Opposite seasons
A heat pump's electricity use follows the heating, and the heating follows the cold, so most of it falls between October and March. Solar panels do the reverse. At the best angle in central Liverpool, each kW of panels makes about 30 kWh in December and 34 in January, against 124 in May and 117 in June (PVGIS 5.3). October to March together supply only 31.5% of the year's output (our arithmetic). Spread across December's 31 days, the December figure works out at about 1.0 kWh a day for each kW of panels (our arithmetic), on the short days when a heat pump is working hardest.
Put a size on it. The Energy Saving Trust treats 4.5 kWp as a typical home system (Energy Saving Trust). On the PVGIS monthly figures, that array would make the following in each season:
| Season | kWh per kW | kWh from 4.5 kWp | Share of the year |
|---|---|---|---|
| December to February | 117 | 527 | 12.1% |
| March to May | 325 | 1,463 | 33.5% |
| June to August | 339 | 1,526 | 35.0% |
| September to November | 188 | 846 | 19.4% |
June to August produces 2.9 times as much as December to February. A heat pump's demand runs the other way, so the two curves cross rather than stack. This guide does not print a figure for what a heat pump uses in a Liverpool home, because it depends on the house, its insulation, the heat pump's efficiency and how warm the household keeps it. Ask any installer for an estimate of the heat pump's electricity use month by month, and set it beside the table above; the gap in the winter rows is what the grid will supply.
None of that makes the pairing a mistake. It means the panels' job in a heat pump home is mostly to cover hot water and everyday use through the brighter half of the year, while the heat pump's winter running is a separate matter of insulation, design and tariff.
Where they genuinely help each other
Hot water is the clearest overlap. A heat pump heats the hot water cylinder all year round, and from May to August that is most of its work, which happens to be when the roof makes the most. Setting the cylinder to reheat in the middle of the day, rather than overnight or first thing, lines the two up. Some heat pump and solar controls can also raise the cylinder temperature when there is spare power on the roof, storing it as heat rather than exporting it. With the heating off in a Liverpool summer, hot water is most of what the heat pump does, and that is the season when the pairing works best.
The shoulder months help too. Each kW of panels still makes about 87 kWh in March and 61 in October, when a heat pump is running but not flat out, and on a mild, bright day in either month the roof can supply some of the heat pump's daytime running. A low, steady flow temperature, which is how heat pumps work best, suits that kind of daytime running.
A battery can stretch the overlap into the evening by storing spare midday power, which matters most from April to September, when there is spare power to store. In midwinter the panels rarely make enough spare power to fill a battery, so its winter role, if any, comes from charging overnight on a cheaper tariff where a supplier offers one. The battery page covers sizes and what North West households paid; a battery's inverter also counts towards the grid limit discussed below. Whatever the house and any battery cannot use is exported, and the rules for being credited for it are in the guide to export payments.
Space is rarely a clash. The heat pump's outdoor unit stands on the ground or a wall at the back or side of the house and the panels go on the roof, though a small terraced yard needs care over where the outdoor unit goes; the page on terraced houses deals with tight roofs and access.
Which scheme pays for which
The Boiler Upgrade Scheme is for heat pumps, not panels. It gives £7,500 (£9,000 until March 2027 where oil or LPG heats the home and there is no mains gas connection, according to GOV.UK) towards an air source heat pump that replaces fossil-fuel heating, which GOV.UK defines to include oil, gas, LPG and electric systems, and it is open to property owners in England and Wales, including landlords; social housing and most new builds are excluded (GOV.UK, Boiler Upgrade Scheme). The conditions change from time to time, so check the current terms on GOV.UK before relying on the figure. Solar panels fitted in the same project are paid for separately.
Liverpool City Council's Warm Homes: Local Grant is broader. The council lists solar panels, batteries, hybrid and ground source heat pumps and insulation among its measures, subject to a full survey and the money available. It is open to owners and private renters in Liverpool homes rated EPC D to G, where the household has a postcode on the council's list, receives a means-tested benefit, or has gross income under £36,000 (or meets an after-housing-costs test) (Liverpool City Council). The council says it is oversubscribed for year two; registering now counts towards year three from 1 April 2027. Its list names hybrid and ground source heat pumps, so ask the council about any other type.
For households that can afford the work, there is no grant for solar panels in England; the government's Warm Homes Plan points them towards low-cost loans instead (Warm Homes Plan). The help with the cost page brings every route together.
Insulation first, then sizing
A heat pump is sized from a calculation of how much heat the house loses on a cold day, room by room. Every improvement to the fabric of the house, from loft insulation to draught-proofing, shrinks that figure, which means a smaller heat pump and less electricity in exactly the months the panels help least. Panels do nothing for heat loss, so they cannot stand in for insulation.
That matters in Liverpool, where much of the housing is old. Among Liverpool homes built before 1930 that have an EPC, only 39.3% reach band C or above, against 60.2% of all homes with an EPC; the median score for the older group is 66, against 70 for the city (ONS). Solid walls, suspended timber floors and large sash windows all affect the heat loss figure, and the page on Georgian and Victorian homes covers what can sensibly be done to them.
SP Energy Networks and the supply
Panels connect to the network run by SP Energy Networks. For a system under 16 amps per phase, 3.68 kW on a single-phase supply, the installer tells SP Energy Networks before or at commissioning and sends the commissioning confirmation within 30 days (SP Energy Networks). Larger systems, and some that include a battery, need the network's agreement first under G99.
A heat pump changes the other side of the ledger: it adds a large new load to the house's supply. Adding both at once, perhaps with a battery, is the point at which someone should check with SP Energy Networks that the supply and the connection can take the combination. Ask who will do that check, before the contract is signed, and how long their recent applications have taken. The guide to SP Energy Networks and your panels explains the two connection routes.
Questions for a combined quote
- Is the heat pump sized from a room-by-room heat loss calculation, and can I see it?
- What will the heat pump use, month by month, and what will the panels make in the same months?
- How will the controls use solar power: hot water timing, a cylinder boost, or nothing?
- Is a battery proposed, and what does it do in winter as well as summer?
- Who checks the connection with SP Energy Networks, and who applies for the Boiler Upgrade Scheme?
- Will both systems have an MCS certificate, and which firm holds the warranty for each?
Watch for a single combined figure for energy produced that mixes the heat pump's heat output with the panels' electricity. They are different things, measured differently, and should be listed separately. Ask for every answer in writing, with the kWh figures, so that two quotes can be compared line by line. Check every firm on the MCS register (MCS) and use the checklist on finding an installer. For the solar half of the price, the cost page shows what North West homes paid per kW, and the guide to Liverpool's weather explains the monthly figures used here.