How Much Electricity Does Commercial Solar Produce in the UK?

How much electricity commercial solar makes in the UK

We asked PVGIS, the European Commission Joint Research Centre's solar tool, for the yearly output of 1 kW of panels in seven UK cities, with its default allowance of 14% for system losses (PVGIS 5.3). Multiply by the size of your system in kW for a rough yearly figure.

The east-west figure is the average of an east-facing and a west-facing panel at 10 degrees, the usual layout on flat roofs. PVGIS uses satellite radiation data for 2005 to 2023 (SARAH3) and terrain shading; it does not know about your trees, chimneys or neighbouring buildings.

Summer, winter and the year's total

In Birmingham, December gives about 33 kWh per kW and June about 117: winter output is roughly a quarter of summer's. Across the seven cities, between 67% and 72% of the year's output comes from April to September, and the further north, the bigger the swing (PVGIS).

• Size against the whole year. A system sized to use everything in December will export a lot in June
• Seasonal businesses. Farms at harvest, holiday parks and cooling-heavy sites line up well with summer output
• Winter-heavy businesses. Heating-led or winter-peaking sites get less from solar when they need most

Orientation, tilt and shading

South facing at around 35 degrees gives the most per kW in the UK of the layouts we checked. Laying panels at 10 degrees on a flat roof cost about 10% of the yearly output in every city, and an east-west layout about 17 to 18% (PVGIS). Shading is often a bigger loss than either, because one shaded panel can pull down a whole string unless the system uses module-level electronics.

For pitched roofs, the direction is fixed. A south-west or south-east roof still produces well; north-facing pitched roofs rarely make sense. See flat roof solar for ballasted and fixed layouts.

East-west layouts

East-west arrays on flat roofs face half the panels each way at a low angle, back to back. They make less per kW, but:

• More panels on the same roof. Low rows need little gap between them, so more kW fits on the roof
• Flatter daily curve. Output starts earlier in the morning and lasts later into the afternoon, matching a working day
• Lower wind loading. Low, back-to-back rows sit closer to the roof

How your estimate is worked out

An MCS certified installer records an estimated system performance in the installation paperwork set out in the MCS standard MIS 3002 (MCS). Many designers also model the roof in PVGIS or design software. Ask how shading was assessed, what losses were assumed and which panels and inverters the figure is based on.

The yearly total only matters if you use it. Laid over twelve months of your half-hourly data, it shows how much the business uses itself and how much is exported. See how much solar you need, system sizes and payback.