Metered, not modelled
Portsmouth vs Blackburn
Portsmouth roofs made about 25% more than Blackburn roofs last year.
919 against 735 kWh per kWp at the median, from 203 and 103 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 Blackburn roof beats a poor Portsmouth one comfortably. Location moves the odds; it does not decide the outcome.
Portsmouth: the middle half of 203 systems made 844–963 kWh per kWp. Blackburn: the middle half of 103 systems made 666–768 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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