Short answer: the limit is on what the kit feeds into your socket: at most 800 W of AC output (800 VA, 3.5 A). Panels can be bigger, up to 2,000 W DC. In the UK the cap costs little: in London, a 920 Wp kit tilted at 35° loses less than 0.1% of its year to the cap, a 2,000 Wp array 18% [calc].
What the texts say
- Law: "a maximum rated alternating current output not exceeding 800 watts" (SI 2026/848).
- Specification, 4.1: apparent power to the home "does not exceed 800 VA and the maximum current does not exceed 3.5 A"; the sum of panel power is at most 2,000 W; above 960 W, makers advise a professional assessment of your installation (IPS v2.0).
- Network: one plug-in microgenerator per household under G98 for now (Ofgem).
What the cap costs, by kit size
| Panels | 35° uncapped (kWh/yr) | 35° capped | lost | Vertical capped | lost |
|---|---|---|---|---|---|
| 460 Wp | 469 | 469 | -0.0% | 342 | 0.0% |
| 800 Wp | 815 | 815 | -0.0% | 594 | 0.0% |
| 920 Wp | 937 | 937 | 0.0% | 683 | 0.0% |
| 1,050 Wp | 1,070 | 1,064 | 0.5% | 779 | 0.1% |
| 1,200 Wp | 1,223 | 1,201 | 1.8% | 889 | 0.3% |
| 1,600 Wp | 1,630 | 1,481 | 9.2% | 1,134 | 4.6% |
| 2,000 Wp | 2,038 | 1,679 | 17.6% | 1,321 | 11.1% |
How we compare: criteria, sources and dates
London, facing south. Hourly PVGIS series 2021 to 2023 capped at 800 W, applied to 2005-2023 monthly averages [calc]. Hourly averages smooth short peaks, so real losses can be slightly higher.
So how big a kit?
- Up to about 1,000 Wp, nearly every kWh gets through. Two panels of 460 or 475 W (920 or 950 Wp) also stay under 960 W, the size above which makers must advise a check of your wiring.
- Bigger arrays add winter and morning output but lose more at midday, and more of their output goes unused at home: see one panel or two.
Run your own size in the generation calculator (the "lost to the 800 W cap" box), and compare kits by watts and price.
Frequently asked questions
Is the 800 W limit per panel or per kit?
Per device: the law caps the device's "maximum rated alternating current output" at 800 W, and the specification caps apparent power at 800 VA and current at 3.5 A. The panels behind it can total up to 2,000 W DC.
Can I have two 800 W kits?
The specification would allow one per final circuit, but G98, which takes precedence, currently allows one plug-in microgenerator per household.