Plug-In Solar in Winter: The Honest Numbers

Solar in winter gets a bad reputation, and some of it is deserved. December in the UK is not June. But dismissing winter generation entirely misses the picture — the shoulder months of March, April, September, and October contribute meaningfully to annual output. Here are the actual numbers.

Why winter output drops

Three factors. Fewer daylight hours: the UK gets 7 to 8 hours of daylight in December versus 16 in June. Lower sun angle: the sun stays closer to the southern horizon, though a tilted panel at 35 degrees actually faces it more directly in winter than in midsummer. More cloud cover: the UK averages significantly more overcast days November to February than May to August.

The combined effect: an 800W south-facing system at 35-degree tilt in central England generates 14 to 22 kWh in December and 16 to 24 kWh in January. In June and July the same system generates 88 to 108 kWh. Winter produces around 15 to 20% of summer output.

Monthly figures for central England (800W, south-facing, 35 degrees)

January: 18 to 24 kWh. February: 28 to 38 kWh. March: 50 to 65 kWh. April: 68 to 80 kWh. May: 85 to 100 kWh. June: 88 to 108 kWh. July: 85 to 102 kWh. August: 75 to 92 kWh. September: 55 to 70 kWh. October: 38 to 50 kWh. November: 20 to 28 kWh. December: 14 to 22 kWh. Annual: 624 to 763 kWh.

What winter generation means for your finances

The winter months (November to February) contribute around 80 to 112 kWh — about 13 to 15% of annual generation. At 26.11p per kWh and 35% self-consumption, that is roughly £7 to £10 of bill saving from the four winter months. Modest, but the system earns its value April to September, with winter and the shoulder months adding on top.

Payback calculations should always use full-year generation, not summer-only figures. The savings calculator uses PVGIS monthly data for your postcode and gives you the full annual picture. For the annual 800W output article with monthly breakdown, see our 800W output article.