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How much will an 800 W plug-in solar kit generate and save?

Short answer

Much less than a roof system. Output is capped at 800 W AC, and kits are often mounted vertically or partly shaded. MCS tables give a vertical south panel about 70% of a 35° one. Which? estimates up to 720 kWh a year and £70–£110 savings for kits costing £400–£500 (September 2026). Exported surplus isn't paid.

Last checked 24 September 2026 · 2 sources

In more detail

  • Plug-in route (GB, from 27 Aug 2026, SI 2026/848): solar-only, ≤800 W AC, standard plug; kits with batteries sit outside it.
  • Which?: panels up to 2,000 W across max four panels; inverter capped at 800 VA; register with the DNO within 28 days.
  • Yield = panel kWp × MCS Kk for its tilt/direction × shade factor, then limited by 800 W clipping and by how much you use at the time.
  • Zone 3 south: 35° = 1,021; vertical 90° = 718 kWh/kWp (MCS).

The facts, dated

  1. 01
    MCS zone 1, south, vertical 90° vs 35° — 695 vs 984 kWh/kWp

    standard · England · checked 24 September 2026 · MCS

  2. 02
    Which? plug-in typical cost / generation / savings — £400-500 / up to 720 kWh / £70-110

    market_data · GB · checked 24 September 2026 · Which?

  3. 03
    Compliant kits on type-test register (16 Sep 2026) — >50 kits

    market_data · GB · checked 24 September 2026 · Which?

What we saw in the field

[QA review 2026-09-24] P-2: two panels at ~35 deg; MCS zone 3 south 35 deg = 1,021 kWh/kWp. Not a plug-in microgenerator. | Earlier notes: Presenter's Jackery SolarVault 3 Pro Max, with two panels on a fence at ~35°: MCS zone tables give ~980-1,090 kWh/kWp for south 35° in southern England. It is a battery system, hardwired via FCU, so it is outside the plug-in route. Jackery's UK page says it must be connected by a qualified electrician, which AGREES. UK early-bird sales start October 2026, and no UK price was published at 24 Sep 2026.

Sources

Last checked: 24 September 2026