Renewable energy systems play an important role in the path towards sustainable development [1]. In the European Union, a goal of 20% was agreed upon in 2008 as the gross final energy consumption to originate from renewable energy sources [1]. In 2010, the German government adopted the German energy concept, which outlines the German energy strategy until 2050. In this concept, renewable energies will contribute the major share to the future energy mix: 18% of the gross final energy consumption by 2020, 30% by 2030, 45% by 2040, and 60% by 2050 [2]. However, when decisions concerning energy infrastructure investments are made, they are often more positive for traditional energy systems based on fossil fuels or nuclear power, which are associated with lower costs in the short run. By contrast, renewable energies are associated with less environmental pollution while exhibiting more local impacts [3]. To implement sustainable development in the energy sector, all of the economical, ecological, and social aspects must be taken into account. Multi-criteria decision-making can assist in this decision-making process.

Because of the different characteristics of the method, Multi-Criteria Decision Analysis (MCDA) (In this article, MCDA is used as an umbrella term for all of the different terms and methods within the field of multi-criteria decision analysis. See chapter 4.2 in [4] for details on the different approaches) is suitable for implementation and evaluation of systems aimed at sustainable development [4,5]. Depending on the MCDA method used, it is possible to consider qualitative data on the basis of ordinal scales. In this manner, social and ecological data can be integrated using qualitative data where quantifiable data are not available in the database.

Furthermore, MCDA offers participatory elements that support transdisciplinary approaches. Because of the mainly decentralized character of renewable energy systems, the perceivable local impact of the plants is more widespread compared with a conventional energy supply. More residents are directly affected by the energy systems; therefore, participatory decision-making is needed in the energy sector. In MCDA, these impacts can be integrated, for instance, by a participative weighting of criteria. Within the Multi-Attribute Decision Making (MADM) methods (In MCDA, MADM and MODM (Multi-Objective Decision Making) are distinguishable. In contrast to MADM, MODM calculates the best solution. For more details on the MCDA theory, see [6,7]), a set of finite alternatives is evaluated according to certain criteria, for example, using sustainability criteria. Stakeholders have the opportunity to assign weights to the criteria in order to be able to combine their evaluation with scientific data to achieve a ranking of the alternatives [6]. In addition, the development of alternatives and criteria from the participation of the stakeholders is possible [4].

Several different approaches to prepare a MCDA process are possible (see [4], [8], and [9] as examples). These generally include many common basic steps. However, the order of these steps may differ depending on the decision context. An outline of the steps acquired from a decision-making manual for communities and local governments in Great Britain [10] is reproduced below:

Other approaches perform the MCDA in cycle processes (see [4] or [9]). Depending on the decision context, undergoing the process more than one time and adjusting for instance criteria, alternatives or weights can be useful.

MCDA has been applied in the energy sector many times. Many case studies have evaluated renewable energy technologies against each other or compared renewable energies with conventional energy technologies or systems [11,12,13,14,15,16]. MCDA has been widely used for energy policy analysis, energy utility operations or environmental control and management [12]. However, in general, those case studies are described from the perspective of MCDA in a research environment and not from the perspective of a real decision context [15]. Often an ex-post analysis is absent, which could provide practice recommendations regarding the application of MCDA in the energy sector [15].

A real world application of MCDA in a bioenergy village is presented in the following paragraphs along with the steps of the MCDA process. The discussion explores the implementation of MCDA in that context and provides an ex-post analysis regarding the practice aspects.

The “Bioenergy-Region Ludwigsfelde”, which began in 2009 in the federal-state Brandenburg, is part of the federal funding for “Bioenergy-Regions” available through the German Federal Ministry of Food, Agriculture and Consumer Protection. The task of this specific project in Ludwigsfelde is to establish a network in the region that supports the development of sustainable bioenergy projects. The concept of “bioenergy villages” has been established in Germany since the successful implementation of the “bioenergy village Jühnde” in 2005 [17]. This concept of consensus orientated to the use of waste heat for district heating evoked the interest of more than 200 inhabitants of a small village in the Ludwigsfelde region.

Since then, the process towards the creation of a “bioenergy village” has been successfully reproduced in five villages near Lower Saxony [18]. Using evidence from this established process, we integrated the MCDA to evaluate the outcomes for sustainability using different scenarios:

In order to introduce the concept of a “bioenergy village”, several meetings and events took place. After a first meeting with the village council, a broad citizens’ meeting for the residents and a best-practice trip to a nearby biogas plant were organized. After that trip, we conducted two MCDA workshops. At this stage, many concerns and questions regarding the transport, smell, noise and other disturbances of the new heating system dominated the discussion among the residents. After the MCDA workshops, further citizens’ meetings were organized.

