Emergency generators that do not use fossil fuel. Alternative generators is the common term in the trade for an engine with an alternator mounted on a frame with a fuel tank is called a generator as it generates useable electrical power which does not use fossil fuel as its main useable fuel to produce power. Used mainly as emergency power and auxiliary power in the event of a power loss, installed as a permanent power protection system for business continuity. Alternative energy systems, in the event of a power outage. Fully automatic critical power systems which turn on if power if lost for true power continuity systems. Usually fuelled by diesel, hence the name, diesel generators. They can be installed outside or inside a building as long as ventilation is provided and exhaust venting.