Clad oct09 acoupar_dnayak (nx_power_lite)

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

0

10

20

30

40

50

60

70

80

90

100

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

0

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