Miscanthus and willow heat production—An effective land-use strategy for greenhouse gas emission avoidance in Ireland?

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Energy Policy 36 (2008) 97–107 www.elsevier.com/locate/enpol

Miscanthus and willow heat production—An effective land-use strategy for greenhouse gas emission avoidance in Ireland? David Stylesa,b,, Michael B. Jonesa a

School of Natural Sciences, Trinity College Dublin, Dublin 2, Ireland Environmental Protection Agency, Richview Business Park, Clonskeagh, Dublin 14, Ireland

b

Received 8 June 2007; accepted 30 August 2007 Available online 1 November 2007

Abstract Recent decoupling of EU direct payments from agricultural production, to land-area-based payments, has accelerated the national trend of declining livestock numbers, presenting opportunities for new agricultural products. This paper uses life-cycle analyses to quantify the national magnitude and area-based efficiency of greenhouse gas (GHG) emission reductions possible from utilising indigenously grown willow and Miscanthus as heating fuels in domestic/commercial premises. Willow and Miscanthus fuel-chain emissions were calculated at 0.045 and 0.062 kg CO2 eq. kWhth, compared with 0.248, 0.331 and 0.624 kg CO2 eq. kWhth for gas, oil and electric heat, respectively. Long-term soil C sequestration where willow and Miscanthus are grown on tillage land could exceed fuel-chain emissions, resulting in heat production better than C-neutral. Net GHG emission reductions ranged from 7671 kg CO2 eq. ha1 a1 where willow displaced grassland and gas to 34,187 kg CO2 eq. ha1 a1 where Miscanthus displaced set-aside and electric heat. A simple, indicative scenario assumed that energy-crops were grown on set-aside and destocked grassland in the ratio of 1:2, and displaced a total of 4728 GWhth combined gas, oil and electric heat. Consequent net GHG emission reductions arising from sole utilisation of either willow or Miscanthus equated to 2.6% or 2.5% of 2004 national emissions, and required just 2.9% or 2.1% of Ireland’s agricultural land area. Net total emission reductions were relatively insensitive to variation in yield and cultivation emissions, but large reductions associated with electric-heat displacement will decline as electricity production becomes less GHG-intensive, and may not be representative of other countries. Energy-crop heat production offers considerably greater GHG emission reduction potential compared with agricultural destocking alone, and appears to represent an efficient land-use option for this purpose. r 2007 Elsevier Ltd. All rights reserved. Keywords: Energy crops; GHG emissions; Heating

1. Introduction Ireland is currently lagging behind its Kyoto commitment. Official reporting shows that 2004 national greenhouse gas (GHG) emissions stood at 68.5 Mt CO2 eq. (McGettigan et al., 2006), 25% above 1990 levels, compared with a Kyoto target of 13% above 1990 levels over the 2008–2012 commitment period. Agriculture contributes a comparatively large 28% of these emissions, based on a large agricultural land area of 4.30 M ha relative to a population of just 4.24 M people (CSO, 2007), and the dominance of livestockCorresponding author. School of Natural Sciences, Trinity College Dublin, Dublin 2, Ireland. Tel.: +353 1 896 3068; fax: +353 1 896 1147. E-mail address: [email protected] (D. Styles).

0301-4215/$ - see front matter r 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.enpol.2007.08.030

supporting grasslands (90% of agricultural area). Full decoupling of EU Common Agricultural Policy (CAP) subsidy payments from production was introduced in January 2005, and is accelerating the trend towards lower livestock numbers and production predicted by Binfield et al. (2003). Consequently, GHG emissions from the agricultural sector are predicted to fall by 2.9 Mt CO2 eq. a1 between 1990 and 2010 (Donnellan and Hanrahan, 2003), and large areas of land will be destocked. Potentially, this destocked land could be utilised for energy-crop cultivation, including the efficient, high-yielding short-rotation-coppice-willow (SRCW) and Miscanthus (a perennial rhizomatous grass). Maximum above-ground biomass yields for the latter have been modelled at up to 26 t dry-matter (DM) ha1 a1 in Ireland (Clifton-Brown et al., 2000).

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The decoupling of CAP payments from production and current high energy prices have combined to make energycrop utilisation an economically attractive proposition, from both a farmer and an end-user perspective. Economic modelling of Miscanthus and SRCW cultivation in Ireland (Styles et al., accepted) predicted that farmers could realise, under typical conditions, discounted1 gross margins of between h211 and h383 ha1 a1. Meanwhile, it was predicted that SRCW wood-chips could produce heat in domestic and small-commercial (e.g. hotel-scale) boilers at considerably lower cost than oil, gas or electric heating, despite the high initial wood-boiler investment costs (Styles and Jones, 2007a). In recognition of the long-term potential for energy-crops in Ireland, a subsidy scheme for SRCW and Miscanthus was announced this year (DAF, 2007), with a small target area of 1400 ha to be planted in the first year, marking the first significant cultivation of these energy-crops in Ireland. Domestic and commercial energy consumption data presented in Howley et al. (2006) highlight the dominance of oil (accounting for 39% and 41%, respectively), electricity (21% and 42%, respectively) and gas (21% and 18%, respectively) as energy sources, primarily for heating. Despite an ideal wood-growing climate, wood energy utilisation in Ireland is confined mainly to large-scale kiln firing in the wood-industry (O’Leary et al., 2006). Recent subsidies for wood-boiler installation, of up to h4200 per household, have encouraged uptake of these boilers to the extent that indigenous wood-pellet production has had to be supplemented with imported pellets. However, it is possible to utilise wood-chips in domestic and small commercial boilers, if these wood-chips are of good quality (i.e. less than 30% moisture content and nominal particle size of 8–15 mm: Kofman, 2006a). Miscanthus would require pelleting prior to combustion in small-scale boilers. Although there may be potentially cheaper sources of biomass, for example from forestry thinnings (Kofman, 2006b), the large area of agricultural land (60% of national land area) relative to forest land (10% national land area), offers greater opportunities for energy-crop biomass production to be coordinated with end users, and feed large-scale demand. This paper combines land-use LCA work presented in Styles and Jones (2007b) with domestic heating LCA work presented in Gustavsson and Karlsson (2002) to quantify life-cycle GHG emissions over the entire fuel-chains of pelleted Miscanthus and chipped SRCW heat production. These emissions are compared with emissions from oil, gas and electric heating fuel-chains. Emission changes incurred by both land-use and fossil-fuel displacement are combined to predict the possible net GHG impact of utilising destocked grassland and set-aside tillage land to produce biomass fuels. The various permutations of land-use and fossil-fuel displacement are then compared, in terms of GHG emission reductions per hectare of land appro1 Net present value approach: 5% discount rate, plantation lifetimes of 16 and 23 years for Miscanthus and SRCW, respectively.

