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#4804416 - 07/03/18 08:13 PM Diesel vs gasoline portable generator efficiency
blackgolds Offline


Registered: 01/08/18
Posts: 12
Loc: California
Hi, portable generator fuel efficiency question. What is the best type of fuel for portable generator fuel efficiency? All, fuel types are accessible so that is not an issue for me, maybe for others. But I just want to save some cash on fuel and keep the gene going. This article suggests that diesel is the most fuel efficient but produces lower wattages compared to gas-powered generators. Seems that there a diesel generators with enough wattages. My question is why do most people have gas powered generators? I was thinking to get a diesel one but just not sure if there is something I am missing.

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#4804423 - 07/03/18 08:24 PM Re: Diesel vs gasoline portable generator efficiency [Re: blackgolds]
UncleDave Offline


Registered: 06/02/14
Posts: 1708
Loc: Ca.
There arent really any "portable" diesels.

There is 20% more energy per unit of fuel in diesel so its hard for gasoline gensets to beat them.

Diesel gensets are all big and go ginormous.

Whats the use case?

UD
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#4804429 - 07/03/18 08:32 PM Re: Diesel vs gasoline portable generator efficiency [Re: blackgolds]
hatt Offline


Registered: 01/03/12
Posts: 4408
Loc: Florida
Diesel gens cost 4-5 times as much as gas units. It's going to take a long time to save any money, if ever. And that's using it a lot. As a backup for when the power goes out you'll never save money. Diesel has other possible benefits if you're looking past the costs.
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#4804439 - 07/03/18 08:45 PM Re: Diesel vs gasoline portable generator efficiency [Re: blackgolds]
JHZR2 Offline



Registered: 12/14/02
Posts: 41896
Loc: New Jersey
Its not clear what you mean, OP, by "more efficient but produces lower wattages..."

For the same power output (wattage), a diesel will burn a significantly lower amount of fuel.

So then it goes to UncleDave's questions. Load level, use case, etc.

The play here is if youre trying to just run a small amount of load, say, keep your refrigerator and some lights going, an inverter gas generator, like the Honda EU2200i, can be as efficient as a constant speed diesel, because it is able to throttle down. They are also quiet.

A diesel has less issues with fuel going bad, carbs clogging (because there isnt one), etc. Gas engines have to be treated a little better.

If you start talking say, 7kW and above, then diesels are the way to go.

I was down in the islands for a total of three weeks after Irma and Maria, and if you look around, anyone with half a brain has a diesel genset. Its easy(ier) to get a 55 gal drum of diesel, and far safer to store it.

Those who were duped into propane gensets were doing without power because the logistics were unable to support refueling, both into the terminals and around the island.

Diesel is the way to go if large, one or two small inverter generators if you want to just deal with a smaller load. That's my recommendation. In a weather emergency or a more dire situation, you dont want to become a target. Additionally, after Sandy, we learned just how hard it was for folks to be able to fuel up - gas stations didnt have any fuel. Youre not looking for luxury, youre looking to keep food cold and run a well pump if necessary.

For realistic use, a $999 Honda EU2200i from Home Depot is the way to go, IMO.

If you truly have a larger load, a simple IDI diesel from a manufacturer like Kubota is ideal, IMO.

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#4804447 - 07/03/18 08:52 PM Re: Diesel vs gasoline portable generator efficiency [Re: blackgolds]
eljefino Offline


Registered: 06/15/03
Posts: 32775
Loc: ME
If you can get untaxed, off road diesel (eg home heating oil) you'll save some money that way, too.

I weighed a dose of gasoline and fed it to my cheapo inverter generator. Did the math and found it cost 5x shore power. Honestly not that bad when you think about it.

But what's your game? Cabin off-the-grid? Emergency power? Most people have gas generators for the same reason they have gas lawnmowers-- the engines are cheap to produce. Someone who needs an emergency generator is looking to spend $300 to save $300 worth of freezer meat once-- anything after that is gravy.

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#4804448 - 07/03/18 08:52 PM Re: Diesel vs gasoline portable generator efficiency [Re: blackgolds]
NYEngineer Offline


Registered: 12/12/06
Posts: 1618
Loc: NY, NY
My family's business is generators and I manage some big ones for Time Warner Corporate for a living.

