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I'm looking at building a sustainable energy project that will convert biogas (methane) into electricity. I haven't found any biogas or methane electric generators for sale. It seems that there are some projects that are using generators to convert the methane gas into electricity, however, I can't tell if this is special kind of generator and I just don't know what it's called or if it is a natural gas or propane generator.

So will off the shelf natural gas or propane generators also run off of methane?

Also, how would I go about trying to calculate how much methane it would take to run the generator to produce enough electricity to say charge a cell phone or another small appliance?

Thanks!

Transistor
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jshaw3
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3 Answers3

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natural gas is methane, so no problems there. an internal combustion engine that is equipped to operate on gasoline can be converted easily to run on gaseous fuels and the conversion kits usually contain a little fitment which allows the user to run the engine on their choice of either propane or methane.

niels nielsen
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The average low heating value (LHV) of biogas is around 5.5 kWh/m³ for a methane % around 40-70%, and Propane has around 24.2 kWh/m³ of LHV, and the Natural gas (NG) has around 10 kWh/m³.

Gas LHV
Methane 40 - 70% 5.5 kWh/m³
Propane 24.2 kWh/m³
Natural gas 10.0 kWh/m³

As you can see, the Propane can be between 4 to 5 times better than biogas, ans NG is twice better than biogas.

If you want to know the amount of gas to charge a PC of 0.4 kW during 4 hours, you would need 1.6 kWh. Then, if the generator efficiency (eta_gen) is 20%, the equation is:
Energy (kWh) = LHV(kWh/m³) × gas_volume (m³) × 0.20

Gas_volume = Energy/(LHV × 0.2)
=1.6 kWh/(0.2x5.5)
=1.45 ≈ 1.5 m³.

If a cow can produce about 0.35 m³/cow*day, you would need about 4.3 cow ≈ 5 cow .

The engine (gasoline, propane or NG engine) should be modified to work with biogas and the amount of gas should be calculated according to the LHV of the new fuel.

Transistor
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Victor Sena
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It depends on the source of the methane. Coal bed methane is relatively sweet. Biomethane has all kinds of crap in it that makes it problematic from a combustion and corrosion standpoint. Engines won't like it and you'll probably have trouble finding tanks and lines and carburetors and such.

Phil Sweet
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