Metered, not modelled
Swansea vs Reading
Swansea and Reading roofs made much the same last year.
775 against 774 kWh per kWp at the median, from 302 and 62 real systems.
Where the two actually overlap
Both areas, grouped by what each system made. The medians differ, but the shapes sit largely on top of one another — a good Reading roof beats a poor Swansea one comfortably. Location moves the odds; it does not decide the outcome.
Swansea: the middle half of 302 systems made 695–841 kWh per kWp. Reading: the middle half of 62 systems made 665–837 kWh per kWp.
Both figures are what real systems metered last year, so the gap mixes sunlight with system age, roof direction and shading. It is the difference in what people actually got, not a difference in sunshine alone.
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Output figures from openclimatefix/uk_pv (Hugging Face, CC-BY-4.0), collected by Sheffield Solar. How we measure.
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How sunlight falls on a UK roof, month by month.
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