The total energy output of the system is dependant several different factors:
Solar PV’s generally are a permitted development, and therefore should not need planning permission. However, you should contact your Local Authority at an early stage to determine the status for your site.
The Solar PV panels will be connected together in a series or parallel arrangement depending on the roof space. The panels will then be connected to an inverter which will convert the DC power from the solar PV panels into mains voltage compatible AC. If your system is less then 3.6kWp you will not need permission, but must inform the electricity company. The electricity produced will be first consumed by your property, and any surplus can then be exported to the grid. You will need to discuss with your electricity company their rates.