Generators - NG vs Gasoline vs Diesel running cost

[HamAndEggs]

I had no idea Gasoline was so expensive, and that NG was THAT much cheaper, and how much more sense Diesel makes to Gasoline.

I estimated a 3kw constant load when running on a portable generator, and a higher 6.25kw load when on my larger NG unit with unlimited fuel. Starting to wonder if I should replace the el-cheapo Champion for a Diesel genset for my backup-backup

 

[theoldwizard1]

Natural gas will not make the same amount of power as diesel or gasoline.

Most generators are for backup and only get used a few hours per year. The one you already own is the best one simply because you would have to run the new one hundreds of thousands of hours to make up the difference.

 

[mike93lx]

Those numbers don't seem surprising at all to me. Natural gas is cheap. Interesting data, for surem

Gasoline isn't used for transportation because of cost. Take out the need for portability and easy storage and natural gas is way better.

 

[mustang5.0]

Natural gas. We live in a hurricane prone area, chances are slim that natural gas will not be on and gas and diesel become scare until power comes back.

 

[HamAndEggs]

For sure natural gas, but the rate and cost of going through gasoline makes me wish my backup to the Generac was Diesel. If I come across a screaming deal on an MEP-1030 or Kubota GL7000, I'm going to jump on it

Makes more sense to use the 70 gallons of stored gas I have for vehicles.

On the plus side, I have an NG kit for the portable generator. Just 2 weeks ago my Generac had an issue that was fixed under warranty, and that same week something started to develop in the gulf, perfect timing

 

[HamAndEggs]

If they got rid of the darn stupid DEF, I'd for sure get a Diesel truck so I could rotate it out easily

 

[reader2580]

The reality is how often do you expect to ever need a backup generator for your whole house generator? I can't imagine it is that often. For the cost of a diesel generator you could probably run your gasoline generator for several weeks at least.

 

[wyliesdiesels]

Comparing a 5KW diesel genset to a 7KW gasoline genset seems like a bad comparison.

From what ive read:

Diesel gensets are most efficient when theyre loaded up close to capacity.

Gas gensets on the other hand have a baseline consumption at a certain load then consume a whole lot more as they get to max load.

 

[HamAndEggs]

Comparing a 5KW diesel genset to a 7KW gasoline genset seems like a bad comparison.

From what ive read:

Diesel gensets are most efficient when theyre loaded up close to capacity.

Gas gensets on the other hand have a baseline consumption at a certain load then consume a whole lot more as they get to max load.

Those MEP's have a LOT of headroom built in, they are essentially 7kw units

But, from what I've seen on the fuel curve for the MEP 803A's, and the Kubota Lowboy generators, it's more linear than you'd expect. As with every engine, you get diminishing returns as you get closer to 0%, but 3kw on a 5kw genset seems fine

Here is the Kubota GL11000



The main reason I've compared the two is that I wouldn't feel very comfortable running my house on a 3600RPM Gasoline 5kw generator, but one of those MEP's at 5kw would be fine as they are prime rated at that capacity. The duty cycle on the portable gasoline gensets are not very good

 

[HamAndEggs]

The reality is how often do you expect to ever need a backup generator for your whole house generator? I can't imagine it is that often. For the cost of a diesel generator you could probably run your gasoline generator for several weeks at least.

Its been my plan all along to get a more reliable portable unit. At some point in the future I want to buy some land, and have a decent generator to haul out there until we get something setup

But, 2 weeks ago the mag pickup on my Generac decided to act up, and I had to get it replaced under warranty. During that time there was some storm developments in the gulf that went nowhere. I'd sure sleep a lot better knowing my house would be powered by a prime rated diesel than a cheap chinese gas generator

 

[scooby074]

Dad has a Kohler propane 12k fully auto gen. I dont know the numbers but that thing must eat propane from how he complains when it runs for any length of time. Hes got a bit torpedo tank and the gen can make a noticeable (to him) difference in cost when he fills up. It is some nice when the power goes out and his whole house switches over with a *Thunk* but the lights dont do so much as flicker. Really living the luxury even if it does cost a lot for the convenience.

