4 RENEWABLE ENERGY FOR ELECTRIC POWER GENERATION
4.5 B IOMASS
4.5.1 Resource assessment
Biomass is any kind of organic matter apart from fossil organic matter. It is primarily formed by autotrophic organisms (plants and some algae and bacteria) through photosynthesis. In the process of photosynthesis, carbon dioxide and water are converted into organic compounds using energy in the form of light. Oxygen is released during this process. The gross efficiency of photosynthesis depends on temperature, humidity and availability of nutrients. It can be as high as 15 %. Only a part of the generated organic substances is used for growth. The rest is used for respiration. This energy metabolism of the organism reverses the process of photosynthesis: the energy-rich organic molecules are broken down into carbon dioxide and water, releasing binding energy when and where it is needed and consuming oxygen. The net photosynthetic efficiency excludes respiratory substance losses.
It can be as high as 9 % for single organisms, but on average it is only around 1 % in European vegetation (Kaltschmitt and Hartmann 2001).
The mass of the organic matter generated is called ‘net primary production’ (NPP). Apart from the growth factors irradiance and light spectrum (photosynthetically active radiation), humidity, temperature, availability of nutrients and soil structure, the NPP depends on the species. Models exist that calculate the amount of grown biomass using meteorological and remote sensing data. By remote sensing, one can obtain information about the type of land cover and in case of plants about the leaf area at a given time. In combination with temporally highly resolved meteorological data, photosynthesis and respiration can be calculated and integrated, resulting in the net primary production in a specified period of time.
Figure 4.4.4: Hydro power cost-potential-curves for the area of investigation from 2010 to 2050. On the left: Run-of-river hydro, on the right: reservoir hydro.
0 0.05 0.1 0.15 0.2
0 100 200 300 400 500 600 700 800 900 1000 TWh
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2010 2020 2050
0 0.05 0.1 0.15 0.2
0 20 40 60 80 100 120 140 TWh
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2010 2020 2050
A bottom up analysis of biomass energy potentials would have to assess net primary production, subtract biomass used up for secondary production (animal biomass) and subtract biomass used for food and as material in high spatial resolution. Such an investigation would be too substantial for this study. In other studies, biomass energy potentials have been assessed on national or global levels based on statistical data on production and competing uses (food, fodder, materials) ((BMU 2005), (EEA 2006), (Hoogwijk 2004)).
Because a bottom-up analysis of biomass potentials was not feasible in the scope of this study, a top-down approach was chosen: national biomass potentials calculated or taken from studies were disaggregated spatially in order to enable regional aggregation independently from national boundaries.
Biomass potentials were calculated with the methods applied in (BMU 2005) with averages of statistical harvest and livestock data for the years 1998 - 2002 from EUROSTAT (EUROSTAT 2006), FAOSTAT (FAOSTAT 2006) and from UNECE/FAO (UNECE/FAO 2005) if available. No information could be found for the countries in North Africa. The biomass potential in these countries was considered negligible for this study since the population there is growing and the fertile earth is likely to be needed for food production. As a conservative assumption for the energy system modelling, only waste wood potentials were considered in North African states while the potential of other biomass fractions was assumed to be zero. The potentials of forest wood, waste wood, agricultural residues (straw), energy crops and other biomass in the investigation area in the year 2000 are shown in table 4.5.1. For the individual country values, see table 10.1.2 in annex 10.
Table 4.5.1: Biomass potentials in the investigation area in the year 2000 in PJ.
Potential
in PJ Source Land cover for disaggregation / additional disaggregation parameters Forest wood 2639 UNECE/FAO 2005, FAOSTAT 2006 Forest
Waste wood 1749 BMU 2005 Artificial surfaces and associated areas Agricultural residues 996 FAOSTAT 2006, EUROSTAT 2006 Agricultural land / NPP
Energy crops 1197 FAOSTAT 2006, EUROSTAT 2006 Agricultural land / NPP Other biomass 979 FAOSTAT 2005, BMU 2005 Agricultural land, grassland Total 7560
The forest wood potential consists of unused increment, fuel wood and residual forest wood (the leftovers of round wood felling). Waste wood comprises industrial waste wood, domestic waste wood and black liquor, a lignin-rich by-product of cellulose production. The agricultural residues here are calculated as a fraction of 20 % of straw which is calculated from harvest statistics and straw-to-grain-ratios given in (Hartmann 2002). The following plant species have been chosen as representatives for all crops: cereals (wheat, barley, rye, oat), corn and rape. These plant species have been chosen as representatives because they have been used for modelling the net primary productivity at the German Remote sensing Data Centre at DLR (Wißkirchen 2004) (see below in section 4.5.2). The amount of Energy crops has been calculated from harvest statistics and straw-to-grain-ratios, too, considering the whole plant as the energy crop. The share of the agricultural area that can be used for energy crop cultivation was taken from the CP-scenario in (BMU 2005). ‘Other biomass’
comprises biogas from manure and grass. Following the methods developed in (BMU 2005), the amounts of biogas from manure were calculated from livestock numbers and typical gas production per livestock unit in different forms of animal breeding. The amounts of biogas from grass were calculated from the available area of grassland, country average yields of
grass and biogas yield from grass fermentation. For detailed information on the methods for the biomass potential assessment see (BMU 2005) and (Gehrung 2009).
