Organizing prosumers into electricity trading communities: Costs to attain electricity transfer limitations and self‐sufficiency goals

Among household electricity end users, there is growing interest in local renewable electricity generation and energy independence. Community‐based and neighborhood energy projects, where consumers and prosumers of electricity trade their energy locally in a peer‐to‐peer system, have started to emerge in different parts of the world. This study investigates and compares the costs incurred by individual households and households organized in electricity trading communities in seeking to attain greater independence from the centralized electricity system. This independence is investigated with respect to: (i) the potential to reduce the electricity transfer capacity to and from the centralized system and (ii) the potential to increase self‐sufficiency. An optimization model is designed to analyze the investment and operation of residential photovoltaic battery systems. The model is then applied to different cases in a region of southern Sweden for year 2030. Utilizing measured electricity demand data for Swedish households, we show that with a reduced electricity transfer capacity to the centralized system, already a community of five residential prosumers can supply the household demand at lower cost than can prosumers acting individually. Grouping of residential prosumers in an electricity trading community confers greater benefits under conditions with a reduced electricity transfer capacity than when the goal is to become electricity self‐sufficient. It is important to consider the local utilization of photovoltaic‐generated electricity and its effect on the net trading pattern (to and from the centralized system) when discussing the impact on the electricity system of a high percentage of prosumers.     

Low‐grade heat‐driven Rankine cycle,a feasibility study

Conversion of low‐grade heat to high‐quality energy such as electricity using the Rankine cycle poses serious challenges. When such conversion is possible, it is invariably expensive or unacceptable due to environmental concerns associated with the working medium. The low‐grade heat can either be from exhaust systems or from solar radiation. Thus, the topic addresses a very useful subject, combining energy efficiency and renewable energy. Although high‐grade heat recovery and energy conversion is a mature technology widely covered by the literature, low‐grade energy conversion, especially using thermodynamic cycles, has not been sufficiently addressed to date. This paper addresses the feasibility of a low‐grade heat‐driven Rankine cycle to produce power using a scroll expander, a low toxicity, low flammability, and ozone‐neutral working fluid. A cost benefit analysis of the recommended system shows that it is a viable option for solar power generation, at about one‐third the cost of a comparable photovoltaic system. Copyright © 2008 John Wiley & Sons, Ltd.     

A secure blockchain‐based demurrage mechanism for energy trading in smart communities

This paper combines additive homomorphic encryption and consortium blockchain technology to provide privacy and trust. Additionally, a dynamic energy pricing model is formulated based on the demand response ratio (DRR) of the load demand of prosumers to address fixed energy pricing problems. The proposed dynamic pricing model includes demurrage fees, which is a monetary penalty imposed on a prosumer, if it failed to deliver energy within the agreed duration. Furthermore, this paper also designs and analyzes a threat model of the proposed system. Experimental evaluations show the effectiveness of the proposed model with regards to low transaction cost, the minimum execution time for block creation, the privacy of prosumers and dispute resolution of demurrage fees. Moreover, the proposed scheme reduces the average system overhead cost up to 66.67% as compared to 33.43% for an existing scheme. Additionally, the proposed blockchain proof‐of‐authority consensus average hash power is minimized up to 82.75% as compared to 60.34% for proof‐of‐stake and 56.89% for proof‐of‐work consensus mechanisms.     

Solar methanol synthesis by clean hydrogen production from seawater on offshore artificial islands

Synthetic fuel production from renewable energy, water, and anthropogenic carbon resources offers a promising alternative to fossil fuels by reducing the consumption of nonrenewable resources and greenhouse gas emissions. This article presents a case study of a solar‐based methanol plant that derives hydrogen and carbon dioxide material inputs from seawater on an offshore artificial island. Photovoltaic cells generate electricity for an electrolytic cation exchange membrane (E‐CEM) reactor that simultaneously produces hydrogen and carbon dioxide, with freshwater for electrolysis via seawater reverse osmosis. Carbon dioxide hydrogenation in a low‐pressure isothermal cascade‐type reactor system produces methanol as a liquid fuel product. Thermodynamic assessment of the integrated system indicates solar‐to‐methanol energy and exergy conversion efficiencies of 1.5% and 1.3%, respectively, with the most significant losses occurring in the offshore concentrator photovoltaic (CPV) and E‐CEM reactor unit.     

A stackelberg game approach for heterogeneous energy market in integrated energy system

With the increasing demand of energy and the growing intensity of energy crisis, various smart energy systems are developed on the distribution level, such as integrated energy system (IES). In this article, a trading mechanism among various energy retailers and consumers is designed under the open market environment. The trading problem is formulated as a multi‐leader and multi‐follower Stackelberg game, which is built with the strategy set of energy bidding price and purchasing pattern. In particular, consumer's demand is described with the price elasticity property of demand, and non‐cooperative competition behavior among retailers is analyzed mathematically. To implement the proposed game approach, a distributed algorithm is presented by combining particle swarm optimization (PSO) and interior point method (IPM). Finally, simulation results show that the proposed trading mechanism will contribute to the development of heterogeneous energy market and the overall profit of retailers in the traditional trading mechanism is 37.8% lower than the profit in the proposed mechanism.     

