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3. Potential of Biomass Feedstocks for Energy Generation in Scotland

3.1 Background

3.1.1 Estimating Bioenergy Potential

There have been many recent attempts to estimate bioenergy potential at continental and even global scales, with a divergent range of values being proposed for equivalent areas. The IPCC Third Assessment Report, for example, estimated a total annual global potential from energy crops in the order of 440 EJ (1 EJ = 1 x 10 ¹⁸ J) by 2050. A recent report by Sims et al. (2006), on the other hand, suggested that the realistically achievable potential (by 2025) might be 2-22 EJ yr ^-1 globally (Table 3.1). Discrepancies in projected values for bioenergy potential result from different underlying assumptions about crucial parameters such as crop yield, energy value per fuel weight and the area available for growing crops. In this chapter, the potential of different biomass feedstocks is evaluated in terms of their physical productivity potential and their energy generation potential for Scotland. Results will be presented both in terms of theoretical maximum capacity, which assumes all suitable land area for production of a given crop will be dedicated to its production and there are no alternative markets for the crop, and in terms of achievable capacity based on more realistic assumptions, outlined in detail below. Imported feedstocks are not considered in this report.

Table 3.1: Literature Estimates of Global Bioenergy Potential from Biomass

Many factors have been highlighted as determinants of achievable bioenergy production. These include population growth, energy prices, food consumption, land-use patterns, competing markets for forestry/agricultural products and the existence of suitable biomass supply chains (Juergens 2005). In Scotland, as in much of Europe, population growth and food production are not major determinants, as population is relatively stable and agricultural surplus is the norm. The EU Biomass Action Plan ( EC 2005), for example, estimates that it is possible for the EU to double its biomass use for energy from 69 million tonnes oil equivalent (mtoe: 1 mtoe=11630 GWh) to 175 mtoe by 2010, without interfering in any way with food crop production or impacting on competing industries. By 2020, this would increase to 210-233 mtoe yr ^-1.

3.1.2 UK and Scotland Biomass Expansion Scenarios

Any scenarios involving future projections are subject to variable degrees of uncertainty as it is not possible to predict future changes with precision. Notwithstanding, it is important to use the information available at present to compare best estimates of future potential for different biomass energy options. The timescale envisaged by this report is up to 2020, as the predictive accuracy of potential estimates decreases progressively as the timescale increases. This time period has also been employed in other studies and proposed targets for biomass energy potential ( RCEP 2004, Bauen 2004, Schröter et al. 2005, EC 2005).

For the UK, the Royal Commission on Environmental Pollution has proposed a four-staged approach for the development of the bioenergy industry:

• 1) immediate future (2004-2012): energy crops utilize a relatively small proportion of set-aside land
• 2) short-term (2012-2018): area required for energy crops increases to an area equivalent to the amount of set-aside land
• 3) medium-term (2018-2025): area required for energy crops increases to an area beyond set-aside land
• 4) long-term (2025-2050): area of land increases to a significant proportion of the total available agricultural land

The first stage (2004-2012) would see an increased uptake in the use of low-grade timber, forestry residues, sawmill offshoots and agricultural residues, primarily in co-firing. At present, co-firing material is almost entirely imported, but regulations under the Renewables Obligation Scheme determine that progressively increasing proportions of purpose-grown indigenous energy crops be grown. In the second stage (2012-2018), energy crops become more important and co-firing remains an important use of biomass, while in the third stage (2018-2025) energy crops will have become established main crops and co-firing will have been largely phased out. Indeed, current rules for the Renewable Obligation Scheme make co-firing ineligible for ROCs beyond 2016, although these rules are currently under review. The fourth stage (2025-2050) represents a firmly established bioenergy industry with a developed network of district heating schemes CHP plants. Another recent study by Bauen et al. (2004) proposed target for 2020 whereby 25% of all available residues (forestry, agricultural and livestock) would be utilized for bioelectricity generation alone and 5% of the total crop, forest and woodland area would be dedicated to the growth of energy plantations. According to the authors of the study, adherence to this target would result in 15% of the electricity demand of OECD countries emanating from biomass sources. The FREDS Report (2005a) also advocates a phased approach for Scotland, where co-firing would be gradually replaced by bioelectricity, biomass-fuelled CHP and bioheat. The electricity and CHP markets would develop earlier than the bioheat market, as they can readily take advantage of the renewable obligations scheme already in place, whereas small-scale bioheat requires the establishment of an alternative incentives scheme, beyond which its popularity should expand rapidly ( FREDS 2005a).

3.1.3 Scenarios Used in This Study

Forestry and Agricultural Products/Residues

Energy generation potential will be presented in terms of theoretical and achievable potential. Estimates of current and future availability of Scotland's future wood fuel for bioenergy (from forestry, woodland management and sawmill co-products), taking into consideration competing industries, have recently been published and refinement of these figures is an ongoing process ( SDC 2005, FCS 2006). These volumes are considered the basis on which the figures of 'achievable potential' are based. For residues where published values of amounts available for bioenergy are not available, best estimates based on knowledge of competitive markets is used to estimate achievable potential. Whenever no informed estimates were possible, achievable potential by 2020 was taken to be 25% of the available residues, as suggested by Bauen et al. (2004).

Simple illustrative energy generation potentials were calculated for each technology from knowledge of the following basic parameters:

• Fuel calorific value: the amount of energy produced by the combustion of a unit weight of fuel.
• Fuel volumes: the theoretical and achievable volumes of fuel available, whenever possible presented in oven dried tonnes (odt).
• Conversion efficiency: For the sake of simplicity, a 30% conversion efficiency was assumed for electricity, although this may be quite high for stand-alone biomass electricity technology. For heat production, a conversion efficiency of 85% was assumed.
• Load factor: the average energy output of a generator over the course of a year divided by it total rated output. For simplicity, a load factor of 100% was assumed in this study. Clearly, this is not a realistic assumption but presents a maximum value which is comparable across different feedstock systems.

Energy Crops

Energy crop estimates are more uncertain as the market for them is just beginning to develop. To estimate energy crop potential in 2020, simple variants of the Bauen et al. (2004) and RCEP (2004) scenarios were used. It was assumed that energy crops would not replace standing forestry land in Scotland, but are only likely to replace agricultural cropland and woodland (non-forest) areas. It is understood, however, that there are no serious biophysical constraints that would prevent SRC from growing on rotational or permanent grassland. The total area under crops, fallow and set-aside in 2004 was 642,000 ha with a further 319,000 under woodland, representing a total of 961,000 ha on which energy crops could be grown. A 5% share of this total (48,050 ha) was taken to represent a similar value to that proposed by Bauen et al. (2004). To facilitate calculations, this figure was rounded up to 50,000 ha, assumed to be on set-aside land.

The second scenario for energy crop expansion was that proposed by RCEP (2004) where all set-aside land would be used for energy crop production. Set-aside land figures are variable and selecting a total set-aside area for 2020 is thus a very subjective process. For example, the total set-aside area in Scotland in 2004 was 71,700 ha, compared to 93,600 in 2003 (Scottish Executive 2005). The difference was due to a reduction in the Arable Area Payment Scheme for set-aside land as a result of the poor EU harvest of 2003. The figure selected for this report was 90,000 ha, which is close to the set-aside land area in 2003. Set-aside land is highly variable in its productivity, and due to this, yield values will be presented as ranges.

