Solar power for a summer house

Most solar arguments have to work around a seasonal mismatch. A summer house does not: you use it in the months the panels are at their best, and largely ignore it in the months they are not.

The seasonal overlap

Solar output in Great Britain is heavily concentrated between April and September. A panel that produces well over 100kWh across those months may manage a small fraction of that in December. For most buildings that is a problem — heating demand runs in the opposite direction. For a summer house, it is the whole point.

A summer house, garden studio or craft room used from late spring to early autumn is occupied in the long, bright part of the year. The lighting, the fan, the radio, the laptop and the kettle are all being used during the hours a plug-in device is generating, so a high share of that generation is consumed on site rather than exported for nothing.

What a summer house uses

• LED lighting: 20–60W, mostly in the evening.
• Laptop, tablet and phone charging: 30–90W.
• Fan or small AC unit: 40W for a fan, 400–900W for a cooling unit on a hot afternoon — and hot afternoons are peak generation, so the match is excellent.
• Small fridge or drinks cooler: 40–80W average while switched on.
• Kettle: 2–3kW in short bursts.
• Craft or hobby equipment: a sewing machine, a small kiln, a soldering station — anything from 50W to well over 1kW.

Used a few afternoons a week over the warmer half of the year, that typically comes to somewhere around 150–400kWh — modest, and a large share of it well within reach of an 800VA device generating at the same time of day.

Cooling is the good news story

Everywhere else on this site, heating is the load that defeats plug-in solar. A summer house flips it. The load that matters is cooling, and cooling demand peaks precisely when generation peaks: a bright, still July afternoon is both the hottest hour in the building and the strongest hour on the panels. A 500W AC unit running at 2pm in July is a load a plug-in device can genuinely carry.

Winter and year-round use

If your summer house has quietly become a year-round studio, the honest picture changes. Winter use means heating, and heating means 1–2kW of demand against a few hundred watts of generation, if that. At that point read our garden room guide instead, which treats heating as the main event.

Setting up

• Many summer houses have light, shallow-pitched roofs that will not carry framed panels. Check before fixing anything; a ground frame alongside is often the better answer.
• Summer houses are frequently sited in the sunniest part of a garden, which is a genuine advantage over sheds and workshops.
• The device must plug directly into a socket on a live mains supply — no extension leads. See the installation guide.
• One device per household, within 800VA AC and 2,000Wp DC, registered afterwards — see rules and limits.

What it is worth

Government modelling puts a south-facing device at 30° at around 690kWh a year, roughly 428kWh of it self-consumed and worth about £110 at the assumed price; a vertical east–west arrangement models at roughly 378kWh generated, 272kWh used, about £70. Those assumptions are set out in the DESNZ plug-in solar impact assessment, with more detail on our savings page. A summer house does not change the generation, but seasonal daytime use puts you on the better side of the self-consumption assumption.