Helping UK homeowners make the right heating choices

Solar Power Diverters: Costs, Benefits & Free Hot Water


Getting free hot water whilst saving on your energy bills sounds like something that’s too good to be true, but thanks to a solar power diverter it can become a reality.

Holding onto any surplus energy generated by solar PV panels is becoming more and more desirable as the government’s Feed-in Tariff, which pays homeowners for every kWh of energy exported from their solar panels, keeps reducing.

Solar batteries are often thought of as the only way to get any use out of surplus energy but solar power diverters offer a completely different way of holding on to it.

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An Introduction to the Solar Power Diverter

During any given day, solar PV panels will produce more energy than can be used by a household, so what happens with the extra energy?

With a solar battery, this energy will be stored for use when the panels aren’t generating any energy (like at night time), otherwise this surplus is sent straight to the National Grid. Solar power diverters are like solar batteries in the sense that they allow you to use any extra energy but they do so in a very different way.

The device will be monitoring the electricity being generated by your system all the time and compares this against how much is being used by appliances in your home. At times when there’s an excess, it will divert this extra electricity to your immersion heater.

Let’s take a look at some of the benefits that a solar power diverter can bring to your home:

  • Free hot water
  • Save on your energy bills
  • Export less energy to the National Grid
  • Your boiler won’t have to work as hard
  • Buy less energy from your energy supplier

Will My Feed-in Tariff Payments Reduce?

Holding onto more energy for yourself and sending less to the National Grid might make you think that your Feed-in Tariff payments will reduce. Good news, they won’t drop at all!

The truth is that energy companies have no idea how much energy you’ve supplied. This is because the vast majority of homes don’t have an export meter (which measures how much energy is used against how much is then exported) fitted to their solar panels. So no matter how much energy you export to them, they’ll be paying you 50% of your generated energy figure.

If you’re in one of the few homes fitted with an export meter, you’ll be paid around 5p for every unit sent to the National Grid. This figure is almost 3 times as high when buying the same amount from an energy supplier to power your home so, at the end of the day, is there much incentive to export?

If you’re generating energy, you’re probably much better off using it yourself.

How Much Could I Be Saving with a Solar Powered Immersion Heater?

In the UK, the average cost of electricity is around 13.33p per kWh*. By those numbers, it costs around 40p to power a 3kW immersion heater for an hour. Based on this figure we’ve estimated some immersion heater running costs.

Size of Immersion Heater Hourly Running Cost (Approximate) Weekly Running Cost (Approximate, Running 2 hours a day) Monthly Running Cost (Approximate, Running 2 hours a day over 28 days) Yearly Running Cost (Approximate, Running 2 hours a day over 52 weeks)
3kW 40p £5.60 £22.40 £291.20
6kW 80p £11.20 £44.80 £582.40

So, what does this table mean for you?

  • Significant costs come with running an immersion heater on standard electricity
  • Energy bills can be reduced by taking advantage of free solar energy

With solar power diverters, you’ll be able to see how much you’re saving first hand thanks to many of them being fitted with a screen that displays savings at that moment in time, from the last week or past month.

Solar Battery vs. Solar Power Diverter

If you like the sound of holding onto more energy generated by your solar panels but are torn between a solar battery and a solar power diverter, there are positives points to having either.

A solar battery is likely to store much more energy than a power diverter will be able to use to heat up your water supply, which means that you won’t be holding onto as much of the energy your home is generating with a power diverter. Power diverters won’t cost you as much and don’t require the ongoing maintenance that batteries do, plus you’ll be taking some of the strain off your boiler while solar batteries can’t be disconnected from the mains.

Both are possible answers if you’re looking to get more out of the energy you’re generating, while saving money on your energy bills and not relying on your energy supplier as much.

You can find out more about solar batteries on Solar Guide.

How Much Do Solar Power Diverters Cost?

Manufacturer Product Wireless? Warranty Approximate Price
Marlec Ing Co Solar iBoost Yes 2 Years £300
SISEM Ltd Immersun Yes 3 Years £320
Apollo GEM Yes 5 Years £275
SolarImmersion SolarImmersion No 1 Years £199

Solar iBoost are the most popular choice of power diverter and can cost between £250-£300 but there’s a growing number of manufacturers bringing their own products to market with competitive prices. Get to know some of the leading manufacturers, their products and prices in the table above.

Want to Know More About Solar Thermal?

Rather than using the sun to create electricity, solar thermal collectors use the sun’s heat to provide your home with hot water. This technology is separate to solar PV panels and requires a hot water tank. You can find out more about solar thermal on Solar Guide.

*According to the Energy Saving Trust (March 2018 figures).

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