Why plug-in solar output is limited

Plug-in solar is small by design. Where a rooftop array might be several kilowatts spread across many panels, a plug-in system is usually one or two panels totalling a few hundred watts. That is not an accident or a shortcoming — it follows from what plug-in solar is for and how it connects to your home.

Before going further: Plug-in solar has been legal to use in Great Britain since 27 August 2026, when SI 2026/848 came into force alongside Ofgem-approved changes to the G98 connection code — provided the kit is listed as compliant on the ENA Type Test Register. Northern Ireland is not covered. We cover the detail on the UK legal status page.

Small by design, not by accident

A plug-in system is meant to be simple and movable: a panel or two that feed your home through a single connection rather than being wired into the building. That design choice sets a natural ceiling on output. A large array needs fixed wiring, mounting and a central inverter sized for the whole roof; a plug-in kit is the opposite of that, so it produces a modest amount of power that a simple connection can carry.

How it compares with rooftop solar

The practical reasons for the limits

Much of the limit is simply practical. A movable kit that plugs in cannot sensibly carry the output of a large array, and it is meant to offset everyday background use rather than run a whole home. Connecting small generation to your home and the network also brings safety and notification considerations — the kind covered by the Energy Networks Association's engineering recommendations — which are more straightforward at modest output than at large scale.

The regulatory reason for the limit

On top of the practical limits, the rules now set a ceiling. Following its consultation, the Government set an 800W maximum rated AC output in the interim product specification given legal effect by SI 2026/848 (in force from 27 August 2026). This is an interim standard while enduring product standards are developed, not a final, settled figure, so we describe it as an interim cap rather than the last word on system size.

What a small system can realistically offset

Because the output is modest, a plug-in system is best thought of as a way to trim your daytime background load — the steady, low-level demand from a fridge, router, and devices on standby — while the sun is up. It will not run a kettle, oven or other high-power appliance, and only the electricity you use as it is generated reduces your bill; anything you do not use is exported. For a realistic sense of the numbers, see our guide on how much an 800W system can generate, and use the output calculator, which uses PVGIS data to estimate output for your specific postcode, orientation and tilt.

Why some compliant kits have more than 800 W of panels

This confuses almost everyone who reads the register for the first time. The 800 VA cap is on what the inverter puts into your socket. It is not a cap on the panels, and the register carries Compliant entries whose model names say far more than 800 W.

When we read the register on 7 October 2026 it listed, as Compliant, kits named “Thunder Bolt 920W”, “Perlight PowerPlug MAX 930”, “Perlight PowerPlug MAX 1000” and “UKSOL Plug-In Solar Pro Max 1260W Two Panel Hybrid Mount Kit”, among others. Every one of those is recorded at 0.8 kW of registered capacity. The number in the product name is the panels; the number the rules care about is the inverter’s AC output.

Why a maker would do that. Panels almost never produce their rated figure. On a bright but cool day a 920 W pair might deliver 700 W; in thin cloud, a fraction of that. Oversizing the panels relative to the inverter means the system reaches its 800 VA ceiling earlier in the morning, holds it longer, and gives more in poor light. In strong sun the inverter simply limits what it passes — makers often call this “clipping”, and Energy Saving Trust uses the same word. You lose the peak and gain the shoulders.

We are not going to put a figure on that gain. It depends on your orientation, shading and weather, and anyone quoting a single percentage is guessing. Our calculator models output from your postcode if you want to compare two sizes.

Where a real limit does appear. Energy Saving Trust’s checklist, written with the Department for Energy Security and Net Zero, says to speak to a qualified electrician if the panels total more than 960 W — the same figure as the government’s interim product specification. That is a threshold for getting your installation checked, not a ban: a 1,000 W kit can be a Compliant register entry, and the advice is to have an electrician look at your wiring before you use it. See whether you need an electrician.

And the panel total is capped: the UK rules allow up to 2,000 W of panels behind the 800 VA inverter. So the order to check things in is the register entry first, then the panel total against that 960 W advice, then the 2,000 W ceiling.