• Energy Research
• 13. Climate action close
• Applied Energy close

Abstract Computable general equilibrium models are becoming popular for simulating emissions trading systems. However, these models make various assumptions about the production structure and the possibilities of substituting energy for productive factors or inputs. Therefore, this study aims to analyze how different options to incorporate energy into the nested production structure of a computable general equilibrium model affect the obtained impacts when an emissions trading system is implemented. A flexible computable general equilibrium model called ECOMODEL is developed, which is the first model that allows choosing any of the three nested production structures most used in the literature (KEL-M, KL-EM, or KLE-M). The Chilean economy is used as a case study since there is a current database with high disaggregation of the energy sector for calibrating the computable general equilibrium model. The results show that the simulated impacts with KEL-M and KL-EM structures are the best when elasticities of substitution equal to the values ​​most frequently used in previous studies are chosen. However, the KEL-M structure that considers energy as a substitute for capital provides overly optimistic environmental results when high elasticities of substitution are used, obtaining the lowest reduction in Gross Domestic Product and the lowest price of the emissions trading system. Furthermore, the KLE-M structure gives unrealistic results regardless of the elasticities of substitution used. In consequence, a KL-EM nested production structure should be prioritized to simulate an emissions trading system since it provides realistic results and is less sensitive to the values of the elasticities of substitution.

Abstract The urge to increase renewable energy penetration into the power supply mix has been frequently highlighted in response to climate change. South Korea was analyzed as a case study for which the government has shown motivation to increase renewable energy penetration. Herein, a hybrid renewable energy system (HRES) including solar and wind energies were selected due to their relatively stable and mature technology. In addition, Power-to-X has been incorporated to cover other renewable energy options such as hydrogen and synthetic natural gas (SNG). Therefore, an approach of forecasting the weather characteristics and demand loading over a relatively long timeframe was implemented via deep learning techniques (LSTM and GRU) and statistical approaches (Fbprophet and SARIMA), respectively. A deployment strategy incorporating HRES and Power-to-X is then proposed in correspondence to the forecasted results of the 15 regions considered in this study. An extension of this, the reliability of the designed system is further assessed based on the probability of the demand losses with the aid of Monte-Carlo simulation. With the proposed deployment strategy, a total annual cost of 9.88 × 1011 $/year and a greenhouse gas reduction of 1.24 × 106 tons/year are expected for a 35% renewable energy penetration. However, only SNG shows relatively competitive cost (at 23.20 $/m3 SNG), whereas the average costs of electricity (0.133 $/kWh) and hydrogen (7.784 $/kg H2) across the regions are yet to be competitive compared to the current market prices. Nonetheless, the priority of deployment across regions has been identified via TOPSIS.

Abstract With the increase of energy consumption and wastes generation due to human activities, anaerobic digestion (AD), a technology which turns wastes into bio-energy, is receiving more and more attention in the world. It is well known that there are at least three stages involved in anaerobic digestion, i.e., hydrolysis, acidification, and methanogenesis. Until now, however, the advances in enhancing acidification and methanogenesis have not been reviewed. This review provides a comprehensive overview of the methods reported to enhance each step involved in anaerobic digestion. More important, enzymes are the key to anaerobic digestion, and the strategies for improving enzyme activity are summarized. As electron transfer has been reported to play an important role in anaerobic digestion, the research progress of the approaches for the acceleration of direct interspecies electron transfer in methane production is also introduced. In addition, the recent advances in increasing the reduction of carbon dioxide to methane, which has been widely observed in methanogenesis step, are reviewed. Furthermore, the techno-economic assessment of anaerobic digestion is made, and the key points for future studies are proposed.

Abstract Wind power technology is one of the cleanest electricity generation technologies that are expected to have a substantial share in the future electricity mix. Nonetheless, the expected increase in the market share of wind technology has led to an increasing concern of the availability, production capacity and geographical concentration of the metals required for the technology, especially the rear earth elements (REE) neodymium (Nd) and the far less abundant dysprosium (Dy), and the impacts associated with their production. Moreover, Nd and Dy are coproduced with other rare earth metals mainly from iron, titanium, zirconium, and thorium deposits. Consequently, an increase in the demand for Nd and Dy in wind power technology and in their traditional applications may lead to an increase in the production of the host metals and other companion REE, with possible implications on their supply and demand. In this regard, we have used a dynamic material flow and stock model to study the impacts of the increasing demand for Nd and Dy on the supply and demand of the host metals and other companion REE. In one scenario, when the supply of Dy is covered by all current and expected producing deposits, the increase in the demand for Dy leads to an oversupply of 255 Gg of total REE and an oversupply of the coproduced REE Nd, La, Ce and Y. In the second and third scenarios, however, when the supply of Dy is covered by critical REE rich deposits or Dy rich deposits, the increase in Dy demand results in an oversupply of Ce and Y only, while the demand for Nd and La exceeds their supply. In the case of an oversupply of REEs, the environmental impacts associated with the REEs production should be allocated to Dy and consequently to the technologies that utilize the metal. The results also show that very large quantities of thorium will be co-produced as a result of the demand for Dy. The thorium would need to be carefully disposed of, or significant thorium applications would need to be found.

