Propane or Diesel fuel for Generator

[katwalatapan]

Hello,

I wanted to inquire if there is a practical size threshold for generators to decide if propane-fired or diesel-fired generators should be procured.

I am working on specifying a 30kW, 3-phase, 120/208V generator to back-up house panel loads in a multi-unit residential facility. The facility has access to delivery for propane as well as diesel fuels.

I understand other factors such as location of the facility, typical weather, etc. play a part in preference for a type of fuel. I wanted to verify, if fuel type could be selected based on the size of the generator i.e. is it practical based on fuel consumption and general generator maintennace, if diesel fuel is preferred for generator size over 30kW whereas propane fuel is preferred for generator size under 30kW.

I'd appreciate your comments on the above issue.

Thank you.

 

[racookpe1978]

How long must the unit run? Are you expecting a 4-hour, a 40 hour, or a 480 hour outage?
If you lose power, you are obviously planning on using the DG for the power. But! What other support do you anticipate remaining "up"?

For example, if a local power line goes down, or a local tornado tears up trees and roads, the gas supply from a natural gas pipeline underground will stay pressurized and available, but the refill truck for a diesel tank may not be able to get through. Area power lines may be down for 2-3 days, perhaps a bit longer, but water is probably still up and pressurized. If a local tornado or forest fire burns power lines between you and the grid, water and other services are still likely up, so diesel fuel might come through another road. If a hurricane wipes out the entire corner of the state, EVERYONE is wiped out, and it might be 6-10 days before recovery. If it is a breaker or single line failure, the power may only be out for less than an hour.

If long-term problems occur, and if the roads are clear and the roads are not flooded, then it is easier to get a single refill of diesel fuel than a propane tank of the right size. But diesel fuel not treated and stored for even a few weeks gets water inside and corrodes the tank, pipe, filters, and engine internals, biologicals grow in the fuel as well. Propane is not susceptible to that problem, and it burns a bit cleaner as well. Both start easily in automatic mode, but if you are on a propane/natural gas pipeline and NOT a tank, then you re trusting the national power gas ines to NOT fail in each pumping station and control station between you and the oil field.

 

[itsmoked]

At 30kW either are viable.

With nothing but "which do I use" the answer is Propane. It is far less problematic than diesel, meaning if you have cranking-battery you're going to have clean combustion and output.

But:

Propane can be a little harder to get on short notice.
Propane has 65% the energy that diesel has so you need a little more storage space for the same run-time.
Sometimes local fire codes limit how much propane can be stored at a site to something useless.

And:
Propane might make way more sense if you use propane for water or space heating or cooking. (very likely)

Or: You have diesel storage already, because this is a farm and you fuel vehicles and turn over your stores continually. (not probably the case)

Keith Cress
kcress -

http://www.flaminsystems.com

 

[wayne440]

As others have mentioned, either fuel is viable for 30kW. You state that the facility "...has access to delivery for propane as well as diesel fuels..." That is all well and good until the usual delivery means is unavailable due to weather, unusual demand or some other event; then what will your customer do? If the customer is willing sit in the dark and wait for delivery, either one is fine. If the customer is the type that might take personal initiative to secure fuel, it is worth mention that diesel fuel can be obtained and transported without special containers or equipment. IF you have to, you can haul diesel fuel in a 5 gallon pail(try that with propane).

I have heard various horror stories about diesel fuel storage issues, but have never had anything worse than a little water to show up in a the settling bowl of my own 15kW home standby installation. The tank is 160 USG and I use about 40 gallons a year out of it, it gets topped up when it gets down to half full.

Another factor is that the diesel set may cost considerably more to purchase.

 

[Compositepro]

Propane is probably best suited for low-cost emergency standby generators. It can be stored for 20 years without problems. Otherwise, diesel is better in most ways, except that the engines cost more. Diesels also do not like to start when they are very cold.

 

[katwalatapan]

Thank you very much for the response.

The use of the generator is for standby purposes only i.e. during a power outage. Local code mandates fuel be available for minimum 24 hour operation.

 

[resqcapt19]

If you use propane, just make sure someone does the vaporization calculations for the minimum size tank that will provide enough vaporization to supply the engine if the propane tank is outside in a cold environment.

 

[maqhawe]

As everyone has stated, according to my experience a gas genset is about 1.5 times more expensive than a diesel genset, on deciding which one to choose, you must also consider that you can have a diesel engine running and take load in 10 to 15 seconds, for a gas you must be prepared to be in the dark for a longer time, as it takes time to start it, and also black starting and loading need to be carefully designed, as a gas engine can only accept a 30% load at a time and allow about 10 seconds recovery time.

a gas engine is more efficient for a continuous operation where you don't have power supply, not for standby operation.

 

[waross]

I have only installed a couple of natural gas sets. I didn't spec. them, just installed to others specs. This was a department store with computerized cash registers. The prime movers were re-purposed automotive V8s (I think Chevys but it was a long time ago). The cash registers could ride through an 8 second power outage. The sets were typically up and online before the cash registers crashed.

katwalatapan: As you can see,there may be no clear cut answer. The choice depends not only on a number of factors but also on the weighing of many of the factors.
You are in the best position to weigh and evaluate the various factors.
Neither choice is wrong. With the suggestions presented here, I am sure that whatever choice you make will be the best choice for your situation.


Bill
--------------------
"Why not the best?"
Jimmy Carter