André Sternberg

Power-to-What? : Environmental assessment of energy storage systems

A large variety of energy storage systems are currently investigated for using surplus power from intermittent renewable energy sources. Typically, these energy storage systems are compared based on their Power-to-Power reconversion efficiency. Such a comparison, however, is inappropriate for energy storage systems not providing electric power as output. We therefore present a systematic environmental comparison of energy storage systems providing different products. As potential products, we consider the reconversion to power but also mobility, heat, fuels and chemical feedstock. Using life cycle assessment, we determine the environmental impacts avoided by using 1 MW h of surplus electricity in the energy storage systems instead of producing the same product in a conventional process. Based on data for several countries including the United States, Brazil, Japan, Germany and the United Kingdom, our analysis determines the highest reduction of global warming and fossil depletion impact for using surplus power in heat pumps with hot water storage and battery electric vehicles. Third highest environmental benefits are achieved by electrical energy storage systems (pumped hydro storage, compressed air energy storage and redox flow batteries). Environmental benefits are also obtained if surplus power is used to produce hydrogen but the benefits are lower. Our environmental assessment of energy storage systems is complemented by determination of CO2 mitigation costs. The lowest CO2 mitigation costs are achieved by electrical energy storage systems.

Life cycle assessment of CO2-based C1-chemicals

Carbon dioxide (CO2) and hydrogen are promising feedstocks for a sustainable chemical industry. Currently, the conversions of CO2 and hydrogen are most advanced for chemicals with 1 carbon atom, the so-called C1-chemicals, with the first pilot plants in operation. For formic acid, carbon monoxide, methanol, and methane, CO2-based C1-chemicals can reduce the impacts of fossil depletion and global warming through the substitution of fossil-based processes. Existing life cycle assessment (LCA) studies for carbon monoxide, methanol, and methane show that a reduction in environmental impacts is achieved if hydrogen is supplied by water electrolysis with renewable electricity. However, in the foreseeable future, renewable electricity will be limited. Thus, from an environmental point of view, renewable electricity should be employed for chemical processes in the order of highest environmental impact reductions. Environmental impact reductions are the difference in environmental impacts of fossil-based processes and CO2-based processes. In this study, we compared the CO2-based production of formic acid, carbon monoxide, methanol, and methane. We determined the reduction of global warming and fossil depletion impacts using 1 kg of hydrogen. Our results show that the CO2-based production of formic acid achieves the highest environmental impact reductions, followed by carbon monoxide and methanol. The lowest environmental impact reductions are achieved for CO2-based methane production. Our analysis reveals that the CO2-based production of formic acid can reduce environmental impacts, compared to the fossil-based process, even if hydrogen is supplied by fossil-based steam-methane-reforming.

Assessing the environmental potential of carbon dioxide utilization: A graphical targeting approach

Abstract Carbon Capture and Utilization (CCU) has the potential to reduce both greenhouse gas emissions and fossil fuel use. However, the conversion of CO 2 is intrinsically difficult due to its low energetic state. Thus, a positive environmental effect of a CO 2 -consuming reaction cannot be taken for granted. In this work, we therefore present a graphical method to identify promising reaction schemes using CO 2 as a feedstock. Reactant mixtures leading to minimal life-cycle greenhouse gas (GHG) emissions are determined. The optimal reaction schemes strongly depend on the reactants global warming potential (GWP); in the case of CCU, the future GWP values of CO2 and H 2 are particularly critical and subject to major uncertainty today. The graphical method therefore provides GWP targets for CO 2 capture and H 2 production technologies. The method is demonstrated for the production of methanol. Five optimal reaction schemes are identified depending on the GWP values of CO 2 and H 2 . Thus, four threshold relations for the GWP of CO 2 and H 2 are derived showing directly under which conditions the utilization of CO 2 as a feedstock is environmentally preferential.

Blending Acceptance as Additional Evaluation Parameter into Carbon Capture and Utilization Life-Cycle Analyses

Carbon Capture and Utilization (CCU) captures and uses CO2 as a feedstock to produce carbon-based saleable products. However, sustainable technology innovations are only attractive to investors and justify (public) subsidies if they provide economical or ecological added value. Therefore, life-cycle analyses (LCA) are applied to identify the environmentally most optimal option of a technology scenario. Since LCA do not address the social dimension of sustainable innovations so far, a study is presented, where acceptance is assessed as additional life-cycle evaluation parameter. A prestudy (qualitative interviews, n = 25 participants) was run to identify acceptance-relevant parameters of CCU site deployment. In a conjoint study (n = 110), which investigated the acceptance of CCU site deployment scenarios, the profitability, CO2-source, and type of CO2-derived product were systematically varied as acceptance-relevant criteria. Findings show, that profitability had the highest impact on CCU technology scenario preferences. Fuel was the most attractive CCU product option and steel plants were the most preferred CO2-source. In sensitivity analyses specific acceptable and nonacceptable CCU technology scenarios were identified. The assessment of acceptance for CCU deployment scenario parameters allows to include acceptance as additional evaluation and weighting parameter into life-cycle analyses of CCU technology scenarios.

CO2 vs Biomass: Identification of Environmentally Beneficial Processes for Platform Chemicals from Renewable Carbon Sources

Conventionally, platform chemicals are produced from fossil feedstock. In recent years, the production of chemicals from renewable feedstock has been considered. One possible renewable carbon source is biomass. Another option is carbon dioxide (CO2). A rigorous comparison of processes employing renewable carbon sources is missing today. We therefore identify the environmentally most beneficial process routes for platform chemicals. All processes are integrated into a single superstructure, which is analyzed using linear optimization minimizing global warming impacts. The optimal solutions exploit synergies between the different process routes and feedstocks.