Planting of short rotation coppice for energy is only just beginning in Scotland, while energy grasses have only been planted on an experimental basis. The predicted yield and energy generation potential of these crops are best estimates based on the literature and are yet to be proven for Scottish conditions. It is important to emphasize that the generation potential figures presented in this chapter are very simple, being based on uncertain estimates of feedstock availability in many instances and on load factors that are clearly not realistic. They are presented with the purpose of comparing the potential of different feedstocks under a uniform set of conditions. They are not based on detailed analyses and are therefore not to be taken as definitive figures.

3.2 Current and Potential Availability/Production of Biomass Feedstocks in Scotland

3.2.1 Wood Fuel Resources

Forestry and Sawmill Co-products

Sixty percent of the UK's forestry resources are in Scotland. This equates to an area of 1.3 million ha, which is approximately 17% of the Scottish land area. Furthermore, the growth increment of Scotland's forest is currently increasing and is expected to peak in 15-20 years time (Scottish Industries Forest Cluster 2004). Improved management practice, however, should help to smooth the bulge in supply, an issue that is currently being investigated by the Scottish Forestry Commission and forestry industry (James Pendlebury, in oral evidence to Scottish Biomass Inquiry). This will result in lower peak volumes than those estimated in the Scottish Industries Forest Cluster report (2004).

Although current annual harvests stand at around 6 - 7 million m ³ yr ^-1 (Scottish Parliament 2006 a, Reid 2006), there is the potential for this rise to over 10 million m ³ yr ^-1 ( FREDS 2005), and the Forestry Commission Scotland estimates that yields of 8-9 million m ³ yr ^-1 could be sustainable. It is necessary to emphasize that the growth of other competing sectors must be taken into account. Preliminary findings from a wood fuel usage survey being carried out by the Forestry Commission Scotland suggest that if all currently planned developments (pulp and paper mills, bioenergy projects, sawmill expansion) come into existence, an annual harvest of 15.8 million m ³ (6.3 million odt yr ^-1) would be necessary (Reid 2006), a clearly unsustainable amount .

The Sustainable Development Commission for Scotland published the report Wood Fuel for Warmth (2005), with figures for wood fuel availability to 2020 which were adjusted from earlier work on the wood fuel resource in Britain prepared by the Forestry Commission (McKay 2003), but which incorporated several practical constraints. The most important wood fuel resources for Scotland appear to be small roundwood (small diameter wood that feeds the board, pallet and paper market) and sawlog by-products from the timber industry. Although all current harvested volume has a market but there is potentially under managed woodland in the private sector which could provide additional resource (Forestry Comission Scotland, personal communication). The authors presented their assessment of wood fuel availability according to three time periods (2005-2006, 2006-2011, and 2011-2016) and three distinct scenarios: 1) immediately available wood not utilized by competing sectors, 2) wood availability under a wood fuel sector growth scenario and 3) theoretical wood availability under the assumption that there were no alternative markets for the product. The results, summarised in Table 3.2, indicate that there is presently an immediate volume of ~ 720,000 oven dried tonnes, which could increase to over 1,000,000 odt by 2012 under a scenario of growth of the wood fuel sector. The wood sources included in the calculation were arboricultural wood, secondary wood generated by the wood processing industries, harvesting residues, wood from early thinnings and stands of low quality, roundwood (stem wood in 7-14 cm and 14-16 cm diameter classes) and sawlog material (stem wood in 16-18 cm and 18 cm + diameter classes).

Table 3.2: Wood Fuel Availability up to 2016 Under Three Different Scenarios

Source: SDC Scotland (2005).

The SDC study also provided disaggregated results for different Forestry Commission districts, with lowest immediate wood resource availability in the Northeast and highest availability in Galloway and the Scottish Borders. Under a scenario of wood fuel sector growth, however, Inverness and Tay would become the regions with greatest availability (see Figure 3.1).

Figure 3.1: Estimated Wood Fuel Availability in Different Regions of Scotland: (a) Immediate Availability in 2005 and (b) Availability in 2016, Accounting for Growth of Woodfuel Sector (in oven dried tonnes)

Source: Sustainable Development Commission for Scotland (2005).

The estimates from the SDC study were slightly lower than those published in the FREDS Biomass Energy Group ( BEG) Report (2005), which suggested there would be 5 million m ³ of wood available for bioenergy use by in the UK by 2020, 60% of which come from Scotland (3 million m ³) although this estimate was based only on resources from forestry. This is equivalent to approximately 1.2 million odt ( SDC 2005). The report estimated that this volume of wood could generate 440 MW of electricity, although the FREDS estimates are currently regarded as being optimistic and appears to have been based on the total estimated wood fuel volume for the UK rather than for Scotland.

Table 3.3 summarises the range of estimates of potential electricity and heat generation from wood fuel (not including recycled wood) in Scotland, based on the wood fuel volumes presented in the SDC and FREDS reports. For the sake of consistency with the remainder of the feedstocks described in the chapter, these have been adjusted so that they assume a conversion efficiency of 30% for electricity and 85% for heat. It must be stated that these are simple calculations based on the wood volume data from the above-cited reports and should be treated with caution.

Table 3.3: Wood fuel Energy Generation Potential to 2020

1) Lower wood fuel volume limits from SDC 2005, higher limits from FREDS 2005 (based on 3 million m ³ volume)
2) Assumes calorific value of 18.6 GJ/odt ( DTI 2004), heat conversion efficiency of 85%.
3) Assumes electricity conversion efficiency of 30%.
4) Assumes 24/7/365 operation.

The recently published Scottish Energy Study ( AEA Technology 2006) states that in 2002, Scotland's electricity demand was 10.34 TWh. According to the above estimates, therefore, woodfuel would be able to supply approximately 1.3 - 1.7% of Scotland's current electricity needs. According to the SDC Report, 700,000 to 1,000,000 odt is able to provide between 5 and 11% of Scotland's domestic space and water heating requirements.

Other Non-conventional Wood Resources

The SDC report and other recent estimates do not consider material that is currently not extracted through conventional forestry operations, such as brash and other residues. Techniques for extracting these are well-developed in mainland European countries such as Finland and their application in Scotland could increase the amount of wood fuel available for bioenergy. Scottish Coal is presently in the process of developing harvesting methodologies for extraction of these residues in Scotland (Scottish Coal 2006).

A Note on Recycled Wood

In addition to the co-products from primary timber processing industry included in the SDC study, recycled wood from other industries (construction, furniture production, etc.) may be an additional source of resources for the bioenergy industry in Scotland. Table 3.4 summarises the results of a study published by WRAP (2004) that detailed the potential volumes available in the UK for recycling and re-use arising from different industries.

Based on simple adjustments to UK data, Remade Scotland (2004) estimated that over 1.5 million tonnes of waste wood is produced by the construction industry alone in Scotland every year, while the packaging industry could theoretically result in a further 140,000 tonnes, the furniture industry in 33,500 tonnes and 6,000 tonnes per year could come from fencing.

