To utilise a hydroelectric system, you need to have access to a fast-flowing water source, such as a stream. You also need the permission to build around it.
If you’re generating more electricity than you need, you can sell the excess to the National Grid.
Does the source you wish to use have flowing water throughout the year? If not, there may not be a large supply during the drier months and you may need to consider having a backup power system.