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tl;dr What is a likely value for fuel consumption for a small portable 4-stroke gasoline-powered inverter power generator in, say, litre / ( kilowatt * hour )?

At times I attend music festivals where you camp outside for a few days and go see bands perform in the afternoon and evenings. Some of them permit the use of power generators, and I got myself one as described above rated for max. 1000 watts continuous power draw. My group won't use that much, but that's what I got when I aimed for the smallest 4-stroke inverter model.

Among my questions is now how to estimate the amount of fuel to bring with me to a given event, and unfortunately the spec sheet and other resources shipped with the unit do not feature any fuel consumption figures/curves/tables.

I do have a rough estimate of the power draw and duration.

Typically the power generator will be run from the morning into the afternoon, let's say 08:00..14:00, which is when people hang out at the camp site killing time until the bands start. From afternoon on it's seeing the bands until late into the night, after which people come back exhausted and in various stages of inebriation and usually just drop into their tents – running a generator at that kind of time is a jerk move that is guaranteed to bring the rightful wrath of your camp neighbors upon you.

While the generator is being used you will run a fridge for the drinks, some music setup for nice tunes, and a bunch of small power supplies charging various devices such as smartphones and power banks. If you're fancy you might have a table fan for when it's really hot. So let's add these up:

  • 80 W - (small) fridge
  • 50 W - music
  • 5 * 10 W - smartphones etc. being charged
  • 40 W - table fan

That's 220 W of continuous power draw (the fridge will be running its compressor continuously because it starts out warm and is made extensive use of). Multiply that with the 6 hours of daily use and we get about 1300 Wh, and if the festival lasts for 4 days we're at about 5300 Wh, or 5.3 kWh, drawn at roughly a quarter of the generator's rated output.

So … how much gas does that roughly equate to? I have been searching around for some ballpark figures, but I only seem to find various tables that are too specific and not readily applicable to my problem.

  • I'm almost sure that the manufacturer provides this information. In (German) Internet shops, fuel consumption is usually stated ib the details. I just saw an 1600W generator with 0.36l/h. – Jasper Feb 24 at 9:16
  • @TomasBy I very much suspect that the load is the deciding factor for fuel consumption, not the time. Sure, there will be an idle fuel consumption when no load is drawn, but my basic understanding of phyics would lead me to assume that while fuel throughput at 80% load might not be quite 4 times that of 20% load, it might be about 3.5 times that. As such the quote relating to the 5,000 W generator seems kind of useless to me (I also found that one). At which load? 30% Half? The full 5000 W (nobody would do that)? – eomanis Feb 24 at 16:10
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    Have you considered adding a deep-cycle battery to the mix, and running the generator full-on to recharge the battery and then shutting it down? Likely the most efficient in fuel/kWh method. And your fridge keeps running all night. – Jon Custer Feb 25 at 19:37
  • Have you looked at the company website for performance? – Sherwood Botsford Feb 25 at 20:13
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Generator run time per gallon varies greatly by manufacture. Just like gas mileage varies per vehicle. Not all small 4 seat cars, driving the speed limit get the same gas mileage, even though they are doing the same work.

Most manufactures include run time per tank or gallon in their literature. Searching online for your make and model of generator should get you answers for your generator.

The are two primary markets for portable generators.

  1. Construction workers

  2. Campers and Survivalists

Both have minimum run time requirements, Construction works want the generator to run while the are working, at a minimum 4 hours. Campers want their generator to run all day, at a minimum 8 hours. As a result most generators run between 5 and 10 hours on one tank of fuel at 50% of rated output.

Personally I run my generators at home, at least twice a year (Spring and Fall), to ensure they are ready for the coming season.

When test running your generator put about a 1/4 tank of fuel in it. Plug in some things and and let it run until it runs out of fuel. This should be between 1 and 3 hours, multiple by 4 and that is how many hours it runs on one tank of fuel.

Fuel stabilizer is important. I always add fuel stabilizer to the fuel I run in my generators. I never know when I will run it again, but I know it could be 6 months, so stabilizer prevents gas break down. At the end of the season I put left over generator fuel in my car/truck and get new fuel (adding stabilizer) for the seasonal test run and reserve fuel.

Edit

No load requires about the same fuel as 50% or less load.

More load requires more fuel, there are multiple ways for manufacturers to balance fuel supply for increased load. Some of these solutions are less efficient then others. If it is important that you have good estimates on fuel consumption per hour, testing (per above) is your best choice.

For really ballpark estimates, figure 4 hours per tank, and in most scenarios you should be fine, with a little extra just in case.

For more info on why inexpensive generators don't scale kWh to fuel consumption see This answer at 'What to look for in a portable generator?'

  • Yes, for vehicles gas mileage varies by type, but it matters much, much more how a vehicle is used. Gasoline passenger cars might typically need 4..8 litre per 100 km; however your "5 l/100km" car will guzzle up upwards of 20 l/100km while you drive steeply uphill with the A/C going full blast, and when you drive back down it will use almost no gas at all. But unlike a car on roads that go up and down, a generator may be used at 90% capacity continuously, which is why I think expressing fuel consumption in run time per volume is misleading without specifying a load. – eomanis Feb 24 at 16:53
  • @eomanis a given generator will use more fuel under more load, but at any given load (220W in your example) every brand generator with a 1000 Watt model will use different amounts of fuel. – James Jenkins Feb 25 at 11:02
  • True, but I doubt that with the same power draw e. g. 1,000 W model A will use 1 l/h while 1,000 W model B burns 10 l/h. I assume the variation among 4-stroke gasoline inverters with, say, 1,000..2,000 W rated power is narrow enough to allow for a rough estimate that is useful in practice. Knowing you'll need 20..30 l gasoline, but not 5 l and not 60 l either would be good enough for me. – eomanis Feb 25 at 14:44
  • @eomanis ho much fuel does the tank on you generator hold? – James Jenkins Feb 25 at 15:26
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    As per the specs in the manual the tank holds 2.8 l (manufacturer web site: 3.0 l). For what it's worth the unit is a Güde ISG 1200-1. The web site does mention a run time of 4.8 h (nothing in the manual). At full load that would mean getting 5 kWh of electricity from 3 l gasoline, is this at all plausible? – eomanis Feb 25 at 15:54

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