Table 3.4: Annual Wood Waste Arisings and Potential for Re-use and Recycling in the UK

Source: WRAP 2004

Unlike wood material arising from forestry and sawmill offshoots, recycled wood material is not very homogeneous in nature and often presents heavy contaminant loads, that may lead to complications in some bioenergy technologies. These may also require burning in compliance with the Waste Incineration Directive ( WID), which necessitates additional abatement measures that can incur considerable extra costs. In a recent written submission to the Scottish Parliament Biomass Inquiry, Scottish Coal expressed their intention to utilise clean recycled wood along with other feedstocks to fuel the proposed Tullis Russell plant in Glenrothes, currently in a planning stage, (Scottish Coal 2006).

Scottish-specific Constraints

Although they are substantial, Scotland's forestry resources are highly dispersed, meaning that transport would be problematic if wood resources were to be used in a highly centralised power plant, for example. Addressing this geographical separation of wood supply and heat demand is a crucially important factor in the ongoing debate about how to best develop the biomass sector in Scotland. The small-scale wood fuel market is currently seen as the most promising use of Scotland's wood fuel resource (Rippengal 2005), but even in this market there are likely to be logistical barriers that need to be overcome.

It is well recognised that the forest sector is a complicated and fragmented market. Nearly all of the extra resource available for wood energy is coming from the private sector. Of Scotland's total current annual forestry production of 6 million m ³, approximately half is in the private sector. Moreover, about 70% of the state-owned forestry production of sawlogs and 100% of small roundwood is committed to existing processors under long-term contracts (Forestry Commission Scotland 2006). There is therefore much more scope for growth in production from privately owned forests. This is not without problems. The early stage of biomass market development in Scotland brings with it an element of risk which may dissuade private growers. The value of the raw material itself is an important consideration and incentives are necessary to encourage growers to make volume available which is currently uneconomic to harvest. Mechanisms are needed that can spread the risk of possible market collapse. To this end, joint venture schemes are suggested as being of great value in the initial stage of development of the biomass industry (Walls 2005).

3.2.2 Agricultural Residues and By-products

3.2.2.1 Straw

Data on straw availability for bioenergy in Scotland is not as readily available as for forestry resources. The amount of straw can be inferred, however, from the total production of the major straw-producing crops grown in Scotland (wheat, barley, oats and oilseed rape) by multiplying the total area of these crops by the reported average straw yield. According to Scottish Agricultural Handbook, published by the Scottish Agricultural College, this is 5.2 t ha ^-1 for wheat, 4.1 t ha ^-1 for spring barley and 5.6 t ha ^-1 for winter barley. Oilseed rape also yields a considerable straw volume, but this disintegrates easily during harvest, so that the collectable straw yield does not typically surpass 2.5 t ha ^-1 (Garrad Hassan 2001). Table 3.5 summarises the production of straw in Scotland in 2004. Based on these yield values, it is estimated that over 2 million odt of straw was produced in Scotland in 2004, but very little of this may actually be available for energy production, due to strong competition from the animal feed and bedding sectors, with some of the straw produced also being ploughed back into the soil (Towers et al. 2004). The assumption that 5-10% of the total straw volume has no other markets would mean that an approximate total of 125,000 - 250,000 tonnes for energy production. This may well be an optimistic assumption and is based on non-existent data. The lower end of the scale would represent the available rape straw, which currently has no other markets, while the upper end would represent an additional small fraction of straw from crops where markets for straw do exist.

Predicting how the straw resource will change in the future is difficult and depends largely on potential fluctuations in the livestock sector, which could release larger volumes for bioenergy use. Conversely, the reformed CAP may reduce the incentive to plant cereals and lead to lower overall straw production.

Table 3.5: Inferred Straw Production in Scotland in 2004.

1) This amount represents the 'collectable yield' stated in Garrad Hassan (2001)

As shown in Figure 3.2, the regions in Scotland with the largest absolute cereal areas are the Northeast and Tayside regions, but the resource is spread over large areas within these regions. Fife and Lothian may actually have higher percentages of their total land area under cereal production. Table 3.6 provides figures for the inferred energy generation potential of straw, but once again these must be interpreted in light of the high uncertainty associated with them and undue significance must not be attached to them.

Figure 3.2: Regional Distribution of Cereal Production in Scotland.

Table 3.6: Inferred Straw Energy Generation Potential in Scotland - 2020.
Source: SEERAD 2003.

1) Assumes no change in planted area of cereals and oilseed rape for 2020. Equivalent to 5-10% of total straw production.
2) Assumes heat conversion efficiency of 85% and calorific value of 15 GJ odt ^-1. ( DTI 2004).
3) Assumes electrical conversion efficiency of 30%.

Scottish-specific Constraints

Large surpluses of cereal straw are common in certain parts of England ( ETSU 1999), but the situation in Scotland is very different from that south of the border. The utilization of straw for energy production in Scotland is heavily constrained by the strong demand for the resource for the animal bedding and feeding sectors, which consumes most of the available production in Scotland (Towers et al. 2004). Although production of straw in Grampian and Tayside exceeds demand by about 500,000 tonnes ( ETSU 1999), much of this is transferred to livestock farms in the west. Although further work is necessary to ascertain how much of a contribution straw could have on bioenergy production in Scotland, it is likely that cereal straw will only play a minor role (Towers et al. 2004). The utilisation of rapeseed straw for energy has thus far been largely overlooked. A trial of burning rapeseed straw at the Elean Power Station in Cambridgeshire recently demonstrated that the overall performance of rapeseed straw is very similar to cereal straws in terms of conversion efficiency, emissions and costs (Newman 2003). Increased production of rapeseed for biodiesel would have the knock-on effect of increasing rapeseed straw availability, which could be utilised for electricity/heat production. Much of the rape straw shatters during harvest, leaving only an amount in the order of 2.5 t ha ^-1 that can be collected for energy production. Using this average straw yield, it is estimated that about 100,000 tonnes of oilseed rape straw was available in Scotland in 2004.

3.2.2.2 Dry Poultry Litter

Figure 3.3 shows chicken numbers in Scotland over the last 10 years. From the graph, it is possible to see that chicken numbers in Scotland have remained stable over the last decade, tending to hover around the 15 million mark, despite a dip in the late 1990's.

Figure 3.3: Poultry Numbers in Scotland Over the Last 10 years.

Source: SEERAD 2005

Highest poultry numbers are in the Northeast, Tayside, Lothian, Fife and the Borders, as shown in Figure 3.4. Dry poultry litter is collected only from housed chickens kept on bedding material comprised of wood shavings, which in Scotland's case make up about 25% of the total. Due to animal welfare considerations, however, there is a trend to keep fewer laying hens in cages and more on bedding material, which may increase the amount of dry litter available and decrease the amount of poultry slurry collected (Garrad Hassan 2001).

Figure 3.4: Poultry Distribution in Scotland

Source: SEERAD 2003

The Westfield power plant in Fife, with an installed capacity of 10 MW_e, currently utilizes 110,000 tonnes of poultry litter per year. According to Towers et al. (2004), this value is approximately half of the total available litter volume for Scotland, although a recent study for SEPA by Sharp and Smith (2005) suggests that Westfield utilizes virtually all of the poultry litter produced in Scotland. Assuming an original amount of 200,000 tonnes of poultry litter available, a gross calorific value of 8.8 GJ t ^-1 for poultry litter and a conversion efficiency of 30% for electricity and 85% for heat, the maximum potential of poultry litter in Scotland is 16.7 MW of electricity and 47.3 MW of CHP/heat. Subtracting current generation at Westfield leaves about 4 MW_e of electricity to be produced from the currently available litter. Table 3.7 summarises the potential energy generation from poultry litter in Scotland. Again, the uncertainty surrounding these estimates needs to be emphasized.

