Generators provide mechanically generated electrical power by converting a fuel source including diesel, liquid petroleum gas or bio-fuels in electrical energy. The generators we most commonly use within a UPS installation are used on what is known as a standby power mode. The alternative to this is prime power mode where the generator is run continuously. Each type of use must be sized correctly if the generator is to be able to provide the power required, for the runtime required and to provide this for a reasonable operating and working life.