Natural gas or Diesel generation vs from grid.......

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dionysius

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WA
Does anybody have some order of magnitude cost numbers to make a case for using a 500 kWatt Diesel or natural gas generator vs the cost from the grid???
 
Based on this chart:

http://www.dieselserviceandsupply.com/Diesel_Fuel_Consumption.aspx

A 500kw generator is going to use ~35 gal/hr at full load. 35 x $2/gal = $70/hr

(our 20cyl GE710 genset at the plant used ~190gph; 4500HP, ran ~2.1MW on the generator. The other plant with twin 12cyl Cats used ~140gph; I think they were 1MW ea).

Not sure how industrial billing would work out cost wise, but 500kw/hr x even just $0.10 = $50/hr.

Genset wouldnt run at max load 24/7, has substantial up-front costs, maintenance, and is not going to be as reliable as the grid.

No idea how natural gas fares vs diesel.

Unless this facility was wayy away from the grid where building the infrastructure to it would be exorbitantly expensive, or PoCo power is the same, I dont see a generator beating it in price or coming close, otherwise many facilities would use them instead of grid power.
 
dionysius said:
Does anybody have some order of magnitude cost numbers to make a case for using a 500 kWatt Diesel or natural gas generator vs the cost from the grid???
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Unless you do cogeneration I don't think you can ever produce it with diesel or natural gas even close to buying it from the grid. Cogeneration using diesel or gas could even be cheaper than the grid in the right application though.
 
Natural gas in my area is (best price) $0.549 per therm. A therm is essentially 100 cubic feet. According to this chart, you need 1.393 therms of natural gas to equal 1 gallon of diesel, so your fuel cost would be $0.765 per gallon of diesel equivalent. So using the above example, your cost is 35 x $0.765 = $26.775 or equal to an electricity cost of ~$0.05 per kWh. The big unknown is what are the infrastructure costs (distribution and delivery); the web site I found didn't include those. Even at a 100% adder, you're equal to $0.10 per kWh, plus or minus. So, at current gas prices it would be a "go". The real question is can those prices hold and where are they likely to go for the economical future, say 10 years because you probably want to depreciate the genset over that time, or longer.
 
JFletcher said:
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A 500kw generator is going to use ~35 gal/hr at full load. 35 x $2/gal = $70/hr
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Probably ought to be conservative use the 1/4 load figure. Note that the consumption isn't linear, the generator is less efficient at partial load. Also $2per gallon is a great price for diesel these days.

Thus (using current average US price of diesel): 11gal/hr *$2.4/gal / 125kW = 21cents/kWh

That's higher than almost every figure in this chart, although certain tiers or time of use rates might be higher.

The answer to the question really depends on whether the capital costs for either the grid or the generator have already been paid for. As far as 'orders of magnitude' go, the costs are within one.
 
jaggedben said:
Probably ought to be conservative use the 1/4 load figure. Note that the consumption isn't linear, the generator is less efficient at partial load. Also $2per gallon is a great price for diesel these days.

Thus (using current average US price of diesel): 11gal/hr *$2.4/gal / 125kW = 21cents/kWh

That's higher than almost every figure in this chart, although certain tiers or time of use rates might be higher.

The answer to the question really depends on whether the capital costs for either the grid or the generator have already been paid for. As far as 'orders of magnitude' go, the costs are within one.
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Yeah I was thinking of regular unleaded being about $1.90 a gallon here... diesel is closer to $2.50.

Even if the generator and associated equipment were free, the maintenance and fuel costs have to be higher than grid power. I'm sure some high paid engineering types for companies like ALCOA (that use an enormous amount of electricity) have already figured it out; afaik, they are tied to the grid, tho there may be POCO incentives and subsidies that skew the true price of power.

The page I linked assumed grid connection and sellback of unused electricity, and that the waste heat can be used elsewhere on site. For it to be competitive in price, the infrastructure for both has to be in place. and we know the generator and gear arent going to be free.
 
JFletcher said:
Yeah I was thinking of regular unleaded being about $1.90 a gallon here... diesel is closer to $2.50.

Even if the generator and associated equipment were free, the maintenance and fuel costs have to be higher than grid power. I'm sure some high paid engineering types for companies like ALCOA (that use an enormous amount of electricity) have already figured it out; afaik, they are tied to the grid, tho there may be POCO incentives and subsidies that skew the true price of power.