Scottish-specific Constraints

The Westfield plant is located at the centre of poultry production in Scotland and thus makes use of the highest concentration of litter resources. The dispersed nature of the remaining resource could provide a logistical constraint for the development of a second plant. It must also be borne in mind that not all of the resource unused by Westfield will be available for further energy production as farmers utilise some of the resource for fertilizer purposes. More information is needed to accurately quantify what additional potential there is for energy generation from poultry litter in Scotland, but the potential is extremely limited in relation to other feedstocks such as wood fuel, for example.

Table 3.7: Energy Generation Potential from Poultry Litter in Scotland in 2020

1) Assume no change in poultry number to 2020. Achievable volume refers to additional energy generation potential beyond that of the current Westfield plant.
2) Assumes gross calorific value of 8.8 GJ t ^-1 ( DTI 2004) and heat conversion efficiency of 85%.
3) Assumes electrical conversion efficiency of 30%.

3.2.2.3 Wet Animal Slurry

Although anaerobic digestion of wet animal manures has made great advances in some European countries, most notably in Denmark (Towers et al. 2004), the UK experience has been limited. Figure 3.5 shows the number of cattle and pigs, the important slurry producers, in Scotland. While cattle numbers have oscillated along the 2 million mark over the last 10 years, pig numbers have been around 500,000. Figure 3.6 portrays the regional distribution of these animals in Scotland. While the distribution of cattle is widespread throughout the country, albeit with notable concentrations in the Northeast, Dumfries & Galloway and neighbouring Ayrshire, the distribution of pigs is heavily concentrated in the Northeast. Slurry can be collected when these animals are housed in conditions which are conducive to slurry production. Some animals are kept on bedding, producing manure that is too solid for use in anaerobic digestion and too aqueous for use in combustion. It is not practical to collect slurry when the animals are kept outdoors. Shifts in cattle housing practices towards greater use of straw bedding would reduce the amount of cattle manure that is available for anaerobic digestion.

Garrad Hassan (2001) estimated that a theoretical potential of 452 GWh _e yr ^-1 (51.5 MW) could be generated from cattle slurry, and that a further 255 GWh _e yr ^-1 and 20 GWh _e yr ^-1 could be produced from poultry slurry and pig slurry respectively, although the details of the background calculations were not provided. Most of the slurry produced ends up being spread over the land as a fertilizer and it is difficult to estimate how much slurry is 'available' for anaerobic digestion. Table 3.8 provides a summary of the energy generation potential of wet animal slurries in Scotland. Virtually all of the cattle and pig slurry produced in Scotland each year is spread on land, with 15 million tonnes of farmyard manure spread on farmland in Scotland every year ( SAC 1998).

Figure 3.5: Cattle and Pig Numbers in Scotland over the Last 10 years

Source: SEERAD 2005

Figure 3.6: Regional Distributions of (a) Cattle and (b) Pigs in Scotland

Source: SEERAD 2003

Table 3.8: Energy Generation Potential of Wet Animal Slurries in Scotland

a) Potential generation figures obtained from Garrad-Hassan et al. (2001). Electricity conversion efficiency of 30% assumed, although not explicitly stated in study.
b) CHP/heat efficiency of 55% assumed for anaerobic digestion (Monnet 2003)
c) Achievable potential based on 25% of theoretical potential +/- 10%.

At present, there are no anaerobic digestion plants operating in Scotland as large as the 2 MW_e Holsworthy plant in Devon, although there are seven farm-scale plants in Southwest Scotland funded by the Scottish Executive on an experimental scale (Chesshire 2005) and there is another under development in Turriff, Aberdeenshire, which uses pig slurry (Scottish Farmer 2006). The motivation behind this is to investigate the potential of anaerobic digestion technologies in the control of faecal microorganisms. This is not the only motivation behind biogas production, however. Currently the University of St. Andrews are developing the potential of using biogas from animal manure as a feedstock for fuel cells ( SHFCA 2006).

If a larger-scale AD plant, such as the Holsworthy plant in Devon, were to be constructed in Scotland, the Northeast of Scotland would be a possible location due to high cattle and pig numbers (Figure 3.8). On the other hand, the intensity of farming and waste production is higher on dairy units in southwest Scotland. Relatively little attention has been paid to the potential of anaerobic digestion in Scotland and a more detailed analysis is necessary to provide more accurate indications of the future potential of this technology.

Wood Chip Corrals

There are trials underway to assess the feasibility of using wood chip corrals for cattle and sheep, with the possibility of utilising the wood chips from the bedding material for energy, in much the same way poultry litter is utilised. The move to wood chip corrals has been driven by the rising price of straw (Forestry Commission Scotland, personal communication).

Scottish-specific Constraints

There are several constraints in the utilisation of cattle slurry for energy production in Scotland. One of these relates to the fact that cattle are only housed in the winter months and it is not practical to collect slurry when they are outdoors (Garrad-Hassan 2001). Anaerobic digestion plants in Scotland, therefore, would not be functional throughout the whole year unless a means of storing slurry over the summer months was possible. In addition to this, some cows are housed on animal bedding, producing solid manure that is not very suitable for energy production. This is especially true of the east of Scotland, whereas in the north and west cattle are generally kept in cubicles, permitting easier collection of slurry. Pig slurries, in contrast to cattle slurries, are generally available for conversion throughout the year. Garrad-Hassan (2001) estimated that about 70% of pigs are currently housed in a manner that permits slurry collection, but noted that there is a trend towards housing pigs on straw bedding rather than in slurry-based systems. This trend, driven by animal welfare considerations, would decrease the future availability of slurry for anaerobic digestion.

3.2.2.4 Animal By-products

The use of animal by-products such as meat and bone meal and tallow could provide Scotland with an opportunity to generate energy from materials with virtually no costs attached to them, except handling costs. The most likely use of tallow is for the biodiesel industry and this is already occurring at the Argent plant in Motherwell. Issues concerning the availability of tallow will be discussed in more detail in section 3.2.4.1, along with other biodiesel feedstocks. Table 3.9 shows the energy generation potential of MBM in Scotland, assuming an annual availability of 80,000 t.

Table 3.9: Total Energy Generation Potential of Meat and Bone Meal in Scotland

a) Calculated by dividing total UK amount by ratio of cattle in UK to cattle in Scotland.
b) Assumes heat conversion efficiency of 70% and calorific value of 18.8 ( DTI 2004)
c) Assumes electrical conversion efficiency of 30%.
d) Based on 25% +/- 10% of theoretical resource.

About 400,000 tonnes of meat and bone meal is produced per year in the United Kingdom ( UK Animal Renderers Association, cited in Towers 2004). Although published Scottish-specific data could not be obtained, a simple comparison of Scottish cattle number to UK cattle number shows that the Scottish cattle herd is about 20% of the UK total. Applying the simple assumption that the same amount of MBM is produced per cow in Scotland as elsewhere in the UK, a 20% share of UKMBM would represent an annual volume of 80,000 tonnes. In fact, some of the MBM is used to generate process heat in rendering industries, so this figure may be optimistic. The PDM animal by-product processing unit in Widnes uses MBM to generate steam and electricity to run the plant and exports 9 MW to the National Grid, supplying electricity to a total of 9000 homes (Smartest Energy 2005). There are no schemes analogous to this one in Scotland yet, where most of the MBM is in fact incinerated.

