Hi Mick. A 4kw system doesn’t produce 4kw. It simply means that you have 4kw worth of solar panels in your system. As part of the design process your supplier should have provided you with a generation forecast using your Irradiation Value. This depends on your location in the UK, the inclination / pitch of your roof and the orientation from the south. This value, will tell you how many watts you will generate per kilowatt installed. Every system is subject to a efficiency loss due to orientation / inclination unfortunately.

Of course using high quality products will have great effect on your production, especially over a longer period.

If you know your postcode, orientation and inclination I can give you a forecast and tell you how much production you should expect.