• Energy Research
• 2021-2025close
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Thermoacoustic technology emerges as a sustainable and low-carbon method for energy conversion, leveraging environmentally friendly working mediums and independence from electricity. This study presents the development of a multimode heat-driven thermoacoustic system designed to utilize medium/low-grade heat sources for room-temperature cooling and heating. We constructed both a simulation model and an experimental prototype for a single-unit direct-coupled thermoacoustic system, exploring its performance in heating-only, cooling-only, and hybrid heating and cooling modes. Internal characteristic analysis including an examination of internal exergy loss and a distribution analysis of key parameters was first conducted in the hybrid cooling and heating mode. The results indicated a positive-focused traveling-wave-dominant acoustic field within the thermoacoustic core unit, enhancing energy conversion efficiency. The output system performance was subsequently tested under different working conditions in the heating-only and cooling-only modes. A maximum output heating power of 2.3 kW and a maximum COPh of 1.41 were observed in the heating-only mode. Meanwhile, a cooling power of 748 W and a COPc of 0.4 were obtained in the typical cooling condition at 7 °C when operating in cooling-only mode. These findings underscore the promising potential of thermoacoustic systems for efficiently utilizing medium/low-grade heat sources for cooling and/or heating applications in the future.

Thermoacoustic technology emerges as a sustainable and low-carbon method for energy conversion, leveraging environmentally friendly working mediums and independence from electricity. This study presents the development of a multimode heat-driven thermoacoustic system designed to utilize medium/low-grade heat sources for room-temperature cooling and heating. We constructed both a simulation model and an experimental prototype for a single-unit direct-coupled thermoacoustic system, exploring its performance in heating-only, cooling-only, and hybrid heating and cooling modes. Internal characteristic analysis including an examination of internal exergy loss and a distribution analysis of key parameters was first conducted in the hybrid cooling and heating mode. The results indicated a positive-focused traveling-wave-dominant acoustic field within the thermoacoustic core unit, enhancing energy conversion efficiency. The output system performance was subsequently tested under different working conditions in the heating-only and cooling-only modes. A maximum output heating power of 2.3 kW and a maximum COPh of 1.41 were observed in the heating-only mode. Meanwhile, a cooling power of 748 W and a COPc of 0.4 were obtained in the typical cooling condition at 7 °C when operating in cooling-only mode. These findings underscore the promising potential of thermoacoustic systems for efficiently utilizing medium/low-grade heat sources for cooling and/or heating applications in the future.

Environmental tax reform (ETR), a shift from labour to carbon taxes, has been mostly modelled using general equilibrium (GE) analysis. Since a low-carbon transition will require deep transformations, one will also have to address out-of-equilibrium dynamics and increased agent heterogeneity. Unlike GE models, agent-based models (ABMs) are well equipped to deal with this. We therefore replicate a recent GE model for ETR using an agent-based approach. This process, known as "agentization", allows assessing similarities as well as differences in policy impacts between the two modelling approaches, in turn providing a test of the robustness of the GE results. We find that the agent-based model is able to replicate many results of the general equilibrium analysis, while revealing strengths and weaknesses of both model types. We discuss concrete implementation steps and difficulties experienced in the GE-ABM translation process. We illustrate the potential of ABM by extending the model in several directions. We show that heterogeneous subsistence consumption can increase the space for combining a double dividend with an equity goal, and that overall macro-economic results can conceal important distributional impacts when green preferences and labour supply elasticities vary.

Environmental tax reform (ETR), a shift from labour to carbon taxes, has been mostly modelled using general equilibrium (GE) analysis. Since a low-carbon transition will require deep transformations, one will also have to address out-of-equilibrium dynamics and increased agent heterogeneity. Unlike GE models, agent-based models (ABMs) are well equipped to deal with this. We therefore replicate a recent GE model for ETR using an agent-based approach. This process, known as "agentization", allows assessing similarities as well as differences in policy impacts between the two modelling approaches, in turn providing a test of the robustness of the GE results. We find that the agent-based model is able to replicate many results of the general equilibrium analysis, while revealing strengths and weaknesses of both model types. We discuss concrete implementation steps and difficulties experienced in the GE-ABM translation process. We illustrate the potential of ABM by extending the model in several directions. We show that heterogeneous subsistence consumption can increase the space for combining a double dividend with an equity goal, and that overall macro-economic results can conceal important distributional impacts when green preferences and labour supply elasticities vary.