Scottish-specific Constraints

The main constraint in utilisation of MBM for electricity in Scotland is the same as in other locations in the UK: lingering association with BSE, creating a perception of possible health risk. MBM has begun to be utilised by the cement industry to provide the heat needed in the cement-making process. At the Lafarge Plant in the Vale of Glamorgan, for example, MBM is being used to provide up to 30% of the required heat. More recently, the Environment Agency has granted Castle Cement permission to burn 90,000 tonnes of MBM per year at their Ribblesdale site in Lancashire. Competition for this feedstock, therefore, is already strong.

3.2.3 Energy Crops

3.2.3.1 Short Rotation Coppice

Short-rotation coppice is recognized as one of the most promising energy crops in the UK, with several grant schemes currently promoting its uptake. The actual area planted with SRC willow in Scotland at the moment is very small, but commercial contracts are already in place with producers to supply the EON Lockerbie Plant (44 MW_e) and there are also plans to use 200,000 tonnes of SRC willow at the proposed Tullis Russel Plant in Glenrothes (50 MW_e) (Renewable Fuels 2005, Scottish Coal 2006). The EON plant will utilise 220,000 oven dried tonnes of fuel yearly, 45,000 tonnes of which will come from SRC willow to be planted by local farmers (Renewable Fuels 2005). EON aims to start operations in December 2007 and has already arranged a fuel supply contract with Renewable Fuels. If current co-firing regulations remain as they are, SRC willow probably is the best option to meet the indigenous biomass co-firing quota of 50% by 2011, as it has a proven potential or growth in Scottish conditions, a fact that still remains to be verified for novel energy grasses.

A GIS-based study by Andersen et al. (2005) estimated that between 170,000 and 520,000 ha of Scottish land are highly suitable for SRC plantation and that a further 1.2-1.3 million ha are moderately suitable (Figure 3.7). Assuming an area of 50,000 ha is planted with SRC to 2020 and yields of 8 - 10 odt ha ^-1, a total annual production of between 400,000 to 600,000 would be possible. Under the more ambitious scenario that 90,000 ha would be planted in 2020, 720,000 to 1,080,000 odt yr ^-1 would be produced (Table 3.10).

Figure 3.7: SRC suitability map for Scotland

Source: Andersen et al. 2005

The energy benefits of two possible scenarios for SRC uptake are shown in Table 3.10. The uptake of 50,000 hectares of SRC by 2020 could generate up to 925 GWh of electricity per year while an uptake of 90,000 hectares, equivalent to the total set-aside land area in Scotland for 2003, would generate up to 1755 GWh of electricity.

Trials by Forest Research suggest that yields of up to 15 odt ha ^-1 may be possible in Scotland, but average yields have been much lower, at 7 - 9 odt ha ^-1. There is reason to believe that these yields can be improved and there is ongoing research to this effect, including work currently being funded by Defra. ( http://www2.defra.gov.uk/research/Project_Data/More.asp?I=NF0424&M=CFO&V=USH)

The yields for short rotation poplar are more variable than those for willow, in some instances outperforming willow by up to sixty percent while in other trials yielding only 30% as much as willow ( RCEP 2004). In Scotland, however, trials with poplar varieties have indicated that average yields are lower than for willow, being on average 5 - 7 odt ha ^-1 although yields of up to 9 odt ha ^-1 have been reported (Forest Research 2005). In England, poplar is much more prone to disease than in Scotland, but this may be a function of having a much higher density in the landscape (Forestry Commission Scotland, personal communication).

Table 3.10: Energy Generation Potential of SRC Willow Under Different Illustrative Scenarios for 2020

1) Assumes value of 18.5 GJ odt ^-1 (Anderson et al. 2005) and heat conversion efficiency of 85%.
2) Assumes electrical conversion efficiency of 30%.

Note on Short Rotation Forestry ( SRF)

There has been increasing interest in short rotation forestry of species such as birch, ash and alder. A recent study for the Forestry Commission (Hardcastle et al. 2006) evaluated the impacts of short rotation forestry on biodiversity, hydrology and landscape as well as providing information on the economics of some of the major species. Use of short rotation forestry for wood fuel is therefore still at a scoping stage and has not yet benefited from the experimental and pilot-scale programmes that have supported the uptake of forestry residues and short rotation coppice for energy. Further research on this topic is currently being planned by the Forestry Commission (James Pendlebury, oral evidence to Scottish Parliament Biomass Inquiry 2006)

Scottish-specific Constraints

Previous unsuccessful attempts to grow short rotation coppice may have lowered farmers' confidence in the crop. The demise of the ARBRE plant in Yorkshire has, unsurprisingly, impacted negatively on farmers' willingness to grow SRC in England (Towers et al. 2004). The problem with the ARBRE plant, however, was not linked to SRC as a fuel but to the advanced gasification system employed by the plant and was therefore a case of over-reliance on a technology that was relatively untested ( RCEP 2004). The success of the EON plant and proposed Tullis Russell plant, both of which plan to use short rotation coppice, will undoubtedly be very important for SRC's future in Scotland.

There are very important concerns about the economics of short rotation coppice in Scotland as it has only been shown to be commercially viable in England and Ireland. Given this, there is a noticeable hesitancy on the part of many in the biomass energy sector in Scotland to develop the crop (see, for example, oral evidence submitted to Scottish Biomass Inquiry). The machinery used to harvest SRC in Scotland will also require special consideration as the lower incidence of ground frost in the winter in Scotland will not permit the use of the heavy harvesting machinery utilized in Sweden. Finally, the abundance of forest residues available in Scotland may lessen the perceived importance of SRC for energy generation. There may also be further complications with rabbit or deer browsing, which would incur extra fencing costs.

3.2.3.2 Energy Grasses

Trials with miscanthus have found yields to be time-dependent, with the yield from the first harvest being only 1-2 odt ha ^-1 (Defra 2004). Studies by Rothamsted Research, for example, recorded increases in yield from 6-7 odt ha ^-1 in the second year of harvest to 15 odt ha ^-1 after 5 years and reaching as much as 20 odt ha ^-1 after 10 years ( DTI 2004). Experts unanimously agree however, that practical yields are considerably lower than those obtained in experimental trials. Indeed, the long-term average for sites in England with well-drained clayey and peaty soils is about 13 odt ha ^-1, while the average on less well-drained soils was found to be around 9 odt ha ^-1 (Defra 2005). Trials with miscanthus in Scotland have been far fewer than in England, but autumn yields of over 19 odt ha ^-1 have been reported in experimental plots in Invergowrie, with harvesting yields in December of 11.9 odt ha ^-1 (Riche 2005). Significantly Invergowrie has one of the most favourable climate regimes in Scotland and it is thought that much of the rest of the country is less suited.

