Greenhouse gas (GHG) emission reduction is one of the most important environmental challenges for the next decades. Carbon dioxide (CO₂) is the most important greenhouse gas, representing approximately three-quarters of the total GHG emissions. Biomass strategies pose an important option for CO₂ emission reduction since CO₂ is fixed during the biomass growth stage. Biomass can subsequently be used as a renewable resource, with zero net CO₂ emissions. This is the basis for all biomass strategies (i.e. groups of activities with similar characteristics, concerning agriculture and forestry and aiming for GHG emission mitigation). The following biomass strategies can be discerned:  

*   Carbon storage above ground in new forests;

*   Carbon storage below ground in soils;

*   Carbon storage in wood materials and products;

*   Substitution of energy carriers with biomass;

*   Substitution of materials with biomass;

*   Energy recovery from process waste and post­ consumer waste.

The land availability and the biomass yield per hectare limit the total amount of biomass. Different biomass strategies compete for the limited amount of biomass and land available. Moreover, these strategies compete with other strategies for GHG emission reduction (e.g. other renewables, energy efficiency). A lot of attention has been paid to carbon storage strategies, to substitution of energy carriers and to materials substitution (e.g. 1-3). However, little attention has been paid to the interaction and the cost-effectiveness of these strategies.

The pervasiveness of GHG emissions complicates the analysis: many GHG emission reduction strategies influence each other's efficiency. For example emission reduction because of a switch to bioelectricity reduces the potential for emission reduction based on the increased efficiency of household equipment. The assessment of biomass strategies is further complicated by co-production and cascading: by-products from wood sawing and waste materials can be used for energy recovery. This illustrates why the assessment of biomass strategies is complicated, and why different studies result in different recommendations, depending on the scope of the study.

This study focuses on Western Europe. Current European policies with regard to biomass are aiming for bioenergy, especially electricity production (4). Transportation fuel research activities have been reduced in the last decade. As of yet, biomaterials strategies have received little attention from a GHG emission point of view. Some reforestation activities represent a continuation of a trend that started decades ago. It is unclear whether the current European biomass policy trends are optimal, given the conflicting study results and rapid technological change. For this reason, an energy and materials' systems engineering model has been developed in order to analyse the optimal use of biomass from agriculture and forestry for energy and/or materials. The selection of optimal biomass strategies has been investigated in the framework of the BRED (Biomass for greenhouse gas emission Reduction) project.

MODEL CHARACTERISTICS

The MARKAL linear programming model was developed 20 years ago within the IEA/ETSAP (International Energy Agency/Energy Technology Systems Analysis programme) framework (5). MARKAL is an acronym for MARKet Allocation. A MARKAL model is a representation of (part ot) the economy of a region. The economy is modelled as a system, represented by processes with physical and monetary flows between these processes. The processes represent all activities that are necessary to provide products and services. Special emphasis is given to new emerging technologies and their potential integration in the energy and materials system. A MARKAL model calculates the least-cost system configuration that meets the fixed demand for products and services given a number of constraints. The selection of process alternatives is based on discounted full life cycle costs. Biofuels for example are characterised by higher costs than fossil fuels, but lower GHG emissions. Consequently, biofuels will only be selected if GHG emissions are endogenised in the costs. This is done on the basis of emission permit prices.

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Figure 1: Biomass model structure

MARKAL is a dynamic model. The time span modelled is generally covering a period of decades. Within such a time horizon, technological change will be a major driving force for a changing systems configuration. Price elasticities of demand are endogenised in the MARKAL Elastic Demand algorithm (6). The least-cost system optimisation algorithm represents the market mechanism. The model user defines the database of processes and the constraints for individual processes and for the region as a whole. Constraints are for example determined by the availability of resources or environmental policy goals. Processes are characterised by their physical inputs and outputs of energy and materials, by their costs and by their environmental impacts. Many products and services can be generated through a number of alternative processes (e.g. electricity production can be based on coal, gas or biomass). The model database contains 1500 processes, covering the whole life cycle for both energy carriers and materials 'from cradle to grave'.

