Table 7 Greenhouse gas emissions of different processes to produce the same quantity of energy (maintaining a 500 kWe biogas plant) in the cocksfoot grass-based biomass-biogas-biomass cycle in the 7-year period (in total 39,917 GJ = 66,528 MWh), with area corrections from Table 6 and saved emissions from substituting the European average energy mix with biogas
Process | SC1 | SC2 | SC 3 | SC 4 | SC 5 | SC 6 | SC7 | SC8 | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
t CO2-eq | % | t CO2-eq | % | t CO2-eq | % | t CO2-eq | % | t CO2-eq | % | t CO2-eq | % | t CO2-eq | % | t CO2-eq | % | |
Direct emissions | ||||||||||||||||
Soil tillage | 191.3 | 1.7 | 75.1 | 0.6 | 82.3 | 0.4 | 93.9 | 0.9 | 69.7 | 0.6 | 61.9 | 0.5 | 55.3 | 0.4 | 54.5 | 0.3 |
Soil cultivation | 124.3 | 1.1 | 48.8 | 0.4 | 53.5 | 0.2 | 61.1 | 0.6 | 45.3 | 0.4 | 40.2 | 0.3 | 35.9 | 0.2 | 35.4 | 0.2 |
Sowing | 53.6 | 0.5 | 21.0 | 0.2 | 23.1 | 0.1 | 26.3 | 0.3 | 19.5 | 0.2 | 17.3 | 0.1 | 15.5 | 0.1 | 15.3 | 0.1 |
Fertilisation (mineral N) | - | - | 153.0 | 1.2 | 164.7 | 0.7 | - | - | - | - | - | - | - | - | - | - |
Fertilisation (digestate) | - | - | - | - | - | - | 141.6 | 1.4 | 210.9 | 1.8 | 272.2 | 2.1 | 323.5 | 2.2 | 387.5 | 2.3 |
Grass cutting collection | 10083.4 | 88.6 | 4608.2 | 35.2 | 4949.2 | 22.4 | 4538.0 | 43.7 | 3379.6 | 29.2 | 2897.3 | 21.9 | 2581.9 | 17.6 | 2463.2 | 14.7 |
Transportation | 77.2 | 0.7 | 66.8 | 0.5 | 62.0 | 0.3 | 64.2 | 0.6 | 69.5 | 0.6 | 71.0 | 0.5 | 71.5 | 0.5 | 73.0 | 0.4 |
Grass storage (ensiling) | 5.1 | 0.0 | 4.3 | 0.0 | 4.1 | 0.0 | 4.2 | 0.0 | 4.6 | 0.0 | 4.7 | 0.0 | 4.7 | 0.0 | 4.7 | 0.0 |
Anaerobic digestion process | 14.1 | 0.12 | 11.8 | 0.1 | 11.3 | 0.05 | 11.7 | 0.1 | 12.7 | 0.1 | 13.0 | 0.1 | 13.0 | 0.1 | 13.3 | 0.1 |
Indirect emissions | ||||||||||||||||
Agricultural machinery | 400.8 | 3.5 | 180.4 | 1.4 | 194.1 | 0.9 | 182.2 | 1.8 | 135.6 | 1.2 | 116.7 | 0.9 | 104.0 | 0.7 | 99.7 | 0.6 |
Indirect emissions of fertiliser applicationa | – | – | 2278.8 | 17.4 | 4897.7 | 22.2 | 4838.4 | 46.6 | 7203.4 | 62.3 | 9300.5 | 70.4 | 11050.5 | 75.3 | 13236.4 | 78.8 |
Indirect emissions of fertiliser productionb | – | – | 5232.3 | 39.9 | 11245.3 | 50.9 | – | – | – | – | – | – | – | – | – | – |
Human work | 13.5 | 0.12 | 546.0 | 0.0 | 5.9 | 0.0 | 6.1 | 0.1 | 4.6 | 0.0 | 3.9 | 0.0 | 3.5 | 0.0 | 3.4 | 0.0 |
Methane loss (0.5% of produced biogas) | 412.9 | 3.6 | 412.9 | 3. 2 | 412.9 | 1.9 | 412.9 | 4.0 | 412.9 | 3.6 | 412.9 | 3.1 | 412.9 | 2.9 | 412.9 | 2.5 |
Total emissions | 11376.2 | 100 | 13099.1 | 100 | 22106.1 | 100 | 10380.7 | 100 | 11568.4 | 100 | 13211.8 | 100 | 14672.3 | 100 | 16799.3 | 100 |
Alternative emissions | − 15079242 | − 15081518 | − 15082025 | − 15063574 | − 15053831 | − 15044694 | − 15037845 | − 15027610 | ||||||||
Saved emissions | − 15067866 | − 15068419 | − 15059919 | − 15053193 | − 15042263 | − 15031482 | − 15023173 | − 15010811 | ||||||||