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Heat Your Water with Solar PV

Heat Your Water with Solar PV

Today, more and more homeowners are having solar PV installed to not only benefit from greener electricity but also to help reduce their energy bills. The challenge with renewable energy, and particularly solar PV, is using all the power generated. Solar panels on a south facing roof will generate peak power at midday when it is most likely people will be out and about. Most homeowners tend to use a lot more electricity in the evening and so won’t use all the solar energy generated by their solar PV system. This leaves an excess amount being exported back to the grid.

The good news is that by installing an Immersion Power Diverter you will be able to maximise your Solar energy usage, and benefit from free hot water. As storage via batteries is still relatively expensive it is a more cost-effective solution to store your excess energy in water. The immersion power diverter has the ability to divert your surplus solar energy into heating your hot water tank.

Immersion diverters are also often referred to as Solar PV Optimisers, Power Diverters, Energy Diverters, and Immersion Optimisers.

How Do Immersion Diverters Work?

  1. Immersion diverters constantly monitor the amount of electricity your solar PV system is generating and how much your home is demanding. This is monitored via a sensor, attached between your main meter and consumer unit.
  2. If your home isn’t demanding any energy, and if your solar batteries are full (if you have them of course!), you will begin to export your excess solar energy back to the National Grid. This is when the immersion diverter comes in to its own and it will detect via its sensor that your Solar PV System is exporting energy to the Grid. The device will then divert this flow of energy to power your hot water tank instead.
  3. When your immersion diverter is working it effectively means that your water cylinder is being heated for free with energy from the sun. This reduces the fuel required by your boiler, thereby cutting fuel costs.
  4. If an electrical appliance, such as a hoover, is turned on in your home the device will reduce the power diverted to the immersion. Electricity usage throughout your home is always given priority use of the energy generated by your solar panel array.
  5. The device ensures that you make the most of the energy your solar PV array generates even when you are not at home. As long as your hot water tank has enough capacity which you can achieve by setting the normal hot water heating to come on after the sun has gone down, you may be able to use 100% of the electricity generated by your PV system.
  6. It makes sense to want to use your own solar energy rather than export it back to the grid with the average import cost of electricity being 28.34p per kWh and the average Smart Export Guarantee payment only being 5.5p per kWh.

Is Your Home Suitable for an Immersion Diverter?

If you wish to install an immersion diverter in your home, you must meet the following criteria:

  1. Your own way of generating energy at home such as the installation of a solar PV array or wind turbine.
  2. A conventional boiler and hot water cylinder system.
  3. Your energy usage must not exceed the amount of energy you are generating as there must be a source of surplus energy for an immersion diverter to work.
  4. The distance between your water tank and utility meter must be less than 30m.

What are the Advantages of Heating Your Water Through Solar PV?

  1. Immersion Diverters are add-on smart devices that don’t have to be installed at the same time as your solar panel system. This makes them a great additional investment at any time.
  2. An immersion diverter means you can heat your water using free green energy which reduces your carbon footprint and energy bills.
  3. Installing a Solar Power Diverter only takes 30 minutes.
  4. Immersion diverters work seamlessly. As soon as you have fitted your immersion diverter and connected it to your solar PV system it will start diverting your excess energy.
  5. Installing an immersion diverter allows you to use 100% of your solar generation, meaning you will have no green energy waste.
  6. There’s a quick return on investment as immersion diverters usually pay for themselves in just two years.
  7. Immersion diverters reduce the use of your boiler, meaning that it can last longer.
  8. If you benefit from the feed-in tariff, installing an immersion diverter will not affect your payments (closed to new applicants in 2019). This is because the Feed-In-Tariff will pay for 50% of the energy you generate, not knowing how much energy you are precisely exporting. So, no matter how much you are sending back to the Grid or to heating your hot water, you will still earn the same.
  9. Finally, Solar PV paired with an immersion diverter is a cheaper, more maintenance free alternative to Solar Thermal. With no moving parts, and with an immersion diverter being an affordable add on, using your Solar PV System to heat your water is a reliable option.


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How is a Solar Diverter Fitted?

A small electronic box is fitted, usually close to your hot water cylinder, and wired in line with the immersion element power supply. Then two Current Transformer CT clamps are fitted, one around your solar PV AC cable and the other around your main incoming mains supply.

Examples of Solar Diverters

  • Solic 200 is a no-frills immersion diverter which can be installed if it can be placed close to your incoming supply. It comes with a 10- year ‘return to base’ warranty and can be Installed for £496 + VAT*.
  • iBoost+ comes with a 2-year warranty but does not cover labour costs so you’ll have to pay for the work required to get the faulty unit swapped out. It can be Installed for £592 + VAT*.
  • Eddi comes with a 3-year warranty that also covers the labour to swap the unit. Eddi can also be linked to other My Energi products like the Zappi EV charger. Both can be monitored and controlled through the My Energi app and is also available on IOS.  It can be Installed for £775 + VAT*.
  • SolarEdge Smart Energy Hot Water is part of the Smart Energy range of products that can divert excess electric. It diverts electricity to an immersion heater and comes with a 5-year warranty that covers labour for the swap out too. It can be installed for £725 + VAT* (you will need to have SolarEdge full consumption monitoring installed already).

*VAT varies, Immersion diverters on the same Order as a Solar PV system attract 0% VAT, Immersion Diverters bought alone attract 20% VAT.

Immersion Diverters vs Batteries

Some solar power diverters like the eddi and iboost are compatible with solar batteries. Your solar PV system will prioritise charging your battery first. If there is any left-over energy after charging your battery this will be diverted to heat your water. Generally, it’s not worth having both an immersion diverter and solar battery installed unless your solar generation far surpasses your usage. In most households a battery should have sufficient capacity to absorb excess solar leaving little for the immersion diverter.

Where Does this Leave Solar Thermal?

A solar thermal system is another way of heating water with solar energy but is a separate technology and process to that of solar PV panels. It also requires a solar compatible hot water tank. Find out more about solar thermal.

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Janet Richardson

Janet is an accomplished director and writer at The Renewable Energy Hub. Janet has worked at a senior level at a number of publishing companies and is an authority on renewable energy topics. Janet is passionate about sustainable living and renewable energy solutions, dedicated to promoting eco-friendly practices and creating a vibrant community of eco-conscious individuals and businesses seeking sustainable energy solutions.


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