What are the best areas in Hertford for solar?

The individual roof matters more than the part of town. PVGIS models a 4.5 kWp system in central Hertford at about 4,624 kWh a year on a south-facing 35 degree slope, about 3,699 kWh facing east and about 3,601 kWh facing west, so orientation makes a difference of roughly a fifth. Shading from trees and nearby buildings, roof pitch and space, and whether the house is listed or inside the conservation area matter more than the neighbourhood name. A survey should model each usable slope on your own roof.