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Short answer: two panels make twice the kWh, but a home with a small daytime load cannot use all of it. With a 150 W round-the-clock baseload, vertical on a south railing in London, one 460 W panel saves about £72 a year and two panels about £96 at 26.32p [calc]. Two panels win if you run appliances in daylight or the price gap is small.
Worked out hour by hour
PVGIS hourly series 2021 to 2023, 800 W cap, against a constant 150 W baseload (fridge, router, standby) [calc]. "Saved" = kWh x share used x £0.2632.
| Town | Panels | 1 panel kWh/yr | used | saved/yr | 2 panels kWh/yr | used | saved/yr |
|---|---|---|---|---|---|---|---|
| London | vertical | 335 | 82% | £72 | 671 | 54% | £96 |
| London | 35° | 465 | 74% | £90 | 931 | 47% | £114 |
| Manchester | vertical | 296 | 83% | £65 | 592 | 57% | £89 |
| Manchester | 35° | 411 | 76% | £82 | 821 | 50% | £107 |
| Glasgow | vertical | 292 | 83% | £64 | 584 | 57% | £87 |
| Glasgow | 35° | 396 | 77% | £80 | 791 | 50% | £105 |
How we compare: criteria, sources and dates
With real prices
- Octopus: £450 for one panel, £650 for two. Payback in London, vertical, 150 W baseload: 6.2 years against 6.8 years [calc].
- City Plumbing: £360 for the 525 W kit and £480 for the 1,050 W kit: here the second panel costs only £120.
Plug-in
Octopus Energy Single panel plug-in solar bundle
460 Wpof panels, as listed
- Panels
- 1 x JA Solar 460 W bifacial (460 Wp)
- Inverter
- Fox ESS microinverter
- Connection
- 3-pin plug, 5 m cable
- Battery
- none
- Availability
- launch price; delivery aimed for end of November
£450price checked 14 Nov
Check price at Octopus EnergyPlug-in
Octopus Energy Two panel plug-in solar bundle
920 Wpof panels, as listed
- Panels
- 2 x JA Solar 460 W bifacial (920 Wp)
- Inverter
- Fox ESS microinverter
- Connection
- 3-pin plug, 5 m cable
- Battery
- none
- Availability
- launch price; delivery aimed for end of November
£650price checked 14 Nov
Check price at Octopus EnergySet your own share in the savings calculator, or compare all plug-in kits. Why the cap does not bite at two panels: the 800 W limit explained.
Frequently asked questions
How many panels can a plug-in solar kit have?
The specification caps the panels at 2,000 W DC in total, with advice to have your wiring checked above 960 W. Octopus says its microinverter takes at most 2 panels for plug-in use.
Does a second panel pay back?
With a 150 W baseload, vertical in London, one panel saves about £72 a year and two about £96 [calc]: the second panel adds £24. At Octopus prices (+£200) that is 8.3 years for the extra panel alone.