Based on the research results achieved so far, it can be concluded, according to Vis et al. (2010), that future research should especially focus on the following issues, which are crucial to enhance the reliability and accuracy of biomass energy potential assessments:
• Experiences with (re) cultivation and knowledge of degraded and marginal soils (that represent a wide diversity of settings) are limited. More research is required to evaluate the severity and type of soil degradation, because at this moment, only coarse resolution datasets are available. Research and demonstration activities required to understand the economic and practical feasibility of using degraded/marginal land are needed;
• Data on the present use of degraded and marginal soils are typically not included in the statistics. Such data can be derived by comparing maps of degraded areas with data on land use or vegetation cover. A limiting factor is that the resolution of data on soil degradation is much lower than of the data on land use or vegetation cover, which make it problematic to determine the current use of degraded areas. Data on marginal areas are usually also not readily available. However, crop growth models that use data on soil and climate in combination with data on crop management can provide insight into the areas marginal lands;
• Experiences with new energy crops are limited to a few experimental field trials, so additional research is required to improve estimates of future yields. Crucial thereby is the crop management system and the availability of water, which can be evaluated using crop growth models in combination with expert judgment. Furthermore, yields on degraded and marginal soils are also highly uncertain, due to a lack of experience;
• The efficiency of agricultural production systems is a crucial parameter for the availability of land for energy crop production. It is important that further insight is gained into the dynamics of increases in the efficiency of the agricultural production systems and the feasibility of such developments;
• The production of animal products is very land intensive because of the losses when converting feed crops into animal products and because of the large pasture areas that are involved. Further research is required to investigate the turnover of biomass in the animal food sector. Typically, only statistics on the amount of feed crops and hectares of pasture land are available, but data on the total biomass throughput and land-use dynamics are scarce, especially in relation to estimations of the feasibility of increases in the efficiency of the animal production system;
• The future costs of energy crop production are highly uncertain due to the uncertain changes in the costs of land, labor, fuel, and other inputs, but also due to the uncertainties when estimating crop yields. Last, but certainly not least, the costs of compliance with sustainability criteria is typically not investigated. The impact of technical developments and technical learning. Both aspects can be crucial for the overall performance, but data are scarce, except for some bio- energy systems, and therefore deserve further attention.
Other issues that are considered important for the assessment of the potential in the use of biomass for the generation of electricity are the following:
• Differences in national forest inventory procedures cause inconsistencies in forest statistics within the EU, e.g., the minimal countable diameter of trees varies between countries and thus leads to uncertainties in estimates of growing stock and the net annual increment (Asikainen 2008). Without any doubt, harmonization of the national forest inventories within the EU will improve the potential assessment in the future use of biomass for the generation of electricity;
• An important uncertainty is the quality of data about degraded and low productive soils. The estimation of current and especially future yields of energy crops is also typically a source of uncertainty and is, therefore, a key target for future research. The efficiency of the animal production systems and the productivity of pastures is a key target for future research too, considering the large areas that are needed for the production of animal products;
• The development of the population distribution should be taken into consideration, i.e., trends in population migration. If necessary, the connection rates for wastewater treatment should be adapted to the demographic development (Ericsson and Nilsson 2006);
• The energy potential of landfill gas depends on the historic and current amounts of biodegradable waste sent to landfill. Even if no new biodegradable waste would be landfilled, landfill gas production would continue for several years;
• The development in population distribution will play an important role as it influences the sewage sludge catchment areas. The drying of sewage sludge will be economically viable and thus realizable only if there is a rather high population density in the catchment area. Furthermore, future plans for building plants that are potential waste heat sources as well as the alternative use options for this heat will influence the potential;
• The future potential of construction and demolition wood mainly depends on the population growth, the activities in the construction and demolition sector as well as on architectural trends; more wood might be used for a certain period of time, which will become waste long after;
• The amounts of waste generated per capita differ greatly between countries and over time, mirroring differences and changes in structure and technology used within the building and construction sector, but also differences regarding what has been categorized as construction and demolition waste. Since there is no central data collection on this waste category neither on national nor at the European level, the exact composition of demolition and construction waste and therefore the potential of construction and demolition wood are not clear. Construction and demolition wood accounts for a significant energy potential which does not cause any competitions with other use options. Therefore, more detailed and exact data collection should be aimed for at European level in order to tap the full potential of this waste category4;
• The future potential of sewage gas and sludge depends, among others, on the amount of treated urban wastewater and thus on the development of the number of households and on the connection rate of households to sewage treatment. Although many of the European countries have reached the (economically possible) maximum connection rate, many countries still have possibilities to increase it. For industrial wastewater treatment, the future potential depends on future building activities.
Moreover, the energy potential of both gas and sludge will likely be influenced by the future development of technologies. These will likely lead to a reduction of sewage sludge and to an increase in energy efficiency (in the combustion of the gas and the sludge). Research is ongoing regarding the drying of sewage sludge without using external energy carriers (e.g., with solar power) which would increase the amount of energy that can be saved.
Since industrial sewage sludge is mostly used internally, there are no data avail- able on the exact amounts of sludge production. However, it probably accounts for a great potential as often there is surplus waste heat available for drying the sludge in industrial plants. For Germany, the potential of industrial sewage sludge is
1.45 million tons and from urban wastewater treatment 2.48 million tons (Fritsche et al. 2004).