priated, alongside emission reductions attributable to destocking alone. A simple scenario is developed to quantify the magnitude of GHG emission reductions possible, and the land area required, through this simple method of energy-crop utilisation. 2. Methodology 2.1. Scope, aims and boundaries A life-cycle approach is used to determine and quantify the major GHG emission sources associated with the production of 1 kWhth of useful heat from Miscanthus pellets, SRCW wood-chip, oil, gas and electricity. Given that the primary focus of this paper is on comparative heat fuel-chain GHG emissions, indirect emissions associated with boiler manufacture and installation, and electricity generation (national average power station construction and fuel transport emissions) were omitted (Fig. 1). It is anticipated that these indirect emissions will be minor, for example being spread over the anticipated 20-year operating lifetimes for domestic boilers, and that their omission should not disproportionately affect any particular heat source. For Miscanthus and SRCW, cultivation emissions of 1938 and 1346 kg CO2 eq. ha1 a1 were applied based on net combustible yields2 of 11.7 and 8.8 t ha1 a1 DM averaged over the entire plantation lifetimes of 16 and 23 years, respectively (Fig. 2). These emissions were quantified through comprehensive and detailed LCA presented in Styles and Jones (2007b). Fig. 1 displays the aspects of fuelchain emissions included in the LCA, and reference sources, for the different fuels. For oil and gas, fuel supply emissions were taken from Gustavsson and Karlsson (2002), who calculated emissions for Swedish circumstances, accounting for GHG emissions arising from leakage and energy consumption during extraction, processing and transmission/transport. The electric-heating GHG burden is based on the average Irish GHG intensity for delivered electricity of 0.624 kg CO2 eq. kWh1, accounting for direct generating emissions and transmission losses (Howley et al., 2006), making it comparable with the fuel-chain emissions excluding indirect boiler-construction emissions calculated for the other fuels (Fig. 1). A net heat output of 3.3 units per unit electricity input (Gustavsson and Karlsson, 2002) was considered for more efficient potential electricity utilisation via heat pumps, as an example of an alternative GHG mitigation option. Inventory mass balance emissions of CO2, CH4 and N2O were summed and converted into a final global warming potential, expressed as kg CO2 eq. considered over a 100year timescale, according to IPCC guidelines (IPCC, 2001): i.e. CO2 ¼ 1, CH4 ¼ 23 and N2O ¼ 296. 2 Account for lower yields in establishment years and no yield in final year for both crops; 90% harvest efficiency and 1% per month DM storage losses for SRCW (Gigler et al., 1999); 30% leaf senescence, harvest and decomposition losses for Miscanthus (Clifton-Brown et al., 2000).

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SRCW and Miscanthus heat

Extraction Direct and indirect emissions associated with locating and extracting oil and gas [b].

Electric heat

Land use Direct emissions(e.g. tractor diesel). Indirect emissions (e.g. fertiliser production). Soil emissions (N2O and soil C balance). Detailed in [a].

Kerosene and natural gas heat

D. Styles, M.B. Jones / Energy Policy 36 (2008) 97–107

Electricity generation Direct power station combustion emissions - average Irish fuel mix [f]. No indirect emissions associated with power station construction, or fuel extraction and transport.

Transport and processing Direct and indirect truck emissions [b]. Drying (storage) [c], chipping [d] and pelleting [b].

Combustion Direct emissions of CH4 and N2O [e]. SRCW / Miscanthus 85 / 90 % efficient. Indirect emissions associated with boiler construction and heating system installation and operation not assessed.

Transport and processing Direct and indirect emissions associated with processing (e.g. oil refining) and transport (e.g. truck emissions, gas leakage) [b].

Combustion Direct emissions of CO2, CH4 and N2O [e]. Oil/ gas 85 / 90 % efficient. No indirect boiler construction, or heating system installation and operation, emissions.

Distribution Transmission losses according to [f].

99

Comparable fuelchain emissions: kg CO2 eq. kWhth-1 useful heat.

Heat conversion 100% efficient. No heating system installation and operation emissions.

Fig. 1. LCA boundaries of fuel-chain GHG emissions for different heat sources, and literature data sources. (a) Styles and Jones (2007b); (b) Gustavsson and Karlsson (2002); (c) Grogan and Matthews (2001); (d) van Loo and Koppejan (2003); (e) McGettigan et al. (2006); (f) Howley et al. (2006).