Unlike Miscanthus, canary grass yields peak early, tending to fall quickly over time, with experiments in England recording a decrease in yield of more than 50% over 5 years ( DTI 2004). Reed canary grass may be more suited to Scottish conditions than miscanthus, however. Yields of reed canary grass in experimental plots in Dundee, for example, were found to be consistently greater than yields in Rothamsted in England, with yields of some varieties reaching almost 20 odt ha ^-1 (Fifth Framework Programme 2000). Riche (2004) reported autumn yields in Invergowrie of 16.6 odt ha ^-1 while yields in experimental sites in England did not reach 11 odt ha ^-1. Further trials have been conducted by the Scottish Agricultural College, who recorded yields of reed canary grass at harvest of up to 9.5 odt ha ^-1 in Aberdeenshire ( SAC 2005), falling in between the 6-12 odt ha ^-1 range obtained in other UK trials.

Switchgrass yields in the UK have been found to be between 8 and 12 odt ha ^-1. Like miscanthus, however, switchgrass has a preference for warmer climates and yields in Scotland could be expected to be well below English yields. Indeed, trials of the Cave-in-rock variety at Invergowrie reported an autumnal yield of 8.7 odt ha ¹ while yields in Rosemaund in England reached maximal autumn biomass of 10.7 odt ha ^-1, with the Shelter variety reaching 14.7 odt ha ^-1 (Riche 2004).

Studies on the theoretical potential production of energy grasses in Scotland are unavailable, but it is likely that areas of agronomic suitability will coincide with the arable production centres, restricted primarily to the eastern part of Scotland. Table 3.11 shows different scenarios for production of energy grasses. Due to the uncertainty in predicting yields for these crops novel to Scotland, the broad category 'energy grasses' has been used with the yield range of 6-12 odt ha ^-1.

Table 3.11: Potential Production of Energy Grasses in Scotland in 2020 Under Illustrative Scenarios

a) Assumes a calorific value of 18.2 GJ odt ^-1 for miscanthus and heat conversion efficiency of 85%.
b) Assumes 30% electrical conversion efficiency.

Scottish-specific Constraints

More detailed suitability studies need to be undertaken in Scotland for all main energy grasses before they are grown on a commercial scale. According to Towers et al. (2004), reed canary grass appears to be the most suitable energy crop to Scottish conditions, followed by switchgrass and then Miscanthus. It must be stressed, however, that more work is needed to identify energy grass genotypes specifically suitable to Scotland.

3.2.4 Transport Biofuel Feedstocks

3.2.4.1 Biodiesel Feedstocks

UCO and Tallow

Of the nearly 120,000 t of used cooking oil ( UCO) produced in the UK, only about 10,000 is produced in Scotland (Booth et al. 2005). Argent Energy uses a significant share of the used cooking oil in the UK. Argent Energy also utilize a considerable portion of th UK's total annual production of 70,000 tonnes of no-risk low-grade tallow to produce biodiesel ( UK Animal Renderers Association, cited in Towers et al. 2004). Ultimately, this means that any increase in Scotland's biodiesel output will come predominantly from crops planted specifically for this purpose, the most important for Scotland being oilseed rape ( OSR).

Oilseed Rape

The suitability of oilseed rape ( OSR) to Scottish growing conditions is such that the highest yields in Europe are achieved here, with average yields for the 2000-2004 period being 3.52 t ha ^-1 for winter oilseed rape ( SEERAD 2005). In 2004, over 39,000 ha of oilseed rape were planted in Scotland, but the total area reached almost 70,000 ha in the 1990's (Figure 3.8). The decline in planted area visible on the graph is closely linked to changes in CAP which reduced the higher differential paid for growing oilseed rape in relation to cereals (Booth et al. 2005). The core of OSR production in Scotland is in the Northeast, Tayside, Borders and Fife, which were together were responsible for approximately 80% of the total OSR area in 2004 (Figure 3.9). Most of this area (34 210 ha) was planted with winter oilseed rape and only a minor fraction was spring oilseed rape (5180 ha).

Table 3.12: UCO and Tallow Production in the United Kingdom and Amounts Required to Meet Scottish RTFO Targets

a) Values taken from Booth et al. (2005)
b) 1 tonne tallow yields 0.9 tonne biodiesel (Hamelinck et al. 2005)
c) Based on total UK non-risk low-grade tallow production of 70,000 tonnes yr ^-1 ( UK Animal Renderers Association, cited in Towers et al. 2004)
d) 1 tonne recycled vegetable oil yields 1 tonne biodiesel (Hamelinck et al. 2005)
e) Based on total UK supply of 120,000 tonnes yr ^-1 (Booth et al. 2005)

Figure 3.8: Oilseed Rape Planted Area in Scotland 1995-2004

Source: SEERAD 2005.

Using an average of 2.5 tonnes of biodiesel produced per tonne of OSR feedstock and an average yield of 3.5 t ha ^-1, Booth et al. (2005) calculated that a planted area of approximately 67,000 ha of oilseed rape would allow Scotland to meet its renewable transport fuel obligation of 5%. This area, although being 182% more than the 2004 area of oilseed rape is entirely achievable and is only slightly less than the planted area in 1998. Utilisation of all the currently planted OSR area in Scotland would result in a 3% share of the Scottish transport fuel market for biodiesel. Table 3.13 summarizes OSR crop requirements to meet different biodiesel targets.

Figure 3.9: Regional Distribution of Oilseed Rape Planted Area in Scotland in 2004

Source: SEERAD 2005

Table 3.13: OSR Feedstock and Area Requirements to Meet Scottish RTFO Targets

Source: Booth et al. (2005).

1) 2.5 tonnes rapeseed yields 1 ton biodiesel.

Scotland-specific Constraints

Scotland currently has no oilseed rape crushing facilities, an obstacle that must be overcome if large-scale biodiesel production is to overcome inertia in Scotland. Scotland's only previous crusher, located in Arbroath, closed in 1999 due to a series of difficulties, including inefficient technology, poor operational logistics of supply and poor economic management (Booth et al. 2005). The development of the biodiesel industry in the UK as a whole may be further constrained if the government introduces duty incentives for the production of diesel standard fuel containing a biofuel component to be produced by oil refineries ( HM Revenue and Customs 2005). This is brought about by the hydrogenation of vegetable oils, allowing their effective integration with mineral diesel. The involvement of major oil companies in this scheme would result in a scale of production larger than achievable by independent biodiesel-producing plants (Booth et al. 2005).

3.2.4.2 Bioethanol Feedstocks

Scotland already grows starchy feedstocks for food that could potentially be used in bioethanol production. These include wheat, barley and potatoes. Potato production in Scotland has focused on high-value seed production, rather than on varieties that provide maximum yields. Scotland is at a deficit for wheat, resulting in high prices relative to other locations, which largely precludes its use for bioethanol production. Barley would therefore appear to be the feedstock of choice for bioethanol production in Scotland, but process yields from bioethanol are lower for barley than for wheat. Table 3.14 lists the areas of crops suitable for bioethanol production in Scotland in 2004 and the totals required to meet different RTFO targets.