I got a honda eu6500 inverter and while it does use fuel, it doesnt really seem that bad to me, usually its in eco mode, so its idled down. No ATS or any of that stuff though

 

[Showkey]

As mentioned ……this appears to be similar to buying an EV for $70k and then figure you out only drive 3000 miles per year.

Yes……there is merit in planning for fuel storage and availability …….especially in hurricane areas.

 

[jeepxj]

tri fuel generators are a thing. gas, propane, NG.

New Tri-Fuel Natural Gas Ready Portable Generator – Champion Power Equipment

Discover the power of the Portable Generator that can also operate on Natural Gas! Champion's Tri-Fuel technology ensures versatility with natural gas, gasoline, and propane.

www.championpowerequipment.com

NG primary, propane backup, oh god the world ended let me siphon from the dead neighbors cars gas.

 

[mcbane]

If red diesel is available in your area it is a lot cheaper than highway diesel. The only downside is that unless you have enough protracted power outages to frequently burn through a tank of fuel (like California), it isn't legal to put the red diesel into a highway vehicle as a means of rotating stock.

 

[reader2580]

Diesel lasts a lot longer than gasoline in storage. I have a vehicle with a 150 gallon diesel tank that sits idle for nine months at a time. It starts right up when I do use it. One thing is I keep the tank full to minimize condensation.

 

[u2slow]

Natural gas prices are on the rise.

There's also a limit to how big a gen you can power on your existing nat gas hookup. Its delivered at very low pressure, and to upgrade your connection may be pricey.

 

[jeepxj]

Natural gas prices are on the rise.

There's also a limit to how big a gen you can power on your existing nat gas hookup. Its delivered at very low pressure, and to upgrade your connection may be pricey.

rough napkin math says 50CFM at .5psi for 10kw. not massive but not trivial if you got a buncha heaters, tankless, etc etc.

 

[Showkey]

Two times (one in IL one in Wis) I was involved with NG supply increase………meter capacity and pressure upgrade was free of charge. But, Obviously would vary with supplier.

 

[Lassen Forge]

When we put in a genset for the house and shop we crunched the numbers. Everyone said "you only need 10% of your total amp draw" but that's nonsense as if I need to run the heaters, the oven, and the shop all at once, paff. Plus it will be running wide open bozo trying to keep up.

We also had an event years ago where we had a propane genset to run our event - it was pushing at 80% capacity 24/7, and we went through our propane supply in 4 days. Not cool. Then I realized - Pulling WOT is pulling maximum fuel to supply the power to spin the windings. The next year, we went 4x the capacity on our genset, and went through 1/3 to 1/4 of the fuel. Hmmm....

So I did ALL the math to figure out what the total draw of EVERYTHING on our property would be if it were all energized (and confirmed it with our smart meter). Turned out to be 19.2 KW. So I Priced a 20 KW Kohler. Everyone said "That's WAY too much, you're crazy"...

We lost power for a week and change shortly after getting our genset installed. I set aside a 300 gallon tank out of our total 1000 gallon "farm" for just the generator. I don't think we went through 100 of those 300 gallons.

The new neighbor went the other way - put in a 6.5KW genset for his house and shop and stuff. Gasoline, but gas is supposed to be more efficient than LPG. He went through 200 and change for the same outage. And that poor genny lasted 3 years. Ours is still going strong.

At my last job we had Kohler Diesel Gensets which were pretty reliable as long as they were serviced regularly (someone forgot to once, and oops....). I honestly don't know what the fuel consumption was, but I know they were huge units (one ran the admin offices and the buildings on one side of the property, another ran the shops on the back side, the third ran the mechanics shop (16 bays). Then again, they were at 550 ft elevation, our place is at 4100 ft.

I can't recommend one over the other, I'm only providing this as what I know and saw. YMMV and all that. For me and my thing, I love my propane system - oil changes are clean, fuel is easy, pretty bulletproof - but you have to see what works best for you and yours.

