The Controversies of Bioenergy

Abstract

Rising carbon dioxide concentrations in the air increase the global temperature since the industrial revolution. Today, there exists a great need to limit global warming, and an energy transition is vital to do so. With the upcoming changes in our energy system, bioenergy is widely discussed, resulting in a heated debate on including or excluding bioenergy in the energy transition. This study aims to identify the least controversial feedstocks out of 40 different ones and if they will help to resolve the controversies around bioenergy. Before a feedstock is deemed controversial, a background of bioenergy was established to see what role bioenergy has in today's energy system and in the future. A literature analysis identifies the role of bioenergy today. Using the 'IAMC 1.5C Scenario Explorer' hosted by IIASA the role in the future is identified. To determine the least controversial feedstocks, a multi-criteria decision analysis (MCDA) is performed. The PROMETHEE II method is used to perform the MCDA and the entropy weight method for weighting the criteria. The ranking and weighting make use of MATLAB. Since the aim is to classify feedstocks as the least controversial, the criteria are deduced from a literature analysis and represent the controversies of bioenergy. The first part of the report indicates a significant role in today's renewable energy system and a shift towards more modern bioenergy implementations like biofuels and bio-electricity. According to the scenario analysis, for the five different shared socio-economic pathways, bioenergy will be used. Besides the identification of a clear use of bioenergy in the future energy system, the scenario analysis of TFE of bioenergy indicated a shift towards modern bioenergy use. It was observed that the solid biomass use reduced and a strong increase in liquid biofuels in the transport sector will happen. These findings are in line with the predictions made by the IPCC. Also, this is in accordance with the observed growth rates and development trends found for today and in the recent years. This all results in the conclusion that bioenergy is important for the energy transition. Due to the observed research and development into biofuels and bio-electricity, traditional bioenergy will be phased out and replaced by modern bioenergy types. The next part of the report considers the controversies around bioenergy. The following controversies are identified and considered the most discussed ones: chain emissions, removal of carbon sinks, the carbon debt, land-use, competition with the food industry, and biodiversity. Identification of the controversies and with that the criteria are necessary for the feedstock ranking. The MCDA ranking shows that residues and wastes feedstocks are the least controversial, followed by alfalfa. The top eight high-scoring crops are alfalfa, oil palm, kenaf, mustard, cotton seeds, prairie grasses, camelina, and hemp. For this top eight, an additional ranking that included water use is done. This ranking shows that incorporating such a detail does not significantly change the results. It was seen that the top four was kept constant except when the simplest form of an MCDA is applied. Cotton seeds drops two to three places in rank. Prairie grasses replace cotton seed at place five when water use is considered. The most remarkable contradiction with literature is that oil palm ranks very high, and miscanthus is not present in the top eight. Oil palm is, in literature, considered a very controversial feedstock, and miscanthus shows promising features. These results indicate that either the data is not specific enough, or the criteria are not detailed enough. Another explanation is that the choice for an objective weighting method is not the best choice since it excludes opinions of the decision makers (the scientist participating in the debate). The debate is opinion and preference driven, which makes that a data based weighting method might not be ideal. Nevertheless, the rank of the waste streams is following the expectations. The results indicate that waste streams are to be used as primary feedstocks when controversies need to be resolved. The PROMETHEE II ranking shows this solution, and a sensitivity analysis supports the results. Reflection of the data for the feedstocks and the controversies shows that the use of residues and waste feedstocks can resolve several controversies with a relatively high degree of certainty (controversy of land use and competition with food industry) and others with some degree of certainty (controversy of chain emissions and biodiversity). Due to the global scope and simplifications, the data used could be improved. Therefore, further research is necessary to back-up the findings. Nevertheless, this research gives insight into the controversiality of several feedstocks and takes a first step in tackling the bioenergy debate.