Table 3.14: 2004 Areas of Bioethanol Feedstocks in Scotland and Amounts Required to Meet RTFO Targets

a) 1 tonne wheat yields .356 t bioethanol (Hamelinck et al. 2005)
b) Based on average wheat yield of 8.05 t ha ^-1 ( SEERAD 2004)
c) 1 tonne potato yields 0.09 t bioethanol (Hamelinck et al. 2005)
d) Based on average yield of 51.2 t ha ^-1 for ware potato ( SEERAD 2004)

Sugar beet results in higher bioethanol yields than any of the starchy feedstocks available in Scotland, but has not been grown here since the 1960s. Re-introduction in Scotland would be possible, but at the moment seems unlikely (Booth et al. 2005). Sugar beet is still being grown in East Anglia and it would make more sense to make the most of its availability in this region for bioethanol production than to promote a systematic re-entry of the crop into the Scottish market.

Scotland's vast forestry residues could represent a valuable opportunity for producing ethanol from lignocellulosics, but this technology is at a research and development stage at the moment.

Scotland-specific Constraints

Whereas Scotland is in deficit for diesel, it is already fully supplied with petroleum (Booth et al. 2005). It would make more economic sense therefore for biofuel production to be focused on biodiesel which would reduce needs for diesel imports rather than on bioethanol which would compete in the fully-supplied petrol market (Booth et al. 2005). Moreover, Scottish bioethanol would find it difficult to compete with the much cheaper imported bioethanol options available on the market such as that from Brazil, for example.

3.3 Current and Potential Bioenergy Market Development in Scotland

3.3.1 Heat

Increasing the use of biomass for heat could lead to considerable savings in carbon emissions, as over 50% of Scotland's primary energy is used for heating, rising to about 80% in the domestic sector ( AEA Technology 2006). It is only very recently, however, that attention has been drawn to the development of a biomass heat market in the UK ( SDC 2005, Biomass Task Force 2005, AEA Technology 2005), whereas there has been considerable stimulus for the utilisation of biomass for electricity, not least through the Renewable Obligation Certificate system. Considering this, it is no surprise that only 1% of the UK's heat was derived from biomass sources in 2004 ( AEA Technology 2005). This preferential treatment of renewable electricity over heat is reflected in several reports about Scotland's/the UK's renewable energy potential, e.g. the Garrad Hassan report (2001).

Despite the abundance of wood resources, the biomass heat industry in Scotland is still at a fledgling stage. It is encouraging, however, that there has been a considerable increase in the number of domestic and community-scale developments in the biomass heat market in recent years. The Sustainable Development Commission for Scotland (2005) reported that in March 2005 there were approximately 50 modern biomass heating schemes in Scotland with a total heat output of 4.5 MW. Progress has been made possible by availability of capital grant schemes, most notably the Scottish Community and Householders Renewables Initiative ( SCHRI) which has been instrumental in funding the majority of the currently operating schemes. The establishment of agencies and organizations that promote uptake of wood fuel, especially in the Highlands, has also helped to kick-start the biomass heat industry in Scotland. A noteworthy example of this is the Highland and Island Development Programme, run by the Forestry Commission, which has been responsible for setting up a network of wood fuel clusters in the Highlands and Islands.

Wood fuels from forestry is deemed to be especially appropriate for small and medium heat initiatives in the Highlands and Islands, where populations are widely scattered and there is a substantial amount of low-grade timber available from the extensive woodlands present in the area, and where delivery to markets further south is not economically viable. Furthermore, there is a strong positive correlation between forested area and population density (Figure 3.10) which lowers the transporation burden of potential wood fuel schemes.

Figure 3.10: Map of Forests/Woodlands and Population Density in the Highlands of Scotland

Source: Highland Birchwoods.

There has been considerable debate over the best strategy for promoting the biomass heat market in the UK. The nature of the heat market is intrinsically different from that of the electricity sector, as heat production is a much more localized activity, involving many different stakeholders and is therefore unlikely that a renewable obligation certificate approach can applied to this market (Biomass Taskforce 2005).

Current schemes in Scotland utilise wood chips, logs and imported pellets. Although harvesting residues are currently being exploited for wood fuel in Finland and Sweden, in Scotland the technology to do this is currently not available and the infrastructure would need to be set up ( SDC 2005). Steps are being taken to overcome these obstacles, however, and trials are already being carried out in Wales and are proposed for Scotland (Forestry Commission Scotland, personal communication). Once such obstacles are overcome and fuel supply chains are further established, the bioheat market is expected to expand greatly in Scotland.

3.3.2 Electricity/Large CHP

In the UK, only 1.5% of electricity stems from biomass sources (Biomass Task Force 2005). Of the 49, 492 GWh of electricity generated in Scotland in 2003, for example, nuclear power accounted for 37.2%, coal for 29.4%, gas and oil for 24.4% and hydroelectric power for 7.4%. All other renewable sources apart from hydroelectric accounted only for 1.7% of Scotland's total electricity generation capacity (see Figure 3.11). Of this amount, biomass (without co-firing) accounted for only 10 MW_e, or .2% of the total renewable electricity produced in Scotland. The difference in biomass market share between England and Scotland becomes more accentuated when the allocation of renewable obligation certificates is considered. In England, biomass attracted 16% of the ROCs generated between April 2003 and March 2004, while co-firing attracted a further 14%. This is in stark contrast to the situation in Scotland, where biomass attracted only 1% of the ROCs generated and co-firing 4% (Ofgem 2005). Given its considerable forestry resources as well as the potential for energy crop production, Scotland has greatly underachieved insofar as biomass energy production in concerned. A recent report by the Forum for Renewable Energy Development in Scotland ( FREDS) demonstrated this by highlighting the virtual inexistence of biomass market penetration in Scotland ( FREDS 2005).

As Table 3.15 shows, there are currently several projects at the construction and planning stages which could significantly improve this statistic should they become operational. These include the E. ON-operated 44 MW_e Lockerbie power plant, under construction, which aims to be the UK's largest power plant to run exclusively on woody biomass. An energy crops supply contract has already been signed with Renewable Fuels Ltd., who will supply the short rotation coppice willow wood chip.

A Note on Co-firing

There are currently only two coal-fired power stations in Scotland: Longannet and Cockenzie. Longannet at Kincardine-on-Forth is the second largest coal-fired power station in the UK, with a total installed capacity of 2400 MW_e. The plant utilised approximately half of Scotland's annual sewage sludge for co-firing with coal, resulting in the generation of over 200,000 ROCs up to September 2005 (Mitsui Babcock 2005). A court ruling last year determined that the power station be upgraded to comply with the European Waste Incineration Directive, however, and sewage sludge is no longer co-fired at the plant. Cockenzie power station in East Lothian, with an output capacity of 1200 MW_e, is currently co-firing wood with coal, generating 9,302 ROCs up to September 2005 as a consequence. Cockenzie has so far been co-firing sawdust with coal, up to a proportion of 10%. In June 2005, the plant also began co-firing wood pellets (E7 2006).

This is a pivotal moment for Scotland's electricity industry as both Longannet and Cockenzie are due for closure in 2015 and Hunterston B nuclear power station possibly closing in 2011 ( FREDS 2005b). Combined, the three power stations are responsible for a capacity of over 4600 MW of electricity and their possible replacement has stimulated much debate about what the future electricity generation mix for Scotland should be (Scottish Affairs Committee 2005). The substitution of the electrical output of these stations with renewables would contribute substantially to the achievement of the aspirational 40% renewable electricity target for 2020 set out by the Scottish Executive. It is estimated that about 6 GW of installed renewable capacity is needed to meet the 2020 target ( FREDS 2005b).

