Propane generators

Re: Propane generators

From what I understand, the Onan is a standby generator (3,600 rpm instead of 1,800 rpm) and probably not the best choice for a generator that may be intended for continuous operations...

So, that really gets back to questioning what your power system is intended to be... If you are off grid and will have lots of need of solar/wind/generator power--then I would suggest that you look at an 1,800 rpm diesel (or even an 1,800 propane/etc.) instead... I believe that diesel will tend to burn less fuel, especially at the lower power ratings (like 25% load). Gasoline, propane, natural gas, etc. generators tend to draw substantial amounts of fuel even when running at part load...

For example, the Onan R1200 takes 184ft3/hr at full load (from www.costco.com web site). My natural gas rate is $1.16 to $1.37 per therm (basically 100 CF)... That generator, running at full load will cost about $2.13 (4.2kWhr/$1.00 or $0.24/kWhr) to $2.52 per hour to run...

From here:

http://www.onan.com/pdf/standby/a-1465.pdf PDF spec sheet for the R1200 generator

at 25% load (2.25 kW instead of of 9kW full load), the unit will still draw ~72 CF/Hr or $0.84 per hour (at baseline gas price $1.16/therm: 2.7kWhr/$1.00 or $0.37/kWhr)...

The gasoline Propane version of the R1200 uses: 1.1 gal/hr (25% load) to 2.0 gal/hr (100% load)... At $2.50 per gallon (my average prices around here in California NOTE: the guess at $2.50 per gallon for propane in volume is just a guess--I do not use propane much here, so check your prices):

100% load = $5.00 per hour to operate or 1.8 kWhr/$1.00 of gas -- $0.556/kWhr on gasoline Propane)
25% (2.25 kW) load = $2.75 per hour to operate or 0.82 kWhrs/$1.00 of gas -- $1.22/kWhr on gasoline propane)

At least, around here, natural gas is going to be much cheaper to run than gasoline Propane... And notice, how the amount of fuel used does not go down in proportion of load with gasoline/propane/natural gas fuel--reduce load by a factor of 4, reduce fuel flow only by a factor of 2... I believe diesel's fuel usage curves will not be near as bad as the other type of engines--but you should check.

So--sizing your load to your generator is also going to be very important... If you plan on running your R1200 near full load (such as charging battery banks, running AC, etc... it is not bad. On propane Natural Gas, the costs are almost the same as electricity from a utility (running at 100% load of 9kW). If, however, you are going to run the generator for your average loads (say 1-2 kWatt loads), your fuel usage costs per kWhr generated will be through the roof...

As an example of using a smaller generator to run my average household loads during a power outage, the Honda portable generator eu2000i (1.6 kW generator) uses about 1.1 gallons for 4 hours of usage at 1.6 kW rating (full load). Using the above numbers ($2.50 per gallon for gasoline)... we get 2.3 kWhr/$1.00 of gasoline, or $0.43/kWhr on gasoline)... Not as nice as running on propaneNatural Gas--but certainly much cheaper than the R1200 running 1.22 kWhr/$1.00 of gasoline propane (at 2.25 kW load or 25% of rated power)

I am sure that others here can recommend brands/models of generators that will last for your application...

So try and get the fuel usage specifications for all of the generators you are considering... and run cost tables out on them (kWhrs per $1.00 of fuel, cents per kWhr--or whatever makes sense in your area). And look at really how much power you will need to generate during an outage and/or while charging your batteries--and try not to over-size the generator by too much.

Have fun,
-Bill

PS: Edited to change mix-ups of when Gasoline was mentioned, it should have been propane... And in some cases, I typed propane instead of natural gas... I made the mistake of not realizing that the R1200 was only available in Nat Gas or Propane... There was no gasoline version available on that spec. sheet (or at all?).

Regarding the price per gallon of Propane--I instead used the price of gasoline... At least in small quantities, propane around here is even more expensive than gasoline--so the places where I used $2.50/gallon for propane, is probably still accurate enough for a first discussion point... -BB