Gas-generator spark spread: net heat rate turns fuel into cost

AI-generated editorial illustration; it does not depict a verified project, actual prices or chart data.

1. Spread is not profit

A gas generator earns an operating contribution only when the value of net electricity exceeds avoidable fuel and other variable expense. The fuel-only spark spread subtracts fuel cost from electricity value; it leaves maintenance, startup and other costs unanswered. For an industrial site, output value may be avoided imported electricity rather than a wholesale sale price. Use the charge that actually disappears when the generator runs: an unchanged monthly connection charge is not an avoided MWh cost.

2. What the 2026 sources establish

The World Bank October 2 release reports Henry Hub 2.77 USD/MMBtu in August and 2.95 in September, and TTF 21.11 and 25.42. These hubs do not include every generator's delivery charge, balancing cost or gas-quality adjustment. The EIA October 6 outlook, based on October 1 inputs, forecasts annual 2026 Henry Hub at 3.48 USD/MMBtu and US wholesale electricity at 52 USD/MWh. They are forecasts, not observed October prices or an industrial tariff pairing. No verified public August/September project genset offer is assumed.

3. Heat rate is the bridge

Net heat rate measures fuel energy divided by electrical output after auxiliaries. At 9 MMBtu/MWh HHV, fuel cost is 9 multiplied by delivered USD/MMBtu. On this basis net electrical efficiency is approximately 3.412 / 9 = 37.91%. Do not multiply an HHV gas price by an LHV heat rate without reconciliation. Gross generator efficiency excludes some site loads; a gross heat-rate guarantee can understate the cost of exported or usable electricity.

The EIA operating table lists 2024 natural-gas fleet heat rate 7754 Btu/kWh, equivalent to 7.754 MMBtu/MWh. Its utility and independent producer population excludes CHP and industrial plants. It is context, not the heat rate of a specific reciprocating engine, turbine or partial-load package.

4. Illustrative dispatch calculation

Assume delivered gas 8 USD/MMBtu HHV, net heat rate 9 MMBtu/MWh, useful electrical value 100 USD/MWh and other variable expense 8 USD/MWh. All are hypothetical nominal USD values, excluding tax, fixed labor, capital, minimum gas take and emissions charges. Fuel expense = 9 × 8 = 72 USD/MWh. Fuel-only spark spread = 100 − 72 = 28 USD/MWh. Variable contribution = 100 − 72 − 8 = 20 USD/MWh.

A 1 MW net package operating 1000 equivalent full-load hours produces 1000 MWh and 20000 USD modeled contribution before the excluded costs. Startup fuel and maintenance events must be allocated to actual dispatch intervals; frequent short runs may consume this contribution. Positive hourly contribution does not establish annual debt service or payback.

5. Sensitivity and break-even gas

Delivered gas 4, 8 and 12 USD/MMBtu gives contribution 56, 20 and −16 USD/MWh. Each 1 USD/MMBtu adds 9 USD/MWh fuel cost. At fixed 100 USD/MWh output value, variable break-even gas is (100 − 8) / 9 = 10.22222 USD/MMBtu. If net heat rate worsens to 10 MMBtu/MWh at the base gas price, contribution falls to 12 USD/MWh. That 8 USD/MWh loss illustrates the cost of partial-load inefficiency without asserting a universal partial-load curve.

Illustrative contribution per net MWh at gas 4, 8 and 12 USD/MMBtu; net HHV heat rate 9 MMBtu/MWh, output value 100 USD/MWh and other variable cost 8 USD/MWh fixed. Negative contribution is possible; fixed costs are excluded.

6. Evidence needed before dispatch or purchase

Obtain measured or guaranteed net heat rate by load, ambient conditions and gas composition; separate meter, transformer and auxiliary boundaries. Verify whether exported power receives the same value as avoided imports. Ask for gas capacity, interruptibility, minimum take and startup limits. Examine emissions permits and any applicable cash emissions charge separately. Demand-charge reduction requires coincidence with the billed peak, not just large annual MWh generation. Protection, islanding and synchronization requirements determine whether the machine can deliver resilience when the grid fails.

7. Frequently asked questions

Can useful heat improve the economics? Yes, if a real heat demand coincides with dispatch. Credit the avoided alternative heat cost, net of recovery equipment and pumps; do not count unwanted heat.

Does a negative spread mean never operate? No. Emergency supply, contract obligations or avoided outage losses may justify operation; identify that value separately rather than hiding it in the electricity price.

Is a wholesale forecast suitable for self-generation? Only if it represents the site's genuinely avoidable cost. Delivered tariffs, export rules and demand charges can create a different boundary.

8. Sources and next decisions

Consult World Bank gas observations, dated EIA forecasts and EIA heat-rate scope. Continue with the industrial bill decomposition and PPA basis risk. Use the ROI calculator for capital only after a realistic dispatch schedule and maintenance budget exist.