The decision-making body in the village was composed mainly of residents, as it was aimed at the collective approach from Jühnde. In this cooperative approach all heat customers and biomass suppliers are common owners of the biomass plant and the district heating [17]. The aim was to involve not only the powerful actors but also the residents who would be affected by the biogas plant in the MCDA process. In order to identify these actors, semi-structured interviews with five key actors were conducted: two farmers that were supposed to supply biomass, the local mayor, the owner of the aquaculture, and a citizen of the village who was strongly convinced of the idea of a bio energy village. The interviews further helped the project team to understand interactional patterns as well as power and trust constellations within the village.

For the MCDA workshops, all of the participants of former events and the key actors identified in the interviews were invited to participate. In the first and second workshop, 11 and 13 actors were involved, respectively.

For the MCDA evaluation of alternatives, the project team identified different bioenergy and fossil fuel scenarios. Based upon the evidence gathered in the interviews, the team attempted to capture the decision of the village: Whether they supported the conversion to a bioenergy system and if so, what that would look like. Participatory development of scenarios with the group of actors was not considered useful at this stage of the project.

The scenarios described the energy supply for the 70 households (with approximately 200 inhabitants) of the village based on either a small biogas plant (biomass of one farmer) or a larger one (including the biomass of a second farmer), combined with different sizes of an aquaculture plant. The energy consumption of each household was assumed to be 4,500 kWh of electricity and 30,000 kWh of heat. The aquaculture, being a closed-loop system, is an additional heat consumer and is thus beneficial for the efficiency of the biogas plant. A certain heat demand of the aquaculture is available even in the summer such that the combined heat and power plants have a better operating grade. Three different plant sizes (50 kW, 100 kW, 150 kW thermal power) for the aquaculture component were modeled. Two fossil fuel scenarios were developed as reference scenarios. The first followed a “business as usual” (BAU) pattern of energy consumption in which all the households maintained their fossil fuel heating. The second scenario included additional central heating gas for a medium-sized aquaculture. Figure 1 provides an overview of the scenarios.

Depending on the heat available from the biogas plant after the subtraction of the aquaculture heat demand and transport losses, the number of houses connected to the district heating was calculated. To ensure a secure heat supply, a central boiler based on woodchips was added to the district heating system. The details are provided in Table 1.

The set of criteria for this case study was based on a literature review, expert discussions and discussions with local actors. The main purpose was a more “holistic” evaluation of energy scenarios based on the concept of sustainable development. Sets of indicators for this purpose have been published many times. Within the framework of the EU-project REQUIRES (New Energy Externalities Developments for Sustainability), Burgherr et al. provide a comprehensive overview on international and national criteria sets for sustainability assessment as well as for energy assessment [19]. Furthermore, sets of indicators are available in MCDA case studies applied in the energy sector [14,16]. For bioenergy, however, notably less research is available. Buchholz et al. [20] present an overview based on an expert survey, and Eigner-Thiel et al. [21] published a detailed elaboration of criteria for the evaluation of bioenergy systems, which was used extensively in this case study.

Based on the literature review, we compiled a first set of 32 criteria. Based on internal and external discussions on data availability, a final set of 27 indicators was selected.

For better handling of criteria, two further hierarchy levels were introduced: 11 “areas of sustainable development” and three columns of sustainability. To maintain an evaluation process that was both manageable and comprehensible for the actors, “areas of sustainable development” were used for the weighting process.

The data were quantified and related to one Megawatt hour (MWh) exergy. With the help of this energy parameter, the scenario output parameters of heat and electricity were made comparable.

In the following section, the criteria and the generation of the data are discussed; Table 2 provides an overview of the set of criteria.

In the weighting process in MCDA, weights are assigned to the criteria or indicators to enable an aggregation of the data and thus a ranking of the alternatives. Both subjective and objective weighting methods are available [14]. In this case study, a subjective weighting method was selected to provide the actors with an opportunity to participate. Despite the risks of participative weighting, such as its difficult elicitation [5], it can produce positive effects on the process; for example, participation can increase trust in the decisions as the actors have the opportunity to bring in their point of view. Furthermore, participative weighting can create more understanding of the viewpoints of other participants [32].

In our case study, the SIMOS method combined with “silent negotiation” was applied for the group weighting. The simplicity of the SIMOS method was easily grasped by the actors. In this method, the actors express their preferences by ranking criteria in the form of cards [33]. To avoid long discussions without any results, Picted and Bollinger separated the decision part from the discussion part; people act in a silent negotiation without discussing their arguments (see [34] for further details). This facilitates a democratic decision-making process where everyone has an equal input.

