In Germany, the expansion of renewable energy sources is advancing at an impressive pace. In the period from 2000 to 2014, their share of the final energy consumption tripled from 3.7 to 12.4 %. Here, the strongest increase could be observed in the electricity sector – from 6.2 to 27.8 %. The declared objective of the German energy transition is to ensure that by the year 2050, renewable energy sources (RE) will cover 60 % of the final energy consumption and at least 80 % of the power consumption.

Besides the undeniably positive effects of using renewable energy sources mainly resulting from the substitution of fossil fuels (coal, oil, natural gas) and the associated reduction of environmentally harmful CO₂ emissions, there is a multitude of further (positive and negative) indirect effects and consequences which have to be identified and evaluated with regard to a comprehensive ecological, economic and societal overall assessment of RE. It is obvious that today's scope of using RE – which has reached a dimension of national importance for the energy sector – also involves consequences relevant for overall economy and society.

For such an overall assessment, impacts along the entire life cycle of the installations for using renewable energy sources have to be taken into consideration – ranging from construction and operation to the reuse and disposal of installations that have become obsolete. The research approach mostly chosen in this context is the so-called life-cycle assessment (LCA). Very often, however, it only focuses on the energy balance as well as on CO₂ and pollutant emissions, as well-developed methods and often very comprehensive quantitative data are available for these aspects.

In contrast, other impacts are not examined in such a comprehensive way, as they are more difficult to identify and depend not only on the technology, but – to a decisive degree – on the location chosen. This includes e. g. aspects of land use, impacts on the countryside, impacts on the local or regional flora and fauna, noise emissions or certain specific risks (in case of geothermal energy e. g. the risk of provoking earthquakes). Last but not least, these impacts are of major relevance, as they often have a decisive effect on the perception and, thus, on the local acceptance of RE projects.

As a matter of principle, a comprehensive overall evaluation would have to take into consideration the consequences of conventional power generation for comparison purposes. Moreover, systemic effects would have to be taken into account as well, e g. the question of the impact which the use of RE will have on the power system.

Objectives and approach

The TA preliminary study shall point out the opportunities and limits existing with regard to an ecological, economic and societal overall assessment of the consequences induced by the expansion of RE. The major aims of the study are to identify research gaps and to define topics which could be analyzed in depth within the framework of a possible main study. Another objective is to make basic methodical considerations in order to be able to concretize the approach and the expected efforts to be made for a possible main study. Thus, a basis shall be provided for the German Bundestag to be able to make a decision in due time on whether and when to carry out such a main study.

Based on the existing results of life-cycle assessments, impact assessments and analyses of external effects or external costs, the approach shall be expanded in order to include in an overall evaluation all substantial consequences that can be identified for the expansion of RE. Positive and negative consequences shall be compared systematically and weighed against each other. With regard to specific usages of bioenergy, for example, there is the benefit of reducing CO₂ emissions on the one hand and the risk of producing air pollutant emissions as well as potential disadvantages involved such as acidification, eutrophication, ozone depletion and/or negative impacts on human health on the other hand. Particular attention has to be paid to possible consequences which have not been focused on systematically or even not at all in previous studies conducted so far.

At the beginning of the project, two thematic areas have been selected to deal with the contents of the topic in depth: wind power and renewable heat. The preliminary study is also intended to identify further thematic areas for which a detailed consideration within the framework of a possible main study seems to be appropriate. Fur this purpose, potential approaches as well as the efforts to be expected shall be outlined in a more concrete way.