This special edition to be published in Applied Energy brings together a range of papers that explore the complex, multi-dimensional and inter-related issues associated with the supply or value chains that make up energy systems and how a focus on them can bring new insights for energy security in a low carbon transition.\ud \ud Dealing with the trilemma of maintaining energy security, reducing greenhouse gas emissions and maintaining affordability for economies and end users are key issues for all countries, but there are synergies and trade-offs in simultaneously dealing with these different objectives. Currently, industrialised energy systems are dominated by supply chains based on fossil fuels and these, for the most part, have been effective in enabling energy security and affordability. However, they are increasingly struggling to do this, particularly in respect to efforts to tackle climate change, given that the energy sector is responsible for around two-thirds of the global greenhouse gas emissions [1]. A key challenge is therefore how to decarbonise energy systems, whilst also ensuring energy security and affordability. This special issue, through a focus on supply chains, particularly considers the interactions and relationships between energy security and decarbonisation.\ud \ud Energy security is a property of energy systems and their ability to withstand short-term shocks and longer-term stresses depends on other important system properties including resilience, robustness, flexibility and stability [2]. Energy systems are essentially a supply chain comprising of multiple and interrelated sub-chains based around different fuels, technologies, infrastructures, and actors, operating at different scales and locations – from extraction/imports and conversion through to end use [3]. These supply chains have become increasingly globalised and are influenced by the on-going shifts in global supply and demand. Thus the aim of this special issue is to explore and discuss how to enable the development of a secure and sustainable energy system through a better understanding of both existing and emerging low carbon energy supply chains as well as of new approaches to the design and management of energy systems. In part, because moving from a system dominated by fossil fuels to one based on low carbon creates a new set of risks and uncertainties for energy security as well as new opportunities.\ud \ud A large number of submissions from over 18 countries were received for this special edition and 16 papers were accepted after peer review. These address a variety of issues and we have chosen to discuss the findings under two key themes, although many of the papers cut across these: (1) Insights from, and for, supply chain analysis. (2) Insights for energy security and its management. We then provide in (3) a summary of insights and research gaps. Table 1 provides a snapshot of the areas covered by the papers showing: theme (s); empirical domains; and geographical coverage.

Abstract Integrating low-carbon technologies (e.g. heat pumps, photovoltaic systems) in buildings influences the stability of the low-voltage grid, which therefore often requires to be reinforced. This article proposes a techno-economic methodology to identify the reinforcements needed to maintain grid stability at the lowest life-cycle cost. Novel contributions include the consideration of three-phase connection of low-carbon technologies as a reinforcement option and the fact that we study to what extent grid reinforcements can mitigate voltage unbalance issues. Additionally, to reduce computing time, a dummy island approach is used, whereby one feeder is modelled in detail and the remainder of the distribution island is represented by an aggregated load. Finally, random repetitions are proposed, to consider uncertainties related to building properties, occupants and the location of low-carbon technologies in the feeders. The methodology is applied to investigate the integration of heat pumps and photovoltaic systems in typical Belgian rural and urban grids. For the rural grid, heat pumps may lead to significant reinforcement costs (up to 1230 €/dwelling), mainly due to voltage stability problems. For the urban grid, heat pump and photovoltaic integration causes low reinforcement cost (

Abstract This paper presents a parametric analysis for a medium to large size (290–500 MW th receiver thermal power) central receiver plant considering the present market trends. The analysis is divided in 4 steps: • Size and location analysis: for a medium to large size central receiver power plant, three turbine power and three different locations that are involved in the development of power tower plants, have been analyzed to assess the impact over the design characteristics of the solar field and receiver sub-systems and over the levelized electricity cost. • Technology analysis: as commercial power tower plants in operation today are mainly using steam and molten nitrate salts, the present analysis compares the two main technologies, without thermal energy storage to evaluate both under similar design conditions. • Storage analysis: thermal energy storage increases the value of electricity produced and the plant capacity factor for both technologies (steam and molten nitrate salts). For this reason, the analysis shows for each optimized solar field and receiver thermal power, the optimum combination of turbine power and thermal energy storage that minimizes the levelized electricity cost, for both technologies. • Component’s cost analysis: market trends are focused on the specific cost reduction by means of larger plant size and through an improved economy of scale. As a result, and based on baseline cost parameters widely accepted in solar industry, an analysis over the specific costs of major components on the electricity cost has been carried out, to lead where the research and development efforts should be made.

