Energy Return on Energy Invested (EROEI)
This is a useful indicator of power generation equipment environmental performance, equipment such as solar cells, wind turbines or nuclear power stations. It is the ratio of energy generated divided by the energy required to build and maintain the equipment.
Little is gained if it takes as much energy to produce the equipment as it produces in its lifetime.
Note that this is very different to the Economic Return on Investment as this depends on local prices.