Off-grid, RV & cabin

Generator fuel cost calculator

Enter your generator size, typical load, and annual runtime. Get your estimated yearly fuel cost across gasoline, propane, and diesel.

Your numbers

1 Project details Optional
2 Generator and usage
Rated continuous running watts, from the generator's spec sheet.
What percentage of rated capacity the generator typically runs at.
Total hours the generator runs per year. Solar-paired backups typically run 50 to 150 hours a year.
3 Local fuel price
Dollars per gallon. Check your local price, since fuel costs vary meaningfully by region and season.

How it works

Three steps to a fuel budget

Step 1

Enter your generator's rated wattage

Use the continuous running watt rating from the spec sheet, not the surge or peak rating.

Step 2

Estimate your typical load and annual hours

Most solar-paired backup generators run far fewer hours a year than people expect, usually well under 200.

Step 3

Pick your fuel type and local price

Fuel prices vary meaningfully by region, so check a local price rather than using a national average.

Understanding generator fuel costs

The direct answer for a typical backup generator

A 3,000-watt generator running at 60% load for 100 hours a year costs roughly $79 in gasoline, $91 in propane, or $58 in diesel at typical U.S. fuel prices. This reflects a light-duty backup role, where the generator mostly sits unused and only runs during cloudy stretches or occasional heavy loads. The DOE's solar photovoltaic technology basics lays out the same rules from the regulator's side.

Why diesel usually wins on fuel cost per hour

Diesel generators typically burn less fuel volume per kWh produced than gasoline or propane units, since diesel fuel holds more usable energy per gallon. Propane generally burns the most volume per kWh, since it holds less energy per gallon than either gasoline or diesel, though propane has other advantages like longer shelf life and cleaner combustion that some owners weigh against the higher per-hour fuel cost. Remote systems are easy to neglect. The panel cleaning frequency calculator in our Maintenance & Lifespan section can help you budget for the maintenance that keeps output from slipping.

Load factor matters more than most people realize

A generator running well below its rated capacity still burns meaningful fuel just to stay running, so very light loads don't scale fuel consumption down proportionally. Running a generator closer to its efficient operating range, rather than drastically oversized for the load it's actually carrying, generally saves fuel over the life of the equipment. The generator backup hybrid sizing tool helps match generator size to actual need rather than guessing large. Fuel price assumptions used throughout come from EIA's data on what drives energy prices. Even off-grid, the money side matters. The 25-year lifetime savings calculator in our Savings & Payback section can help you compare the system cost with the cost of extending the grid.

Annual hours is the single biggest driver of total cost

A generator used purely as a solar backup, running only during cloudy stretches, might see 50 to 150 hours a year and a correspondingly modest fuel bill. A generator used as a primary or near-primary power source can run thousands of hours annually, and the fuel cost math changes entirely at that scale. Confirm which scenario matches your actual use case before comparing generator fuel cost against a larger solar investment. The cost per kWh produced calculator in our savings and payback tools is a useful way to put generator fuel cost on the same footing as solar's cost per kWh.

What to check once you have a fuel cost estimate

Compare this annual cost against propane or diesel solar cost comparisons to see how it stacks up against expanding your solar system instead, and check the hybrid generator solar runtime calculator to estimate how many hours your specific system will actually need the generator. If a larger solar array ends up the better long-term option, the federal ITC calculator in our rebates and incentives tools and DOE's solar photovoltaic technology basics are both useful next stops.

Questions

Frequently asked

A 3,000-watt generator running at 60% load for 100 hours a year costs roughly $79 in gasoline, $91 in propane, or $58 in diesel at typical U.S. fuel prices. Actual cost scales directly with how many hours the generator runs annually.

Diesel generators are typically the most fuel-efficient per kWh produced, followed by gasoline, with propane usually burning the most volume per kWh since it holds less energy per gallon. Actual cost per year depends on both the fuel's efficiency and its local price.

Yes. A generator running at 30% load burns meaningfully less fuel per hour than the same generator at 80% load, though not in exact proportion, since generators run somewhat less efficiently at very light loads. Sizing a generator closer to your typical running load, rather than drastically oversized, usually saves fuel.

A solar-paired backup generator commonly runs 50 to 150 hours a year, mostly during winter cloudy stretches. A generator used as a primary power source, rather than backup, can run 2,000 hours or more a year, which changes the fuel cost math dramatically.

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