A generator burns fuel and converts roughly a third of its chemical energy into electricity; the rest leaves mostly as hot exhaust gas, plus a small share as radiated/mechanical loss. A conventional plant vents that exhaust straight to the atmosphere — it counts as pure waste, capping overall efficiency near 35–45%. A cogeneration (CHP) plant instead routes the same exhaust through a heat-recovery unit into a second use — process steam or building heating — so most of what used to be wasted becomes useful output, pushing overall efficiency to roughly 70–90%, even though the electrical output itself never changes.
- Fuel input rate — total chemical energy burned per second; scales electricity, heat and losses together.
- Conventional — exhaust plume vents upward and disperses; the Sankey diagram shows a large orange "wasted heat" flow.
- Cogeneration (CHP) — a damper redirects exhaust into the heat-recovery unit and loop; the orange flow nearly vanishes and a teal "useful heat" flow appears instead.
Real-world relevance: industrial cogeneration is one of the highest-leverage efficiency retrofits available — it needs no new fuel source, only reusing the heat a generator already produces.