For community-owned solar, every kilowatt counts. When generation falls below expectations, it doesn’t just mean lost clean energy; it can also mean less income flowing back into local communities. Repowering London manages a growing portfolio of community-owned solar installations across London, making it increasingly important to spot underperforming sites quickly and understand what is causing the problem. Working with OpenWeather, we tested whether independent weather-based modelling could provide a clearer picture of how individual solar installations are performing and help identify problems that might otherwise be missed at the Westway Sports & Fitness Centre and The Dalgarno Trust.
OpenWeather compared each site's actual meter data against its own cloudy-sky generation model, an independent estimate of how much electricity the solar arrays should have produced based on the actual weather conditions over the past 18 months. This provided a clear benchmark against which to identify whether variations in generation were normal or a sign that something needed attention.
Westway proved the method. Across its two roof arrays, measured generation came in at 99% of the OpenWeather model, with the actual and predicted generation matching very closely day to day. When a site is healthy, the model tracks it precisely, which means any real gap between the two is a signal worth trusting.
Dalgarno showed why that matters. Through 2025, the site tracked the model almost perfectly, at 100% of expected output. Then, from February 2026, its generation fell to 40–60% of the model. This mirrored what Repowering London had itself seen, which later led to an inverter being replaced. However, OpenWeather’s analysis showed that the site continued to underperform following the replacement. The analysis helped identify that an underlying issue remained, prompting further investigation on site.
Crucially, the analysis also distinguished this genuine underperformance from data errors: along the way, it identified physically impossible meter spikes and missing data. So, this wasn’t bad weather or a bad sensor. It was a real fault that could cost the community money.
For a community-energy organisation whose generation directly funds local benefit, that visibility is the whole point. On these two sites, the independent baseline helped distinguish healthy performance from underperformance and showed where further investigation was needed. Applied more widely, the same approach could help Repowering London prioritise maintenance and protect the value generated by its community-owned solar assets.
Lorraine Haskell, Head of Asset Management at Repowering London:
“Good monitoring and analysis can make a real difference to the performance of community energy projects. In the case of Dalgarno, the analysis helped us identify that the site was continuing to underperform even after an inverter had been replaced. For community-owned solar, being able to spot and understand these issues means we can protect generation, improve the long-term performance of our assets and make sure more of the value of the energy we generate stays with the community.”