Biomass is an integral part of the energy system being not only used in the chemical industry, but also as a basic raw material for the bio-economy sector, which is promoted worldwide. However, its potential can only be exploited sustainably if biomass is cultivated and governed appropriately. Consequently, governance systems are needed to ensure sustainability throughout the bioenergy value chain to maximise the benefits and minimise possible negative impacts. This study investigates how sustainability is put into effect in the German biogas market, the largest biogas market worldwide. The development of Germany's biogas market is described according to the structure of a four-phase market model of Heuss: the introduction, expansion, maturing, and stagnation phase. Within each of these market phases, the most important German legislation for development of the biogas market was analysed, namely the Renewable Energy Act and legislation addressing associated sustainability issues. The development of the biogas market was controlled and steered by the adaptive Renewable Energy Act, particularly by incentivising cultivation of energy crops. Efforts to promote sustainability started during the transition from market expansion to market consolidation. The effects of these efforts on greenhouse gas emission reductions have been monitored and reported for more than 15 years, but assessment of other aspects of sustainability has varied. In general, legislation regulating the agriculture sector was changed to address new sustainability concerns with some delay. Sustainable development of the agricultural biogas market requires elements of governance, including adaptive legislation within the energy sector as well as monitoring and regular reporting of environmental impacts and related developments in areas of the agriculture sector, such as meat production. Rapid growth of capacity in the biogas sector combined with a significant increase in meat production, dependent on increased fodder production, created risks to sustainability. It can be concluded that the sustainable development of biogas requires additional instruments, possibly national regulation, in addition to legislation applied to the broader agricultural sector.

Bioenergy contributes significantly towards the share of renewable energies, in Europe and worldwide. Besides solid and liquid biofuels, gaseous biofuels, such as biogas or upgraded biogas (biomethane), are an established renewable fuel in Europe. Although many studies consider biomethane technologies, feedstock potentials, or sustainability issues, the literature on the required legislative framework for market introduction is limited. Therefore, this research aims at identifying the market and legislative framework conditions in the three leading biomethane markets in Europe and compare them to the framework conditions of the top six non-European biomethane markets. This study shows the global status and national differences in promoting this renewable energy carrier. For the cross-country comparison, a systematic and iterative literature review is conducted. The results show the top three European biomethane markets (Germany, United Kingdom, Sweden) and the six non-European biomethane markets (Brazil, Canada, China, Japan, South Korea, and the United States of America), pursuing different promotion approaches and framework conditions. Noteworthy cross-national findings are the role of state-level incentives, the tendency to utilise biomethane as vehicular fuel and the focus on residues and waste as feedstock for biomethane production. Presenting a cross-country comparison, this study supports cross-country learning for the promotion of renewable energies like biomethane and gives a pertinent overview of the work.

This study reviews energy policy evaluation approaches on their capability to estimate a successful implementation of renewable energy policies. This is predominantly done via energy system modeling and analysis. Although modeling the possible success and effects is not a precondition for policy making, it is a powerful tool to support decision makers in policy making. This awareness has led to the development of numerous modeling approaches with many case studies. Therefore, effort has to be made to evaluate recent modeling approaches that could be suitable for renewable energy policy evaluation. It is the aim of this paper to provide an overview on recent renewable energy policy modeling approaches that are capable in evaluating the success and side effects to other sectors of renewable energy policies. We will highlight advantages and drawbacks of these approaches and provide a framework assessing the suitability of the presented methodologies for the evaluation of renewable energy policies. We provide a tabular overview that enables the reader to quickly derive information on the suitability of the several modeling approaches to evaluate renewable energy policies. Keywords: Policy evaluation, Renewable energy, Policy modeling, Decision support ReviewIn 1980, the term Energiewende was first used in a study of the Öko-Institut [1]. Since then, several policies were installed to follow the idea of a decarbonized energy system. This includes among others the support of the development of renewable energy and associated technologies, efficiency actions, renewable fuels, reduced import independence from fossil fuels, rural development, the decrease of long-term economic costs in kind of external effects, and R&D support [2][3][4]. International Energy Agency (IEA) defines renewable energy as energy derived from natural sources like sunlight, wind or some forms of biomass in terms of being not finite like fossil fuels having simultaneously a smaller impact on the environment [5]. Interplay between renewable energies, energy efficiency like green buildings, and a sustainable transport sector is crucial for achieving the imposed goals of the German Government and the Energiewende. Renewable energy is characterized by replenishing at a faster rate than being consumed. Like Germany, several countries implemented strategies, policies, and stimulus packages to promote the transition towards a renewable energy system and increase their overall share of renewable energy in the energy system. However, increasing the share of renewable energy is often associated with sustainability challenges [6,7]. The key elements of a sustainable development like economic performance, environmental protection, and social responsibility need to be considered in designing or evaluating support schemes, policies, or stimulus packages. But the design and evaluation of renewable energy promoting policies is a difficult task considering the multiple aspects policy designers and decision makers have to consider. Governmental intervention...

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