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Industrial CO2 use - An overview: Technologies for CO2 utilisation have recently been gaining in importance. Some CO2 uses, such as the production of urea and methanol, are practised on an industrial scale. Many others are being tested. Good progress has been made in the production of plastics and synthetic fuels. The use of carbonised CO2, e.g. for the production of building materials, can lead to the longterm storage of CO2. Synthetic fuels, however, only store the used CO2 for a short time, but prevent the use of fuels made from petroleum. Re-sequestration keeps the CO2 in the cycle. Synthetic methane can play an important role for energy storage and ammonia for the transport of green hydrogen. Overall, however, the contribution of CO2 uses to climate protection is rather limited. To limit global warming, a combination of many climate engineering methods is required in addition to a drastic reduction of global emissions.

Viele Sektoren können durch Elektrifizierung direkt erneuerbare Energien einsetzen. Im Flug und Schwerlastverkehr sowie diversen anderen Anwendungen wird man auch zukünftig auf flüssige synthetische Kraftstoffe angewiesen sein. Kraftstoffe auf Biomassebasis sind schon länger eine Möglichkeit, jedoch ist deren Potential begrenzt (Biomass to Liquid). Durch die Synthese von Wasserstoff und aus der Luft oder indust riellen Prozessen abgeschiedenes Kohlendioxid lässt sich Synthesegas erzeugen, mit dem viele unterschiedliche Kraftstoffe produziert werden können (Power to Liquid). Die direkte Erzeugung von Synthesegas aus Wasser und Kohlendioxid mit Solarkollektoren (Su n to Liquid) ist eine Möglichkeit, die aber noch in der Entwicklung ist.

The aim of prospective Life Cycle Assessment (LCA) is to assess the ecological impacts of emerging or future technology developments and thus to identify (undesirable) impacts at an early stage in line with the precautionary principle. Various methods can be used to collect foreground Life Cycle Inventory (LCI) data of such technologies that are used for prospective LCA, e.g. scenario techniques, learning curves or expert interviews. For prospective background LCI data futurized ecoinvent databases are available via premise.This contribution shows different approaches to prospective LCA using three technology examples of different TRL. Firstly, future developments of alternatively powered ferries (DBEV, FCEV, BEV) were surveyed by means of expert interviews and workshops. Secondly, learning curves and cumulative capacity curves were used to determine future technological developments for the rotor blades of offshore wind turbines from two manufacturers (Siemens Gamesa, Vestas). Furthermore, premise was applied to achieve a more realistic picture for future environmental impacts. Thirdly, to investigate potential environmental optimization potentials of a magnesium battery (Mg-S) based on expert judgement at very early TRL. Furthermore, the influence of different electric energy grid mix usage for production was analyzed. The technology developments were environmentally assessed by an LCA partly in comparison with conventional or rather status quo technologies, the results of which are presented in this contribution.

The "MCDA for sustainability assessment – insights to Helmholtz Association activities" Working Paper aims to compile and reflect previous and on-going work within the Helmholtz Association related to MCDA, in particular, to present use cases and key methodological aspects. It has a focus on but is not limited to energy technologies and systems and is mainly based on the presentations held at the online workshop “Multi criteria decision analysis for sustainability assessment of energy technologies and systems”. The workshop was organized within the activities of the Helmholtz program ESD Topic 1 "Energy System Transformation" and took place on November 22nd, 2021.

To bring about a successful energy and mobility transition, multifaceted technologies are developed. Hydrogen and Fuel Cell Electric Vehicles (FCEV) cannot only replace fossil fuels and accelerate the electrification of the mobility sector, they also have the advantage of fast refuelling, compared to battery electric vehicles. Next to technical advantages, environmental, economic and social aspects must be considered. Especially the social implications for various stakeholders are often neglected, but no less important. It can affect them to a various extend and in regard to manifold risks and opportunities.Environmental aspects along the whole life cycle of a product, e.g. resource extraction, production, use and end-of-life, can be estimated with the method of Life Cycle Assessment (LCA). Analogously the concept of Social Life Cycle Assessment (S-LCA) addresses social aspects. The goal of this study is to identify possible societal risks and opportunities associated with a production of FCEVs in Germany. In a cradle-to-gate scope, local manufacturing is considered, comprising battery, electric motor, hydrogen tank, glider, and proton exchange membrane fuel cell. By conducting an S-LCA, valuable knowledge about societal hotspots can serve as a basis for further actions.

Reducing greenhouse gas (GHG) emissions in the transport sector is one of the biggest challenges in the German energy transition. Furthermore, sustainable development does not stop with reducing GHG emissions. Other environmental, social and economic aspects should not be neglected. Thus, here a comprehensive sustainability assessment for passenger vehicles is conducted for 2020 and 2050. The discussed options are an internal combustion engine vehicle (ICEV) fuelled with synthetic biofuel and fossil gasoline, a battery electric vehicle (BEV) with electricity from wind power and electricity mix Germany and a fuel cell electric vehicle (FCEV) with hydrogen from wind power. The life cycle-based assessment entails 13 environmental indicators, one economic and one social indicator. For integrated consideration of the different indicators, the MCDA method Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) is chosen. For the assessment, a consistent assessment framework, i.e. background scenario and system boundaries, and a detailed modelling of vehicle production, fuel supply and vehicle use are the cornerstones. The BEV with wind power is the most sustainable option in 2020 as well as in 2050. While in 2020, the second rank is taken by the ICEV with synthetic biofuel from straw and the last rank by the FCEV, in 2050 the FCEV is the runner-up. With the help of MCDA, transparent and structured guidance for decision makers in terms of sustainability assessment of motorized transport options is provided.