AbstractThe UK government heat strategy is partially based on decarbonisation pathways from the UK MARKAL energy system model. We review how heat provision is represented in UK MARKAL, identifying a number of shortcomings and areas for improvement. We present a completely revised model with improved estimations of future heat demands and a consistent representation of all heat generation technologies. This model represents all heat delivery infrastructure for the first time and uses dynamic growth constraints to improve the modelling of transitions according to innovation theory. Our revised model incorporates a simplified housing stock model, which is used produce highly-refined decarbonisation pathways for residential heat provision. We compare this disaggregated model against an aggregated equivalent, which is similar to the existing approach in UK MARKAL. Disaggregating does not greatly change the total residential fuel consumption in two scenarios, so the benefits of disaggregation will likely be limited if the focus of a study is elsewhere. Yet for studies of residential heat, disaggregation enables us to vary consumer behaviour and government policies on different house types, as well as highlighting different technology trends across the stock, in comparison with previous aggregated versions of the model.

Abstract This study aimed to investigate the applicability of the solar heating system in different geographical regions with different meteorological conditions, of which parabolic trough solar collectors (PTCs) were operated with the absorption heat pumps (AHP) and oil/water heat exchanger (OWHE) at medium and low operating temperature respectively. The heat transfer model for PTCs was constructed with a lumped parameter method and validated by experimental results. The thermal performance of the system was evaluated by the index of primary energy ratio (PER). The results showed that on overcast days with low direct normal irradiance (DNI), the operation of the PTC + AHP/OWHE system was not cost-effective. On cloudy days with high DNI lasting for a short period (e.g. 2 h), the operation of the PTC + OWHE system was better than that of the PTC + AHP system as the latter needed more preheating energy before the system operation. While on sunny days with high DNI lasting for a longer period (e.g. 8 h), the PTC + AHP system was suggested to be operated as it owned higher PER values. Besides, the solar energy distributions in China could be divided into four categories, i.e. rich (S1), relatively rich (S2), available (S3) and absent (S4). In S1 region the PTC + AHP system was suggested to be operated. In S4 region the PTC + AHP/OWHE system was not suggested to be operated. While in S2 and S3 region, whether the operation of the PTC + AHP/OWHE system was suggested depending on the meteorological conditions. With these findings the developing strategy of the solar heating system in different geographical regions can be devised and the operating strategy on a specific day with different weather conditions can be developed, which is helpful to guide the application of solar energy and improve the energy structure in domestic heating.

Abstract The correlation between effectiveness of multiple operating parameters is a complicated issue and significant to the safe operation of solid oxide fuel cell/gas turbine (SOFC/GT) hybrid system. This paper presents a numerical analysis on biogas-fueled SOFC/GT hybrid system with a recirculation process using combustor exhaust gas. With consideration of safety constraints for critical components (fuel cell thermal crack, reformer carbon deposition, turbine blade overheat), the interaction mechanism of recirculation ratio, steam/carbon ratio and fuel/air ratio is studied from the perspective of thermodynamic analysis. Results show that the recirculation process could increase the electrical efficiency of system from 58.18% to 62.8%. However, for the safety consideration of SOFC, the acceptable recirculation ratio should be controlled between 0.17 and 0.32. Meanwhile, there exists a minimum point of turbine inlet temperature at the recirculation ratio of 0.3. With recirculation ratio switched from 0.1 to 0.3, impact of steam/carbon ratio variation on SOFC temperature gradient shrinks from 52.5% to 17.9% of the reference value. On the other hand, effect of fuel/air ratio variation on SOFC temperature gradient is promoted from 20.8% to 44.3% of the reference value, due to that oxidation reaction of biogas becomes a dominant factor. Based on these results, a parametric comparison is carried out to quantitatively describe the impact of recirculation process on the effectiveness of other parameters. Short discussion is conducted on parameter selection to acquire higher system efficiency and sufficient safety range, in which case the total output power of 176.8 kW and electrical efficiency of 61.78% could be achieved.