How to get hot water from your solar pv panels

Integrated Solar Photovoltaic (PV) systems and Hot Water Smart Switches

How can you use Solar PV generated electricity to heat water?

There are systems on the market which you can connect to your immersion heater and use excess Solar PV-generated electricity, which would otherwise be exported to the grid, to heat your water. These units monitor the amount of electricity generated as well as the amount that your home is using. When there is a surplus this energy is diverted to your immersion heater to heat water instead of being exported to the grid.

This type of system does not affect your FIT generation payments because you are still paid for exporting 50% of the electricity you generate regardless of whether you use it in your home or export it to the National Grid.

One of the Solar PV Smart Switches our Customers use.

Solar hot water switch

Here’s a Summary of how a Solar PV Hot Water Smart Switch works

  • The Smart Switch unit fits into your airing cupboard and connects to the immersion heater electrical supply; the example above measures 260mm x 130mm x 64mm.
  • The Smart Switch unit receives information continuously from a wireless sender device clamped over your house’s “live” supply cable.
  • The sender monitors the flow of electricity in and out of your house.
  • When there is surplus electricity flowing out of the house it tells the “Smart switch” to start using this surplus electricity to heat hot water.
  • This activates the system to start heating your water and adjust how much electricity is used to heat the hot water by only using the surplus energy generated by the Solar PV system – it doesn’t use any electricity from the National Grid.
  • It works with normal household immersion heaters rated up to 3kW. No modifications are needed.
  • You can override or program the unit for total flexibility.

No two households’ hot water use is the same, it depends on the number of occupants, how many showers they take, how long they shower for etc. Likewise the amount of solar PV electricity generated varies with the size of the Solar PV system and the amount of sunshine being converted into electricity at any one point in the day.

Hot water use and available electricity will affect how long it takes to achieve a return on the cost of the Smart PV switch. Below is a typical example of the costs and savings in an average UK home.

Typical cost savings from a PV solar hot water system*

  • The average house with a 4kWp Solar PV system is estimated to produce 3600kWhr of electricity a year and is deemed to export 50% of this annually.
  • The average hot water cylinder is 150 litres and the energy required to heat the water in it to 60 degrees C is approx 9kWh. If you pay 15p/kWhr for your electricity (inc standing charge & VAT), a tank of hot water would cost:

9kWh x 15 pence/ kWh = £1.35.

  • If you heat your hot water by electricity every day (at £1.35/day) this will cost £493/yr.
  • The Solar PV system is most productive during the April – Sept. It should provide enough surplus electricity for the smart switch to use to heat your hot water. So you will save ½ of £493, i.e. £246 a year. There will be surplus electricity which can be used by the smart switch Oct – Mar but possibly not enough to heat a whole tank.
  • Some days the tank will retain enough hot water to only need to be “topped-up” with Solar PV generated electricity.

An average cost to supply and fit a solar PV hot water switch with a Solar PV system is around £400. So in 2 years you will have recovered the cost of the unit and started to make significant savings on your hot water bills.

To talk to one of our Solar PV experts about a installing a photovoltaic system with a solar PV hot water switch, please call us now on 01480 819 740 or use our request a call back form.

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2 thoughts on “How to get hot water from your solar pv panels”

    1. Hi Ian
      Yes, however on a 1.75kWp system the amount of electricity that is surplus to the house’s needs will be less than the 4kWp in the example.
      Therefore the amount of electricity available to “drip-feed” into your hot water tank will be less.

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