The MARKAL MATTER 4.2 model has been used for this analysis. Documentation on input data and analysis results can be found on the internet (7) and in a large number of publications (e.g. 8,9). The model covers more than 25 energy carriers and 150 materials. More than 100 products represent the applications of these materials. 30 categories of waste materials are modelled. The model has been developed especially for the analysis - of GHG emission reduction strategies. Four GHG emission permit prices have been analysed: 20, 50, 100 and 200 EUR/t CO₂, The base case is the run without a permit price. In the emission reduction cases, the permit prices increase from zero in the year 2000 to their maximum level in 2020 and stabilise afterwards.

...... Figure 1 show a general overview of the model structure for biomass, showing the close relation between food, energy and materials crops. Europe is split into a northern region, a middle region and two southern regions in order to account for different climates and soil types. All important agricultural crop types are - covered (including energy crops like miscanthus and sweet sorghum). Afforestation (i.e. new forests on formerly agricultural soil, planted after 1990) is considered as a carbon storage strategy. Model input data for biomass (production and consumption processes) have been reported in five separate volumes (e.g. 10,11).

With the MARKAL MATTER 4.2 model, three scenarios have been analysed:

1.   Globalisation, characterised by rapid technological progress, globalisation of economic activities and market liberalisation

2.   Fortress Europe, characterised by moderate economic development and heavy reliance on transportation and building sectors

3.   Sustain, characterised by environmental reorientation of society (initiated by lifestyle changes)

A more detailed discussion of the model and the results can be found in the final report (12).

Results

Figure 2 shows the changes in agricultural land use for the 'Globalisation' scenario in - 2030. The figure shows the reference year 1990, the base case and permit price levels of 50,100 and 200 EUR/t CO₂, In the base case and the 50 EURIt case, the use of biomass crops is negligible but some afforestation is introduced (based on a lower bound that represents current policy plans). Afforestation increases markedly in the 100 EURIt and 200 EUR/t cases and dominates biomass crops. The results show that the full land area is not yet used at lower, more realistic, permit price levels. This suggests that land availability should be no major issue in the biomass strategy discussion: the costs are the main driving force. The I preference for afforestation is a major difference with earlier modelling studies.

Figure 2: Agricultural land use, 'Globalisation', 2030

 

Western Europe has reached a status where its agricultural production potential exceeds food and fodder demand. This is largely accounted for by the steadily increasing agricultural productivity. If this trend continues, 10-20% of the agricultural land (both arable land and pastures) may become available for other purposes. If this land is used for high yield biomass crops, it can yield up to 500 Mt biomass per year. As a consequence, agricultural biomass crops can constitute an important option for GHG emission reduction. The results regarding biomass supply depend to a large extent on trends in agricultural productivity and trends in global markets for agricultural products. Extensification is not recommended from a GHG emission reduction point of view.

The use of biomass for energy and materials applications will increase by up to 200 Mt (compared to the case with no permit price) if significant greenhouse gas policies (i.e. emission permit price of 200 EUR/t CO₂) are introduced. The growth mainly takes place in the energy market. Also the materials market grows up to a permit price level of 100 EUR/t. Figures 3 and 4 show the division of biomass use (both from forestry and from agriculture) into energy and materials applications at a permit price level of 100 EUR/t CO₂ in 2030.

 

 

 

 

Figure 3: Bioenergy applications, 100 EUR/t CO₂, 2030

Figure 3 shows significant changes in the biomass use for energy purposes between 1990 and the base case in 2030. The total biomass use increases significantly from 80 Mt to 200 Mt. While the biomass use for heat production nearly disappears, the energy recovery from waste biomass (mainly for electricity production) increases significantly and remains at a constant level up to the 200 EUR/t permit price. The energy recovery from lignin (via gasification and subsequent cogeneration) increases at 100 EUR/t, but declines again at 200 EUR/t. These changes are related to the ethanol production from wood from 100 EUR/t upward, which results in lignin by-products that are used for energy recovery. However in the 200 EUR/t case, part of the residual lignin is used for Hydro Thermal Upgrading (HTU) oil production. From 50 EUR/t upward, biomass use increases significantly, up to 390 Mt biomass in the 200 EUR/t case. The main increase can be attributed to the production of transportation fuels, especially ethanol and (at 200 EUR/t) HTU biodiesel. Figure 3 shows that the differences between the scenarios are limited, indicating that the GHG permit price level has more impact than the scenario characteristics.