Small diesels cost way more than gasoline engines because of liquid cooling, diesel injection pumps, injectors and so on. A diesel powered engine will make power at a lower rpm for a longer amount of time than a gasoline engine. Diesel is also more stable and can sit in wait longer. Once you have a diesel generator, I guess it would be cheaper to operate than a gasoline gen but like Hatt said, your pocket won't realize any savings any time soon.

My brother sells lots of natural gas/ propane units ranging between 8 and 20 kW. They're air cooled and relatively inexpensive. Excellent units. Big bonus is nat gas doesn't go bad and gum up the carburetor and, as long as you pay your bill, the gas supply is relatively endless.

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#4804459 - 07/03/18 09:00 PM Re: Diesel vs gasoline portable generator efficiency [Re: NYEngineer]
JHZR2 Offline



Registered: 12/14/02
Posts: 41896
Loc: New Jersey
Originally Posted By: NYEngineer

My brother sells lots of natural gas/ propane units ranging between 8 and 20 kW. They're air cooled and relatively inexpensive. Excellent units. Big bonus is nat gas doesn't go bad and gum up the carburetor and, as long as you pay your bill, the gas supply is relatively endless.


NG perhaps, unless they shut it down (like after Sandy when in some areas it was bubbling up from underground broken lines).

Propane is another story. The logistics issues with propane can be as bad if not worse than other fuels.

After Maria, we were helping folks rig up marine batteries and 12V inverters to their cars, as they had "invested" in "green" LPG gensets, and couldnt get delivery.

I flew American once and Delta once, to the Caribbean after the hurricanes. They were letting anyone and everyone bring on inverter generators.

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#4804471 - 07/03/18 09:16 PM Re: Diesel vs gasoline portable generator efficiency [Re: blackgolds]
CT8 Offline


Registered: 10/09/14
Posts: 11230
Loc: Idaho
You mentioned you read an article. You did not mention what are you going to use the generator for ?
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#4804489 - 07/03/18 09:42 PM Re: Diesel vs gasoline portable generator efficiency [Re: blackgolds]
Snagglefoot Offline


Registered: 12/31/17
Posts: 1909
Loc: SE British Columbia, Canada
If you are out in the country with a 500 gallon propane tank, then a dual fuel gasoline and propane generator would be a good option.

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#4804697 - 07/04/18 07:24 AM Re: Diesel vs gasoline portable generator efficiency [Re: blackgolds]
Cujet Offline


Registered: 02/15/03
Posts: 7238
Loc: Jupiter, Florida
The following is a post I placed on another board:

A post about generator efficiency and fuel consumption. For understanding.

1) A portable generator is not an efficient device. Regardless of brand or type.
2) Generator produced power (for our purposes, portable and stationary household sized) is very expensive when compared to the utility company, regardless of fuel type and fuel costs. Even with free fuel, the costs exceed the utility company's charges per KWH.
3) Inverter generators are NOT more efficient in many situations. They are quieter and better suited to very low/no load conditions.

Here are some numbers: (note, look at KWH/gal, higher is better)

Honda EU2000i inverter generator

1,600W 4.75 kWh/gallon Run time 2.97 hours/gallon.
555W 4.47 kWh/gallon Run time 8.06 hours/gallon

The Honda is almost as efficient at low loads as it is at high loads. This is fantastic when you need very little power. But it's not as good as a conventional genset at high loads, as we will see below.

Generac GP3250
2300W, 5.53 KWH/gallon
1900W, 5.35 KWH/gallon
1150W, 4.45 KWH/gallon
744W, 3.84 KWH/gallon

Yamaha EF3000is
2300W, 4.50 KWH/gallon
1900W, 4.42 KWH/gallon
1150W, 4.38 KWH/gallon
744W, 3.89 KWH/gallon

Notice the inverter Yamaha is not better than the Generac until it's at 1/4 load or lower. At which point, you will save some fuel.

