A Carbon Calculator for Wind farms on Peatland
A Carbon Calculator for Wind farms on Peatland Nayak D 1, Perks M 3, Miller D 2, Nolan A 2, Gardiner B 3 & Smith JU 1 1 University of Aberedeen, Aberdeen, UK 2 Macaulay Institute, Aberdeen, UK 3 Forest Management Division, Forest Research, Midlothian, UK
The Scottish Government has ambitious targets for electricity generation by renewables 31% by 2011 Scottish Government (2008) http: //www. scotland. gov. uk/Topics/Business-Industry/Energy/19185/17612 50% by 2020
Wind farms are likely to be developed on peats – Less productive than arable mineral soils no pressures on land use – On exposed sites high capacity factor
Will greenhouse gas emissions from peatlands exceed carbon savings due to the wind farm? Calculate carbon payback time If (carbon payback time) > (lifetime of wind farm), wind farm does not provide carbon benefit
Carbon Payback Time Total losses (t CO 2 eq. ) Carbon payback time (years) Annual emission savings (t CO 2 yr-1)
Annual Emission Savings …depend on counterfactual energy source Counterfactual Energy Source Emission factor (t CO 2 MWh-1) Grid Mix 0. 43 Fossil Fuel Mix 0. 607 Coal Fired 0. 78 Baggott, et al (2007). http: //www. naei. org. uk/reports. php. Report AEAT/ENV/R/2429 13/04/2007 DUKES (2007). http: //www. berr. gov. uk/energy/statistics/sourc e/electricity/page 18527. html
Carbon emission savings of wind farms Annual emission savings (t CO 2 yr-1) Capacity factor (%) Number of turbines Annual energy output (MW yr-1) Emission factor (t CO 2 MWh-1) Turbine capacity (MW).
Total Losses Total losses (t CO 2 eq. ) C fixing potential Production, transportation, erection, operation, dismantling Backup power generation Dissolved organic carbon Removed peat Loss of C due to drainage Forestry clearance Habitat improvement
Change in C dynamics of peatlands 1. Loss of carbon fixing potential of bog plants 2. Loss of carbon from removed peat 3. Loss of carbon from drained peat 4. Loss of Dissolved and Particulate organic carbon 5. Gain of C due to habitat improvement
Loss of carbon (CO 2) from drained peat Site Specific Methodology Rate of CO 2 emissions (t CO 2 eq. yr-1) Water table depth (m) Peat temperature
Loss of carbon (CH 4) from drained peat Site Specific Methodology Rate of CH 4 emissions (t CH 4 yr-1) Water table depth (m) Peat temperature
Example site – Central Scotland 480 ha felled & improved plantation 385 ha improved degraded bog 15 m 67 x 2 MW turbines 15 m 20 m 2 m deep Site fully restored on decomissioning 30% capacity factor 40 m Access tracks: 24600 m floating roads Extent of drainage: 100 m
Emission Factors Bog Emission factor Rate of CO 2 emission in drained soil (t CO 2 ha-1 yr-1) 24. 3 Rate of CO 2 emission in undrained soil (t CO 2 ha-1 yr-1) 0. 26 Rate of CH 4 emission in drained soil ((t CH 4 -C) ha-1 yr-1) -0. 005 Rate of CH 4 emission in undrained soil ((t CH 4 -C) ha-1 yr-1) 0. 50 Fen Rate of CO 2 emission in drained soil (t CO 2 ha-1 yr-1) 64. 62 Rate of CO 2 emission in undrained soil (t CO 2 ha-1 yr-1) 5. 12 Rate of CH 4 emission in drained soil ((t CH 4 -C) ha-1 yr-1) -0. 004 Rate of CH 4 emission in undrained soil ((t CH 4 -C) ha-1 yr-1) 0. 56
Example site – Central Scotland 400000 Greenhouse Gas Emissions (t CO 2 eq. ) 350000 300000 250000 Carbon emissions 200000 150000 100000 50000 0 Carbon savings -50000 -100000 -150000 Turbine life Backup Bog plants Total carbon payback time 2. 3 years Forest felling Soil organic carbon Dissolved and Improved felled Restored particulate degraded bogs forestry borrow pits organic carbon
