Many consumers who have some understanding of how a heat pump works know that it uses energy from the outside air or the ground to produce heating and hot water for your home and/or business.
To run the heat pump it uses electricity, so an air source heat pump can produce 3KW or more (dependent on the heat pump COP) from 1KW of electricity and a ground source heat pump can produce 3.5KW or more (again dependent on the heat COP) from 1KW of electricity.
Consumers also know solar PV panels are used to generate electricity by absorbing energy from the sun and converting it from DC to AC electrical current. So, heat pumps require electricity to run, and by installing Solar PV to produce electricity and alongside one could naturally assume (or are sometimes told) the solar PV will cover all or most of the heat pump electrical requirements.
Free heating forever! It sounds like the perfect combination, doesn’t it?
The problem with this combination is that solar PV panels produce a relatively small amount of electricity at the time of year when your heating and hot water demands are at their highest, and furthermore the time of day that the PV produces any excess energy is during the day, not the typical timings of a heating system.
As you can see from the graphs the times of the year you need your heating don’t match with the time of the year solar PV works the best. Solar PV panels will have minimum impact on lowering costs for running a heat pump during the cold months, during the summer your heat pump you won’t be using heat pump much other than to heat hot water and with correct control timings and adequately sized Hot Water cylinders, this can be maximised to give you near free hot water 3-4 months of the year.
However, there is another solution to reduce the use of your energy in the summer if you have solar PV. By installing a solar PV immersion controller, you can divert any extra electricity generation to your immersion in your thermal store or cylinder to heat your hot water for free instead of exporting it back to the national grid. Any qualified electrician can install this for you.
There are number of different solar PV immersion controllers on the market, ranging from £200 and upwards and will give you similar potential savings.
Heat pumps and Solar PV still both have a strong argument and financial benefit, but combining isn’t going to make you any significant savings over a simple immersion controller, and before you shout BATTERY – have a think about when you will be generating excess to put into the battery.
So lets look at a typical Solar PV 5kW system with a 10kWh battery in a 3 or 4 bed detached home with a heat demand of 9KW.
In the height of winter, with a COP of 3 on your heat pump, you will be drawing 3kW of power for heating. Your PV system will (during 6-7 daylight hours) be producing 10% of its peak capacity, barely enough to run your homes standard appliances, let alone charge a battery or run the heat pump.
There will of course be those winter days with clear skies and a stronger free supply of electricity, but is not the norm, and with clearer skies often comes colder air temperatures without the clouds forming a blanket, meaning more power for the Heatpump is needed.
Solar PV and with a Heatpump is positive and will create greater returns on investment for both renewable technologies. Adding a battery is also a wise purchase, but only when you can also utilise cheaper off-peak grid-supplied electricity.
