We typically recommend that the maximum domestic solar PV system size is 4kWp, or 16 standard panels (240W-250W) and takes up around 26m² of the roof area – the equivalent of just under two and a half parking spaces.
The reason we recommend this is that once you install a system larger than this size, the rate you are paid per unit of electricity you generates decreases, often meaning that to obtain the same returns you need to have a 7-8kWp system or more. Many homes do not have this amount of roofspace and may only be able to install 5-6kWp.
Systems greater than 4kWp can also require extra electrical permissions (depending on your existing electrical supply) which can add to the cost of the system if extra electrical components are required or if a local grid upgrade is needed.
However if you have sufficient roofspace and the local grid can handle the extra capacity you will be adding then systems up to 10kWp can be a great option.