2.2. Energy-crop supply and combustion It is assumed that destocked grassland and set-aside are associated with no net GHG emissions or soil C sequestration (on the basis that set-aside is usually rotated and therefore subject to regular tillage). When SRCW or Miscanthus displace set-aside, there is a soil C sequestration effect equivalent to 0.61 and 1.16 t C ha1 a1 (continues for 100 years), based on measurements and modelling by Grogan and Matthews (2001). It is assumed that there is no net soil C change when energy-crops are planted on grassland. For comparison, average cattle and sheep rearing GHG emissions were assumed to represent the emission reductions attributable to destocking, on a per hectare basis. Following from Gigler et al. (2004), it was assumed that covered outdoor storage of bale-harvested SRCW for 6 months was adequate to reduce moisture content from the 55% wet-weight typical at harvest to 20% or less. Similarly, following Lewandowski et al. (2000), it was assumed that covered outdoor storage of chopped or baled Miscanthus was adequate to bring moisture content down to less than 20%. These are important assumptions as they negate the need for costly forced drying of harvested biomass (Gigler et al., 2000) before it can be utilised in small-scale boilers. Van Loo and Koppejan (2003) attribute an energy consumption of 54 MJ t1 DM for wood chipping. An identical energy requirement is assumed for Miscanthus chopping, supplied by diesel combustion.3 Similarly, the 3

A lower heating value of 35.9 MJ L1 was used (Dalgaard et al.,, 2001), and emissions were calculated based on 1 kg (1.198 L) diesel combustion emitting 3.767 kg CO2 eq., including indirect emissions (Flessa et al., 2002).

21 kJ energy required to pelletise each MJ (energy content) of wood detailed in Gustavsson and Karlsson (2002) was applied to Miscanthus pelleting, and supplied by electricity from the national grid.4 At 20% moisture content, energycrop biomass has a lower heating value of approximately 18 GJ t1 DM (van Loo and Koppejan, 2003), and this is applied in the LCA. Boiler conversion efficiencies to useful heat are assumed to be 85% for oil and wood-boilers, 90% for gas and Miscanthus pellet boilers, 100% for electric heating elements and 330% for electric heat pumps. Direct combustion emissions for biomass, gas and oil were based on national reporting data (McGettigan et al., 2006). Only CH4 and N2O direct-combustion emissions were considered for biomass, as ‘young’ biomass CO2 emission represents cycling of atmospheric CO2. 2.3. Indicative scenario A simple scenario was constructed to indicate the scale of GHG emission reductions possible from utilisation of energy-crops as a source of heat. The scenario was run with either SRCW or Miscanthus as the sole feedstock, to compare the two crops. It was assumed that SRCW woodchips or Miscanthus pellets could replace oil, gas and electric heating in equal proportion, within 7.5%5 of the 1,469,500 households registered in Ireland as of 2006 (CSO, 2007)—i.e. displacement of each fossil-heat source in 2.5% of households. Average household heat consumption is 4 GHG burden of 0.624 kg CO2 eq. kWh1 delivered (Howley et al., e 2006). 5 The figure of 7.5% penetration by wood-heat in domestic households, displacing equal oil, gas and electric heat, was chosen merely as an indicative, feasible example.

ARTICLE IN PRESS D. Styles, M.B. Jones / Energy Policy 36 (2008) 97–107

100

GHG emissions (kg CO2 eq. ha-1)

6000

4000

2000

0

Miscanthus

SRCW

-2000

-4000 *Potential soil C sequestration, on tillage land

Cattle

Sheep

*Soil C seq.

Soil prep + planting

Maintenance

Harvest

Enteric fermentation

Housing + feed

Soil emissions

Other indirect

-6000 Land use Fig. 2. Land-use GHG emissions attributable to Miscanthus and SRCW cultivation, and typical cattle and sheep rearing systems, calculated in Styles and Jones (2007b).

21,249 kWhth a1, or 76.50 GJth a1 (SEI, 2006). Identical fuel displacement was considered to occur in commercial and public sector buildings, on the basis of lower overall heating demand from these sectors, but greater convenience and cost-savings for wood-heat in larger buildings (Styles and Jones, 2007a). It was assumed that energy crops would be cultivated on destocked grassland and set-aside in the ratio of 2:1, with set-aside-grown biomass SRCW displacing gas and oil heat, and grasslandgrown biomass displacing electric, gas and oil heat (Box 1).

Box 1 National energy-crop heat-production scenario.

3. Results

Displaced fuel: 186 ML heating-oil, 162 Mm3 natural gas, 1575 GWh electricity (equates to 7.5% domestic heating energy, plus an identical displacement of public/commercial heating energy) Heat produced: 4728 GWhth a 1

3.1. Net fuel-chain emissions

Either: Land area:

Fig. 3 compares fuel-chain GHG emissions for SRCW, Miscanthus, oil, gas and electric heat. For SRCW and Miscanthus, these equated to 0.045 and 0.062 kg CO2 eq. kWh1 th , compared with 0.248, 0.331 and 0.624 kg CO2 eq. kWh1 th for gas, oil and electric heat. Consequently, SRCW and Miscanthus heat emissions were 86% and 81% lower than for oil heating, 81% and 75% lower than for gas heating, and 93% and 90% lower than for electric heating, respectively. Potential energy gains achievable using electricity through heat pumps would result in fuelchain emissions of 0.189 kg CO2 eq. kWhth—still three to four times higher than for Miscanthus and SRCW heat. Energy-crop fuel-chain emissions were dominated by cultivation, which accounted for 79% and 61% of SRCW and Miscanthus heat emissions. Cultivation emissions were similar when expressed per DM tonne of combustible SRCW and Miscanthus, at 153 and 166 kg CO2 eq., respectively. However, Miscanthus emissions included a 23% contribution from pelleting (‘indirect’ category in Fig. 3), which accounted for most of the difference with SRCW heat emissions. Indirect emissions were

Combustible biomass: National GHG reduction: Or: Land area:

Combustible biomass: National GHG reduction:

SRCW 125,430 ha SRCW displacing 83,620 ha grassland and 41,810 tillage 1.107 Mt a 1 DM SRCW 1.765 Mt a

1

CO2 eq.

Miscanthus 89,092 ha Miscanthus displacing 59,353 ha grassland and 29,676 ha tillage 1.042 Mt a 1 DM Miscanthus 1.687 Mt a

1

CO2 eq.

relatively small for oil and natural gas heat production, accounting for 4.7% and 5.8%, respectively. Natural gas transport contributed 4.4% towards total gas heating emissions.

