Orientation of your property is very important in being able to figure out what your solar panel system will produce. The government have something called a SAP calculation(Standard Assessment Procedure) and there is one for solar PV and solar thermal systems. Both of these take into account the orientation of the panels that you propose to fit, the figures of what the panels produce will change depending on this. First thing to take into account is which way the panels will face. If you look at the diagram above (4kW system –......