The weighting process in the case study was performed in the first workshop. Time constraints did not permit researchers to perform an individual ranking as presented in other case studies (see e.g., [35]). However, to provide the actors with an opportunity to make up their mind about their own preferences, they were given a list of the criteria with an explanation before the survey. For the ranking procedure, cards were arranged in a horizontal row on a large table. To simplify this process, the number of cards was reduced from 13 to 11 by aggregating some areas of sustainable development. In the beginning, all of the cards had the same importance. In the first part of the process, people needed to move the cards from the horizontal arrangement to a more vertical one by moving cards one row up or down. This process was repeated three times depending on the time schedule and the number of actors. In the first round, three moves were allowed; in the second, two moves were allowed; and in the last round, one move was allowed to obtain rapid results in the beginning that could not be significantly changed later during the process. The results obtained are presented in Table 3.

Developments occurring at the ground level of the project at this stage indicated that people considered the “security of supply” criterion as very important. At that time, only one farmer was ready to supply biomass, so the entire demand of biomass was not secure. In general, one could observe that all the criteria with direct effects on the actors’ financial situation and personal environment were weighted higher than more removed criteria such as the ecological ones.

To achieve a ranking of the scenarios, scientific data and weights were aggregated using an aggregation method of MCDA. After this, a sensitivity analysis was conducted to analyze the stability of the results.

The “principle of participation” ensures that the broader community will participate in searching for, evaluating and implementing sustainable ways of life. Without implementing that principle, sustainability processes at different levels of society have little uptake. Therefore, many chapters in Agenda 21 call for the implementation of this principle: “The primary objective is … to achieve, as soon as possible, substantial improvements in … participation of people in setting priorities and in decision making relating to sustainable development” ([24], chapter 35.6) and “The objective is to promote broad public awareness as an essential part of a global education effort to strengthen attitudes, values and actions which are compatible with sustainable development. It is important to stress the principle of devolving authority, accountability and resources to the most appropriate level with preference given to local responsibility and control over awareness-building activities” ([24], chapter 36.9). Violating the principle of participation may result in protest movements against certain developmental paths on the national level (for instance, the anti-nuclear movement in Germany) as well as on the regional level. The massive resistance of citizen initiatives in Germany against the building of high currency cable nets or factory farming projects demonstrated the high costs of excluding people from the development process. For this case study, elements of the principle of participation were included in a local planning process because implementing sustainable solutions presupposes that people of a region or a village collectively reflect about the restructuring alternatives to find one that is shared by the majority of citizens [38].

In the process of transitioning to a bioenergy village, the implementation of MCDA has demonstrated many benefits but also some challenges that must be addressed. According to the experience of the case study, the following conclusions can be drawn:

The evaluation of the different scenarios based on scientific data served to resolve the questions of the participants for a preferable manner of restructuring their village. In the first citizens’ meetings conducted before the MCDA workshops, a lot of time was spent on discussions about transport, noise, smell and other issues. Having had presented the data that helped to address those questions, the following discussions concentrated more on solving the open challenges such as how to motivate other residents for the project. While those questions could have been addressed in another manner, the structured, comprehensive data sets used in the MCDA evaluations seemed to have a beneficial influence on the on-going process.

Furthermore, the MCDA presents an opportunity to address all open questions, doubts and prejudices. Throughout the interviews, key actors, especially antagonists of the project, were identified and later involved in the process. The MCDA workshops offered a platform for controversial discussion such that conflicts could come to the surface instead of ending in citizens’ initiatives against the project. However, it was difficult to overcome the initial resistance of some antagonists to attend the two informative MCDA workshops.

Both the weighting procedure and the development of alternatives and criteria provided opportunities to let actors participate in the decision process towards sustainable development [4]. Due to time constraints, the set of criteria and the scenarios were almost finalized by the project team before the first workshop occurred. In this preparation phase, the residents had no strong influence on the process. To achieve more comprehensive participation, it would be beneficial to involve the actors in those preparatory steps. The villagers would have possibly developed more or different alternative scenarios than those that were developed. Developing the scenarios with the participation of actors in a workshop would have meant a long break in the process because of the extensive data compilation required. A long break between the workshops may have been counterproductive because we anticipated that some of the actors in the village may have changed their decision under the pressure to make a decision or that many variables in the context might have changed. A new decision context would have meant a new MCDA application with different alternatives. Research is necessary on the flexibility of the MCDA process such that short-term modifications are possible and thus more participatory elements are involved.

The application of the “silent negotiation” weighting process confirmed the positive experience of Picted and Bollinger [34]. The separation of weighting and discussion allowed every participant to participate in the process. This tool helped the facilitator/moderator to receive the input of all of the participants and not only of the powerful actors. It was noted that as people shared their experiences, they were caught up in the process and remained focused. In the workshops, the facilitators aimed at creating an informal, fun atmosphere that had been proven in former studies to be a successful factor in sustainability projects [39]. In the case study, this atmosphere helped to change the mood of the group from “very skeptical towards the biogas plant” to “we will give it a try”. In terms of the results of the weighting, the weights were observed to be strongly affected by the stage of the project. In the discussion it became clear that the “security of supply” attracted the highest weight, as the issue of biomass supply was still open at that time.