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0.7 Direct

CO2 eq. / kWh heat

0.6

Transport

0.5

Indirect Cultivation

0.4 0.3 0.2 0.1 0 Nat. gas

Gasoil

Kerosene

Electric

ElectricHP

SRCW

Misc. pellets

Fuel Fig. 3. Fuel-chain life-cycle emissions for natural gas, gasoil, kerosene, electric (standard resistance and heat pump conversion; electric-heat emissions specific to Irish fuel-mix, conversion and transmission efficiencies), SRCW and Miscanthus heat.

Table 1 Heat production, avoided heat emissions and land-use emissions change, when SRCW and Miscanthus displace destocked grassland and set-aside, expressed per hectare and per GJth heat produced Energy crop

Fuel replaced

Miscanthus Elec. Oil Gas SRCW

Elec. Oil Gas

Ag. Heat prod. Soil CO2 seq. (kg replaced (GJth ha1 a1) CO2 eq. ha1 a1)

Heat GHG red.a (kg Ag. GHG red. (kg CO2 eq. ha1 a1) CO2 eq. ha1 a1)

Total CO2 eq. Net heat emissions red. (kg ha1 a1) (kg CO2 eq. GJ1)

S’Aside Grass S’Aside Grass S’Aside Grass

191 191 191 191 191 191

4265 0 4265 0 4265 0

31,860 31,860 15,343 15,343 11,171 11,171

2326 1938 2326 1938 2326 1938

34,187 29,922 17,669 13,404 13,497 9232

5.6 17.3 5.6 17.3 5.6 17.3

S’Aside Grass S’Aside Grass S’Aside Grass

136 136 136 136 136 136

1881 0 1881 0 1881 0

23,194 23,194 12,155 12,155 9017 9017

535 1346 535 1346 535 1346

23,729 21,848 12,690 10,809 9552 7671

1.5 12.6 1.5 12.6 1.5 12.6

5237 3751

5237 3751

Extensification Cattle Sheep a

Based on net energy-crop heat GHG emissions, minus cultivation emissions (considered under ‘Agricultural GHG reduction’).

Table 1 displays whole fuel-chain GHG emissions and emission reductions arising from the use of energy-crop biomass in heat production. When SRCW and Miscanthus are grown on tillage land, predicted soil C sequestration equivalent to 1881 and 4265 kg CO2 ha1 a1 exceed cultivation emissions of 1346 and 1938 kg CO2 eq. ha1 a1, respectively, resulting in net land-use-change GHG emission reductions. This results in cultivation contributing negatively (i.e. acting as a net CO2 sink) in the energy-crop fuel chains where tillage is displaced. Consequently, each GJ of heat produced from energy-crops displacing tillage land is associated with a net GHG emission reduction, of 5.6 and 1.5 kg CO2 eq. for Miscanthus pellet and SRCW wood-chip heat, respectively (Table 1).

3.2. Combined emission reductions Cultivation on destocked grassland results in land-use emission increases corresponding to life-cycle cultivation emissions in Fig. 2. The net annual combustible yields of 8.8 and 11.7 t DM ha1 a1 for SRCW and Miscanthus equate to annual useful heat production of 191 and 136 GJth ha1, respectively. These in turn equate to displaced heating emissions of 23,190 and 31,860 kg CO2 eq. ha1 a1 where SRCW and Miscanthus displace electric heat, 12,155 and 15,343 kg CO2 eq. ha1 a1 where SRCW and Miscanthus displace oil heat, and 9017 and 11,171 kg CO2 eq. ha1 a1 where SRCW and Miscanthus displace gas heat, respectively. Thus, total emission

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reductions per hectare converted to energy-cropping vary considerably, from 7671 kg CO2 eq. ha1 a1 where SRCW displaces grassland and gas heat, to 34,187 kg CO2 eq. ha1 a1 where Miscanthus replaces tillage and electric heat (Table 1). The net land-use GHG emission increases where energy-crops are grown on destocked grassland offset between 6% (SRCW displacing electric heating) and 17% (Miscanthus displacing gas heating) of avoided heat emissions (Table 1). 3.3. Potential national reductions and sensitivity The indicative national scenario of 7.5% of all households converting from oil, gas and electric heat in equal quantity to either SRCW wood-chip or Miscanthus pellet heat, with equal commercial displacement, would result in useful heat production of 4728 GWh a1 (Box 1). In total, 1.86 ML kerosene, 1.62 Mm3 natural gas and 1575 GWh electricity usage would be replaced with either 1.107 Mt DM SRCW wood-chip or 1.042 Mt DM Miscanthus pellets, per annum. The avoided conventional-heating GHG emissions would equate to 1.896 Mt CO2 eq. a1, just over half of which (0.983 Mt) is attributable to avoided electricity consumption. Including SRCW wood-chip and Miscanthus pellet fuel-chain GHG emissions, the net national GHG emission reduction from the indicative scenario is either 1.765 or 1.687 Mt CO2 eq. a1 depending on sole utilisation of either SRCW or Miscanthus. These net emission reductions represent 93% and 89%, respectively, of displaced conventional heat emissions. Net landuse-change emissions equate to an increase of 90,158 t CO2 eq. a1 for the 125,430 ha that would need to be converted to SRCW cultivation, or 46,032 t CO2 eq. a1 for the

