Editing Net energy gain (section)

==={{anchor|Energy payback time}} Sustainables===
{{details|topic=the EPBT for solar PV|Crystalline silicon#Energy payback time}}

The situation is different with [[sustainable energy]] sources, such as [[Hydroelectricity|hydroelectric]], [[Wind power|wind]], [[Solar power|solar]], and [[geothermal energy]] sources, because there is no bulk reserve to account for (other than the Sun's lifetime), but the energy continuously trickles, so only the energy required for extraction is considered.

In all energy extraction cases, the life cycle of the energy-extraction device is crucial for the NEG-ratio. If an extraction device is defunct after 10 years, its NEG will be significantly lower than if it operates for 30 years. Therefore, the '''energy payback time'' (sometimes referred to as energy amortization) can be used instead, which is the time, usually given in years, a plant must operate until the running NEG becomes positive (i.e. until the amount of energy needed for the plant infrastructure has been harvested from the plant).