The page I linked assumed grid connection and sellback of unused electricity, and that the waste heat can be used elsewhere on site. For it to be competitive in price, the infrastructure for both has to be in place. and we know the generator and gear arent going to be free.
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Skip the diesel, use NG.
 
don_resqcapt19 said:
You have to watch using NG if you have large "step loads" (starting and stopping large motors would be one example)....NG does not handle those types of loads near as well as diesel does.
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That's interesting. What is it about the operation of NG-fueled generators that makes them problematic in that case? What percentage of generator capacity would be considered "large"? Wouldn't the use of VFD's reduce the issue?
 
keep in mind that if you are using diesel for power generation it is less expensive than the motor fuel diesel you buy at the gas station because there are no motor fuel taxes.

it is also cheaper than the special diesel you have to use for the rental generators.

with the relative cost of NG versus diesel, I can't imagine too many places would want to run on diesel.

the only serious issue with NG is getting a big enough pipe.
 
gadfly56 said:
That's interesting. What is it about the operation of NG-fueled generators that makes them problematic in that case? What percentage of generator capacity would be considered "large"? Wouldn't the use of VFD's reduce the issue?
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The last time I was looking at Cat generators, the supplier said that the fuel system for NG generators does not respond as well as diesel generators for a large increase in load...he was talking about 25% or more of total load. Not sure if the VFD would make much difference.
 
Let's say a generator can last 20,000 hours. To put things into perspective, a car going 60 mph will travel 300,000 miles in 5000 hours.

20,000 hours is about 2 1/4 years, if the generator is always running. So, in addition to maint. costs, figure total replacement every 2 1/4 years.
 
K8MHZ said:
Let's say a generator can last 20,000 hours. To put things into perspective, a car going 60 mph will travel 300,000 miles in 5000 hours.

20,000 hours is about 2 1/4 years, if the generator is always running. So, in addition to maint. costs, figure total replacement every 2 1/4 years.
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with regular maintenance and rebuilding they can pretty much last indefinitely.

I seem to recall the first GE gas turbine unit lasted 30 some years before it was taken out of service. not because it failed but because it was just not efficient enough to be worth running compared to getting a new one.
 
K8MHZ said:
Let's say a generator can last 20,000 hours. To put things into perspective, a car going 60 mph will travel 300,000 miles in 5000 hours.

20,000 hours is about 2 1/4 years, if the generator is always running. So, in addition to maint. costs, figure total replacement every 2 1/4 years.
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IIRC, gensets intended to be in use 24/7 are very different quality from those intended to run for a couple days or even a couple weeks for backup purposes.
 
petersonra said:
with regular maintenance and rebuilding they can pretty much last indefinitely.

I seem to recall the first GE gas turbine unit lasted 30 some years before it was taken out of service. not because it failed but because it was just not efficient enough to be worth running compared to getting a new one.
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For a piston engine, if you include piston, rings, bore job and bearings to be 'regular maintenance' you are correct.

As for the turbine, there is a reason power companies use turbines. They have fewer moving parts and thus less wear, by a substantial amount over a piston engine.
 
gadfly56 said:
IIRC, gensets intended to be in use 24/7 are very different quality from those intended to run for a couple days or even a couple weeks for backup purposes.
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All the ones I have seen were turbines. I have never seen a continuous use or base line generator using a piston engine as a prime mover. If there is such a thing I would like to see a picture of it.
 
A good analysis would also take into account that you would probably require a Tier 4F rated genset in lieu of Tier 2 or Tier 3. A Tier 4F will also consume urea or diesel exhaust fluid and have much more maintenance associated with the emissions equipment.
 
K8MHZ said:
All the ones I have seen were turbines. I have never seen a continuous use or base line generator using a piston engine as a prime mover. If there is such a thing I would like to see a picture of it.
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Lotsa old Fairbanks Morse genset videos on youtube; apparently some were used as backup power to the grid in small cities many a year ago.

Back in the day we had a diesel turbine at Nansemond WWTP; biggest pile of junk ever. Had a propensity for flaming out and not wanting to restart. It was supplanted/replaced with two 12cyl Cats.

Something else to consider if using internal power with a grid tie-in: if you normally generate more power than you need, or pull just a bit from the grid, your peak demand charges will be quite low. If you lose the generator w/o shutting down most of the plant, and pull 500KVA off the grid for a billing block of 15-30min, the POCO will send you a nice fat bill for it.

If generators w co-generation were cheaper to operate than buying power from the grid, more companies would be running generators. HRSD only had generators because of the size of the facilities require maintaining treatment even during power outages; I believe 3 days was the requirement. The last plant I worked at had 2 8,000 gallon diesel tanks, which if full provided 84 hours run time at full load. Quite a behemoth; the sump on that unit held 8, maybe 9 barrels of oil, and the battery bank for the starters was in its own 8 x 15' room. 4300 HP @ 900 rpm for almost indefinitely; I bet that unit would run 5 years continuous with no major maintenance.
 
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