Listeroid 6/1 diesel with belt drive ST generator head (notice that it's twice as efficient as the Honda/Yamaha inverter generators when heavily loaded, and exceeds the inverter's efficiency all the way down to 500W) (at which point, it consumes about 1/10 gallon per hour, on par with the Honda)
3000W, 8.57 KWH/gallon
2000W, 7.69 KWH/gallon
1000W, 5.71 KWH/gallon
500W, 4.2 KWH/gallon Run time 8 hours per gallon (exactly the same as the Honda, this showcases the diesel's efficiency)

15000W Generac portable (gasoline) (note, the bigger the generator, the more efficient)
15KW, 8.3KWH/gal
7.5KW, 5.9KWH/gal
3750W, 3.8KWH/gal

30,000W John Deere turbodiesel generator (note, diesels are often very efficient at a wide range of loads, and sometimes worse at very high loads)
30KW, 11.4KWH/gal
15KW, 11.5KWH/gal

200,000W JD turbodiesel generator
200KW, 15.5KWH/gal
100KW, 15.5KWH/gal (or roughly 20c/KWH at $3/gal) (still double the local utilities price, and the unit's capital costs are enormous)


Edited by Cujet (07/04/18 07:24 AM)
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#4804707 - 07/04/18 07:36 AM Re: Diesel vs gasoline portable generator efficiency [Re: blackgolds]
Cujet Offline


Registered: 02/15/03
Posts: 7238
Loc: Jupiter, Florida
blackgolds,

I prefer high quality, 11 to 13HP 340-390cc, (go by displacement or HP, not bogus watt ratings) portable, open frame, conventional gas generators for the following reasons: (in no particular order)

1) ease of repair/carb cleaning, troubleshooting
2) light weight/portability, it can go anywhere it's needed
3) robustness, especially if overloaded
4) ease of inside storage (very important)
5) enough power to run a water heater
6) price
7) excellent surge load capability

Here is a capable favorite, 390cc Honda engine, McAlte gen head (excellent) :

https://www.northerntool.com/shop/tools/product_200467366_200467366
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#4804709 - 07/04/18 07:38 AM Re: Diesel vs gasoline portable generator efficiency [Re: blackgolds]
Rand Offline


Registered: 08/20/03
Posts: 12728
Loc: NE,Ohio
I like dual fuel as well. they have relatively low priced ones often.

if your cabin has a couple hundred pound propane tanks.. you dont have to worry about storing gas.
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#4804710 - 07/04/18 07:39 AM Re: Diesel vs gasoline portable generator efficiency [Re: blackgolds]
Donald Offline


Registered: 03/21/04
Posts: 20565
Loc: Upstate NY
The small portable diesel generators are [censored]. Avoid. If you want a large generator get a 1800 RPM diesel but take into account how to start it when it's cold.

For most homes propane or natural gas is best.

If you are off the grid there is always the Lister diesel.
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#4804714 - 07/04/18 07:44 AM Re: Diesel vs gasoline portable generator efficiency [Re: blackgolds]
Cujet Offline


Registered: 02/15/03
Posts: 7238
Loc: Jupiter, Florida
Low quality, air cooled, 10HP Chinese diesel gensets are nothing but trouble. They may be more efficient, due to diesel fuel's increased energy content, but they are not smart choices when backup power is really needed. There are many examples of the cheap Chinese diesel engines destroying themselves. In particular, the shock loads due to the diesel combustion cycle tend to destroy the roller bearings on the crankshaft and break cam gears.
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#4804736 - 07/04/18 08:19 AM Re: Diesel vs gasoline portable generator efficiency [Re: blackgolds]
NYEngineer Offline


Registered: 12/12/06
Posts: 1618
Loc: NY, NY
My mom lives down in Naples, Florida and she had no power for 13 days after whatever that big hurricane was that hit them last year. She had a camp stove and a diner a short distance from her house had power so she was able to make do.
I wanted to bring a generator down for her but there was no guarantee I'd be able to get gas to get down there so we agreed to sit tight. She toughed it out and after the smoke cleared, we got her a Honda inverter generator. We went through how to use it to power the refrigerator and then unplug that and use the microwave and so on. She lives in a condo so I can't just put a whole house unit next to her home. They're funny like that.
Only drawback is this thing runs on gasoline so we also got a few five gallon explosafe gas cans. There's a shed where they can stay.

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