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Bioenergy conversion technologies have been frequently described and analysed in the literature, but a comprehensive and detailed comparison between the complex individual characteristics of each technology is still lacking. Therefore, the paper contains a description of the technical, economic and environmental properties of each technology with a special focus on the German bioenergy sector. The study presents an analysis of different bioenergy applications with regard to their specifications, power/heat output range and their areas of application. Due to the fact, that biomass combustion applications are the most widespread and market proven renewable conversion technologies, a detailed analysis of decentralised, biomass-fired CHP plants is presented in the paper. The overview of the individual characteristics of different biomass conversion routes shows that biogas plants achieve high electrical efficiencies, are available with a broad range of capacities and belong to the established technologies. Although the investment costs of biogas plants are relatively high, biomass conversion with anaerobic digestion can be seen as one of the most promising option for a sustainable energy supply in Europe. [ABSTRACT FROM AUTHOR]

Abstract: A clear consensus exists in German society that renewable energy resources have to play a dominant role in the future German energy supply system. However, many questions are still under discussion; for instance the relevance of the different technologies such as photovoltaic systems and wind energy converters installed offshore in the North Sea and the Baltic Sea. Concerns also exist about the cost of a future energy system mainly based on renewable energy. In the work presented here we tried to answer some of those questions. Guiding questions for this study were: (1) is it possible to meet the German energy demand with 100% renewable energy, considering the available technical potential of the main renewable energy resources? (2) what is the overall annual cost of such an energy system once it has been implemented? (3) what is the best combination of renewable energy converters, storage units, energy converters and energy-saving measures? In order to answer these questions, we carried out many simulation calculations using REMod-D, a model we developed for this purpose. This model is described in Part I of this publication. To date this model covers only part of the energy system, namely the electricity and heat sectors, which correspond to about 62% of Germany's current energy demand. The main findings of our work indicate that it is possible to meet the total electricity and heat demand (space heating, hot water) of the entire building sector with 100% renewable energy within the given technical limits. This is based on the assumption that the heat demand of the building sector is significantly reduced by at least 60% or more compared to today's demand. Another major result of our analysis shows that – once the transformation of the energy system has been completed – supplying electricity and heat only from renewables is no more expensive than the existing energy supply. [Copyright &y& Elsevier]

Abstract: A clear consensus exists in the German society that renewable energies have to play a dominant role in the future German energy supply system. However, many questions are still under discussion; for instance the relevance of the different technologies such as photovoltaic systems and wind energy converters installed offshore in the North Sea and the Baltic Sea. Also concerns exist about the cost of a future energy system mainly based on renewable energies. In order to be able to address the raised issues on a scientifically sound basis we have set up a new simulation model REMod-D (Renewable Energy Model-Deutschland) that models the energy balance of the electricity and heat sector including all renewable energy converters, storage components and loads for a future German energy system for a whole year based on an hourly energy balance. The target energy systems modeled use a high fraction up to 100% of renewable energies to cover the electricity and heat demand (heating and hot water). The model includes also energy retrofit of buildings as a measure to reduce future heat loads of the building sector. A mathematical–numerical optimizer is applied in order to identify system configurations with minimal overall annual cost. In this first part of a two-paper series we describe the methodology of the REMod-D model and discuss cost and performance values of all included components and in the second part we will discuss the results. [Copyright &y& Elsevier]

Abstract: Germany has set a target of a minimum of 80% renewable energy in the power sector for the year 2050. Among renewables, a very high share of fluctuating sources is foreseen, which may substantially decrease the security of the energy supply and grid stability. Biomass-based conversion systems offer technical alternatives for flexible power generation to compensate for such fluctuations and the resulting residual load. Demand-oriented electricity can be provided by storing untreated biomass or solid, liquid, or gaseous biofuels in the existing infrastructure or by developing biological and technical alternatives. Making existing plants more flexible will increase costs due to larger storage capacities and conversion units and reduced full-load hours, but higher income can be obtained by selling electricity at peak times and by taking advantage of legislative incentives. This paper summarizes the current legislative and market conditions in Germany for demand-oriented power generation, describes possible technical solutions based on solid, liquid and gaseous biofuels, and provides an economic assessment of selected technical concepts. The results show the potential for bioenergy, especially biogas and combined heat and power (CHP) systems to play a significant role in ensuring the security of the energy supply system that is in transition in Germany. [Copyright &y& Elsevier]

The use of semi-natural grasslands for the production of renewable energy through conventional conversion techniques faces major limitations because of chemical and physical properties of the biomass. A new conversion procedure was developed which separates the biomass, as silage, into a liquid phase for biogas production and into a solid fraction to be used as fuel. Separation (mechanical dehydration) is carried out with a screw press after mashing with water (hydrothermal conditioning). The effect of hydrothermal conditioning at different temperatures (5, 60 and 80°C) and mechanical dehydration on mass flows of plant compounds into the press fluid was investigated for five grassland pastures typical of mountain areas of Germany. Results show that 0·18 of the crude fibre was transferred into the fluid, whereas more digestible organic compounds, such as crude protein and nitrogen-free extract, showed mass flows of 0·40 and 0·31 respectively. While 0·52–0·89 of potassium (K), magnesium (Mg) and chloride (Cl), which are detrimental for the combustion of the press cake, were transferred into the press fluid, more than 0·50 of calcium, which has positive combustion properties, remained in the press cake. Significantly ( P < 0·05) higher mass flows were detected at conditioning temperatures of 60°C (K and Mg) and 80°C (crude fibre and nitrogen-free extract) compared with the 5°C treatment. Because of the separation of solids and liquids, high proportions of P (0·61–0·74) and K (0·64–0·85) but only 0·32–0·45 of nitrogen exported from the grassland would be recycled with an application of the digestates from the anaerobic digestion of the press liquid. [ABSTRACT FROM AUTHOR]