Math Question: Which Generator is Most Fuel Efficient @ 2500W Load?

[Best F100]

I was looking at the current listed Honda generator lineup the other day. Just for kicks, for comparison (and argument) sake, I thought up the following question. I realize real world power outage demands vary from hour to hour (and appliance to appliance).

Question: What is the most efficient Honda generator(s) to use during a 7 day power outage, for a constant 2500W household load? (while taking price of the generator out of the equation). All generators will be using the Honda Eco throttle system. Also, what is the least fuel efficient generator to use?

Generator 1> Two Honda EU2200i paired together (in parallel). Each rated at 2200W max, 1800W rating. Up to 8.1 hrs of run time on 0.95 gallons of fuel @ 1/4 load. 3.2 hours @ rated load.

Generator 2> Honda EU3000is. 3000W Maximum rating. Rated at 2800W. Up to 20 hours of run time on 3.4 gallons of fuel @ 1/4 load. 7 hours @ rated load.

Generator 3> Honda EU7000is. 7000W Maximum rating. Rated at 5500W. Up to 18 hours of run time on 5.1 gallons of fuel @ 1/4 load. 6.5 hours@ rated load.

 

[doitmyself]

Oops, I misinterpreted your "rated load" variable. I don't know if generator efficiency is linear from 1/4 load to rated load.

 

[eljefino]

I would get a non-inverter, constant 3600 RPM generator for these duties, probably sized around 3250 running/ 4000 surge.

If you install your 120v transfer switch, you can plug it into an extension cord and use a kill-a-watt to see instantaneous and continuous use. EG how many kwh did the fridge consume overnight, and figure out its duty cycle from there.

 

[bubbatime]

Originally Posted by eljefino
I would get a non-inverter, constant 3600 RPM generator for these duties, probably sized around 3250 running/ 4000 surge.


The op is going for fuel efficiency here.

 

[eljefino]

Originally Posted by bubbatime
Originally Posted by eljefino
I would get a non-inverter, constant 3600 RPM generator for these duties, probably sized around 3250 running/ 4000 surge.


The op is going for fuel efficiency here.


Yes, and a gas engine running at about 60% load is the sweet spot for efficiency.

Generating DC then rectifying it to AC incurs some loss.

The killer app of inverter generators is being able to throttle back and run at lower RPM for light loads, but in the scope of this question he'll consume 2500 watts constantly.

I don't think he will, and would encourage him to discover his loads are actually lighter most of the time.

 

[Linctex]

Yes - the truth is that a constant load on a direct driven generator will always be the most fuel efficient.

The only reason inverter generators often get better economy is things are constantly turning on and off, like the compressor in the AC or in the fridge.

 

[MolaKule]

Originally Posted by eljefino
Originally Posted by bubbatime
Originally Posted by eljefino
I would get a non-inverter, constant 3600 RPM generator for these duties, probably sized around 3250 running/ 4000 surge.


The op is going for fuel efficiency here.


Yes, and a gas engine running at about 60% load is the sweet spot for efficiency.

Generating DC then rectifying it to AC incurs some loss.

The killer app of inverter generators is being able to throttle back and run at lower RPM for light loads, but in the scope of this question he'll consume 2500 watts constantly.

I don't think he will, and would encourage him to discover his loads are actually lighter most of the time.

I personally would not sacrifice power output for fuel efficiency if certain loads like refrigerator and heating systems were important.

 

[Donald]

For fuel efficiency, get a diesel running at 1800 RPM.

 

[Cujet]

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)







Note, even the DIY Lister diesel generator makes only 8KWH/gallon ($3/gal) or roughly 40 cents per KWH. Almost 4 times more expensive than my local utility company.

Also, understand that (my favorite) small "suitcase type" inverter/generators have a place. When running a fridge, for example, the load is not constant, with much of the day having no or low load. So the inverter generator idles down under low/no load conditions while still producing 120V 60HZ. This is a BIG DEAL when running a fridge for (example) a month. As the total fuel consumption will be considerably lower than a conventional 3600RPM direct drive generator. How much lower depends on load.

Put another way, "IF" you are running constantly high loads, such as driving an air conditioner in death valley, an inverter/generator will not save you fuel. It may be better to choose a conventional generator in this case.

 

[Cujet]

Originally Posted by Donald
For fuel efficiency, get a diesel running at 1800 RPM.


This is generally the best advice. It's no surprise that many of the small, marine gensets run at 1800 RPM. Not only is the noise less bothersome, but the fuel consumption per KWH produced is significantly reduced.


On another note: as a general rule, electronics are not sensitive. Most power supplies will run a TV, audio equipment or computer on 50-70 HZ 90-240 volts. They convert AC power to DC as required by most electronics.

What can be sensitive to power quality are induction motors. Many people notice that low quality power will cause induction motors to make more noise.

