The British solar reality
The UK is one of the least sunny populated places on earth. London averages around 1,500 sun hours a year; Manchester 1,300; Lerwick 1,100. The system you build must survive a fortnight of grey December rain with three hours of dim daylight a day. Get this right and you are genuinely off the grid; get it wrong and you are tied to an inverter generator and the same fuel suppliers you wanted to leave behind.
| Region | Dec | Mar | Jun | Sep |
|---|---|---|---|---|
| South England (e.g. Devon) | 0.9 | 2.8 | 5.4 | 3.2 |
| Midlands | 0.7 | 2.4 | 4.9 | 2.8 |
| Wales / NW England | 0.6 | 2.1 | 4.6 | 2.5 |
| Central Scotland | 0.5 | 2.0 | 4.7 | 2.4 |
| Highlands / NI | 0.4 | 1.8 | 4.5 | 2.2 |
Step 1. Honest load audit
Before you buy a single panel, list every device, its wattage, and the hours per day you actually use it. Off-grid living rewards ruthlessness. Every 100W of unnecessary draw means another £400–600 of panels and battery.
| Load | Watts | Hours/day | Wh/day |
|---|---|---|---|
| LED lighting | 30 | 6 | 180 |
| Fridge (DC compressor) | 40 | 8 | 320 |
| Laptops + phones | 60 | 4 | 240 |
| Water pump | 120 | 0.5 | 60 |
| WiFi router + 4G | 10 | 24 | 240 |
| Misc (kettle on gas, no electric heat) | , | , | 200 |
| Total | 1,240 Wh |
Step 2. Panel sizing for December
Take your daily load (1,240 Wh in the example above), divide by your worst-month PSH (0.7 for the Midlands), divide again by system efficiency (0.75 is realistic for off-grid losses) to get array size:
2,362 W
Required panel array
1,240 Wh ÷ 0.7 PSH ÷ 0.75 efficiency
Round up to standard panel sizes. Six 400W panels (2.4kW) is the sensible build for the example above. South Scotland or Wales might need 2.8–3kW. The same load in southern Spain would need just 900W.
Step 3. Battery sizing for British winters
Solar fights cloud, not just night. Plan for 3 days of autonomy in case of a winter weather front. With LiFePO4 chemistry you can safely use 80% of nominal capacity.
4,650 Wh
Minimum usable battery
1,240 Wh × 3 days ÷ 0.8 DoD
Round up to a 5kWh battery for southern England, 8–10kWh for Scotland, north Wales or anyone running a winter heat-pump-assisted load. LiFePO4 cells last 10+ years; lead-acid is half the price and a quarter of the life. False economy at this scale.
Step 4. Plan for the generator you don't want
What it costs in 2026 (UK)
| System | Panels | Battery | Inverter | Total |
|---|---|---|---|---|
| Weekend cabin (300Wh/day) | £250 | £600 | £250 | £1,100 |
| 2-person cabin (1.2kWh/day) | £900 | £2,200 | £700 | £3,800 |
| Small family home (4kWh/day) | £2,800 | £6,500 | £1,500 | £10,800 |
| Off-grid smallholding (8kWh/day) | £5,500 | £12,000 | £2,500 | £20,000 |
UK regulation. What you can DIY
You can install your own off-grid solar (that is, a system with no connection to the National Grid) without an MCS certificate, G99 form or DNO notification. The moment you connect to the grid for export, full Smart Export Guarantee and DNO approval rules apply. Off-grid stays mercifully outside that system.
- Off-grid: no permit required, no MCS, no DNO notification.
- Standard Part P electrical rules apply for any 230V AC wiring inside the cabin.
- Battery installations over 28kWh need building control notification (rare at this scale).
- Planning permission only if panels exceed permitted development limits on the roof (and most off-grid systems are ground-mounted).
Frequently asked questions
Sources
- UK climate averages , Met Office
- Smart Export Guarantee , Ofgem
Written by
UK Homesteading Team
Editorial team
The UK Homesteading editorial team, offering UK-specific, evidence-led guidance on growing, keeping, preserving and the law.
