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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
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2010 2015 2020 2025
Year
Ele
ctric
ity g
ener
atio
n by
ren
ewab
les
(%)
The Scottish Government has ambitious targetsfor electricity generation by renewables
31% by 201
1
50% by 2020
Scottish Government (2008) http://www.scotland.gov.uk/Topics/Business-Industry/Energy/19185/17612
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
fuel
totpayback S
Lt
Carbon payback time (years)
Total losses(t CO2 eq.)
Annual emission savings
(t CO2 yr-1)
Carbon Payback Time
Annual Emission Savings
Counterfactual
Energy Source
Emission factor (t CO2 MWh-1)
Grid Mix 0.43
Fossil Fuel Mix 0.607
Coal Fired 0.78
…depend on counterfactual energy source
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
fuelturbturb
capfuel 100
36524 Ecnp
S
Carbon emission savings of wind farms
Annual emission savings
(t CO2 yr-1)
Emission factor
(t CO2 MWh-1)
Capacity factor (%)
Number of turbines
Turbine capacity (MW).
Annual energy output (MW yr-1)
timprovemenforestDOCindirectdirecfixbacklifetot LLLLLLLLL t
Backup power generation
Total Losses
Total losses(t CO2 eq.)
Production,transportation,
erection,operation,
dismantlingHabitat
improvement
Forestry clearance
Dissolvedorganic carbon
Removed peat
Loss of C due to
drainage
C fixing potential
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 (CO2) from drained peatSite Specific Methodology
Rate of CO2 emissions
(t CO2 eq. yr-1)
)800)T54.72(()))50)100W((0515.0exp(26.0exp(6700((1000
12/44(Bog)R
2CO
Peat temperature
)T23.153()))50)100W((073.0exp(175.0exp(16244((1000
12/44(Fen)R
2CO
Water table depth (m)
Loss of carbon (CH4) from drained peatSite Specific Methodology
Water table depth (m)
Rate of CH4 emissions
(t CH4 yr-1)Peat temperature
)67.36)T529.3(())100W()1234.0exp(500((1000
1(Bog)R
4CH
)T662.0())100W()097.0exp(62.56310((1000
1(Fen)R
4CH
Example site – Central Scotland
385ha improved degraded bog
480ha felled & improved plantation
2m deep
15m15m
20m40m
67 x2MW turbines
30% capacity factor
Access tracks: 24600m floating roads
Extent of drainage: 100m
Site fully restored on decomissioning
Emission FactorsBog 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
Example site – Central Scotland
Total carbon payback time 2.3 years
Turbine life Backup Bog plants Forest felling Soil organic carbon
Dissolved and particulate
organic car-bon
Improved degraded
bogs
Improved felled forestry
Restored borrow
pits
Stop drainage of foundations
-200000
-100000
0
100000
200000
300000
400000G
ree
nh
ou
se
Ga
s E
mis
sio
ns
(t
CO
2 e
q.)
Carbon emissions
Carbon savings
Example site – Central Scotland
385ha improved degraded bog 480ha felled &
improved plantation
2m deep
15m15m
20m40m
67 x2MW turbines 30% capacity factor
Access tracks: 24600m floating roads
Extent of drainage: 100m
Site fully restored on decomissioning
480ha felled plantationNot improved!
Example site – Central Scotland
Total carbon payback time 7.3 years
Turbine life Backup Bog plants Forest felling Soil organic carbon
Dissolved and particulate
organic car-bon
Improved degraded
bogs
Improved felled forestry
Restored borrow
pits
Stop drainage of foundations
0
500000
1000000
1500000
2000000
2500000
3000000
3500000
4000000
4500000Greenhouse gas emissions
Gre
en
ho
us
e G
as
Em
iss
ion
s (
t C
O2
eq
.)
Example site – Central Scotland
2m deep
15m15m
20m40m
67 x2MW turbines
30% capacity factor
Extent of drainage: 100m
Floating roads sink
2m deep
15m15m
20m40m
Extent of drainage: 100m
Floating roads sink
Example site – Central Scotland
67 x2MW turbines
30% capacity factor
2m deep
15m
15m20m
40m
30% capacity factor
Extent of drainage:
200m
Floating roads sink
2m deep2m deep
15m
15m
15m
15m20m
40m
20m40m
30% capacity factor
30% capacity factor
Extent of drainage:
200m
Floating roads sink
Example site – Central Scotland
67 x2MW turbines
Very High
Total carbon payback time 23 years
Example site – Central Scotland
Turbine life Backup Bog plants Forest felling
Soil organic carbon
Dissolved and particu-late organic
carbon
Improved degraded
bogs
Improved felled
forestry
Restored borrow
pits
Stop drainage
of founda-tions
0
500000
1000000
1500000
2000000
2500000
3000000
3500000
4000000
4500000 Greenhouse gas emissions
Gre
en
ho
us
e G
as
Em
iss
ion
s (
t C
O2
eq
.)
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
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 turbinefelled, 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
No
fel
lin
g
Key
ho
lin
g
Cle
arin
g
Key
ho
lin
g
Lar
ge
clea
rin
g
Key
ho
lin
g
Lar
ge
clea
rin
g
Standard Forestry Practice Clearfell SRF replanting outwith SRF replanting within
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50000
100000
150000
200000
250000
300000
An
nu
al p
ow
er
ou
tpu
t (M
W)
Annual power output (MW)
Life time carbon emissions
No felling Keyholing Clearing Keyholing Large clearing Keyholing Large clearingStandard Forestry Practice Clearfell SRF replanting outwith SRF replanting within
0
1000000
2000000
3000000
4000000
5000000
6000000
Gre
enh
ou
se G
as E
mis
sio
ns
(t C
O2
eq.)
Carbon payback time
No
fel
lin
g
Key
ho
lin
g
larg
e cl
eari
ng
Key
ho
lin
g
Lar
ge
clea
rin
g
Key
ho
lin
g
Lar
ge
clea
rin
g
Standard Forestry Practice Clearfell SRF replanting outwith SRF replanting within
0.0
5.0
10.0
15.0
20.0
25.0
Ca
rbo
n p
ay
ba
ck
tim
e (
ye
ars
)
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