One of the key drivers to bioenergy deployment is its positive environmental benefit, in particular regarding the global balance of green house gas (GHG) emissions. IEA Bioenergy Task 38 (Greenhouse Gas Balances of Biomass and Bioenergy Systems) investigates all processes involved in the use of bioenergy systems on a full fuel-cycle basis with the aim of establishing overall GHG balances. This is not a trivial matter, because biomass production and use are not entirely GHG neutral. In general terms, the GHG emission reduction as a result of employing biomass for energy, read as follows:

Budget breakdown of GHG emission savings

+

avoided mining of fossil resources

emission from biomass production

+

avoided fossil fuel transport (from producer to user)

emission from biomass fuel transport (from producer to user)

+

avoided fossil fuel utilisation

 

The real gains are made with the last issue, i.e. that of avoided emissions from the use of fossil fuels. There are indications that the balance of the other four matters is not neutral, and in fact slightly negative for the biomass system. Two GHG emission types are omitted from the above balance: the negative emission (capture) as a result of biomass growth, and the positive emission as a result from using the biomass fuel. They are considered to cancel out.

GHG emission balances for biomass-fuelled electricity and heat applications
GHG balances for a wide range of technologies to produce electricity and heat were prepared by Elsayed, Matthews and Mortimer (2003). System boundaries encompassed the entire chain from fuel production to end-use. Some biomass systems show net GHG emissions savings of more than 40% of the substituted fossil alternatives, while some others only score 4%. Thus, the span of the environmental benefit is wide, and the effective value will depend on the particular application situation (technology, scale etc). The total GHG emissions from contaminated biomass fuels (non-tradables) are set at 0, since these fuels are available anyway. There existence cannot be avoided, and all GHG emissions associated with their production should be allocated to the products from which they are the unavoidable result.
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GHG savings for selected technologies to produce electricity and heat from biomass fuels

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Source: Elsayed, Matthews and Mortimer (2003). 

 

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GHG emission balances of selected bio-transport fuels

For an assessment of GHG emission reduction that result from replacing fossil transport fuels by biofuels, the entire life cycle of the respective fuels is usually considered from well to wheel. A complete life cycle analysis (LCA) of emissions takes into account the direct emissions from vehicles and also those associated with the fuel’s production process, which includes: extraction, production, transport, processing and distribution. Ranges in data result from local variations between fuel routes and differences in technology, which may occur at all stages of the well-to-wheel fuel chain. The pivots indicate the uncertainty related to the used data.

The substitution of biodiesel for petrol results in a total GHG emission reduction of 45-80%. If replacing fossil diesel fuel, this emission reduction is smaller, because diesel shows lower CO2-equivalent well-to-wheel emissions than petrol. The range of ethanol-starch is quite broad, which can be partly explained by differences in crop (corn, sugar beet, molasses), and differences in technology.

Short-term well-to-wheel GHG emissions of Light Duty Vehicles running on various fuels

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Source: IEA, 2003. 

Long-term well-to-wheel GHG emissions of Light Duty Vehicles running on various fuels

 

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Source: IEA, 2003. 

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GHG savings for selected bio-transport fuels

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Source: Elsayed, Matthews and Mortimer (2003).

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Global GHG emission savings
From the White Paper issued in 1997, it appears that biomass would be the biggest contributor in absolute terms to the CO2 emissions reduction effort.

Estimated CO2 benefits from the increase of renewable energy in the EU primary energy supply

 

 

Additional capacity

(1997-2010)

 

CO2 reduction

(Mt CO2-eq./year)

 

Biomass

 

90 Mtoe

 

255

 

Wind

 

36 GW

 

72

 

Hydro

 

13 GW

 

48

 

Solar collectors

 

94 Mio m2

 

19

 

Geothermal

 

2.5 GW

 

5

 

Photovoltaic

 

3 GWp

 

3

Source: White Paper, 1997