The opportunities and challenges of applying micronutrients (MiNs) in full-scale anaerobic digestion (AD) plants has been reviewed. The review discusses the underlying mechanisms and the role of different micronutrients (Fe, Ni, Co, Mo, Zn, Cu, Se) in the enhancement of AD performance, as well as their environmental and economic implications in full-scale AD systems. Bioavailability is a key factor affecting the effectiveness of micronutrients application on the biochemical aspects of AD. Accordingly, the technical aspects of AD with a direct impact on bioavailability have been identified and critically addressed. Mono-supplementation is not the most favorable strategy to increase micronutrient bioavailability due to limited solubility, formation of insoluble compounds, interaction with other compounds, and specific microbial requirements. Nonetheless, co-supplementation can increase the bioavailability due to the simultaneous synergetic effects of co-micronutrients supplementation on the biochemical aspects of AD. However, the inconsistency of reported lab-scale results and the lack of protocols or guidelines for analyzing the bioavailability of micronutrients limit results interpretation and full-scale application. The environmental and economic implications of these micronutrients are other critical factors that need further research. The economic results showed that the mono-supplementation can be economically favorable when a methane enhancement of 20% is achieved. Co-supplementation of micronutrients is the most economically feasible option since this strategy allows reducing the total dosage of micronutrients when compared with mono-supplementation. The authors are grateful for the scholarship from the TUM SEED Center of the Technical University of Munich, which is part of the DAAD (German Academic Exchange Service) program “exceed” supported by DAAD as well as the German Federal Ministry for Economic Cooperation and Development (BMZ) and in cooperation with the hosting Chair of Urban Water System Engineering of TUM. Sergi Astals is thankful to the Spanish Ministry of Science, Innovation and Universities for his Ramon y Cajal. Peer Reviewed

The opportunities and challenges of applying micronutrients (MiNs) in full-scale anaerobic digestion (AD) plants has been reviewed. The review discusses the underlying mechanisms and the role of different micronutrients (Fe, Ni, Co, Mo, Zn, Cu, Se) in the enhancement of AD performance, as well as their environmental and economic implications in full-scale AD systems. Bioavailability is a key factor affecting the effectiveness of micronutrients application on the biochemical aspects of AD. Accordingly, the technical aspects of AD with a direct impact on bioavailability have been identified and critically addressed. Mono-supplementation is not the most favorable strategy to increase micronutrient bioavailability due to limited solubility, formation of insoluble compounds, interaction with other compounds, and specific microbial requirements. Nonetheless, co-supplementation can increase the bioavailability due to the simultaneous synergetic effects of co-micronutrients supplementation on the biochemical aspects of AD. However, the inconsistency of reported lab-scale results and the lack of protocols or guidelines for analyzing the bioavailability of micronutrients limit results interpretation and full-scale application. The environmental and economic implications of these micronutrients are other critical factors that need further research. The economic results showed that the mono-supplementation can be economically favorable when a methane enhancement of 20% is achieved. Co-supplementation of micronutrients is the most economically feasible option since this strategy allows reducing the total dosage of micronutrients when compared with mono-supplementation. The authors are grateful for the scholarship from the TUM SEED Center of the Technical University of Munich, which is part of the DAAD (German Academic Exchange Service) program “exceed” supported by DAAD as well as the German Federal Ministry for Economic Cooperation and Development (BMZ) and in cooperation with the hosting Chair of Urban Water System Engineering of TUM. Sergi Astals is thankful to the Spanish Ministry of Science, Innovation and Universities for his Ramon y Cajal. Peer Reviewed

Abstract While it is generally accepted that our fossil fuel-dominated energy systems must undergo a sustainable transition, researchers have often neglected the potential impacts of this on water and land systems. However, if unintended environmental impacts from this process are to be avoided, understanding its implications for land use and water demand is of crucial importance. Moreover, developed countries may induce environmental stress beyond their own borders, for instance through extensive imports of bioenergy. In this paper, Germany serves as an example of a developed country with ambitious energy transformation targets. Results show that in particular, the politically-driven aspiration for more organic farming in Germany results in a higher import quota of biomass, especially biofuels. These imports translate into land demand, which will exceed the area available in Germany for bioenergy by a factor of 3–6.5 by 2050. As this will likely bring about land stress in the respective exporting countries, this effect of the German energy transformation ought to be limited as much as possible. In contrast, domestic water demand for the German energy system is expected to decrease by over 80% through 2050 due to declining numbers of fossil-fuelled power plants. However, possible future irrigation needs for bioenergy may reduce or even counterbalance this decreasing effect. In addition, energy policy targets specific to the transport sector show a high sensitivity to biomass imports. In particular, the sector-specific target for greenhouse gas reductions will seemingly promote biomass imports, leading to the above-described challenges in the pursuit of sustainability.