It could be deduced from both the weighting results and in the discussion that consideration of the social criteria was very important for the residents. In addition, the presentation of “perceived values” based on the experience of other residents in other bioenergy villages seemed to address the persisting doubts. However, from a scientific perspective, the quality of data can be enhanced by further research. The results of the survey by Wüste and Schmuck [18] helped to find a difference between bioenergy and fossil fuel-based scenarios but not between the bioenergy scenarios themselves. Thus, only the difference between fossil fuel-based and bioenergy scenarios is illustrated in the assessment. This problem could be solved by using surveys based on the scenarios that were evaluated in the MCDA, which would extend the period of data compilation that is required.

In general, an emphasis was made on criteria that were able to address the questions of the local actors. For instance, we examined the after-tax profit of the cooperative or the heat-price-package for the heat consumers, as this information was highly requested. However, regarding sustainable development, evaluation criteria such as “life cycle costs” would have been more meaningful as they represent the total costs over the life cycle (31). Further research is necessary to bridge the gap between scientific and practical requirements.

Furthermore, the quality of the data must be improved by considering the LCA of closed-loop aquaculture. Consideration of “heat sinks” is necessary as the aquaculture in our case study created a challenge for the evaluation of energy systems. To provide a fair evaluation of the project, all processes linked to it must be considered and assessed completely. Otherwise, there is a danger of supporting “heat sinks”, as they increase the efficiency of the biogas plant without considering its price (in our case, the environmental burden resulting from fish-feed for the aquaculture). A general solution for the problem of how to manage those side processes without further extending the period of data compilation is necessary.

In general, the effort of data compilation is immense in that there is a real risk that decisions are made before the data are available. Data generation depends highly on the point of time when MCDA is implemented in the process. If MCDA evaluation occurs early in the decision process, when scenarios are still very unclear, data from the literature can be useful for the actors to gain an idea of what influences could be generated by the scenarios. However, if the decision context is advanced, people require an answer on real alternatives. In this case it might not be sufficient to evaluate any biogas plant; at that point in time, data on the actual biogas plant should be presented. Those data in general are available only from manufacturers and operators and are difficult to obtain. Additionally, the amount of data makes the entire process very inflexible, such that short-term amendments of alternatives are difficult to consider. Further work should be performed on standardized procedures and databases for the evaluation of energy systems that allow flexible data generation. Further work must be performed on the compatibility of LCA and MCDA. According to the experience of this case study, LCA and databases such as GEMIS are suitable data sources for MCDA, especially concerning ecological criteria. In LCA, much research has been performed to capture all columns of sustainability as life-cycle costs and social LCA are improved [40]. The effective application of those assessments for assisting decision makers aiming at a sustainable energy supply must be analyzed in future research.

Although many issues remain, MCDA is considered a very useful tool in supporting communities on their path towards a renewable energy supply because it accounts for the advantages and drawbacks of renewable energy systems that are difficult to quantify. Therefore, the effects that are usually excluded from the evaluation due to a lack of data can be integrated to provide a better understanding of the complexities involved.

In the selected case study in a village transitioning to a “bioenergy village”, the participation of community members in the decision-making process achieved obvious positive outcomes: The MCDA process offers a platform for the exchange of arguments and different perspectives; provides data that are able to answer the questions of the residents; and combines scientific data with the perspectives of actors such that well-balanced decision making is possible. The “silent negotiation” weighting procedure is highly applicable to this evaluation process as it was easy to under represent the actors and seemed to make the process more “fun”. Stable rankings of the energy scenarios could be achieved by convincing the group that the bioenergy scenarios were more sustainable for the village than those based on non-renewable energy sources. However, the data compilation was comprehensive and thus very time intensive. As a result, the procedure can be inflexible and have difficulties adapting to change in the decision context, thus requiring further research.

An overall conclusion from the case study that is in line with the conclusions drawn by other researchers [4] is that MCDA can achieve good results on the path to sustainable development if the focus is on the process and not only on results. If the researcher restricts his role to the calculating process and disregards the social context of the process, then the probable uptake of the data for assisting the decision-making is low. The ways in which the participatory elements of the method are used and implemented in the decision context have a strong influence on the success of the method as a whole. Greater attention must be given in future research to combine methods from operations research and psychology in a fruitful manner to support sustainable development projects [41,42]. The evidence presented in this case study may provide insights that can help to chart this path.