 

[American Locomotive]

All generators are more efficient at full load than partial load. In general, a smaller generator working harder will use less fuel than a larger generator idling along. Especially if you're comparing conventional gasoline powered generators. Diesel generators don't seem to drop off efficiency as hard as gasoline engines do at partial loads. You can't really compare fuel usage during an outage between two different houses, because you have no idea of the loads the generators were under. If you had 1kw of load, and your neighbor had 2kw of load - their fuel consumption will literally be double yours just because they turned on a space heater.

As to the OP: You really need to determine how often you have outages, and how much fuel the purchase price of a diesel generator could buy for your gasoline unit. If they "pay off" would be 15+ years, I probably wouldn't bother.

Personally I think LPG or NG is the way to go for backup generators. LPG keeps forever, is easy to store, and the engine components are simple. Diesel keeps for a long time as well, but the initial purchase price is very high, and engine components are extremely expensive.

 

[Showkey]

All generators are more efficient at full load than partial load. In general, a smaller generator working harder will use less fuel than a larger generator idling alo

All never works as absolutes never work…….

All generators????????
New modern 7000 watt inverter running a 1500 watt load would be just sipping fuel.

Its just a matter of time when the stand by whole house units run inverter units.

 

[American Locomotive]

All never works as absolutes never work…….

All generators????????
New modern 7000 watt inverter running a 1500 watt load would be just sipping fuel.

Its just a matter of time when the stand by whole house units run inverter units.

Yes, all generators. Even inverter units.

EU7000is: 6.4 Hours run time @ rated load, 16.0 hours at 1/4 load.

Full Load: 35.2 kWh/tank (6.9 kWh/gal)
1/4 Load: 22.0 kWh/tank (4.3 kWh/gal)

EU2200i:
Full Load: 5.76 kWh/tank (6.06 kWh/gal)
1/4 Load: 3.65 kWh/tank ( 3.84 kWh/gal)

It's significantly more efficient to have a tiny EU2200i scream away with 1400w of load, than an EU7000i idle along at ~1400w. In general, it will be about a 35% difference in efficiency at part-load vs. full load on a modern inverter generator. On a conventional generator, the full-load vs. 1/4 load efficiency difference could be 50% or more.

Even Lassen Forge's big 20KW Kohler LP generator:
Full Load: 5.12 kWh/m^3 LP Gas
1/4 Load: 2.94 kWh/m^3 LP Gas

It's 43% more efficient at full load, than 1/4 load.

Inverter generators do well at part load for two reasons:
1) They are typically much smaller than the 7,000-10,000 watt standard generators that are cheap and readily available these days. Since they're smaller, they're running much closer to their rated load - making them more efficient. Plus a lot of people are replacing old decrepit flathead generators (which have truly abysmal efficiency) with inverter units.

2) The inverter low-load engine slow down feature does improve part-load fuel consumption, but that's really only because conventional gasoline/lpg/ng generators have absolutely abysmal part throttle efficiency.

If you really care about fuel efficiency of your backup generator, size your generator to the absolute smallest you can possibly get away with. Going overkill over-sizing your generator will cost you dearly in terms of part-load efficiency.

 

[Showkey]

^^^^^^^^^^^^Think your math and assumptions 1/4 load are flawed……..

Real life….it does work that way, not even close:
I used a propane Onan RV generator 3500 that ran a constant speed no matter the load.
Constant speed is the down fall. It never idles
Used it on two long weekends running AC in 90* with no shore power and it was obvious 25 gallons of propane was not sufficient.
Switched to two EU2000 in parallel to run the same variable load AC etc …….on 5 gallons of gas. Using that setup for 9 years. Variable load is the reason for the savings. Especially with AC at night. It idles for hours on end.
Onan gets used on rest areas to run the microwave or toaster. 10 years is has 60 hours of total run time.

An Inverter genny will charge 4 RV batteries at idle.

