UK Solar Generation by System Size (kWh Estimates)

Annual solar generation in the UK is often discussed in kWh per year. The exact number depends on location, roof orientation, pitch, shading and equipment performance — but you can still make a sensible estimate for planning purposes.

A simple way to estimate generation

A practical approach is to estimate kWh per kW installed per year, then multiply by your system size. This is not a guarantee — it’s a planning estimate to help you compare scenarios.

Common UK factors that change generation

• Shading: trees/chimneys can materially reduce output.
• Orientation: south-facing often performs best, but other aspects can still be worthwhile.
• Pitch: roof angle affects seasonal performance.
• Location: UK regions differ in annual sunlight.
• System design: inverter choice, panel layout, and stringing can affect performance.

How to use this with the calculator

If you have an installer estimate for annual kWh, use that as your “expected” scenario. Then run a conservative scenario by reducing generation (for example, by 10–20%) to understand downside risk. If you don’t have quotes yet, use a mid-range estimate and revisit later.

System size matters — but so does matching your usage

Bigger systems generate more, but “better economics” often comes from higher self-consumption. If you oversize a system and export most of it, payback can worsen depending on export rates. A right-sized system + usage shifting can be more effective.

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