1. A Carbon Calculator for Wind farms on
Peatland
Nayak D1, Perks M3, Miller D2, Nolan A2, Gardiner B3 & Smith JU1
1University of Aberedeen, Aberdeen, UK
2Macaulay Institute, Aberdeen, UK
3Forest Management Division, Forest Research, Midlothian, UK

2. The Scottish
Electricity generation by renewables
100
90
Government has 80
ambitious targets 70
60
for electricity
(%)
50
generation by 40
30
renewables 20 50%
10 by 2020
0 31%
2010 by 2011 2015 2020 2025
Year
Scottish Government (2008)
http://www.scotland.gov.uk/Topics/Business-Industry/Energy/19185/17612

3. 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

4. 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

5. Carbon Payback Time
Total losses
(t CO2 eq.)
Annual emission
savings
(t CO2 yr-1)
Carbon payback
time (years)

6. Annual Emission Savings
…depend on counterfactual energy source
Counterfactual Emission factor
Energy Source (t CO2 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/source/electricity/page18527.html

7. Carbon emission savings of wind farms
pcap
S fuel = 24 × 365 × × nturb × c turb × E fuel
100 Emission
factor
(t CO2 MWh-1)
Capacity Number of Turbine
Annual emission
factor turbines capacity
savings
(%) (MW).
(t CO2 yr-1)
Annual energy output (MW yr-1)

8. Total Losses
Ltot = Llife + Lback + Lfix + Ldirec t + Lindirect + LDOC + Lforest + Limprovemen t
Total losses
(t CO2 eq.) C fixing
potential Dissolved
organic carbon
Removed
peat Forestry
Production, Loss of C clearance
transportation, due to
erection, drainage
operation, Habitat
dismantling improvement
Backup power
generation

9. 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

10. Loss of carbon (CO2) from drained peat
Site Specific Methodology
44 / 12
R CO 2 (Bog) = × ((6700 × exp(− 0.26 × exp(− 0.0515 × (( W × 100) − 50))) + ((72.54 × T) − 800)
1000
Water table
Rate of CO2 emissions depth (m) Peat temperature
(t CO2 eq. yr-1)
44 / 12
R CO 2 (Fen) = × ((16244 × exp(−0.175 × exp(−0.073 × (( W × 100) − 50))) + (153.23 × T )
1000

11. Loss of carbon (CH4) from drained peat
Site Specific Methodology
1
R CH 4 (Bog) = × ((500 × exp(− 0.1234) × ( W × 100)) + ((3.529 × T) − 36.67)
1000
Rate of CH4 emissions
(t CH4 yr-1) Water table Peat temperature
depth (m)
1
R CH 4 (Fen) = × ((−10 + 563.62 × exp(−0.097) × ( W × 100)) + (0.662 × T )
1000

12. Example site – Central Scotland
480ha felled &
improved plantation 67 x 30% capacity factor
2MW turbines
385ha improved
degraded bog
15m
15m
40m Access tracks:
20m 24600m floating roads
2m deep
Extent of drainage:
100m
Site fully restored
on decomissioning

13. Emission Factors
Bog Emission factor
Rate of CO2 emission in drained soil (t CO2 ha-1 yr-1) 24.3
Rate of CO2 emission in undrained soil (t CO2 ha-1 yr-1) 0.26
Rate of CH4 emission in drained soil ((t CH4-C) ha-1 yr-1) -0.005
Rate of CH4 emission in undrained soil ((t CH4-C) ha-1 yr-1) 0.50
Fen
Rate of CO2 emission in drained soil (t CO2 ha-1 yr-1) 64.62
Rate of CO2 emission in undrained soil (t CO2 ha-1 yr-1) 5.12
Rate of CH4 emission in drained soil ((t CH4-C) ha-1 yr-1) -0.004
Rate of CH4 emission in undrained soil ((t CH4-C) ha-1 yr-1) 0.56

14. Example site – Central Scotland
400000
Gre enhous e Gas Em iss ions (t CO2 e q.)
300000
Carbon emissions
200000
100000
0
Carbon savings
-100000
-200000
Total carbon payback time
2.3 years

15. Example site – Central Scotland
480ha felled plantation
Not improved! 67 x
2MW turbines 30% capacity factor
385ha improved
degraded bog 480ha felled &
improved plantation 15m
15m
40m Access tracks:
20m 24600m floating roads
2m deep
Extent of drainage:
100m
Site fully restored
on decomissioning

16. Example site – Central Scotland
Greenhouse gas emissions
4500000
Greenhouse Gas Emissions (t CO2 eq.)
4000000
3500000
3000000
2500000
2000000
1500000
1000000
500000
0
Total carbon payback time
7.3 years

17. Example site – Central Scotland
67 x 30% capacity factor
2MW turbines
15m
15m
40m
20m
Floating roads sink
2m deep
Extent of drainage:
100m

18. Example site – Central Scotland
67 x 30% capacity factor
2MW turbines
15m
15m
40m
20m
Floating roads sink
2m deep
Extent of drainage:
100m

19. Example site – Central Scotland
actor
ap acity f
30% c
67 x
2MW turbines
15m
15m 40m
sink
20m g roads
Floatin
ge:
of draina
Extent 00m
2
ep
2m de Very High

20. Example site – Central Scotland
4500000 Greenhouse gas emissions
Gre enhous e Gas Em iss ions (t CO2 e q.)
4000000
3500000
3000000
2500000
2000000
1500000
1000000
500000
0
Total carbon payback time
23 years

21. New Developments in collaboration with Forestry Commision
Forests-turbines-soils Calculator
• Forest accumulated carbon calculated through
simplified version of 3PGN 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

22. Management option Details
No felling Trees remain right up to turbines
Key holing 100m 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 25yr
rotation ~10m height leaving 3.14 ha bare for
each turbine. SRF used as biofuel
Key hole SRF (within) 100m radius (3.14 ha) around each turbine
felled, area keyholed replanted with SRF on 25yr
rotation ~10m height. SRF used as biofuel
Large clearing SRF Clearfell occurs, replanted with SRF on 25yr
rotation ~10m 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 25yr rotation ~10m height. SRF used as
biofuel

23. Annual power output (MW)
300000
250000
Annual power output (MW)
200000
150000
100000
50000
0

24. Life time carbon emissions
6000000
Greenhouse Gas Emissions (t CO2 eq.)
5000000
4000000
3000000
2000000
1000000
0

25. Carbon payback time
25
20
Carbon payback time (years)
15
10
5
0
Keyholing (Outwith): 3.5 yrs
Large clearing (Within): 7.2 yrs

26. 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.

27. 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)

28. Thank you All