> As a backup generator, is propane or gasoline cheaper per KwH of generated power?

I am told propane tends to gum up backup generators less, propane stores forever, and it may pass small engine requirements (CARB/CEPA) easier.  I say propane is the winner.  It's only a little more expensive.

ChatGPT said:

When comparing propane and gasoline as fuel sources for backup generators, the cost per kilowatt-hour (kWh) of generated power can vary depending on local fuel prices, but generally, propane tends to be more expensive per kWh than gasoline. Here's a more detailed breakdown:

1. Energy Content:

Gasoline: 1 gallon of gasoline contains about 33.6 kWh of energy.

Propane: 1 gallon of propane contains about 27 kWh of energy.

Propane has slightly less energy content per gallon than gasoline, so you will typically need more propane to generate the same amount of power.

2. Fuel Cost:

Fuel costs fluctuate by location, but generally, gasoline is cheaper per gallon than propane. As of recent trends (though prices can vary):

Gasoline may cost around $3.50 to $4.50 per gallon.

Propane may cost around $2.50 to $4.00 per gallon.

3. Fuel Efficiency (Generator):

Gasoline-powered generators tend to have higher fuel efficiency compared to propane-powered ones because gasoline engines are optimized for gasoline use.

Propane generators typically have a slightly lower efficiency (about 10–20% lower).

4. Cost per kWh Calculation:

To simplify, let's assume a scenario with these prices:

Gasoline costs $3.50 per gallon and provides 33.6 kWh of energy per gallon.

Cost per kWh for gasoline:

$3.5033.6 kWh≈$0.104 per kWh
33.6kWh
$3.50
    ​

≈$0.104per kWh

Propane costs $3.00 per gallon and provides 27 kWh of energy per gallon.

Cost per kWh for propane:

$3.0027 kWh≈$0.111 per kWh
27kWh
$3.00
    ​

≈$0.111per kWh
5. Conclusion:

In this example, gasoline is slightly cheaper per kWh, primarily due to its higher energy content per gallon and generally lower fuel cost. However, the actual price difference will depend on your local fuel prices, and the fuel efficiency of your specific generator.

If you're looking for long-term cost-effectiveness, gasoline may have the edge. However, propane might be more convenient or suitable in certain situations (like for longer storage or in rural areas with less access to gasoline).