Diesel vs. propane

[fsck]

I'm looking for case studies on propane vs. diesel costs in a standby power application of 15-25KW.

Obviously, the relative fuel costs will favor diesel, while the initial purchase & lower maint. costs favor propane. At some # of hours/year, the lines cross. My goal is get some numbers to figure out where that point is.

 

[itsmoked]

I know not the curve and wouldn't pay any attention to it anyway.
Depending on the number of run hours anticipated I would ALWAYS go with propane. Both Diesel and Gasoline have horrid aging issues. If you keep either of those fuels around for a year they are greatly degraded and will eventually cause failures of different sorts. To prevent this you have to run them enough to consume the fuel or cycle the fuel out on a schedule, which is typically a stinky messy ordeal done only once...

If you never expect to run more than the size of a reasonable propane tank definitely go that route. If you can anticipate a multi-day - week operation go with a mixed fuel setup, gasoline and propane. Then as your projections and usages shape up during an emergency you can work on securing more propane or some gasoline in a timely manner.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[fsck]

I agree that Diesel is a PITA. But have you priced propane vs Diesel recently? Twenty four hour plus long failures are the norm at this location. The plan was for a 1000gal tank.

Plus, they already have a menagerie of other equipment that uses Diesel; not just a tractor or 3, but also a road grader, full-size dozer, backhoe, etc. So

Plus, there seems to a good secondary market in Diesel generators; much less so in propane.

That is why I want to be able to put numbers to things; so we can look at the real costs, and then decide.

 

[fsck]

This says it for me:


When you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge of it is of a meager and unsatisfactory kind; it may be the beginning of knowledge, but you have scarcely, in your thoughts, advanced it to the stage of science.

Sir William Thompson, Lord Kelvin (1824-1907)

 

[oldfieldguy]

I concur that the consideration of the effects of long-term storage of fuel is a consideration.

It's not the only consideration, though. Think about what happens when the tank runs empty. In the aftermath of Hurricane Rita it was impossible to get propane delivered into the hurricane zone in any quantity. A couple of drums of diesel fit in the bed of a pickup truck.

old field guy

 

[rmw]

Sounds to me like you have your mind made up that you want diesel.

itsmoked has made some very valid points, but if that won't be an issue to you, diesel is your obvious choice.

I am potentially in the market for a stand-by generator, and it won't be diesel. It will be natural gas or propane. In other engine driven applications, I am a natural diesel fan and have owned my share of them. But not for one where the fuel has to be stored for long periods.

rmw

 

[fsck]

Sounds to me like you have your mind made up that you want diesel.

Not at all. First off, it's not my call; I'm just getting options together. Second, I don't know the costs yet.

But it costs a bit to fill up a 1000g propane tank; so I think some due diligence is called for at this stage.

If there was natural gas; there'd be no discussion. Dual fuel from it or propane would win hands down. But he's as likely to get FIOS as that....i.e. not in his my lifetime or his.

Nod re: refuelling Afterwards. Post-911, the several server hotels in Lower Manhatten had a major problem getting refuelers to their buildings. Those shutdowns days later were the only Internet failures of any note. This is an earthquake and wildfire zone, just to make life interesting.

He will have smaller generators that run off gasoline, and maybe a PTO-driven one off the 'dozer. We'll see.

 

[FreddyNurk]

Out of interest (its partly related to the application) how does one deal with the potential hazardous areas arising from use of gas as a fule for the generator?

Are we talking small enough that a tank such as a forklift tank is adequate, and thus its easy to deal with?

We've got an installation we inherited with a gas powered 300kW set, but theres been no designation of any sort of hazardous areas. I would have thought that compliance with the standards, at least in terms of regular inspections and so on would seriously sway the balance.

I'm in IEC land for reference, I have no knowledge of the NEC requirements.

 

[fsck]

I doubt IEC code is your biggest problem. It's going to be your equals to EPA and the fire marshal...and your insurance company.

 

[catserveng]

In my own experience, mainly from the Southern California area, is that in the size range mentioned I think diesel is by far more reliable and cost effective.

I worked for an engine dealer for a number of years, at one time we had nearly 1000 standby generators under CSA's. Even though natural gas and propane units made up a fairly small percentage of the population, they had a larger number of failures and problems. I don't think a lower knowledge level was the issue since we had a large number of larger natural gas and some propane units in prime power and cogeneration service, and we serviced competitors units as well. We also did a fairly large number of NG pump units for irrigation, with far fewer problems than similar units in standby service.

Some issues from my experience,

SI engines suffered more problems from running at no or low loads, included plug fouling, fuel system problems and failures to start when commanded.

Found a large number of propane units had failed to start, either during regular testing or during an outage. Root cause, tank was empty. Hopefully fuel tank level monitoring has improved since then, but it was a big problem.

Propane vaporizers seemed to be problematic, one of our most frequent reasons for service call.

The governing systems provided, especially on auto-derived engines, seemed problematic, poor control of speed/Hz and erratic droop response, probably due to low cost. Hopefully newer engines use electronic governing or better mechanical governors. If it seems nit picky, most standby customers I dealt with wanted "utility like performance" from the cheapest standby they could buy.

I worked the aftermath of both the Northride and Oakland earthquakes, and a number of fires over the years, I'll second OldFieldGuys comment about diesel fuel in the back of a truck. Seen a propane tank during a wildfire? You may also be able to find someone from LA County Watewater to tell you about a small number of spectacular "launching" of pump houses that housed propane engine powered pumps. After that I was told they no longer considered propane as a suitable standby fuel.