89,092 ha that would need to be converted to Miscanthus cultivation. The areas required for SRCW and Miscanthus cultivation (Box 1) equate to 12% and 8.5% of tillage area; 2% and 1.4% of grassland area; 2.9% and 2.1% of Ireland’s total agricultural land area. Table 2 indicates the results of sensitivity analyses performed for the indicative national scenario, assuming either SRCW or Miscanthus as the sole fuel. Varying transport distance has negligible impact on fuel-chain GHG emissions, with a 50% variation in transport distance causing SRCW and Miscanthus fuel-chain emissions to vary by less than 0.01 kg CO2 eq. kWh1 th (Table 2). If cultivation emissions per tonne DM produced increased by 50%, each kWhth produced by SRCW wood-chip and Miscanthus pellets would be associated with net GHG emissions of 0.063 and 0.081 kg CO2 eq., respectively. Compared with gas heat, these emissions would still represent decreases of 78% and 71%, respectively. Reducing yields by 50% was estimated to correspond with cultivation emission reductions of 37% and 40% per hectare for SRCW and Miscanthus, and result in slightly increased life-cycle emissions of 0.054 and 0.070 kg CO2 eq. kWh1 th , respectively (Table 2). Life-cycle emissions would decrease slightly to 0.042 and 0.060 kg CO2 eq. kWh1 th , for SRCW and Miscanthus heat, under the higher yield scenario. 4. Discussion 4.1. Land-use emissions SRCW and Miscanthus cultivation emissions are dominated by the manufacture and post-application soil N2O

Table 2 Variation in GHG emissions per hectare and per kWhth heat produced, and indicative national scenario area and emission reduction, according to variation in yields, cultivation emissions and transport distance by 750% Cultivat. emis. (kg CO2 eq. ha1 a1)

Trans. dist. (km)

Gross heat emis.a (kg CO2 eq. kWh1 th )

Net heat emis. red.b (kg CO2 eq. ha1 a1)

Land-use GHG red. (kg CO2 eq. ha1 a1)

Area GHG red. (kg CO2 eq. ha1 a1)

Subst. area (ha)

Total GHG red. (Mt CO2 eq. a1)

Miscanthus 50% +50% 11.7 11.7 11.7 11.7

1169 2697 50% +50% 1938 1938

150 150 150 150 50% +50%

0.070 0.060 0.043 0.081 0.062 0.063

9729 29,187 19,458 19,458 19,416 19,500

252 1275 453 1485 517 517

9981 27,912 19,911 17,973 18,899 18,984

178,184 59,395 89,092 89,092 89,092 89,092

1.778 1.658 1.774 1.601 1.684 1.691

SRCW 50% +50% 8.8 8.8 8.8 8.8

839 1852 50% +50% 1391 1391

60 60 60 60 50% +50%

0.054 0.042 0.028 0.063 0.045 0.046

7394 22,183 14,789 14,789 14,775 14,802

212 1225 46 1392 719 719

7182 20,957 14,743 13,397 14,056 14,084

250,860 83,620 125,430 125,430 125,430 125,430

1.802 1.752 1.849 1.680 1.763 1.767

Yield (DM t ha1 a1)

a

Gross heat emissions, based on fuel life-cycle. Based on net heat emissions (minus cultivation emissions considered under land-use change).

b

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release associated with modest fertiliser-N application. For example, the plantation-lifetime average fertiliser N-application rate of 87.5 kg ha1 a1 contributed 68% towards Miscanthus cultivation emissions (Styles and Jones, 2007b). The increase in cultivation emissions associated with higher yields in the sensitivity analyses was largely attributable to increased fertiliser application. Utilisation of liquid (e.g. brewery waste, waste-water) and solid (e.g. sewage sludge) wastes could reduce the net life-cycle emissions associated with energy-crop cultivation, and enhance revenues (Perttu and Kowalik, 1997; Borjesson, 1999; Rosenqvist and Dawson, 2005; Styles et al., accepted). Recently, trial SRCW plantations in Ireland have been planted and are being utilised to treat brewery waste (Clearpower, 2006). Thus, emissions arising from energy-crop cultivation could be reduced below the values applied here, although these emissions are already low compared with the livestockrearing and dairying, which dominate Irish agricultural production. Soil C sequestration offset a substantial proportion of overall cultivation emissions within the indicative scenario, accounting for 78,652 or 126,561 t CO2 eq. where SRCW and Miscanthus displace set-aside. Soil C accumulation rates were based on Grogan and Matthews (2001), and will be dependent on numerous site-specific factors such as initial soil C content, soil characteristics such as texture and moisture content, aspect, climate and biomass productivity. Whilst some studies have observed a rapid increase in organic matter mineralisation and associated CO2 and N2O emissions after grass or legume cover crops have been incorporated into the soil (Flessa et al., 2002; Grigal and Berguson, 1998; Jug et al., 1999), the long rotation and extensive fine-root system of SRCW, and the below-ground rhizome mass of Miscanthus, are expected to contribute to long-term below-ground C storage equal to or greater than under grassland systems (Grigal and Berguson, 1998; Zan et al., 2001; Lettens et al., 2003). Long-term experimental research is required to verify this under Irish conditions. 4.2. Heat-production GHG emissions Biomass heating is not C-neutral. However, life-cycle GHG emissions for SRCW and Miscanthus fuel chains represented decreases of between 75% and 93%, per unit of useful heat produced, compared with conventional heating systems. Crucially, SRCW and Miscanthus fuel-chain emissions were less than one quarter of those for natural gas—the least C-intensive conventional heating fuel—and considerably lower than efficient electricity utilisation via heat pumps. Nationally, emissions associated with electric heating should decline with the forecast increases in gas and wind electricity generation (Howley et al., 2006; Conlon et al., 2006). Internationally, emissions associated with electric heating will vary substantially depending on the fuel mix and conversion efficiencies. As an indication of this effect, and to put heating emissions into context,

