How much electricity will solar panels generate in Letchworth?

PVGIS, the European Commission's solar model, estimates about 1,023kWh a year per kWp for a south-facing roof at 35 degrees at the centre of the SG6 postcode district, using SARAH3 data for 2005 to 2023 and 14% system losses. That is about 4,604kWh for a 4.5kWp system. The same roof models at about 818kWh per kWp facing east and 796kWh facing west. Letchworth's older roofs are steeper than that default: the council's conservation area appraisal records pitches of 45 to 50 degrees. Re-running PVGIS at 45 degrees leaves a south roof unchanged but takes about 3% off an east slope and 4% off a west one.