Example site – Central Scotland 480 ha felled plantation Not improved! 385 ha improved degraded bog 480 ha felled & improved plantation 15 m 67 x 2 MW turbines 15 m 20 m 2 m deep Site fully restored on decomissioning 30% capacity factor 40 m Access tracks: 24600 m floating roads Extent of drainage: 100 m
Example site – Central Scotland Greenhouse Gas Emissions (t CO 2 eq. ) 4500000 Greenhouse gas emissions 4000000 3500000 3000000 2500000 2000000 1500000 1000000 500000 0 Turbine life Backup Bog plants Total carbon payback time 7. 3 years Forest felling Soil organic carbon Dissolved and particulate organic carbon Improved degraded bogs Improved felled Restored borrow forestry pits
Example site – Central Scotland 67 x 2 MW turbines 15 m 20 m 2 m deep 30% capacity factor 40 m Floating roads sink Extent of drainage: 100 m
Example site – Central Scotland 67 x 2 MW turbines 15 m 20 m 2 m deep 30% capacity factor 40 m Floating roads sink Extent of drainage: 100 m
Example site – Central Scotland 67 x 2 MW turbines Very High
Example site – Central Scotland Greenhouse Gas Emissions (t CO 2 eq. ) 4500000 Greenhouse gas emissions 4000000 3500000 3000000 2500000 2000000 1500000 1000000 500000 0 Turbine life Backup Bog plants Total carbon payback time 23 years Forest felling Soil organic Dissolved and carbon particulate organic carbon Improved degraded bogs Improved felled forestry Restored borrow pits
New Developments in collaboration with Forestry Commision Forests-turbines-soils Calculator • Forest accumulated carbon calculated through simplified version of 3 PGN model • Various felling options around turbine i. e. key holing, large clearing……. . • Option to replant SRF • Impact upon turbine output calculated through simple windflow / turbulence model
Management option Details No felling Trees remain right up to turbines Key holing 100 m radius (3. 14 ha) around each turbine i. e. 195 ha Large clearing 500 ha felling in a block around the turbines, 500 ha forestry remaining Clearfell All surrounding 1000 ha of forest cleared Key hole SRF (Outwith) Clearfell occurs, replanted with SRF on 25 yr rotation ~10 m height leaving 3. 14 ha bare for each turbine. SRF used as biofuel Key hole SRF (within) 100 m radius (3. 14 ha) around each turbine felled, area keyholed replanted with SRF on 25 yr rotation ~10 m height. SRF used as biofuel Large clearing SRF Clearfell occurs, replanted with SRF on 25 yr rotation ~10 m height leaving 500 ha block bare for turbines. SRF used as biofuel Large clearing SRF 500 ha felling in a block around the turbines, 500 ha forestry remaining, area felled replanted with SRF on 25 yr rotation ~10 m height. SRF used as biofuel
Annual power output (MW)
Life time carbon emissions
Carbon payback time Keyholing (Outwith): 3. 5 yrs Large clearing (Within): 7. 2 yrs
Conclusion 1. Highest C losses from decomposition of soil organic matter 2. This can be reduced by developing wind farms on mineral soil. 3. With good management practices, carbon benefits can be achieved even on peats 4. Preliminary results shows keyholing with SRF can be a good forest management practice.
Acknowledgements – – – – – Sally Baillie (Forestry Commission) Clifton Bain (Royal Society for Protection of Birds) Andrew Coupar (Scottish Natural Heritage) Helen Jones (Scottish Government) Sue Kearns (Scottish Government) Martin Mathers (Scottish Renewables Forum) James Pendlebury (Forestry Commission) Geeta Puri (project officer, Scottish Government). Peter Singleton (SEPA) Guy Winter (Scottish Government)
Thank you All
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