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Hondo (2005) attributed life-cycle GHG intensities of 0.975, 0.742, 0.519, 0.029, 0.024 and 0.011 kg CO2 eq. kWhe to coal, oil, liquid natural gas (combined cycle), wind, nuclear and hydroelectric electricity generation, respectively, in Japan. In countries where electricity generation is dominated by the latter three sources, electric heating (particularly if heat pumps are employed) could be superior, in terms of GHG avoidance, to Miscanthus or SRCW heat. Using these crops to produce heat is more efficient, and consequently results in lower emissions (but also lower emission avoidance), compared with co-firing with peat and coal for electricity generation. Styles and Jones (2007b) calculated life-cycle emissions of 0.131 and 0.132 kg CO2 eq. kWh1 for Miscanthus and SRCW elece tricity, compared with 1.150 and 0.990 kg CO2 eq. kWh1 e for peat and coal electricity generation, respectively. Whilst cultivation, and ultimately fertiliser-N application, dominates energy-crop fuel-chain emissions, soil C sequestration on tillage land could exceed these emissions, resulting in heat produced from SRCW and Miscanthus grown on such land being better than C-neutral. Pelleting and additional transport requirements increased fuel-chain emissions for Miscanthus compared with SRCW. Forced drying of wood-chips could increase SRCW heat emissions (Gigler et al., 2000), although large, commercial-scale boilers are capable of using wet wood-chips (with reduced lower heating value), and may also be able to use chopped Miscanthus (experimentation is ongoing). Coordinated supply strategies will minimise emissions, but more essentially will reduce costs. 4.3. National emission avoidance potential and sensitivity The relatively low population density of Ireland, with hundreds of towns scattered across a largely agricultural landscape, and low forest cover, present a particularly promising opportunity for energy-crop utilisation. In the relatively conservative indicative national scenario developed here, significant net GHG emission reduction equivalent to approximately 2.5% of 2004 national emissions required just 2.9% or 2.1% of national agricultural land area, depending on sole utilisation of SRCW or Miscanthus. Whilst SRCW achieves lower combustible yields than Miscanthus, and thus requires a greater land area for a given output, it is potentially suitable for more marginal agricultural soils (further agronomic experimentation is required in Ireland), and the wood does not need to be pelleted prior to combustion, making it a more likely fuel for heat production in the short term. Logistical and economic issues surrounding pelleting may be resolved in response to a possible consolidation of the emerging market in biomass fuels. In the meantime, the high yields and soil C sequestration potential of Miscanthus may be realised through utilisation as a feedstock for peat power stations, as outlined in Styles and Jones (2007b). Combining the compatible indicative scenario of

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energy-crop co-firing outlined in that paper with the scenario presented here results in a total national GHG emission reduction of 3.67 Mt CO2 eq. a1 (5.4% of 2004 emissions) through energy-crop cultivation on 4.6% of national agricultural land area. This would represent approximately half the emission reduction required for Ireland to comply with its Kyoto commitment—equivalent to the purchase of approximately h180 M of CDM credits over the 2008–2012 commitment period.6 Sensitivity analyses indicate remarkably little variation in the net GHG emission savings achievable through the indicative scenario, according to variation in yield and cultivation emissions. In part, this is because fertiliser application, the dominant source of cultivation emissions, was varied in proportion to yield in the cultivation LCA. Lower yields resulted in lower area-based emissions, but slightly higher emissions per tonne biomass produced, and thus per kWhth, and substantially lower area-efficiency of emission avoidance. Yield is more critical to the economics (Styles et al., accepted) and feasibility, rather than the net GHG emission savings, of energy-crop utilisation. Even with substantial cultivation emission increases, emission avoidance from displaced conventional heating would be large, and thus national emission reductions would not be greatly impacted. Although transport is often cited as a significant source of life-cycle emissions for various products, it made a minor contribution to SRCW and Miscanthus heat fuel-chains. Thus, the GHG emission avoidance potential of energy-crop heat production appears robust to variation in key parameters. The major determinant of GHG emissions savings arising from energy-crop heat production will be the fuel displaced. In Ireland, wood-heat could offer substantial financial savings compared with oil, gas and, especially, electric heating (Styles and Jones, 2007a). Here, GHG emission savings were almost three times higher where wood-heat displaced electric heat, compared with gas heat. However, feasibility issues (electric heat is often used in apartments) may restrict the potential substitution of electric heat with wood-heat. The continued high rate of construction in Ireland (93,419 new dwellings built in 2006: CSO, 2007) means that there is scope for considerable GHG emission avoidance through incorporation of centralised heating, or combined heat and power (CHP), systems powered by biomass in new apartment buildings (although increased application of CHP, even without biomass firing, could realise substantial emissions reductions given the high GHG intensity of Irish electricity). This may require central or local government intervention, for example through planning requirements. In the meantime, substitution of oil heating is a low-tech, financially and environmentally attractive option that demands only

6

Current government policy to comply with Kyoto commitment, and based on current trading prices for 2008–2012 delivered CDM credits (PointCarbon, 2007).

the initiation of commercial wood-chip production and a continuation of current oil prices. 4.4. Limitations and additional considerations National boundaries were not considered in LCA, given that GHG emissions are an international issue. Some of the life-cycle emissions considered here will occur outside Ireland, in particular those associated with oil and gas extraction and transport, and fertiliser manufacture and machinery construction considered for energy-crop cultivation. Excluding these emissions from the calculations would reduce the national life-cycle emissions attributable to SRCW and Miscanthus cultivation significantly, although this would have little impact on displaced heat emissions, which are dominated by direct combustion. Applying a national boundary to LCA would result in lower land-use emissions, and emission avoidance slightly greater than that calculated here for the indicative national scenario. The scenario presented here did not involve the displacement of any agricultural production, so should not contribute to increasing global land-use competition between energy and food crops (Pimentel and Patzek, 2005; Cassman, 2007). There may be potential conflict between utilisation of set-aside land to cultivate these energy-crops, or liquid biofuel crops such as sugar-beet or rape-seed, which may be encouraged to comply with the EU Biofuels Directive (2003/30/EEC). From an environmental perspective, SRCW and Miscanthus utilisation would be preferable to sugar-beet and rape-seed utilisation owing to the former crops’ superior energy balances (typical rape-seed and sugar-beet oil-energy yields are around 50 and 120 GJ ha1 a1, respectively) and lower life-cycle emissions. Pimentel and Patzek (2005) argue that energy-crop ethanol production in the US is a highly inefficient use of resources (largely owing to high calculated energy-inputs for feedstock processing) that reduces world food supplies, but refer to the efficient energy balances of pelletised switchgrass for heating. Combined with the competitive economics predicted for Miscanthus and SRCW cultivation (Styles et al., accepted), and SRCW heat production (Styles and Jones, 2007a), we would suggest that heat production from these crops could offer an efficient ‘no pain’ GHG emission reduction option for Ireland, if fuel prices remain at current levels. It is important to note that this paper is limited in scope to the GHG emission implications of Miscanthus and willow heat production. Further work will combine LCA and economic data, and attribute appropriate monetary values to avoided GHG emissions, in order to more comprehensively assess the efficiency of energy-crop utilisation as a policy option. Ultimately, there is a need to extend integrated research—combining LCA and costbenefit-analyses—to the multitude of alternative GHG mitigation options, thus enabling a quantitative comparison. There may be more efficient or more easily realised

