Energy Return as a Scientific Criterion for Energy Investment

Investment decisions during an energy crisis are usually driven by capital cost, levelized cost, carbon intensity and nominal conversion efficiency. These indicators are necessary but incomplete, because every energy technology also consumes energy for extraction, manufacture, conversion, storage, control and replacement. This review uses energy returned on energy invested (EROEI) as a common physical basis and follows the energy chain from conventional oil and gas to photovoltaics, wind, hydropower, hydrogen and electrical storage. It separates four quantities that are often conflated: source EROEI, round-trip efficiency, manufacturing energy per unit of storage capacity, and lifetime energy stored on energy invested (ESOI). For lithium-ion batteries, a widely cited 2017 review estimated 350 to 650 MJ of manufacturing energy per kWh of capacity, about 97 to 181 kWh, before the energy embodied in upstream materials is added; newer gigafactory data show large reductions but do not yet support a single universal value. A simple combination rule shows that the complete-chain return of stored electricity is always lower than both the operational return and the ESOI of the storage device, so that cycle life can matter as much as chemistry. At small energy-harvesting scales, sensing and control can consume a material fraction of the captured energy; Energy Returned on Invested Energy for Embodied Intelligence (EROIE) extends the same accounting to Reflex Policy control architectures. The paper concludes with a minimum energetic due-diligence protocol to be applied before major energy investments.