Generator Fuel Cost Over a Multi-Day Outage
A generator's real annual cost is not just its purchase price, it is the fuel actually burned during the outages it runs through. This tool nets that fuel cost against the outage cost avoided, for a fuller picture than the generator's purchase price alone.
At your inputs, the generator, fuel cost included has an NPV of -$4,070 over 10 years, with a discounted payback of no discounted payback within this horizon.
| Net cost after confirmed incentives | $6,000 |
|---|---|
| Annual savings | $250 |
| Net present value | -$4,070 |
Breakeven: No discounted payback occurs within the selected horizon.
- This uses planning estimates you entered, not a contractor quote or guaranteed savings.
- Actual fuel cost during an outage depends on outage length and load, which vary; treat this as a planning estimate.
What this also tells you: A positive NPV means the option is worth more than its cost even after discounting future savings back to today; a negative NPV means the upfront cost outweighs what the savings are worth today.
This is a planning estimate based on your entries. It does not size equipment, determine electrical or building-code compliance, verify incentive eligibility, or replace a contractor quote or professional energy audit.
Why this decision comes up
A generator's fuel cost during actual outages is easy to underestimate when shopping, since it only shows up on a bill after the fact, well after the purchase decision is made.
How this is calculated
This discounts the annual outage-cost difference, net of fuel burned during actual use, back to today's dollars over your ownership horizon, netted against the generator's cost, to produce an NPV.
A worked example
With the defaults ($6,000 net cost, $500/year outage cost without a generator dropping to $250/year net of fuel, 10-year horizon, 5% discount rate), the annual savings is $250 and the NPV comes out negative at about $4,070 at these modest-outage defaults, similar to the standard generator payback tool's honest long-horizon result.
Common mistakes
A common mistake is pricing a generator purchase without factoring in realistic fuel cost during actual outage use, which can meaningfully change the total cost picture over a multi-day event.
Limitations
This uses an averaged annual fuel-cost estimate rather than modeling specific outage durations. A longer single outage will burn more fuel in one event than this averaged figure implies.
Common questions
How much fuel does a standby generator use?
It depends on the generator's size and load, but a whole-home standby unit can burn a meaningful amount of propane or natural gas per hour of runtime during an extended outage. Check your unit's specifications for an accurate estimate.
Does this apply to a portable generator too?
The same logic applies, though a portable generator's fuel type (usually gasoline) and consumption pattern differ from a standby unit's. Adjust your entered annual cost to reflect your actual equipment.
How is this different from the basic generator payback tool?
That tool nets fuel cost into the general payback calculation already. This one uses the discounted NPV method instead of simple payback, useful for a longer-horizon, more conservative view.
Does propane versus natural gas change this calculation?
Fuel type affects cost per hour of runtime. Use the price and consumption rate for your specific fuel source and generator model rather than a generic assumption.
What if I don't know how many outage-days to expect per year?
Check your utility's or local records for typical outage frequency and duration in your area, or use your own household's recent history as a starting point rather than guessing.