 

[American Locomotive]

My math isn't wrong. There aren't even any assumptions being made. Those fuel consumption specs are literally from the manufacturer of generators. The more heavily loaded a generator is, the more efficient it is. Period. It is more efficient to run a smaller generator flat out, than have a larger generator idle along. This is a fact, backed up by the data from the manufacturers themselves. I really don't even understand how you think your example disproves my point? Your 3500 watt rated fixed speed flat-head engine generator uses more fuel at low-load than your 1800w rated inverter generators ...exactly what I said would happen.

Inverter generators do BETTER at partial load situations compared to fixed-speed generators, but they still loose efficiency at low loads - just not as much. Honda's own numbers literally spell that out. If the efficiency stayed the same, the 1/4 load run time would be exactly 4x the full load run time. It's not.

An EU7000is is rated at 6.4 hours full load, so at 1/4 load it should last for 25.6 hours, right? Well according to Honda, it will only last for 16 hours. That is because the efficiency starts to drop as low decreases.

I will reiterate: All things equal - same fuel, same basic engine technology (OHV, OHC, whatever), roughly the same genhead , a smaller generator working harder will use less fuel than a larger generator running the SAME load.

 

[ripperd]

I also doubt the op's 14c/kwh figure for a home NG generator.

That's cheaper than many utilities that have far more efficient generation.

How was that number arrived at?

 

[HamAndEggs]

As mentioned ……this appears to be similar to buying an EV for $70k and then figure you out only drive 3000 miles per year.

Yes……there is merit in planning for fuel storage and availability …….especially in hurricane areas.

My F150 has 7200 miles and is from 2019! Switching to work from home really flipped how much I drive

tri fuel generators are a thing. gas, propane, NG.

New Tri-Fuel Natural Gas Ready Portable Generator – Champion Power Equipment

Discover the power of the Portable Generator that can also operate on Natural Gas! Champion's Tri-Fuel technology ensures versatility with natural gas, gasoline, and propane.

www.championpowerequipment.com

NG primary, propane backup, oh god the world ended let me siphon from the dead neighbors cars gas.

My cheap Champion has a Tri-Fuel kit on it, actually runs better on NG than gasoline, would you believe

If red diesel is available in your area it is a lot cheaper than highway diesel. The only downside is that unless you have enough protracted power outages to frequently burn through a tank of fuel (like California), it isn't legal to put the red diesel into a highway vehicle as a means of rotating stock.

I think I'd have to drive pretty far out to get it, and then I'd need a good way to move it around. I did look at getting it delivered, but thats way expensive

Natural gas prices are on the rise.

There's also a limit to how big a gen you can power on your existing nat gas hookup. Its delivered at very low pressure, and to upgrade your connection may be pricey.

I had the meter upgraded and bumped to 2PSIG, I'm good for around 1.2 Million BTU's. My Generac RG027 does 25kw on NG, and uses 360,000 BTU's at 100% load

Cost $350 and was included in the cost of the generator

When we put in a genset for the house and shop we crunched the numbers. Everyone said "you only need 10% of your total amp draw" but that's nonsense as if I need to run the heaters, the oven, and the shop all at once, paff. Plus it will be running wide open bozo trying to keep up.

We also had an event years ago where we had a propane genset to run our event - it was pushing at 80% capacity 24/7, and we went through our propane supply in 4 days. Not cool. Then I realized - Pulling WOT is pulling maximum fuel to supply the power to spin the windings. The next year, we went 4x the capacity on our genset, and went through 1/3 to 1/4 of the fuel. Hmmm....

So I did ALL the math to figure out what the total draw of EVERYTHING on our property would be if it were all energized (and confirmed it with our smart meter). Turned out to be 19.2 KW. So I Priced a 20 KW Kohler. Everyone said "That's WAY too much, you're crazy"...

We lost power for a week and change shortly after getting our genset installed. I set aside a 300 gallon tank out of our total 1000 gallon "farm" for just the generator. I don't think we went through 100 of those 300 gallons.

The new neighbor went the other way - put in a 6.5KW genset for his house and shop and stuff. Gasoline, but gas is supposed to be more efficient than LPG. He went through 200 and change for the same outage. And that poor genny lasted 3 years. Ours is still going strong.

