Generator Cost per kWh by Fuel, Size, and Load: Comparison Table

Generator cost per kWh equals hourly fuel spending divided by actual electrical output in kW. Using the illustrative prices below, the selected models produce electricity at approximately $0.25–$0.91 per kWh in fuel alone. These are model- and load-specific examples, not universal cost ranges for each fuel. Maintenance, equipment, and installation costs are additional.

What the Comparison Table Answers

Start with your expected running load and delivered fuel price. The table shows fuel-only generation cost at published operating points for a small gasoline inverter generator, a residential propane/natural-gas standby generator, and a larger diesel standby generator. Fuel consumption comes from the identified manufacturer sources; dollar results are calculated using explicitly assumed prices.

Example Fuel Prices

All calculations use U.S. dollars and these illustrative inputs—not current market averages or supplier quotes:

• Gasoline: $3.50 per US gallon.
• Diesel: $4.00 per US gallon.
• Propane: $3.00 per US gallon of liquid fuel.
• Natural gas: $15.00 per 1,000 cubic feet, equivalent to $0.015 per cubic foot.

Replace these prices with your delivered cost, including applicable variable delivery charges and taxes. For natural gas, the price and consumption volume must use a compatible pressure, temperature, and volume-correction basis. A bill priced per therm cannot be substituted directly for a price per cubic foot.

Generator Cost per kWh Comparison Table

“Load” means a percentage of the applicable fuel-specific electrical kW rating—not a percentage of starting watts or engine horsepower. Each example assumes steady operation at the stated output.

The Honda hourly rates are estimates derived from published tank capacity and runtime, not directly published fuel-flow measurements. They assume the stated tankful is consumed over the stated runtime; actual usable fuel and operating conditions can change the result. Calculations retain unrounded values before rounding the final cost. Honda lists 2.2 kW maximum output but 1.8 kW rated output, so the table uses 1.8 kW.

The Generac gaseous model has different output ratings on propane and natural gas. Its 50% natural-gas operating point is therefore 9.75 kW, not 11 kW. The linked product page does not state the gas-volume reference conditions or heating-value basis alongside its consumption figures; confirm those details before using the natural-gas rows for a site budget.

For the SD100, use fuel consumption—not total fuel-pump flow. The specification separately lists 29.1 US gal/h for combustion plus return flow; returned fuel is not fuel burned. These rows use the published standby consumption figures and do not establish suitability for routine prime-power service.

How to Calculate Generator Fuel Cost per kWh

For a steady operating point:

[
C_{\text{fuel}}=\frac{q \times p}{P}
]

Where:

• (C_{\text{fuel}}) = fuel cost, in dollars per kWh.
• (q) = fuel consumption, in US gal/h or ft³/h.
• (p) = fuel price, in dollars per matching fuel unit.
• (P) = actual electrical output, in kW.

The units reduce to dollars per kWh because one hour of operation at (P) kW produces (P) kWh. Use electrical kW—not kVA or fuel heat input—in the denominator. When using manufacturer electrical-output and fuel-consumption data together, do not apply another assumed engine or alternator efficiency factor.

Worked Example: A 100 kW Diesel Generator at Half Load

Using the SD100’s published 50% standby-load consumption of 4.2 US gal/h, assume a constant 50 kW load, diesel at $4.00 per US gallon, and 10 hours of operation.

• Fuel used: (4.2 \times 10 = 42) US gallons.
• Fuel spending: (42 \times $4.00 = $168).
• Electricity generated: (50 \times 10 = 500) kWh.
• Fuel cost per kWh: ($168 \div 500 = $0.336/\text{kWh}).

At a hypothetical utility energy rate of $0.20/kWh, the same 500 kWh would cost $100 in energy charges, compared with $168 in generator fuel. That comparison excludes generator maintenance and ownership costs, and it does not mean utility power would be available during an outage.

To adjust any table result for a different fuel price while keeping the same operating point:

[
C_{\text{new}}=C_{\text{table}}\times
\frac{p_{\text{new}}}{p_{\text{table}}}
]

This proportional adjustment applies to fuel price, not to load-dependent fuel consumption.

Why Load and Generator Size Change the Result

In the selected examples, lower output reduces hourly fuel use but increases fuel cost per kWh. The SD100 burns 4.2 US gal/h at half load versus 7.3 US gal/h at full load: half the electrical output still requires about 58% of the full-load fuel. Dividing that fuel spending by fewer generated kWh raises the unit cost.

The table does not isolate an economy-of-scale effect or establish which fuel is always cheapest. The models differ in size, engine design, operating method, and rating category, while the assumed fuel prices also differ. Compare candidate machines at your actual required kW—not merely at the same percentage of their nameplate ratings.

For a changing load, calculate each operating period separately and divide total fuel spending by total generated energy:

[
C_{\text{fuel,period}}=
\frac{\sum_i q_i p_i t_i}
{\sum_i P_i t_i}
]

Here, (t_i) is the duration of each period in hours. Include fuel burned during unloaded operation in the numerator even though it produces no useful load energy. At zero delivered kWh, a cost-per-kWh result is undefined.

Do not assume fuel consumption scales directly with output. This table uses only the listed operating points; it neither interpolates nor extrapolates. For intermediate loads, obtain the model’s fuel curve or use clearly identified interpolation between adjacent published points.

Comparing Generator Costs With Grid Electricity

Use the utility charges that would actually change if generator output replaced grid purchases:

• Include applicable per-kWh supply, delivery, and time-of-use charges.
• Keep fixed customer charges separate if they remain payable.
• For commercial accounts, calculate demand-charge effects from the tariff and billing demand rules rather than assuming every generated kWh reduces them.

The EIA’s average retail electricity-price table provides state and customer-sector benchmarks. Those averages are useful context, not a substitute for the rate applicable to your account.

For a full annual cost comparison, divide annual fuel, maintenance, repairs, and appropriately annualized equipment and installation costs by annual delivered kWh. Include exercise fuel and standby auxiliary electricity where applicable. Use the maintenance schedule for the exact model and duty rather than adding a universal maintenance allowance per kWh.

Checks the Cost Table Cannot Replace

A low calculated fuel cost does not establish that a generator can start or carry your equipment. Confirm running kW, kVA and power-factor limits, motor-starting and load-step performance, and available output under the site’s altitude and temperature conditions. The SD100 specification, for example, provides separate motor-starting data and identifies possible site-related derating.

A full-load row is a cost calculation at a published operating point—not permission to operate indefinitely at that rating. Confirm the exact unit’s nameplate, permitted duty, fuel supply, and operating instructions before using it for sustained generation.

For a building-connected installation, have a qualified professional check transfer equipment, fuel-system capacity, exhaust arrangements, and applicable local requirements against the exact equipment documentation. This cost comparison does not determine installation compliance or replace those checks.