Power plant heat rate — the efficiency figure operators are judged on — is a ratio of fuel energy input to electrical output. The output side is usually measured precisely; the input side, fuel flow, carries most of the uncertainty in that ratio, and it propagates directly into heat rate, into cost-per-megawatt-hour reporting, and into emissions calculations that regulators actually audit.
Gas fuel flow measurement is particularly sensitive to conditions that change with load: pressure and temperature swings during ramp-up and ramp-down shift gas density right when accurate measurement matters most for dispatch decisions. A meter calibrated at steady-state design conditions can carry noticeably wider uncertainty during the transient conditions that make up a large share of a peaking plant's operating hours.
Emissions reporting compounds the exposure. CEMS-linked mass emissions calculations for a gas-fired unit typically derive stack emissions from fuel flow and standard emission factors rather than direct continuous stack measurement of every species — which means fuel flow uncertainty doesn't stay contained to a heat rate number; it becomes part of a regulatory emissions filing.
The practical fix isn't a more expensive meter — it's a properly built uncertainty budget that accounts for how gas density and composition actually shift across the plant's real operating envelope, not just at the single design point the meter was originally calibrated against.
Done well, that budget turns fuel flow from a number everyone trusts by default into one that holds up when a heat rate figure or an emissions filing gets challenged.