Yup, diesel fuel does degrade during storage, seems the newer fuels do it faster, likely due to the fact that the sulphur probably helped combat biological growth and older fuels had lower levels of light ends. I would bet anyone can make a better case for one over the other based on his perspective.

But I think a small diesel, especially under the current HP limit for emissions regulations, with a simple robust fuel injection system and solid governing is going to be hard to beat for shear reliability. And I can't imagine anyone who buys the size units we are discussing is going to spend much on maintaining the units to assure most reliable operation.

my 2 cents worth.

Mike L.

 

[davidbeach]

There are fuel maintenance systems. And there is a reason why engine driven fire pumps are required to have compression ignition engines. Given a choice I'd always go for the Diesel over any spark ignition engine.

 

[fsck]

While Diesels have no doubt improved, gas engines in cars at least have gone lightyears in reliability. I was talking about this with several friends... while we were putting bushings in my 19 YO CRX's rear trailing arms.

I can't recall the last time a car did not start, save a dead battery or out of gas. Fuel injected/closed loop control have solved so many things, inc. fouled plugs, idle while cold, and oil dilution.

Have stationary powerplants been following along; or are they like GA aircraft engines, still using the finest WWII technology?

 

[catserveng]

Car engines are not like standby engines, a big mistake lots of folks make. Just had this discussion with a guy wearing an eagle on his collar at a local military base after four "critical" standby units failed an annual set of inspections and tests. If your car engine sat unattended and unlooked at for 30 to 90 days at a time, and you expected it to start and run every time, would it? How about if you did start and run that car every week, except never put it in drive or took it out of the driveway except once a year for a short run around the block? Would it still be reliable?

Sometimes at remote job sites I run my truck long hours at idle to run my inverter for power, a newer Dodge Ram 1500 with a "modern" control system, guess what, after that kind of operation a couple times a week, it has problems too.

As for the technology, how many auto-derived industrial gas engines have the same level of ECU and controls as an automotive application? Likely not as much, since the industrial market is a lower much volume and automakers build overall system controls into the ECU, not just for the engines.

Sorry to seem blunt, but comparing a car engine to an engine in standby generator service is like comparing house wiring to an electrical distribution system at a large industrial facility, the general idea is the same, but the actual application, maintenance and equipment selection needs to be different, at least in my opinion.

Mike L

 

[waross]

It sounds as if you will be using enough fuel that fuel aging will not be an issue. Consider a day tank with enough fuel capacity for 8 to 12 hours of operation at full load. Use automatic controls to fill the day tank from a larger tank. I would add a circuit that automatically topped up the day tank whenever the diesel set stopped. If you can use the fuel system that supplies the diesel machinery, that will take care of the fuel aging issues.



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

 

[fsck]

I did not mean to imply that cars & power plants were the one & the same. I did/do hope that they have moved ahead from the points & condenser era....despite the lower production volumes.

(Consider how well your '72 Dodge truck would run after idling for 6 hours....I used to work on police car radios, & long idling times were a major issue with the dept's...that and the stinking tiny MOPAR alternators of the era.)

I talked options with the owner. He's going to see if we can get outage stats from the utility. Neighbors estimate that they are black 75-100 hrs a year; unless there's been a quake, then all bets are off. Longest outage they've had was 8-10 days.

Their current fuel management scheme is take the empty 55g drum back to the farm supply, and get a new one. With a Diesel generator, he'd get a rack at least. I concur about fuel transfer schemes.

One possible Plan B is a PTO generator run by his new Kuboto L4400HST, but I have not found a 3-phase one of appropriate size. We're going to look at both fuel options for Plan A.

 

[waross]

PTO alternators are a farmers solution to a farmers problem. Generally when a specific task arises that needs remote power, such as irrigation pumping, grain drying, or possibly welding in the field, the PTO generator is mounted and used. The operation is planned ahead. It is not something to mount and connect in the middle opf the night to cope with a power failure.


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

 

[fsck]

Agreed, hence the Plan B label. We'd still get a in-place generator, cycled as needed by the inverter/battery system.

But the PTO solution gives us an alternative; one that burns Diesel.

And in theory, the priority 1 loads are within the envelope of the PV system. In other words, at during sunny days, we should need no IC engine going at all; or maybe for an hour.

The water tankage has 25' of head vs the house, so everything short of the showers will work regardless, albeit more slowly.

 

[fsck]

I should also say that the inverter system gives us, at worst, gap-filling.

The generator can shut down, and the P-1 house loads will stay up. Lower priority loads such as the freezer will drop off.

Thus you can refuel, and restart; or if need be, drive the tractor over and start up the PTO generator.

One of the TBD questions is how many minutes of batteries does the client want to buy.

Another one is: what kind of remote tank gauge technology can I use on Diesel or propane tanks? When I was in the pipeline business, the tankgauges were a major pain, and not to be trusted.

 

[itsmoked]

There's always the trusty sight glass.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[fsck]

Camera watching sight-glass -> TCP/IP to house image-processing system -> evaluate image ->graphics module to create image -> display digital countdown timer on power mgmt page...."xx:yy:zz until blackout!"

I'll need some Flo Control software

http://tinyurl.com/2apww6p