At my last job we had Kohler Diesel Gensets which were pretty reliable as long as they were serviced regularly (someone forgot to once, and oops....). I honestly don't know what the fuel consumption was, but I know they were huge units (one ran the admin offices and the buildings on one side of the property, another ran the shops on the back side, the third ran the mechanics shop (16 bays). Then again, they were at 550 ft elevation, our place is at 4100 ft.

I can't recommend one over the other, I'm only providing this as what I know and saw. YMMV and all that. For me and my thing, I love my propane system - oil changes are clean, fuel is easy, pretty bulletproof - but you have to see what works best for you and yours.

Do you have anything to verify those numbers like Sense or other energy monitoring? I did all the math and came out to 20kw, in the end however the highest load I've ever seen on my electrical panel is just 12kw. Still happy to have all that headroom on the generator though

I also doubt the op's 14c/kwh figure for a home NG generator.

That's cheaper than many utilities that have far more efficient generation.

How was that number arrived at?

That 14c/kwh is based on my Generac RG027 running at 25% load (Which is around what I'd see during an outage), per the chart in the original post

Here is my math:

Here is the CCF/hr ratings



Here is a sample of my last bill



And here is the math



I'm not taking the $18 base fee in, because I have to pay that no matter what

 

[Lassen Forge]

Do you have anything to verify those numbers like Sense or other energy monitoring? I did all the math and came out to 20kw, in the end however the highest load I've ever seen on my electrical panel is just 12kw. Still happy to have all that headroom on the generator though

Yep, from my post...

So I did ALL the math to figure out what the total draw of EVERYTHING on our property would be if it were all energized (and confirmed it with our smart meter). Turned out to be 19.2 KW. So I Priced a 20 KW Kohler. Everyone said "That's WAY too much, you're crazy"...

IDK... how accurate is a smart meter on a service entrance? We had literally EVERYTHING that we had on the property electrical energized. Lights, heaters, AC units, shop tools, drained our water system down to get all our pumps going, fans, baseboard heaters, our electric stove and oven... Probably made PG&E happy... But yeah, I like knowing in a pinch we can run whatever we want.

The nice thing is during our seasonal blackouts we can have heat or AC or whatever. So yeah, that overhead capacity is nice!

 

[ripperd]

That cost is cheap. Even with NG prices in California you could probably just skip connecting to the electrical grid and run generator 24x7x365 and be at or under the california electric rates, especially if you are on a TOU plan.

 

[HamAndEggs]

That cost is cheap. Even with NG prices in California you could probably just skip connecting to the electrical grid and run generator 24x7x365 and be at or under the california electric rates, especially if you are on a TOU plan.

The oil changes every 200 hours would sure eat into it though. May as well just get solar and batteries

My effective solar cost right now is $0.03/c kwh. But, the gravy train of 1:1 net metering seems to be slowing down. More and more plans here are limiting just how much you can feed back. I'm busy getting quotes for 4 x Enphase Encharge 10's which also do generator integration and can start/stop the generator as needed

If I end up with them, a secondary generator won't be needed. and hopefully I can still keep my costs well under utility rate

 

[u2slow]

I had the meter upgraded and bumped to 2PSIG, I'm good for around 1.2 Million BTU's. My Generac RG027 does 25kw on NG, and uses 360,000 BTU's at 100% load

Cost $350 and was included in the cost of the generator

Thats good value. Stepping up the gas supply at my folks' place was in the thousands. I forget what size gen it could handle; it was never installed. A portable/trailer diesel genset (~30kw) is being used instead.

 

[HamAndEggs]

Thats good value. Stepping up the gas supply at my folks' place was in the thousands. I forget what size gen it could handle; it was never installed. A portable/trailer diesel genset (~30kw) is being used instead.

Watch out for wet stacking on such a large unit

Out here the generator installers ALWAYS skip it, I'm betting that 80% of the people in the area have undersized gas meters

 

[HamAndEggs]

Yep, from my post...



