Every power source must first spend energy to build and run itself — mining, manufacturing, construction, fuel processing, decommissioning — before it delivers any usable energy back to the grid. Energy Return on Investment is the ratio of lifetime energy delivered to lifetime energy invested:
EROI = E_out / E_in
Net energy = E_out − E_in = E_in · (EROI − 1)
Energy Payback Time = plant lifetime / EROI
An EROI of 1 means a source barely breaks even. Historically fossil fuels and nuclear ran high (dozens to nearly a hundred), while today's best renewables (hydro, wind) are competitive and utility solar sits lower but keeps improving.
- Source buttons — seven real generation technologies, each with a literature-representative EROI.
- Methodology toggle — "Unbuffered" uses primary-boundary EROI (fuel + plant only); "Storage-buffered" follows the Weissbach et al. (2013) approach of charging intermittent sources for the batteries/pumped-hydro needed to deliver firm power, which lowers wind and solar sharply while leaving dispatchable sources close to unchanged.
- Plant scale slider — sets the input energy stream (E_in); net energy scales with it, EROI and payback time do not (they're ratios).
- Lifetime slider — the assumed operating life used to convert the EROI ratio into a payback time in years.
- The flow diagram is literal: a fixed stream flows into the converter as invested energy, and a stream scaled by EROI flows out into the taller output silo. Drag to pan the diagram, scroll/pinch to zoom.
- The bar chart below always shows all seven sources at once under the current methodology, so the selected source's bar can be read against the full field.
Figures are order-of-magnitude literature estimates (Hall, Murphy, Weissbach and others' EROI surveys) meant to illustrate the mechanism, not a single authoritative dataset — published EROI numbers vary by methodology and boundary assumptions.