The given potentials are valid for the year 2000. They include biomass that is already used for energy supply today, such as fuel wood and black liquor. Some minor biomass sources have not been considered: agricultural residues from viticulture and other permanent crops, waste from beer breweries, slaughterhouses, dairies and other food processing industries.
Therefore, the potential considered here is around 12 % lower than the potential reported in the CP-scenario in (BMU 2005) and 5 % lower than the potential reported in the E+-scenario in the same study. The distribution of the total biomass resource is shown in figure 4.5.1. The distributions of the single biomass fractions are shown in figure 10.2.1 - 10.2.5 in the annex.
The resources of each biomass type are listed in table 10.1.3 in the annex.
The yields in agriculture are continuously increased and more land is assumed to become available for energy crop cultivation. The energy crop potential was assumed to grow until 2020 as given in the CP-scenario in (BMU 2005). For the later years, no information is given in (BMU 2005). As a conservative assumption, no further growth was assumed. The growth factors for the energy crops fgrowthBIO,energycrops are given in table 4.5.2.
Because of its energy density and storability, biomass can also be used as a fuel (plant oil, plant oil methyl ester, ethanol, methane, …), enabling the continued use of existing mobility infrastructure with relatively low effort for technical and behavioural adaption. It can also be used for heating. In (BMU 2010), assumptions about the development of the share of the biomass that is used in Germany for the generation of power and combined heat and power Figure 4.5.1: Total biomass energy resource available in TJ/km2/a (annual integral, year 2000).
(CHP), of heat and of fuels are made. These assumptions have been adopted here by only using the share for electricity and combined heat and power as input into the energy system model. The shares of the single biomass fractions regarded here were not given in (BMU 2010). They have been chosen such that the total amounts of biomass for power and combined power, for heat and for fuel equal the total amounts assigned to these categories in (BMU 2010).
It was not possible in the scope of this study to find similar studies for all countries. Therefore the factors given for Germany were applied to all countries in the investigation area. The shares fpchpBIO of the total biomass potentials that can be used for power and CHP generation are given in table 4.5.2.
Table 4.5.2: Shares for power and combined heat and power generation and energy crop growth factors.
Symbol Unit 2000 2010 2020 2050
Energy crop potential growth factor fgrowthBIO,energycrops - 1 2.9 6.6 6.6 Total annual biomass potential EannualBIO ,chem PJ 7560 9866 14265 14265 Share for
power and combined heat and power
Forest wood fpchpforestwood - 0.34 0.28 0.40
Waste wood fpchpwastewood - 1.00 1.00 1.00
Straw fpchpstraw - 0.72 1.00 1.00
Energy crops fpchpenergycrops - 0.00 0.20 0.32 Other biomass fpchpotherbiomass - 1.00 1.00 1.00
In the scenario in (BMU 2010), the electricity generation from biomass without cogeneration of heat is decreasing while the biomass use in combined heat and power plants is strongly increasing. In the optimisation model runs, other results can occur when biomass plants are used for balancing load and generation fluctuations such that the overall operating hours are low. High shares of combined heat and power generation are likely when the operating hours can be high because balancing can be performed more cost-efficiently by other system components such as storage plants.
In (EEA 2006), the biomass resource available for energy use in EU-25 in the years 2010 (2020; 2050) was assessed to be around 189 (235; 283) MTOE, equalling 7892 (9826;
11865) PJ. The potential calculated or adopted in the present study for EU-28 is 8037 (11889; 11889) for the year 2010 (2020; 2050).