How do I size solar for an EV or heat pump?
If you have, or plan to add, an electric vehicle or heat pump, size your solar to 6 to 7 kWp (15 to 18 panels) and consider a battery. An EV typically adds 2,000 to 3,500 kWh to annual electricity use, and a heat pump can add several thousand more, so a larger system keeps more of that demand off the grid.
Extra demand to plan for
| Addition | Extra kWh/year | Effect on sizing |
|---|---|---|
| Electric vehicle | 2,000 to 3,500 | Size up, add a battery |
| Heat pump | 2,500 to 5,000+ | Larger system, winter import likely |
| Both | 5,000+ | Maximise roof, battery and smart tariff |
Battery and tariff matter too
Solar plus a battery and a time-of-use tariff lets you charge cheaply overnight and run on free solar by day. A heat pump's biggest demand is in winter when solar is lowest, so solar offsets some but not all of its running cost. Flag an EV or heat pump in the SunSum calculator so the recommended size reflects it.
Frequently asked questions
- Can solar fully power an EV?
- It can cover a meaningful share, especially in summer, but most drivers also charge overnight on a cheap tariff in winter.
- Should I get solar before or after a heat pump?
- Either order works. Sizing solar with the heat pump in mind avoids having to expand the system later.
Related questions
Indicative estimates based on UK average data. Last updated 27 May 2026.