Figure 3.11: Electricity Generation by Sources for Scotland in 2003

Source: Scottish Executive 2005.

Table 3.15: Current Status of Bioelectricity and CHP Projects in Scotland.

Source: Scottish Renewables (2005). Represents situation on April 14, 2006.

3.3.3 Transport Biofuel Production

Of the 97 million hectares of total arable land in the EU in 2005, 1.8 million were used to produce feedstocks for transport biofuel production ( EU 2005). Figure 3.12 shows the indicative percentage share of biofuels in the transport fuel market for several EU countries in 2005. The figure shows quite clearly that the UK biofuel market is presently markedly less developed than that of many other EU countries. While in Sweden and Austria, biofuels occupy an indicative 3% and 2.5% market share, in the UK this figure is only about .3%. The market growth rate has also been much slower in the UK than in most EU countries. In fact, of all the EU-25 countries, only Denmark, the Republic of Ireland and Finland have witnessed a slower growth of the biofuels market in the last two years ( EU 2005).

The Argent Plant in Motherwell is currently the only biodiesel plant operating in Scotland and produces biodiesel from used cooking oil ( UCO) and tallow from the rendering industry. The plant produces 50 million litres (50,000 tonnes) of biodiesel annually. For Scotland to meet its 5% renewable transport fuel obligation in 2020, Booth et al. (2005) estimated that 94,700 tonnes of biofuel are necessary, meaning that the Argent plant, with an annual production of 50,000 tonnes, supplies about half of Scotland's biofuel target, whilst utilizing a significant portion of the country's tallow and recycled vegetable oil resources. If Scotland were therefore to meet its RTFO target in a self-sufficient manner, agricultural feedstocks such as oilseed rape would have to be grown. It must be emphasized, however, that the RTFO is a UK-wide target.

Figure 3.12: 2005 Indicative Biofuel Market Share in Certain EU Countries

Source: EU Biomass Action Plan (2005).

3.4 Comparison with other Renewables

Garrad-Hassan et al. (2001) carried out a review of the potential of each of the major renewable technologies for energy generation in Scotland. The results of the study are summarised in Table 3.16.

Table 3.16: Electricity Generation Potential of Different Renewable Technologies for Scotland

a) Values taken from Garrad-Hassan et al. (2001).
b) Marine refers to both wave and tidal.
c) Refers to new hydro potential, disregarding existing capacity.
d) Refers to combined landfill gas and municipal solid waste potential.
e) Achievable potential taken from FREDS (2005b). In the case of onshore wind, this is based on the number of grid connection applications currently being dealt with, as reported in FREDS (2005b).

Onshore wind will almost certainly be the major player in driving the Scottish renewable energy industry forward, acting as a catalyst for the development of other technologies including biomass ( FREDS 2005). Offshore wind, on the other hand, has not been the focus of much activity to date, although Talisman Energy, in conjunction with Scottish and Southern Energy ( SSE) is planning the construction of an offshore wind farm demonstration project at Beatrice Field (Scottish Executive 2004). Hydropower, although accounting for most of Scotland's current renewable energy output, has a comparatively restricted expansion potential, as does energy from waste sources. Marine energy is increasingly viewed as an important source of renewable electricity, with the FREDS Marine Energy Group estimating a total output of 1.3 GW by 2020.

Table 3.17: Renewable Electricity Projects in the Scottish Planning System

Source: Scottish Renewables (2005). Information correct for situation on April 14, 2005.

Table 3.17 summarises the current state of development in Scotland of the major renewable energy technologies in April 2006. It becomes clear from the table that wind energy dominates the immediate future of renewable energy in Scotland, with other technologies playing a much smaller part.

3.5 Energy Generation Potential Conclusions and Recommendations

Electricity and Heat

Figures 3.18 and 3.19 provide illustrative electricity and heat generation potentials (2020) for different biomass feedstocks in Scotland. For straw, poultry litter, wet slurries and meat and bone meal, it was assumed there would be no change in availability until 2020. Several general conclusions can be drawn about the current utilisation and potential of different biomass feedstocks in Scotland:

• The current market share of biomass for energy in Scotland is considerably lower than in England and most other European countries;
• Forestry material and sawmill co-products are Scotland's most expressive and most readily available biomass feedstocks;
• Short rotation coppice is the energy crop which offers most immediate expansion potential for Scotland, even though commercial planting is only just beginning. The short harvesting times means that large volumes of the crop could be produced relatively quickly, whereas the harvesting times of short-rotation forestry species are considerably greater. There are, however, concerns about the economics of SRC in Scotland.
• There is still very little practical experience of energy grass cultivation in Scotland, but reed canary grass appears to be the most suitable to Scottish conditions;
• Agricultural residues appear to have very limited energy generation potential for Scotland, due to alternative markets or uses;
• The utilisation of forestry material for small-scale heat or CHP would make much more logistical sense and be more efficient than for electricity;
• Although biomass has the capacity to make an important contribution to renewable energy generation in 2020, its potential is significantly lower than that of wind energy.

Figure 3.18: Summary of Illustrative Electricity Generation Potential (2020) of Biomass Feedstocks of Relevance to Scotland

Assumptions: 1) SRC: 50,000 ha @ 8-12 odt ha ^-1, 2) MBM: 25% of theoretical total of 80,000 tonnes, 3) Animal slurries - 25% of theoretical total estimated in Garrad Hassan, 4) Poultry litter: 150,000 - 200,000 tonnes, includes material being used at Westfield, 5) Straw: estimated total of 100,000 - 200,000 includes rape straw, 6) wood fuel: 800,000 - 1,200,000 odt yr ^-1 based on SDC (2005) and FREDS (2005), does not include recycled wood.

Figure 3.19: Summary of Illustrative Heat Generation Potential (2020) of Biomass Feedstocks of Relevance to Scotland

Assumptions same as Figure 3.15.

Additionally, there are some areas that deserve closer attention. These are:

• Short rotation forestry: This is a longer-term option which is attracting considerable interest at present and could be integrated with farm woodland management practices to provide an extra income source for farmers. Detailed biophysical and economic assessments are required in addition to the development of practical management advice. The potential of short rotation forestry for bioenergy is currently being investigated by the Forestry Commission (Hardcastle 2006).
• Biogas: There is very little in the literature about the potential of biogas production from anaerobic digestion of animal manures in Scotland, although experimental farm-scale AD plants are currently operating in the southwest of Scotland. There may be the possibility of developing a number of centralised AD facilities in Scotland, but this appears not to have been investigated yet.
• Matching supply and demand: There is currently an active debate about the direction that the biomass sector in Scotland should take. Large-scale electricity and CHP plant, while able to strengthen supply chains, are likely to be constrained by the scattered distribution of available wood fuel resources. Spatially explicit analytical studies which investigate different resource supply and demand scenarios may be able to provide invaluable information regarding the optimal utilisation of Scotland's wood fuel resources.

Transport biofuels:

• As far as transport biofuels are concerned, biodiesel holds more value for Scotland than bioethanol production, due to present market conditions where Scotland is at a deficit for diesel and where cheap bioethanol alternatives are available;
• Production of biodiesel from oilseed rape is likely to be necessary if Scotland is to meet its RTFO targets without relying on imports, although this may not be entirely necessary.

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