BIOENERGY FOR EUROPE: WHICH ONES FIT BEST?

7.1 Country specific life cycle comparisons 137
All biofuels under study result in savings of greenhouse gas emissions. The substitution of natural gas
with biogas saves 404 g CO2 eq./MJ useful energy, diesel oil with SME 144 g CO2 eq./MJ useful energy
and light oil with straw 87 CO2 eq./MJ useful energy. Straw instead of natural gas saves 74 CO2
eq./MJ useful energy.
The advantage of biogas in this impact category can be attributed to CH4 use as a fuel in the biogas
chain instead of its uncontrolled release to the environment in the reference system as well as the
avoided CO2 emissions from the substitution of a fossil fuel with a biofuel.
Acidification – Greece
Acidification is an impact category in which all biofuels under study present worse results than the reference
fossil fuel. The least favourable biofuel is biogas emitting 1.7 g SO2 eq./MJ useful energy more
than natural gas due to increased SO2 and NOx emissions from biogas combustion. The increased acidifying
emissions in the SME chain (0.5 g SO2 eq./MJ useful energy) are in the agricultural part mainly
due to NH3 emissions from nitrogen fertilisation while in the case of straw increased emissions are due
to straw combustion.
g SO2 eq. / MJ useful energy
6
5
4
3
2
1
0
Eutrophication – Greece
Processing & Utilisation
Agriculture/forestry part
Fossil fuel life cycle
Agricultural reference
system
SME Diesel Biogas Natural gas Straw Light oil Natural gas
In the impact category eutrophication all biofuels present worse results compared to their fossil counterparts.
In the biogas chain NOx emissions from biogas combustion are mainly responsible for the
increased emissions of the biogas chain (0.52 g NO3 eq./MJ useful energy more than in the natural gas
chain).In the SME chain as shown in the above figure 7.37 g NO3 eq./MJ useful energy are subtracted
from the total emissions of the chain due to system expansion (see Chapter 3.2.4., glycerine and sunflower
meal) and therefore SME emits 0.67 g NO3 eq./MJ useful energy more than diesel oil through its
life cycle due to increased emissions in the agriculture/forestry part. Wheat straw proves to be the least
disadvantageous biofuel in this impact category emitting 0.16 NO3 eq./MJ useful energy more than light
oil and natural gas.