A modeling approach for investigating climate change impacts on renewable energy utilization

In this study, an integrated community‐scale energy model (ICEM) was developed for supporting renewable energy management (REM) systems planning with the consideration of changing climatic conditions. Through quantitatively reflecting interactive relationships among various renewable energy resources under climate change, not only the impacts of climate change on each individual renewable energy but also the combined effects on power‐generation sector from renewable energy resources could be incorporated within a general modeling framework. Also, discrete probability levels associated with various climate change impacts on the REM system could be generated. Moreover, the ICEM could facilitate capacity–expansion planning for energy‐production facilities within a multi‐period and multi‐option context in order to reduce energy‐shortage risks under a number of climate change scenarios. The generated solutions can be used for examining various decision options that are associated with different probability levels when availabilities of renewable energy resources are affected by the changing climatic conditions. A series of probability levels of hydropower‐, wind‐ and solar‐energy availabilities can be integrated into the optimization process. The developed method has been applied to a case of long‐term REM planning for three communities. The generated solutions can provide desired energy resource/service allocation and capacity–expansion plans with a minimized system cost, a maximized system reliability and a maximized energy security. Tradeoffs between system costs, renewable energy availabilities and energy‐shortage risks can also be tackled with the consideration of climate change, which would have both positive and negative impacts on the system cost, energy supply and greenhouse‐gas emission. Copyright © 2011 John Wiley & Sons, Ltd.     

Design and analysis of an integrated concentrated solar and wind energy system with storage

This study analyzes a renewable energy‐driven innovative multigeneration system, in which wind and solar energy sources are utilized in an efficient way to generate several useful commodities such as hydrogen, oxygen, desalted water, space cooling, and space heating along with electricity. A 1‐km² heliostat field is considered to concentrate the solar light onto a spectrum splitter, where the light spectrum is separated into two portions as reflected and transmitted to be used as the energy source in the concentrated solar power (CSP) and concentrated photovoltaics (CPV) receivers, respectively. As such, CSP and CPV systems are integrated. Wind energy is proposed for generating electricity (146 MW) or thermal energy (138 MW) to compensate the energy need of the multigeneration system when there is insufficient solar energy. In addition, multiple commodities, 46 MW of electricity, 12 m³/h of desalted water, and 69 MW of cooling, are generated using the Rankine cycle and the rejected heat from its condenser. Further, the heat generated on CPV cells is recovered for efficient photovoltaic conversion and utilized in the space heating (34 MW) and proton exchange membrane (PEM) electrolyzer (239 kg/h) for hydrogen production. The energy and exergy efficiencies of the overall system are calculated as 61.3% and 47.8%, respectively. The exergy destruction rates of the main components are presented to identify the potential improvements of the system. Finally, parametric studies are performed to analyze the effect of changing parameters on the exergy destruction rates, production rates, and efficiencies.     

Three options to calculate the percentage renewable energy: An example for a EU policy debate

The European Commission proposed a renewable energy directive with binding targets for the percentage renewable energy, usually calculated with the primary energy method. This method has the disadvantage that for hydro and wind electricity production is counted, whereas for thermal electricity the higher input to power plants is counted. Therefore, the Commission looked for an alternative: the final energy method. Also this method has disadvantages. Firstly, electricity consumption is weighed equally to fuel consumption for heat and transport, neglecting higher primary energy demand for electricity. Secondly, non-energy consumption of energy commodities is neglected, artificially raising the percentage renewable energy. Therefore, I introduce a simple substitution method, which measures renewable energy by comparison with hypothetical equivalent conventional energy. Calculations for EU-27 show that the method strongly affects the contributions of different sectors (electricity, heat and transport), sources and countries. Concluding, any credible calculation method should reflect the trade off between conventional and renewable primary energy. A simple substitution method fulfills this condition, contrary to the primary and final energy method. Using these biased methods may result in policies that are inefficient in terms of saving conventional fuels and avoiding CO₂ emissions, the main underlying goals of the proposed directive.     

