There are, of course, a few rules which have to be followed to make sure you will not need planning permission. Commercial solar panel systems that are roof mounted should be no more than 20cm off the roof. On a flat roof you are allowed 1m off the roof in order that frames for the panels can also be fitted without need for permission. For ground mounted solar systems, only 9m squared in area is allowed without the need for planning permission. The ground mounted frame is not allowed to be more than 4m tall. Ground based systems must also be at least 5m away from the boundary of the property.
Unfortunately, the rules for a solar panel system that is ground mounted will mean that not a very large system is allowed to be fitted regardless of the space you have available. If you have a larger space that you wish to use, then it is probably still worthwhile seeking planning permission for the system.