IDK... how accurate is a smart meter on a service entrance? We had literally EVERYTHING that we had on the property electrical energized. Lights, heaters, AC units, shop tools, drained our water system down to get all our pumps going, fans, baseboard heaters, our electric stove and oven... Probably made PG&E happy... But yeah, I like knowing in a pinch we can run whatever we want.

The nice thing is during our seasonal blackouts we can have heat or AC or whatever. So yeah, that overhead capacity is nice!

I must have skimmed that part, my 12~kw is usual load, not turning everything possible on. Maybe I need to go do that exercise! I can't imagine I'll get anywhere near 25kw though

 

[u2slow]

Watch out for wet stacking on such a large unit

Out here the generator installers ALWAYS skip it, I'm betting that 80% of the people in the area have undersized gas meters

Its a construction generator. Home backup is its secondary job.

The gas line was being moved/redone anyhow, so it was time to size it for a backup gen. It was made bigger, but technically still short of the intended machine size. Had to compromise due to cost. The final straw was the installed cost of the ng genset. The diesel trailer gen was a lightly used unit on auction, and an easy business write-off.

 

[HamAndEggs]

I've been tempted a few times with old light towers. I'd just remove the lights. All the ones I've looked at have nice Kubota 3 cylinder engines and are all prime rated generators too, and have large fuel tanks already built in

 

[CarBikeGuy70]

Light tower is the way to go. Kubota 3 cylinder engine will run several thousand hours with minimal service required. Most light towers also have a 220 outlet that will allow you to power a well pump. Treat fuel in tank when out of service and you are ready for the next power outage. Use a battery tender and life will be good.

 

[jeepxj]

I've been tempted a few times with old light towers. I'd just remove the lights. All the ones I've looked at have nice Kubota 3 cylinder engines and are all prime rated generators too, and have large fuel tanks already built in

i been eyeing these hoping for a set more local to me. comes with a genset, battery and solar. plus a trailer!

2016 DC Solar MSG SCT 20 Hybrid Light Tower Configuration B Trailer Vin#4HXSC172XGC184384

**15% BUYER'S PREMIUM** DC Solar MSG (mobile solar generator) with Kubota GL11000 Lowboy II, 11KW diesel generator with 37 hours since new. GNB Flooded Classic Platinum industrial batteries 468 AH capacity 48 volt, ECI 113 gallon fuel tank with locking cap and gauge, (2) US Tower Corp...

bid.cunninghamauctions.com

 

[HamAndEggs]

I don't have much use for that, but I'd like one anyway

 

[Lassen Forge]

I must have skimmed that part, my 12~kw is usual load, not turning everything possible on. Maybe I need to go do that exercise! I can't imagine I'll get anywhere near 25kw though

It (literally) surprised the (figurative) **** out of me, but I figured I'd rather be shocked up front rather than have a job I was working on interrupted by the woeful lack of being able to keep the house warm AND complete my work.... Had I not the experience of wiping out tanks of propane on another project with a generator undersuited for the task, I might have gone undersized. As it is, I am more than thrilled by my generator "sipping" propane during outages while my (now former) neighbor's generator was burning gasoline by the gallon trying to keep his home warm and his genset running during the last "power safety" outage...

 

[Bretny]

For a backup generator a fuel that I can not move my self would be a no go. I have no natgas here but even propane in anything but a 20lb tank can be a problem getting.

I have a diesel mep802. For my houses load it uses 6.5gal for 24hrs run. Per KW it actualy burns less fuel than a honda EU2000...but theres no gas to go bad and no carb to clean. I'm on a 6 month test run cycle with this mep802. It sits next to enough fuel to run it non stop for 30days. We havent lost power since I put it in.

 

[dcg9381]

I assume diesel has long term storage issues too? Certainly not as bad as gasoline, but that was largely why I didn't consider diesel to be an option for us... We have 500 gallons of propane available - so the choice was pretty easy for me. But yes, our consumption with a 3600 RPM air-cooled generator is much higher than diesel. Our genset is a on a 1-week exercise cycle.