Is my Watford roof suitable for solar?

It depends on direction, shading and roof structure, which a survey confirms. The European Commission's PVGIS model estimates that in Watford a 35-degree roof produces about 1,013 kWh a year per kWp facing south, 965 kWh facing south-east, 943 kWh facing south-west, 816 kWh facing east and 788 kWh facing west, assuming 14% system losses. East- and west-facing roofs therefore still produce roughly 78 to 81% of a south-facing array. The Energy Saving Trust notes that panels work best with no shading from nearby trees or buildings, and these PVGIS figures do not include that kind of shading. On a flat roof in a conservation area, an array needs an application to the council for a prior approval determination before work starts.