Estimating your portable generator running cost can be fairly difficult, given the various factors involved, but there are some ways to help understand what the costs might look like overall for each type. Most electric generators are fueled by gasoline, propane, natural gas, or diesel – with gasoline being the most common for portable consumer units. Prices of these fuels vary, which will affect how much you will spend running your generator.
24-Hour Portable Generator Running Cost
Gasoline
A typical 3,500 Watt gasoline-powered generator, running at 1/2 load (1,750W), will run approximately 2 hours on a gallon of gasoline. Currently (February 2017), the average price of gasoline in the United States is about $2.28 per gallon. You will spend about $27-34 running your generator for an entire 24 hour period, assuming you aren’t running it at full capacity the entire time – and, really, this is really the thing to keep in mind.
It’s important to consider what kind of load you will be putting on your generator, as well as its capacity and efficiency. Using a smaller, more efficient generator to run only 800-1200 watts should only cost around $12-16 to run for 24 hours. This is why it’s so important to calculate your electricity needs, the minimum output you need generated, and how much it will cost to run before buying a generator.
Diesel
Most diesel generators are very large and used in commercial or industrial applications. There are a number of small, portable diesel generators available, though they are much less common than portable gasoline powered units.
Diesel prices are typically about 20-30 cents higher than gasoline prices (as of February 2017, the average price of diesel fuel in the U.S. is currently ≈ $2.50). There is a lot of variation in fuel consumption for diesel-powered generators, just as there is a wide range in output (keep in mind that diesel is more commonly seen in large-scale generation units for commercial/industrial use).
Most modern portable diesel generators are fairly fuel efficient – such as the Generac XD5000E, which burns through less than half-gallon of fuel an hour while running at 1/2 capacity, allowing it to run for 32.4 hours on 12 gallons of diesel. That works out to 2,500 Watts, 24 hours straight, for about $30.
Compare this to a typical gas-powered model that will cost a bit more in fuel, while supplying less power. Although the generator running cost is impressive for diesel, the major trade-off is the equipment cost; the XD5000E runs about $3700, which is typical for portable diesel units of its size.
Propane
The average cost of propane is around $2.33 per gallon (January 2017 U.S. average) – when purchased in bulk (think 100-gallon+ tank). Those 20-pound tanks that you use with your grill contain about 4.7 gallons. So, if it costs $20 to swap one of them out at your local Home Depot or supermarket, you are effectively paying about $4.26 per gallon.
Propane has 91,333 BTU per gallon (source), so a 20-pound tank has about 429,265 BTU. A small portable generator (like the Yamaha EF2000iS) producing a max running output of 1,600 watts will consume about 32,000 BTU per hour at full load. This works out to about 0.35 gallons per hour.
So the generator running cost in this example, for a full 24 hours, may range from:
- About $20 with bulk propane
- About $36 with 20-pound LP tanks (you’ll use a little under 2 full ones).
(Above, left to right: 100, 40, and 20 pound LP tanks) Propane tanks are available in a variety of sizes, including those that hold several hundred pounds or more. For larger tanks, propane is typically sold in bulk and delivered, with refilling done on-site. Image courtesy of mbloore
Of course, 1,600 watts probably isn’t enough to run your whole house (there’s a reason non-portable standby generators are typically rated to produce at least 15,000 watts (15kW) continuously). Depending on your load and generator, you might burn more or less per hour – though, most outages don’t last 24 hours.
The fuel cost savings for buying in bulk is nice but, for most people, it would not be cost-effective to install a large tank just to be able to get bulk prices on propane for occasional generator use. If you already have a large propane tank on-site, a propane generator is certainly worth investigating.
Propane can be an excellent choice for occasional outages, even if you’re just using 20 lb. LP tanks you have on-hand for grilling. And, since you can swap them out at a variety of places including the hardware store and supermarket – propane might be more available than gasoline or diesel during outages when gas stations don’t have power to pump these fuels.
Natural Gas
Natural gas is in a class of its own when it comes to generator running cost, as natural gas generators burn through fuel at a much slower rate than most other generators. Natural gas is not delivered in tanks and is not measured in gallons. Likewise, no portable generators will run solely on natural gas, although many are designed to use natural gas alongside other fuel sources. (It’s worth noting that Natural Gas is more commonly seen as a fuel source for installed “whole house” home backup and emergency standby generators, rather than portable models. But they do exist.)
Natural gas is typically measured in its cost per therm. A “therm” unit is the amount of energy required to raise the temperature of a pound of water by one degree. Generally, one therm is approximately 23.9 kWh or 100,000 British Thermal Units (BTU). Natural gas is generally the cheapest way to power a backup generator (particularly for installed “whole house” types). The average cost for natural gas per therm in December 2016 was $1.109. If a generator burns about 1 therm per hour, users can expect to pay about $1.11 per hour, or approximately $27 per 24-hour period.
Cost of Operation vs. Other Factors
- Those seeking the most continuous wattage will want to purchase a diesel generator. These also offer a ground in running cost, although are more pricey in terms of initial unit cost. They are also less portable due to the heaviness of diesel fuel.
- Gasoline generators are a great option for those seeking portability and short periods of power generation, but are not the most cost efficient option for longer power outages. In addition, storing gasoline for long periods is not ideal, due to oxidation, evaporation, condensation (leading to water in your fuel). There are fuel additives available, though, and many users simply siphon out the unused gas into their cars or lawn mowers after outages have ended (one benefit of using the same fuel for everything).
- Propane can be a little costlier than gasoline if you are running your generator from a 20-pound LP tank. However, the results of the generator running cost calculation will quickly change if you already have larger propane tanks on-site. However, despite the slightly higher running costs of a small tank, the added convenience of propane over gasoline might still win out – for the occasional brief outage, you simply move the tank from your propane grill to your generator (and then back again once grid power returns).
- Finding a generator that operates using natural gas is a great option for those who live in areas much more prone to power outages. However, it is important to note that you must already have a natural gas hook up installed in your home before you can utilize this as an option. If you have frequent outages and this option seems attractive, you should also consider having a “whole house” natural gas standby generator installed as an alternative.
For more information on selecting a generator, see our guide: What Generator Fuel Type is Best?
