Propane VS Diesel in ~20-30kW generator ranges.

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tortuga

tortuga

Code Historian
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Oregon
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Electrical Design
Greetings all, I'd like to here your thoughts and experiences with Propane Vs Diesel in the 20 - 30 kW range.
It seems like upper end 'residential market' generators above 20kW are a fraction of the prince of a diesel 25kW.
And I am just curious what the real differences are.
I know a few of you on here tinker around with engines.
I know propane stays good forever.
The typical application for us is 'optional standby', budget light commercial with an ATS to a generator loads panel, such as a gas/convenience store, small businesses that need to keep refrigeration going, agricultural farms that need to keep some power going during 0.5-72 hour outages etc.
 
Diesel generally will get more power out of a smaller package, will have design aspects that can make it cost more upfront, as they operate at much higher compression than propane/gasoline design engines.

More power you need the more desirable diesel engine may become other than the fact that propane stores forever in comparison to diesel or gasoline.

Diesel may last more running hours before needing major repair or replacement as well.

Fuel leak/spill, diesel doesn't have a low flash point or give off much for vapors.
 
kwired said:
Diesel may last more running hours before needing major repair or replacement as well.
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Which is debatable, propane and natural gas does not wash the oil off the cylinder walls, where gas can, so they have a longer life than a standard gasoline motor. I just hooked up a diesel temporary generator last week that has DEF, which seems to be affecting diesel longevity.
 
Generally a diesel generator of that size will be of better quality and design than your typical Junkerac residential/ light commercial carbureted or fuel injected units. If I were specing something for a possible 72 hour runtime I would stay away from residential/light commercial stuff. There's a reason why it cheaper.

-Hal
 
Those cheap propane units generally aren't rated for prime. Diesel you can run indefinitely, save for shutting down for oil changes, as long as you can get fuel. As far as diesel storage, a $500 fuel polisher takes care of that. I feel like a diesel unit is going to be more reliable.
 
Thanks all, it interesting how much the price per kW jumps,
Here is a little cost comparison of a few major brands using MSRP's to get a price per / kW:
Make​
Model​
MSRP price​
kW​
price Per kW​
Fuel​
Generac​
7209​
4999​
24​
208.29​
Propane​
Generac​
7042​
4609​
22​
209.50​
Propane​
Kohler​
20RCA​
4662​
20​
233.10​
Propane​
Generac​
RG025​
9099​
25​
363.96​
Propane​
Kohler​
24RCL​
10954​
24​
456.42​
Diesel​
Generac​
RD02025​
12499​
20​
624.95​
Diesel​
Its too bad you cant synchronize the smaller ones like utilities do.
 
Also, the Kohler (and probably the Generac) diesel generators run at 1800 rpm, while the propane ones are running at 3600 rpm.
 
tortuga said:
Greetings all, I'd like to here your thoughts and experiences with Propane Vs Diesel in the 20 - 30 kW range.
It seems like upper end 'residential market' generators above 20kW are a fraction of the prince of a diesel 25kW.
And I am just curious what the real differences are.
I know a few of you on here tinker around with engines.
I know propane stays good forever.
The typical application for us is 'optional standby', budget light commercial with an ATS to a generator loads panel, such as a gas/convenience store, small businesses that need to keep refrigeration going, agricultural farms that need to keep some power going during 0.5-72 hour outages etc.
Click to expand...
I don't think as a practical matter it makes much real difference for a typical residential backup generator.

The diesel unit might be arguably "better" but it is not like you are going to run the genset all that much. It will start and run for 15 minutes once a month or so and that might be all it ever runs.

Diesel is safer to store than propane but has other issues.

Personally I think a NG generator is a better option. No storage needed at all.

Look at it this way for a business. How much frozen food do you have to lose to make up for the cost of the genset? And how many times in a typical year do you lose power? And for how long? An hour or two of power loss is not going to be an issue and most power losses don't exceed that kind of time frame.
 
I suspect that the fuel cost per kwh is lower with diesel. Not an issue for infrequent, standby use.

Applications that anticipate hundreds of hours per year of highly-loaded usage it needs to be considered.

LP seems quite expensive around here and it gets even worse in the winter. Right now, I can buy diesel cheaper than gasoline, even with the higher road tax.
 
hillbilly1 said:
Which is debatable, propane and natural gas does not wash the oil off the cylinder walls, where gas can, so they have a longer life than a standard gasoline motor. I just hooked up a diesel temporary generator last week that has DEF, which seems to be affecting diesel longevity.
Click to expand...
DEF is injected into the exhaust and shouldn't effect anything within the cylinder.

Fuel injected gasoline engines don't have such problems either, under normal functioning anyway.
 
petersonra said:
I don't think as a practical matter it makes much real difference for a typical residential backup generator.

The diesel unit might be arguably "better" but it is not like you are going to run the genset all that much. It will start and run for 15 minutes once a month or so and that might be all it ever runs.

Diesel is safer to store than propane but has other issues.

Personally I think a NG generator is a better option. No storage needed at all.

Look at it this way for a business. How much frozen food do you have to lose to make up for the cost of the genset? And how many times in a typical year do you lose power? And for how long? An hour or two of power loss is not going to be an issue and most power losses don't exceed that kind of time frame.
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Yeah, exactly thats why I am looking at cost per kW.
Its more economical to put in two 22kW propane on a light commercial or large farm / ranch than one large one as there are typically different panels.
We just installed I think 5 generator inlets for a large county park, as that was cheaper than putting a 12.5kV ATS.
There is no natural gas service out in the rural areas (although plenty of methane gone to waste).
We're getting summer shutdowns due to gusty winds, old overhead distribution and wild fire danger.
The POCO shutdown a few chunks of rural territory yesterday, all of the gennys we installed are running, one overloaded.
Then in the winter we have folks that go a week plus on a generator.
So its starting to happen more often.
 
