Resources / Solar
Should I Install Solar Before or After a Heat Pump?
Either order can work. The expensive mistake is sizing one without a plan for the other — or skipping fabric and heat loss entirely.
Quick Answer
If the boiler is failing, comfort is urgent, or Boiler Upgrade Scheme timing matters, heat pump first is often forced. If the roof is already being scaffolded and the heating plant is healthy for a few years, solar first can make sense.
The ideal sequence is still: reduce heat loss where it pays → design the heat pump and emitters properly → size solar to residual electricity use → add a battery only if self-use and tariffs justify it. Same year is fine if budget and project management allow. Winter heat demand still peaks when solar is weakest — solar helps the annual bill; it does not make January free.
View printable checklist Planning aid — not a quote
Why the order question comes up
Homeowners hear two true things at once:
- •A heat pump increases electricity use (especially in winter)
- •Solar cuts imported electricity (especially in brighter months)
So it feels logical to “get solar first so the heat pump is free.” That is only half right. Solar generation is lowest when heat demand is highest. The stack still works — as an annual cost and carbon story — but order should follow urgency, grants, roof works and design quality, not a myth that PV runs the heat pump all January.
More on the combined system: heat pump, solar and battery combined.
When heat pump first is the better call
| Situation | Why HP first |
|---|---|
| Boiler failed or failing | Comfort and hot water cannot wait for a roof project |
| Leaving oil or LPG | Running cost and grant case often strongest here (£9,000 BUS where eligible) |
| BUS timing matters | Grant sits on the heat pump install path, not on PV |
| Emitters / UFH being redesigned | Do the heating system properly once; solar can follow |
| Roof not ready (shade, structure, planning) | Do not force a weak PV install just to “go first” |
Design the heat pump from heat loss, not from “we will add solar later so size does not matter.” Solar does not fix an undersized outdoor unit on a design day.
When solar first is the better call
| Situation | Why solar first |
|---|---|
| Scaffold / roof works already booked | One access cost; PV while the roof is open |
| Heating plant still healthy | No urgent comfort risk; cut imports now |
| High daytime electricity use already | Strong self-use before a heat pump arrives |
| Budget staged over years | PV now, heat pump when cash and grants align |
| Export / tariff opportunity clear | You understand payback without waiting for HP data |
If heat pump is likely within a few years, leave electrical capacity and consumer-unit space in the conversation so the second install is not a rewire surprise.
Doing both in one project
One coordinated programme can mean:
- •Single electrical design (supply capacity, consumer unit, earthing)
- •Fewer repeat visits and less disruption
- •Clearer self-use and tariff strategy from day one
- •Scaffold once if roof and plant room works align
It needs budget and someone who owns the whole picture — not three separate quotes that never talk to each other.
Planning tools: combined estimator · heat pump estimator · solar estimator.
The winter gap (order does not remove it)
In Devon and Cornwall, short winter days and high heat demand coincide. Solar output is lowest when the heat pump works hardest. A domestic battery helps shift energy across hours and shoulder seasons; it does not store a winter of heating.
So: install solar before or after the heat pump as practicality dictates — but size the heat pump for heat loss and design outdoor temperature either way. Solar improves the annual electricity bill; it is not a substitute for correct heating design.
Electrics: the bit people forget
Heat pumps and solar both touch the electrical installation:
- •Main fuse / supply capacity
- •Consumer unit space and protection
- •Cable routes and isolation
- •EV charger interaction if you have or plan one
Whichever comes first, ask the installer to design with the second technology in mind. A tiny consumer unit and a borderline supply make the second install harder and more expensive.
Grants and money timing
The Boiler Upgrade Scheme supports eligible heat pumps (£7,500 in most cases; £9,000 for many oil/LPG replacements with no mains gas — confirm live GOV.UK rules). It does not pay for the solar array.
Solar has its own economics: install cost, self-use, export (SEG), and optional battery. Payback is not the same spreadsheet as the heat pump grant.
Guides: grants in Devon & Cornwall · solar payback · heat pump costs.
Fabric still comes before both (when you can)
Loft insulation, draughts and obvious fabric fixes reduce the heat pump size and the annual electricity the solar is trying to offset. If cash is tight, a naked loft plus a big heat pump plus a small PV array is the wrong priority stack.
Whole-house framing: planning a whole-house retrofit.
Decision guide
Start here:
- Is heating urgent (failed boiler, no heat, leaving oil this winter)? → Heat pump path first
- Is the roof open / scaffold booked and heating stable? → Solar can go first
- Can you fund a coordinated design this year? → Do both with one electrical plan
- Either way: is heat loss done, and is PV sized to real residual use — not a sales target?
Common mistakes
- •Assuming solar removes the need for correct heat pump sizing
- •Fitting PV with no space left electrically for a heat pump later
- •Buying a battery to “run the heat pump all winter” from a small array
- •Ignoring self-use — export rates rarely match import prices
- •Three separate installers, no shared design ownership
Honest bottom line
Install solar before or after the heat pump based on urgency, roof opportunity, grants and budget — not on the idea that PV makes winter heating free.
What always matters: heat loss and emitters for the heat pump; realistic solar yield and self-use for the array; electrical capacity for both. Get those right in either order and the stack works. Get them wrong and the sequence will not save you.
Frequently asked questions
Will solar make my heat pump free to run?
No. It can cut annual imports a lot. Midwinter heating still draws from the grid on most homes.
Should I wait for solar before booking a heat pump?
Only if heating is not urgent and the roof project is imminent. Do not sit in a failed oil system waiting for panels.
Does solar change the heat pump size I need?
No. Peak heat loss on a cold evening is a kW problem. Solar is an energy (kWh) offset over the year.
What about a battery in the middle?
Useful for self-use and tariffs when the numbers work. Not a reason to undersize the heat pump. See is a battery worth it?
Can one installer do both?
Sometimes. Often you still want clear design ownership across heating and electrical/PV even if trades differ. Coordination matters more than one van.
We’re on oil in rural Devon — does that change the order?
Often strengthens the case to prioritise the heat pump (running costs + possible £9,000 BUS). Solar can follow or join if budget allows. Confirm grant rules on GOV.UK.
Next step
Get a realistic planning band for your home, then use the checklist when you speak to installers.