of electricity you produce. This is known as the generation tariff, and currently the rate is just over 14p / kWh – about the same price as buying the electricity from the energy company. The amount of electricity you produce is recorded through a generation meter.

As part of the Feed-in tariff, you also get paid for exporting electricity back to the grid, through a subsidy known as the export tariff. This pays you in theory for every unit of electricity you export back to the wider energy grid for others to use. The reason we say ‘in theory’ is that when the solar PV is installed, the systems are rarely installed with a export meter, instead the energy companies take the generation meter readings and half them – as if you are exporting 50%.

Based on the fact you are going to get paid 50% of what you generate via the export tariff, it is irrelevant if you actually export 0%, 50% or 100%, you are going to always be paid as if you have exported just half, therefore it is not worth exporting any electricity. To maximise your solar PV investment you in fact want to export 0% of the electricity you produce – this means you still get paid the export tariff, but you have this ‘free electricity’ to use in your home.

The solar power diverter allows you to do just that – never again will you export any electricity from your solar PV installation!

Another reason for not exporting electricity you produce

Even if you are one of the few to have an export meter installed, using the electricity you produce in the home is better than exporting it because you only get paid4.64p for each unit (kWh) you export. If you find a way to sensibly use the electricity, then it means you don’t need to buy that unit from the grid, and so this produces a saving on your energy bill of about 15p/kWh.

Therefore it is approximately three times better to use the electricity you create rather than exporting it – although this will be saving on the bill rather than a cheque paid to you.

>>> The cost of heating your home with gas versus electricity <<<

What is the best way to maximise the return?

It is important to note though that you shouldn’t just increase the amount of electricity you are using just for the sake of it – ideally you need to use the same amount of electricity, but just change your usage patterns so you are using it during the day when the sun is shining and you are producing it.

There are obviously behavioural changes that you can adopt to use more electricity during the day. For example you can set your washing machine / dishwasher to start as you leave to go to work. This will mean that they run during times of peak electrical output for your Solar PV panels.

The link between Solar PV panels and the immersion heater is a great way to maximise electricity usage in the home, providing you have a system or regular boiler (i.e. you have a hot water tank). If you have a combi boiler unfortunately this isn’t going to work for you.

How do Solar PV optimisers link Solar PV and Immersion heaters?

All solar PV optimisers involve clipping a sensor on to electrical cables that can accurately determine in real time whether electricity is being used or exported. Once it detects that electricity is being exported it diverts the electricity to the immersion heater to heat the water. This means that you then don’t need to use gas to heat your water, thereby lowering your heating bill (which normally makes up about 70% of your energy bill).

This technology is ideal if you produce your own electricity since it allows you to use any surplus energy you create during the day to heat water via the immersion heater. So despite me talking about solar above, you can apply this technology to wind turbines and hydroelectric electricity production too.

The great thing is that it will work with your existing immersion – and there is no other equipment required to make it work, making it a simple and elegant solution.

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