Further uncertainties concern the amount of energy that can be produced com- busting sewage sludge. If external energy carriers are used for drying, more energy might be needed than can be saved. Therefore, only waste heat or other heat sources (solar power) should be used for drying. However, there are big differ- ences between European countries concerning such technologies. In Germany and Scandinavia, there is a long tradition of combusting (biodegradable) waste, and thus, an infrastructure has been developed that can be used for drying and com- busting sewage sludge. In contrast, in Southern European countries, such an infra- structure is not yet well established, and thus, likely lower energy efficiencies will be achieved. If possible, biomass potential assessments should take into consideration these differences.
Finally, it is important to highlight the following: The EU-27 bioelectricity demand assumes (in their NREAPs) around 232 TWh bioelectricity productions in 2020, contributing to approximately 6 % of the total electricity demand. However, such ambitions can only be realized when and if the appropriate policy instru- ments are in place to overcome both techno-economic and non-technical barriers. According to the recent policy measures announced by the EU member states and included in their NREAPS, it is expected that in 2020, around 221 TWhe can be produced from biomass, decreasing to 211 TWhe in 2030. While these figures indicate that the NREAPs set targets in 2020 is achievable with some further efforts, the deviations are significant at the EU member state level. It is also expected that after 2025, utilization of biomass declines. This decline is due to the reduction of certain feedstock potentials (i.e., black liquor, digestible biomass such as forage maize and cereals), the decline in coal-fired power plant capacity, or completion with other renewable energy source options for certain countries (Uslu et al. 2012).
Undoubtedly, biomass has the capability to contribute strongly to meeting the EU’s renewable targets for both heat and electricity in 2020. A significant major- ity of the biomass required can be produced within the EU. In order to realize this potential, the primary supply of solid biomass and biogas within the EU will have to increase substantially. This increase in EU biomass production will not occur with- out the introduction of significant additional supporting policies and measures.
IEA projections suggest that the biomass share in electricity production may increase from the current 1.3 % to between 3 and 5 % by 2050 depending on assumptions. This is a small contribution compared to the estimated total biomass potential (10–20 % of primary energy supply by 2050), but biomass are also used for heat generation and to produce fuels for transport. Main barriers remain related to the use of biomass for the generation of electricity. These are as follows: costs; conversion efficiency; transportation cost; feedstock availability (competition with industry and biofuels for feedstock, and with food and fiber production for arable land); lack of supply logistics; and risks associated with intensive farming (fertiliz- ers, chemicals, and biodiversity).
Finally, from the analysis of the 23 NREAPs, it appears that the cumula- tive renewable energy share in gross final consumption will be between 20.2 and 22.4 % by 2020 and the 20 % target is expected to be met both by the EU as a whole and by each member state. For several EU member states, it will only be possible to meet the 20 % target, if they are able to attain a predicted improvement in energy efficiency and associated drop in gross final energy consumption. Other countries are expected to meet the target on more pessimistic assumptions.
Bioenergy (biomass, bioliquids, and biofuels) accounts for almost 54.5 % of the 2020 renewable energy target in the NREAPs examined, with a significant increase in absolute values anticipated. Bioenergy will remain the main contributor in the renewable energy sector. Overall, the bioenergy contribution to final energy consumption is expected to more than double, from 5.4 % in 2005 to almost 12 % in 2020. Solid biomass and forestry biomass in particular will continue to be the major source for bioenergy and are estimated to represent 36 % of the EU renewable energy target by 2020.
Bioenergy’s contribution to total renewable electricity supply in Europe will remain at low levels, but will increase to an estimated 17.7 % by 2020. The importance of the more efficient combined heat and power plants (CHPs) is foreseen to grow slightly by 2020, but the cumulative contribution at the EU level will be not more than 10 % of the renewable electricity target.
Bioenergy will have a quasi-dominant role in the renewable portion of the EU heating and cooling sector and is foreseen to contribute with more than 80 % to the sectorial target. Solid biomass is expected to take around a 71 % share in renewable heating and cooling gross final consumption. District heating and cooling is expected to be further developed and to supply around 15.5 % of the heat, but remains quite marginal in some EU countries, notably in the UK.
By 2020, the individual use of biomass for heating in households will remain widespread with a share of up to 31 % in renewable heating and cooling gross final consumption. Some countries count on the increased use of high caloric content biomass (i.e., pellets) rather than the direct combustion of forest biomass which seems to remain important in some other countries. The latter raises ques- tions of sustainability and more careful monitoring will be required in terms of the technology used and the related combustion efficiency.
The technology for bioenergy generation must be carefully monitored in order to ensure that the biomass is used in an efficient way and with low associated GHG emissions. An important role could be played by further research and development initiatives. Improving the technical efficiencies of the most promising bioenergy technologies and subsequently increasing their market availability during the relatively short period remaining to 2020 will be critical in shaping the carbon profile of the sector and its contribution to a sustainable energy future (Atanasiu 2010).
A brief description on the use of biomass for the generation of electricity in a selected group of countries is included in the following paragraphs