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options (e.g. home insulation improvements; domestic solar-panels; use of forestry residues) that should be prioritised. For example, Murphy and McCarthy (2005) suggest that lignocellulosic digestion of waste-paper provides an economically and environmentally superior (near-term) feed-stock for ethanol production compared with sugar-beet. As a land-use option, forestry may be associated with multiple amenity and product uses, including energy generation as a final step. Whilst fuel-chain GHG emissions calculated here for energy-crop heat production should be applicable internationally, the attractiveness of energy-cropping as a landuse strategy for GHG avoidance will vary according to (i) the fuels used for heat production; (ii) the relative GHG intensity of electricity generation (Section 4.2); and (iii) the relative abundance of agricultural land. The situation in many EU countries, adapting to the reformed CAP, and largely dependent on oil, gas and electricity for heating, is likely to be similar to Ireland. However, Ireland does have a particularly large proportion of ‘surplus’ agricultural land, with consequently low (foregone) opportunity costs associated with potential utilisation for energy-cropping. Densely populated and developing countries are likely to have considerably less surplus agricultural land, and higher opportunity costs, especially where climate and soils enable multiple annual harvests. Food production, and alternative energy-crops such as sugar-cane, are likely to be prioritised in such countries. 4.5. Policy implications The increase in land-use emissions associated with cultivating energy-crops on destocked grassland highlights the importance of a multi-sectoral perspective for assessing national GHG emission reduction strategies. The net landuse emission increases of 90,158 or 46,032 t CO2 eq. calculated for SRCW and Miscanthus in the indicative scenario would have a marginal impact on the 2.9 Mt CO2 eq. a1 decrease in agricultural emissions forecast to occur between 1990 and 2010 as a result of large-scale destocking, and are minor compared with avoided fossil- and electricheat emissions of 1.896 Mt CO2 eq. Per hectare GHG emission reductions attributable to energy-crop heat production range from 1.5 to 9 times greater than emission reductions attributable to cattle and sheep destocking alone. The magnitude of destocking anticipated following EU CAP reform creates scope for both substantial energycrop cultivation and large-scale extensification of livestock production. Good agricultural planning could ensure that energy-crop cultivation complements remaining livestock production, through utilisation of animal waste as fertiliser, and locating on buffer strips adjacent to vulnerable water bodies, where compliance with the EU Water Framework Directive (200/60/EC) may restrict conventional agricultural uses. The relatively low fertilisation requirements, efficient nutrient cycling and dense root-mat of SRCW and Miscanthus should mitigate potential negative impacts

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of continued agricultural production on soil and water quality. However, there remains a need for potential biodiversity and landscape impacts to be assessed in an Irish context. Optimising the balance of potential positive and negative impacts in the context of sustainable development will require a coordinated spatial strategy, integrating both agricultural and end-user sectors, and considering environmental, economic and social implications. The projected economic competitiveness of energy-crop biomass as heating fuel is based on current, historically high oil and gas prices. Previous studies, conducted when fossil-fuel prices were lower, indicated low potential for energy-crop utilisation (e.g. van den Broek et al., 2001; SEI, 2004), and specifically wood-heat (Hoyne, 2001) in Ireland. Meanwhile, some authors claim that energy-crop utilisation, particularly as liquid biofuel, has limited global potential and is economically unsound, benefiting from explicit and hidden subsidies (e.g. Pimentel and Patzek, 2005). Realisation of potential (so far theoretical for Ireland) benefits of energy-crop heat outlined in this paper and others, under current market conditions, has so far been subdued owing to three main factors: (i) the long leadin time (4 years from planting to first harvest for SRCW) and commitment period (23 years for SRCW7) for energy-crop plantations; (ii) the relatively high investment costs for energy-crop producers and end-users8; and (iii) uncertainty about future energy prices. Market uncertainty combined with modest returns, and poor contemporary quantitative information (regarding energy-crops and alternative GHG avoidance options), deters both investors and policy makers from committing to energy-crop heat-production strategies. Kopetz (2007) laments the relatively low priority given to biomass heating within EU renewable-energy policy, highlighting the high conversion efficiencies compared with biomass use for electricity generation and transport fuels. Previous ‘false-dawns’ for alternative fuels may also linger in the consciousness of policy-makers. Helby et al. (2006) analysed the experience of willow cultivation in Sweden, where initial high expectations encouraged rapid establishment to supply high biomass demand in the early 1990s, but were followed by widespread farmer dissatisfaction and even plantation abandonment. Despite economic returns failing to match expectations as Swedish wood-chip prices fell in the late 1990s, most farmers cite agronomic rather than economic reasons for their dissatisfaction— weed control, frost impediments and dry soils. Helby et al. conclude that full establishment grants encouraged opportunistic and poorly planned planting, often on inappropriate soils.9 This experience projects a note of caution. 7 To realise the gross margins identified in Styles et al. (accepted)— payback period shorter. 8 Plantation establishment costs up to h3000 ha1, whilst domestic wood-boilers cost up to h10,000 to install (h4200 government subsidy available). 9 Planting location and management (e.g. weed clearance) critical for successful establishment and long-term productivity of SRCW.

