Solar power for a garden office

Of everything people plug solar into, a garden office is the neatest fit — not because it uses little electricity, but because it uses it at exactly the hours the panels are working.

The timing argument, properly explained

Solar saves you money in two quite different ways, and they are worth a lot less than each other. Electricity you generate and use yourself displaces a unit you would have bought, so it is worth the full retail rate. Electricity you generate and do not use is exported, and for a plug-in device that is usually worth nothing at all — plug-in solar does not qualify for the Smart Export Guarantee, which requires an MCS-certified installation.

In an ordinary home that distinction hurts. The peak of the generation curve lands at midday, when the house is empty; the peak of the demand curve lands at 6pm, when the panels are winding down. In a garden office it is the other way round. You are at the desk from nine until five with the lights on, two monitors lit, a laptop charging and a router running. The two curves sit on top of each other, and the self-consumed share — the part that actually pays — goes up.

A typical working week

Take a full-time garden office worker, Monday to Friday, roughly 8:30 to 17:30. The steady load looks something like this:

• Laptop and dock: 45–90W while charging and working.
• Two 27-inch monitors: 40–70W together at typical brightness.
• Desk and ceiling lighting: 20–50W with LEDs.
• Router, switch, printer standby: 15–30W, generally around the clock.
• Video calls: a webcam, ring light and harder-working CPU add perhaps 20–40W while you are on them.
• Kettle: 2–3kW, but only for a couple of minutes at a time — a few hundred watt-hours across the day.

That is a baseline of roughly 150–250W for most of the working day. An 800VA plug-in device producing 300–700W across the middle of a spring or summer day covers that baseline outright, with headroom for the kettle boils and the occasional heavier task. Across the year the desk-and-lighting load is something like 200–450kWh; in the lighter half of the year a well-sited kit can cover a large majority of it.

Winter, honestly

Two things happen at once in December, and both go the wrong way. Generation collapses to a fraction of the summer figure — short days, low sun angle, more cloud. And demand jumps, because a garden office in a British winter needs heating from the moment you open the door.

Heating is where the argument stops. A 2kW panel heater draws more than twice what a plug-in device can produce at its absolute maximum. Even an efficient air-source unit at 600–900W will consume more than the panels supply on a grey January morning. Expect solar to trim the edges of your winter bill, not to change it.

What actually helps in winter

• Insulation and draught-proofing, which repay far faster than any generation.
• A small air-source heat pump or AC unit in heating mode, which delivers several units of heat per unit of electricity.
• Heating the person — a heated chair pad or footwarmer — rather than the whole room.
• Timers, so you are not warming an empty building.

What the numbers look like

Government modelling for the plug-in solar policy puts a south-facing device at 30° tilt at around 690kWh of annual generation, of which roughly 428kWh is self-consumed in a typical household, worth about £110 a year. A vertical east–west arrangement models much lower, at roughly 378kWh generated and 272kWh used, worth around £70. Those are household averages with stated assumptions, published in the DESNZ plug-in solar impact assessment.

A garden office occupant sits at the favourable end of the self-consumption assumption rather than the middle of it, because the demand is genuinely there in the daytime. That does not change the generation, only how much of it earns full retail value. We work through the arithmetic and the payback period on the savings page.

Setting one up sensibly

• Site the panels where nothing shades them between mid-morning and mid-afternoon. Fences, hedges and the house itself are the usual culprits.
• Tilted and broadly south-facing beats flat, and flat beats vertical. If you can only face east or west, expect materially less.
• The device plugs directly into a socket. Never an extension lead — see our installation guide.
• Keep the office socket circuit in mind: the device feeds the household circuits, so the more of your load is running at the time, the more of the generation is used on site.
• Register the device after installation, as covered in the registration guide.

Can you power a garden office without mains?

Not with a plug-in solar device — it needs a live grid connection to operate at all, and it shuts down in a power cut by design. Genuinely off-grid garden offices exist, but they are a different product category: a battery bank, a charge controller, an off-grid inverter and careful load management. That route is covered in our shed and workshop guide, which deals with the off-grid question head on.