James Stanley tested whether cleaning visibly dusty solar panels improves output. His 16 panels (two banks of eight) hadn't been cleaned in at least two years. He washed one bank while monitoring the power ratio between banks to control for sun angle and cloud cover.

The experiment showed a 2%-5% increase in power output after cleaning, translating to roughly £60-£150/yr in additional revenue, decaying to zero over a few years. Results were messy: the ratio dropped when the first panel was washed, rose as more were cleaned, then fell again once all were done—possibly due to water evaporation leaving a frosted-glass effect. Stanley also felt a tingling sensation while cleaning, likely capacitive leakage from the transformerless inverter at a microscopic skin puncture.

On upgrading: the 15-year-old, 3.7 kW system could gain ~60% output with modern panels costing ~£5000, a ~3-year payback. However, the legacy feed-in tariff pays a high rate on all generation, not just export. Adding capacity would push new output onto today's far worse tariff, creating a disincentive to upgrade.