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Policies to promote energy-crop cultivation should ensure that suitable locations are selected for planting, based on sound agronomic research, and should be accompanied by widely disseminated agronomic and economic advice for farmers. Production-related subsidies may encourage appropriate planting and management practices. It is important that the Swedish experience is heeded, although there are signs that market conditions—reflecting fossilfuel supply issues attributable to extraction capacity, costs and geopolitics, and carbon-pricing—will ensure more sustained momentum behind biomass energy than previous ‘false-dawns’. Ultimately, practical experience will be necessary to fully assess the potential of relatively novel energy-crops such as Miscanthus and willow, which could improve considerably with advances in crop breeding and management techniques (e.g. McLaughlin and Kszos, 2005). 5. Conclusions Heating fuel-chain emissions for SRCW and Miscanthus were calculated at 0.045 and 0.062 kg CO2 eq. kWhth, respectively, representing a reduction of between 75% and 93% compared with oil, gas and electric heating fuelchains. Cultivation emissions dominate GHG emissions over the energy-crop fuel-chains, reducing the GHG emissions avoided through displacement of conventional heating by 6–17%. However, where SRCW and Miscanthus are planted on tillage land, predicted soil C sequestration could result in heat production better than C-neutral. Per hectare, potential fuel-chain emission reductions range from 7.7 to 34.2 t CO2 eq. a1, and are 1.5–9 times greater than emission reductions attributable to cattle and sheep destocking alone. These results were extrapolated up to an indicative national scenario in which gas, oil and electric heat were displaced in equal measure among 7.5% of households, with equal commercial/public sector displacement. The net national emission reduction equated to either 1.765 or 1.687 Mt CO2 eq. a1 depending on sole utilisation of either SRCW or Miscanthus (2.6% or 2.5% of 2004 emissions), yet required just 2.9% or 2.1% of national agricultural land area. These emission reductions were not particularly sensitive to variations in cultivation emissions or yields, and were insensitive to variation in biomass transport distance. The higher yields of Miscanthus could ultimately result in greater emissions savings per hectare of land used for cultivation, compared with SRCW, but the uncertain economics of pelleting are likely to delay realisation of this potential. The large potential financial (Styles and Jones, 2007a) and emission benefits of wood-heat compared with electric heat (based on Irish electricity-generating fuel mix) may require government intervention to be fully realised. For example, large apartment buildings could be required to install communal, biomass heating (or CHP) systems, with administrative burdens likely to be significantly outweighed by substantial environmental and

economic benefits. Based on the small proportion of agricultural land area required in the indicative scenario, and high emission avoidance per hectare appropriated, there is scope for large reductions in national GHG emissions through energy-crop utilisation in Ireland. These results may be applicable to other EU countries that rely heavily on oil, gas or fossil-based electricity for heat generation, and have surplus agricultural land following CAP reforms. There is an urgent need for extensive contemporary life-cycle and economic research to quantitatively assess the potential of alternative GHG avoidance options, to compare with energy-crop utilisation and to enable rational policy prioritisation. Acknowledgements The authors are grateful for ERTDI funding received to undertake work presented in this paper, provided by the Irish Environmental Protection Agency. The comments and suggestions of anonymous reviewers are also appreciated. References Binfield, J., Donnellan, T., Hanrahan, K., Westhoff, P., 2003. The Luxembourg CAP Reform Agreement: Implications for EU and Irish Agriculture. Teagasc, Dublin, pp. 1–79. Borjesson, P., 1999. Environmental effects of energy crop cultivation in Sweden—I: Identification and quantification. Biomass and Bioenergy 16, 137–154. Cassman, K.G., 2007. Climate change, biofuels, and global food security. Environmental Research Letters 2, 011002. Central Statistics Office (CSO) web site /http://www.cso.ieS. Last accessed May 2007. Clearpower homepage /http://www.clearpower.ie/S. Accessed April 2006. Clifton-Brown, J.C., Neilson, B., Lewandowski, I., Jones, M.B., 2000. The modelled productivity of Miscanthus  giganteus (GREEF et DEU) in Ireland. Industrial Crops and Products 12, 97–109. Conlon, M.F., Basu, M., Jayanti, N.G., Gaughan, K., 2006. A survey of the installed wind generation capacity in Ireland. p. 55 In: Conference Proceedings for Renewable Energy in Maritime Climates, DIT Bolton Street, 26–28 April 2006, p. 55. DAF, 2007. Minister Coughlan announces details of new bioenergy initiatives. /http://www.agriculture.gov.ie/index.jsp?file=pressrel/2007/ 18-2007.xmlS Accessed February 2007. Dalgaard, T., Halberg, N., Porter, J.R., 2001. A model for fossil energy use in Danish agriculture used to compare organic and conventional farming. Agriculture, Ecosystems and Environment 87, 51–65. Donnellan, T., Hanrahan, K., 2003. Greenhouse Gas Emissions from Irish Agriculture. Teagasc, Dublin. Flessa, H., Ruser, R., Dorsch, P., Kamp, T., Jimenez, M.A., Munch, J.C., Beese, F., 2002. Integrated evaluation of greenhouse gas emissions (CO2, CH4, N2O) from two farming systems in southern Germany. Agriculture Ecosystems and Environment 91, 175–189. Gigler, J.K., Meerdink, G., Hendrix, E.M.T., 1999. Willow supply strategies to energy plants. Biomass and Bioenergy 17, 185–198. Gigler, J., van Loon, W.K.P., Vissers, M.M., Bot, G.P.A., 2000. Forced convective drying of willow chips. Biomass and Bioenergy 19, 259–270. Gigler, J.K., van Loon, W.K.P., Sonneveld, C., 2004. Experiment and modelling of parameters influencing natural wind drying of willow chunks. Biomass and Bioenergy 26, 507–514.

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