Can solar panels run a heat pump?
Running a heat pump with solar may sound like fiction but it’s more feasible than you might think
Heat pumps require electricity to run. This means they aren’t strictly renewable. But they are extraordinarily efficient, so for every unit of energy you put in, you can get about three units of heat out if it’s working well. This makes the technology a lot more efficient than gas boilers. Unfortunately, unit for unit, electricity currently costs about three times as much as gas. So even though your new heat pump may be three times as efficient as a gas boiler it often costs about the same to run. The less efficient the system, the more electricity required and the colder the weather, the more electricity needed.
Pairing your heat pump with solar panels could reduce the amount of electricity drawn from the National Grid (which still burns fossil fuels) and, as a result, your carbon footprint and electricity bill. Sounds like a no-brainer, doesn’t it. Unfortunately, it's not quite as simple as that. Here we at examine whether this is a feasible option and size and cost of solar system required.
Solar panels more affordable
Rocketing energy bills have promoted a big rise in demand for solar panels. Solar photovoltaic (PV) panels were fitted on more than 190,000 UK rooftops in 2023, according to the Microgeneration Certification Scheme (MCS), which registers installations. That figure is close to the all-time high of 203,000 rooftops in 2011 when homeowners cashed in on generous feed-in-tariffs (ended in 2019) that paid them to generate clean energy.
A global energy crisis exacerbated by the war in Ukraine have pushed up energy bills. Last month (January 2024), the average household’s energy bill rose by 5 per cent to £1,928 as Ofgem, the energy watchdog, raised the direct debit price cap for the next quarter. A decade ago, a typical solar panel set-up cost £20,000 and would take about ten years to recoup those costs. But prices of standard solar panels, which have been VAT free since 2022, have fallen about 60 per cent since then. Spiralling energy prices have also slashed the time taken for the system to pay for itself. Meanwhile, solar batteries are also getting cheaper. The fact that renewable energy helps protect the planet also makes solar an attractive option.
Heat pumps
Heating our homes accounts for as much as 16% of the planet-warming carbon dioxide emissions. The front-runner to replace boilers (gas and oil) is the heat pump. Heat pumps collect energy from an external source – it could be the air, ground or water - and then concentrates it. Heat pump technology requires electricity to run it. Pairing your heat pump with solar panels seems like a sensible move to reduce your reliance on the National Grid and electricity bill. The UK’s electricity network still relies on burning natural gas, a largely important fossil fuel. That said, renewable energy sources – a mix of wind, solar, bioenergy and hydroelectric sources – are increasingly important. Renewables were used to generate 41% of electricity supplied by the National Grid in 2023, up from 2% in 1991.
There are two different types of solar energy – solar thermal and solar photovoltaic. Solar thermal captures the sun’s heat to warm your hot water. This kind of system connects solar panels to the same circuit as the heating element of your heat pump – and reduces the amount of electricity required to meet your needs. It goes a step further than using solar thermal energy on its own, but it requires a hot water cylinder as it can’t produce hot water on demand.
Despite the technology being more efficient than gas boilers and able to provide adequate hot water, pairing a heat pump with solar panels in this way will only provide enough heat for water and not for home heating as well,” says EcoQuote. “The only exception to this is thermally efficient homes, which have a lower space heating demand. If you need both hot water and space heating, it’s better to go with a standard heat pump and used solar photovoltaic to reduce your electricity demand,” suggests EcoQuote.
Solar photovoltaic (PV) systems convert sunlight into electricity. This electricity can be used to help power your heat pump and/or be stored in a battery. By running your heat pump with PV panels, you can reduce the amount of electricity it draws from the grid.
How many solar panels could power a heat pump?
Combining an air source heat pump with solar PV panels is a combination that can work well. “It’s entirely possible that solar panels would be able to produce all the electricity you need to run your heat pump depending on the size of solar array. That is on balance you would generate more electricity than you would use over the course of a year, although this would not be applicable to night-time usage,” says Viessmann on its website.
But Nigel Griffiths, director of the Sustainable Buildings Alliance, disagrees. In an article for Build It, he says combining PV with an air source heat pump (ASHP) is not a particularly effective combination as there is a “mismatch” between supply and demand. “PV produces best in summer when there is no demand for space heating and an ASHP is needed most for space heating in winter when PV production is at its lowest. That’s not to say that there aren’t periods in shoulder months of spring and summer when PC can power a heat pump.”
Meanwhile, Tom Gill, from Eco Expert, says: “Heat pumps work well with solar panels, but you’ll need a large system to meet the pump’s considerable demands. Typically, you’ll need to double your solar panel system to power both your home and a heat pump at the same time.” For instance, an average three-bedroom house will use around 4,000 kWh for heating with a heat pump. This means you’ll need a 5.6 kW solar panel system. “Even then you’ll only be able to supplement your heat pump’s electricity needs with solar panels because you won’t always have enough sunlight to power it.” Solar panels generate less electricity in winter months, when homes need heating most, he adds.
Experts from Hampshire-based Eco Quote Today broadly agree with Gill. “By linking your heat pump with solar panels, you will most likely be able to power half your home’s needs while making up for the rest though the national grid. To be solely reliant on solar power you would need the right size system.” According to Eco Quote Today 20 panels are required to power a 20kW heat pump. “This will produce around 5kW of power a day which is enough to power the heat pump, but nothing else. Plus, the heat pump will only run when the solar panels are capturing energy.” According to this analysis, about 40 panels will be required to power a heat pump and the average home – more than could be fitted on the average sized roof.
Can a solar battery run a heat pump?
“Instead of simply supplementing your heat pump with solar panels, it could be more beneficial to install a solar battery as well. This way, your heat pump will use renewable energy at night when the demand for space heating is higher,” suggests Eco Quote Today on its website. But be aware, you will need a big enough solar system and battery to run a heat pump effectively.
On sunny days, battery storage can help to transfer daytime storage to nighttime load, agrees Griffiths, but it won’t help with the inter-seasonal problem, he adds. “At best it might help get you through 24 hours in some days during spring and autumn.” But even then, heating your home this way is not going to save you much money, considering the high upfront cost of storage batteries and heat pumps. It will, however, be kinder to the planet.
What would a heat pump with solar panels cost?
Air source heat pumps cost around £10,000, while ground source heat pumps are around the £30,000 mark. The Boiler Upgrade Scheme (BUS) can reduce these costs by about £7,500, but with a solar array averaging £6,000 and a suitable battery system around £4,000, the bill soon adds up. Even without a battery, you can end up forking out more than £10,000 for a heat pump with solar panels, according to Eco Quote Today. With a battery and the BUS discount applied, you can expect to pay around £12,500 at the cheaper end of the scale. Costs will vary depending on the manufacturer, how many solar panels you need and which battery you buy.
Homeowners who have installed solar panels and a battery to help power their heat pumps often say it has reduced their electricity bills. But it’s not a solution open to everyone as it requires a hefty upfront investment and you'll need the right type of property– well insulated and ideally with a south-facing roof.