 

[Rand]

Originally Posted by Cujet

Note, even the DIY Lister diesel generator makes only 8KWH/gallon ($3/gal) or roughly 40 cents per KWH. Almost 4 times more expensive than my local utility company.



I'd agree with everything except the utility price/4x price calculation. The distribution charges are enormous chunk of it here.

So while they say its 9cents an hour if you divide my power bill dollars/kwh its more like 17cents after all the taxes, charges,fees, bill stuffing etc most of these are per kwh charges that directly track.. some are one time charges such as "connection charge" type fee.

of course this all varies by your power company and how they bill you. Not to take away anything from your argument and data.. I feel its very true.. except that one statement of 4x cost.

 

[Rmay635703]

http://www.centralmainediesel.com/order/yanmar_4kw.asp?page=yanmar_4kw

This is the most efficient I am aware of

 

[eljefino]

Found my post from when I got the super cheap 600 watt Lifan inverter generator:

From home depot. The online instructions indicate it's only good for 500 watt continuous, 600 surge but my paper one reads 600/700! Other inconsistencies are my paper instructions read a 5 hour run time at full load vs the Depot ad reading 3 hr at 50%.

I broke it in for 30 minutes until it ran out of gas then put 213 grams of gasoline in 'er. This is 0.07513 gallons or 20 cents for you nerds. . I'm running it with a 360 watt load on eco-mode with a kill-a-watt meter and video camera to see what I get out of it: Got .22 KwH out of that fuel or 2.93 kWH per gallon. I pay 19 cents/ KwH for shore power or $1.07/ KwH for this.

 

[Cujet]

Originally Posted by Rmay635703
http://www.centralmainediesel.com/order/yanmar_4kw.asp?page=yanmar_4kw

This is the most efficient I am aware of

Originally Posted by Rmay635703
http://www.centralmainediesel.com/order/yanmar_4kw.asp?page=yanmar_4kw

This is the most efficient I am aware of


I question that units ability to produce 13kwh per gallon. That level of efficiency is reserved for very large units. Even the very best 1800 rpm single cylinder marine units are often around 8kwh/gal (such you may find in sailboats)

 

[Best F100]

Most of these responses are appreciated.

However, based on the information given, which of the three generators offered would the most and least fuel efficient at a constant 2500W load? Or to make the question more realistic, at an AVERAGE 2500W load?

 

[Rmay635703]

Originally Posted by Cujet
Originally Posted by Rmay635703
http://www.centralmainediesel.com/order/yanmar_4kw.asp?page=yanmar_4kw

This is the most efficient I am aware of

Originally Posted by Rmay635703
http://www.centralmainediesel.com/order/yanmar_4kw.asp?page=yanmar_4kw

This is the most efficient I am aware of


I question that units ability to produce 13kwh per gallon. That level of efficiency is reserved for very large units. Even the very best 1800 rpm single cylinder marine units are often around 8kwh/gal (such you may find in sailboats)


Large gensets like a train are nearing 18kwhr per gallon, 13 is likely at a steady load but not unreasonable considering how tech has marched on

 

[Astro_Guy]

Originally Posted by Best F100
However, based on the information given, which of the three generators offered would the most and least fuel efficient at a constant 2500W load? Or to make the question more realistic, at an AVERAGE 2500W load?
Assume for a moment that the fuel consumption is linear between 1/4 and full load. Find the slope of the line representing consumption in GPH vs. Watts. Now interpolate to find consumption at 2500 watts. And our survey says...

Two Honda EU2200i paired together (in parallel) = 0.387 GPH

Honda EU3000is = 0.441 GPH

Honda EU7000is = 0.420 GPH

Intuitively it would be the one running closest 1/2 load, and the calculations bear that out. Gensets.xlsx

 

[Cujet]

I don't think the eu2200's are going to be that efficient. Honda claims 10% better than the eu2000. Which would burn .54 gal for 2500 watts over an hour.

Guess it's right at 1/2 gal.

 

[Astro_Guy]

Originally Posted by Cujet
I don't think the eu2200's are going to be that efficient. Honda claims 10% better than the eu2000. Which would burn .54 gal for 2500 watts over an hour.
I myself am quite skeptical, but he asked for the basic math and I gave it to him. The best advice I've seen in this thread has to do with 1800 RPM diesel generators. This will definitely be the most fuel efficient option in terms of gallons per hour. Diesel costs more, but can be had in "off road" form without highway taxes. Diesel will be far and away the most cost effective solution if purchased in its off road form.

Note to the OP: Inverter generators will work well and very efficiently if you have highly variable loads. Lighting is what it is, and is very steady. Refrigeration can be all over the map, especially if you have multiple units. I power three refrigerators (two of mine, one at the neighbor's) and a 15 cubic foot freezer with a 3500 watt gasoline powered generator. Even with all of that I am running at 50% load, on average.