How does plug-in solar work?

There is no clever trick in a plug-in solar device. A panel makes DC, a small inverter turns it into mains-shaped AC, and it goes into a socket. Everything interesting is in the detail of that last step.

1. The panel makes DC

Photovoltaic cells convert sunlight into direct current. Output tracks light intensity, so it climbs through the morning, peaks around the middle of the day and falls away in the evening. It also falls on cloudy days — not to zero, but typically to a fraction of clear sky output. A plug-in kit uses one or two panels, up to a combined 2,000Wp DC.

2. The microinverter converts and synchronises

The microinverter does three jobs. It converts DC to 230V AC. It synchronises that AC precisely with the mains waveform already present at the socket, so the two combine smoothly. And it enforces the 800VA ceiling: however much the panels produce, the device will not push more than 800VA into your wiring.

That 800VA cap is why kits can be sold with more than 800Wp of panels. Extra panel capacity does not raise the peak — it fills in the shoulders of the day, when a smaller array would be well below the limit.

3. Anti-islanding: the safety mechanism

The inverter only produces when it can detect a healthy mains supply. Remove the grid — a power cut, or simply unplugging the device — and it shuts down within moments. This is called anti-islanding, and it exists so that a device cannot energise a network section that an engineer believes is dead.

4. The electricity is used in the house first

Once the AC enters the socket it behaves like any other current on that circuit: it flows to the nearest demand. If the fridge, the router and a laptop charger are drawing 250W and the device is producing 400W, the house takes all 400W it can use and the remaining 150W travels back through the consumer unit and out to the grid.

You cannot steer it. There is no way to send solar output specifically to the garden office rather than the kettle. What you can do is time your consumption — running the washing machine at midday raises the share you keep. That share is the whole economic story, set out on the savings page.

5. The meter does not run backwards

Old spinning-disc meters could, in principle, be driven backwards. Modern smart and digital meters cannot: they measure import and export as separate registers. Surplus from a plug-in device is recorded as export, and because these devices are not MCS-certified installations they do not qualify for the Smart Export Guarantee, so that export is usually unpaid.

What it deliberately does not do

• No battery. Storage is outside what the plug-in route permits — see batteries.
• No rewiring. It is designed to plug into an existing socket, which is precisely why no installer is required — see installation.
• No off-grid operation. No mains, no output.
• No more than one per household. A limit of the rules, not the hardware — see rules and limits.