Fuel cost for generator

northerner
northerner Solar Expert Posts: 492 ✭✭✭✭✭✭
in Off Grid Solar & Battery Systems #1
I attempted to figure out how much less it costs to run a generator on natural gas (NG) versus gasoline.

I calculated my variable cost of NG from billing of the past month to be $5.44 per GJ which is about $5.74 per mmBTU. I figure this works out to 19.7 cents per liter of gasoline equivalent (ie if one was to compare with the use of gasoline). If that is correct, that works out to 1/6 the cost of running on gasoline, as it is priced at about $1.20 per liter in the area I live. Does that sound about right?
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #2
    Re: Fuel cost for generator

    In my area, the charge per Therm (100,000 BTU). The conversion from Therm to GJ is:

    http://www.unitconversion.org/energy/gigajoules-to-therms-ec-conversion.html

    1.0 Therm = 0.1055056 GJ

    Currently, we are paying around $1.00 per Therm in San Francisco area...

    1 Gallon of gasoline is around 112,000 BTU (in can be as high as 125,000 BTU per gallon depending on formulations?) -- And we pay around $3.50 (+/-) per gallon. So, the gallon equivalent of heat based on $1 per therm for natural gas would be:

    $3.50 per gallon * 100,000 BTU per $1 of natural gas * 1/112,000 BTU per gallon = ~$3.12 worth of gasoline per $1 of natural gas

    With your 1/2 price for natural gas and more expensive gasoline--Yep, looks reasonable.

    I am not sure how efficient a converted gasoline engine is running on natural gas--But even is it took 2x more natural gas to generate the same amount of electricity--You would still be way out ahead on natural gas. (perhaps, it is just the maximum available HP from the engine is reduced with natural gas, and not the overall thermal efficiency).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • northerner
    northerner Solar Expert Posts: 492 ✭✭✭✭✭✭
    #3
    Re: Fuel cost for generator

    I used the table at the bottom of this link:http://www.nat-g.com/why-cng/cng-units-explained/ to determine the conversion of cost of NG as it relates to GGE (gallon of gasoline equivalent).

    Here's another interesting calculator that will determine payback from converting a gasoline vehicle into CNG (compressed natural gas).

    http://www.cngnow.com/vehicles/calculator/Pages/information.aspx
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  • vibeline
    vibeline Registered Users Posts: 24 ✭✭
    #4
    Re: Fuel cost for generator

    I have a question about this topic.
    How much power would the generator lose if he switched it to natural gas?
    If natural gas has less BTU's than gasoline, it must make less power.
    sorry for the hijack,
    happy new year folks,
    Cheers
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  • RCinFLA
    RCinFLA Solar Expert Posts: 1,485 ✭✭✭✭
    #5
    Re: Fuel cost for generator
    vibeline wrote: »
    I have a question about this topic.
    How much power would the generator lose if he switched it to natural gas?
    If natural gas has less BTU's than gasoline, it must make less power.
    sorry for the hijack,
    happy new year folks,
    Cheers

    Depends a little on your altitude above sea level but generally a small to mid-side engine de-rates by about 85% in horsepower. A 15 KVA gen becomes 12 KVA. This holds for propane versus nat gas.
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