Where the temperatures get very cold in the winter, Diesel units will need heaters and even then are more likely to experience difficulty starting.
 
tortuga said:
Yeah, exactly thats why I am looking at cost per kW.
Its more economical to put in two 22kW propane on a light commercial or large farm / ranch than one large one as there are typically different panels.
We just installed I think 5 generator inlets for a large county park, as that was cheaper than putting a 12.5kV ATS.
There is no natural gas service out in the rural areas (although plenty of methane gone to waste).
We're getting summer shutdowns due to gusty winds, old overhead distribution and wild fire danger.
The POCO shutdown a few chunks of rural territory yesterday, all of the gennys we installed are running, one overloaded.
Then in the winter we have folks that go a week plus on a generator.
So its starting to happen more often.
Click to expand...
Since you seem to have certainty that downtimes will happen more frequently as well as for longer durations than for many other areas longevity/durability of the unit maybe deserves a little more consideration when it comes to what is worth the investment.
 
tortuga said:
Thanks all. It is interesting how much the price per kW jumps,
Here is a little cost comparison of a few major brands using MSRP's
It is too bad you cant synchronize the smaller ones like utilities do.
Click to expand...

I'm not positive, but I think you can with the proper ATS. But, if you went that route, the ATS price would be a deal killer.
 
The big thing, IMHO, is that the smaller air cooled gas generators have a MUCH shorter life span...upwards of 10:1. Water cooled is better but you are still looking at nearly 4:1.

If environmental concerns are a factor the gas generators fair a lot better.

Overall, if I had natural gas and considered it reliable I'd go that way. I'd avoid in areas prone to earthquakes though. Probably the best bet on the eastern side of the country.

For anything ranch/farm I'd consider the need for diesel for the rest of the equipment. Chances are they are already dependent on it so I would go that way.

If you want to get in and out cheap, propane might get you a sale. It might also cost you a customer eventually. I mean if a customer pays good money for protection.....sees a 72 hour outage once a month.....how will they feel if they need a new generator in 7 years.....regardless of what they saved up-front?

Now the average home owner that buys a 7Kw air cooled gasoline generator might be perfectly happy if that generator got him through 3 hurricanes in a 7 year period.......but a gas station? Farm/Ranch?
 
Russs57 said:
The big thing, IMHO, is that the smaller air cooled gas generators have a MUCH shorter life span...upwards of 10:1. Water cooled is better but you are still looking at nearly 4:1.
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Where do you get numbers like that? IIRC, residential air cooled generators are rated for something like 500 hours of use. The chances of someone needing to use a generator for 500 hours over say a 20 year span is remote.

Russs57 said:
If environmental concerns are a factor the gas generators fair a lot better.
Click to expand...
why would it even matter? it runs so little that whatever it does to the environment just won't make any difference.

Russs57 said:
Overall, if I had natural gas and considered it reliable I'd go that way. I'd avoid in areas prone to earthquakes though. Probably the best bet on the eastern side of the country.
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I agree with the NG idea unless there is a realistic possibility of the NG supply being cut off. Earthquakes and floods can do that.

Russs57 said:
For anything ranch/farm I'd consider the need for diesel for the rest of the equipment. Chances are they are already dependent on it so I would go that way.
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A lot of farm equipment is gas powered but if they have diesel already it makes having a diesel genset simpler, and reduces the problems of storing diesel for long periods of time because it can be readily rotated.

Russs57 said:
If you want to get in and out cheap, propane might get you a sale. It might also cost you a customer eventually. I mean if a customer pays good money for protection.....sees a 72 hour outage once a month.....how will they feel if they need a new generator in 7 years.....regardless of what they saved up-front?
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The chances of having a 72 hour outage once a month is extremely remote. That is almost 900 hours a year. Even a heavy duty engine would need to be rebuilt every couple of years in such a situation. might be cheaper to just buy a new genset every year or so.

Russs57 said:
Now the average home owner that buys a 7Kw air cooled gasoline generator might be perfectly happy if that generator got him through 3 hurricanes in a 7 year period.......but a gas station? Farm/Ranch?
Click to expand...
Why would the gas station need it more hours than a HO in the same area? The power would be off the same amount of time. But 7 kw might not be enough to run a typical gas station.
 
petersonra said:
Where do you get numbers like that? IIRC, residential air cooled generators are rated for something like 500 hours of use. The chances of someone needing to use a generator for 500 hours over say a 20 year span is remote.


why would it even matter? it runs so little that whatever it does to the environment just won't make any difference.


I agree with the NG idea unless there is a realistic possibility of the NG supply being cut off. Earthquakes and floods can do that.


A lot of farm equipment is gas powered but if they have diesel already it makes having a diesel genset simpler, and reduces the problems of storing diesel for long periods of time because it can be readily rotated.


The chances of having a 72 hour outage once a month is extremely remote. That is almost 900 hours a year. Even a heavy duty engine would need to be rebuilt every couple of years in such a situation. might be cheaper to just buy a new genset every year or so.


Why would the gas station need it more hours than a HO in the same area? The power would be off the same amount of time. But 7 kw might not be enough to run a typical gas station.
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Farmers here have diesel readily available in most cases. In fact many of them don't have a self powered genset but rather a tractor PTO driven generator. Thing in more recent years is most their tractors have much more available output than the generator needs and therefore are pretty inefficient fuel wise compared to a genset with motor and generator of similar rating.

That said larger livestock operations often will have automatic standby generator - often is still diesel powered. Those places are stand alone sites and the owner doesn't normally have his house on the same site like in the past with smaller farming operations.
 
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