面向碳中和的多源异质全可再生能源系统优化规划方法研究

为有效应对气候变化与能源危机,早日实现碳达峰与碳中和目标,提出多源异质全可再生能源热电气储耦合系统,在供能侧实现100%全可再生能源。首先,构建了全可再生能源系统的物理架构,并对系统内典型设备进行建模;然后,以系统年总经济成本最小为目标函数,构建了可实现系统结构、设备配置与运行策略协同优化的混合整数线性规划模型;最后,通过具体算例分析,验证了所提优化模型的正确性和可行性,确立了所提出的多源异质全可再生能源热电气储耦合系统在降低碳排放、实现全额消纳可再生能源等方面的有效性。     

An energy system for the integration of renewable energy with energy storage in a frigid plateau region

面向高原高寒地区对稳定供热和供电的迫切需求,本文提出了一种新型的可再生能源与储能集成供能系统。该系统包括风力发电、光伏发电、水力发电、槽式太阳能集热器、储热系统、储电装置以及集成控制系统,实现了多种可再生能源高效利用;制定了一种考虑热电设备性能的实时能量管理策略,并建立了以年成本为主要优化目标的容量配置方法;利用该系统与优化方法对高原高寒地带民用住宅群的供能系统进行了优化设计,通过案例对比分析,验证了该集成供能系统容量配置方法和能量管理策略的可行性。研究结果为高原高寒地区供能系统的选择提供了有益的参考。     

Governance of the emerging bio-energy markets

Despite its promising prospects, a growing global bio-energy market may have sustainability risks as well. Governing this market with respect to installing safeguards to ensure sustainable biomass production might reduce these risks. Therefore, proposals for governance systems for bio-energy are discussed in this article. The proposals are based on comparative case study research on the governance of comparable commodities. By assessing the governance system of global coffee trade, fair trade coffee, the global and the EU sugar market and Forest Stewardship Council (FSC) wood, strong and weak points of governance systems for commodities are discerned. FSC is selected as the best performing case study and serves as the proposal's basis. FSC's weaknesses are minimized by, among others, using the lessons learned from the other case studies. This results in a system consisting of two pillars, a bio-energy labelling organization (BLO) and a United Nations Agreement on Bio-energy (UNAB). Although consulted experts in the research process are critical about this system they do suggest several conditions a governance system for bio-energy should meet in order to be effective, such as a facilitative government, professional monitoring and using progressive certification combined with price premiums. These conditions have been taken into account in the final proposal.     

Technical development of rotary desiccant dehumidification and air conditioning: A review

Rotary desiccant air conditioning system, which combines the technologies of desiccant dehumidification and evaporative cooling, is advantageous in being free from CFCs, using low grade thermal energy and controlling humidity and temperature separately. Compared with conventional vapor compression air conditioning system, it preserves the merits of environment-friendly, energy saving, healthy, comfortable, etc. Ongoing research and development works suggest that new desiccant materials and novel system configurations have significant potential for improving the performance and reliability and reducing the cost and size of rotary desiccant dehumidification and air conditioning system, thereby increasing its market competitiveness and breaking out the current fairly small niche market. For the purpose of providing an overview of recent efforts on these issues and showing how rotary desiccant air conditioning systems can be designed and coupled to available thermal energy, this paper presents and analyzes the status of rotary desiccant dehumidification and air conditioning in the following three aspects: the development of advanced desiccant materials, the optimization of system configuration and the utilization of solar energy and other low grade heat sources, such as solar energy, district heating, waste heat and bioenergy. Some key problems to further push forward the research and development of this technology are also summarized.     

Turning industrial aerobic fermentation plants into thermal power stations

The industrial aerobic bioprocess of baker's yeast production requires large amounts of water to cool down large bubble column bioreactors. As result, an appreciable quantity of low‐grade heat is generated. Because of the low temperature level of the water (~25°C) exiting the bioreactors cooling system, very little attention has been dedicated to heat recovery and conversion from this stream, which is usually released in rivers, streams, and canals. In this work, we simulated the generation of low‐grade heat (up to 14.4 MW) from an industrial baker's yeast production plant consisting of seven 150‐m³ bioreactors. Subsequently, a dedicated transcritical carbon dioxide heat pump system for the conversion of this low‐grade heat into fourth generation district heat (~16.2 MW) was successfully designed. Fourth generation district heat employs low‐temperature water (30‐70°C) as heat carrier and is expected to play a major role in future sustainable energy system. Finally, an economic study confirmed the feasibility and the applicability of our approach and a concept for long‐term energy storage including state‐of‐the‐art phase change material (PCM)–units was discussed.     

Integrated energy systems and local energy markets

Significant benefits are connected with an increase in the flexibility of the Danish energy system. On the one hand, it is possible to benefit from trading electricity with neighbouring countries, and on the other, Denmark will be able to make better use of wind power and other types of renewable energy in the future. This paper presents the analysis of different ways of increasing flexibility in the Danish energy system by the use of local regulation mechanisms. This strategy is compared with the opposite extreme, i.e. trying to solve all balancing problems via electricity trade on the international market. The conclusion is that it is feasible for the Danish society to include the CHP plants in the balancing of fluctuating wind power. There are major advantages in equipping small CHP plants as well as the large CHP plants with heat pumps. By doing so, it will be possible to increase the share of wind power from the present 20 to 40% without causing significant problems of imbalance between electricity consumption and production. Investment in increased flexibility is in itself profitable. Furthermore, the feasibility of wind power is improved.     

Global warming agreements,international trade and energy/carbon embodiments: an input–output approach to the Italian case

In the Kyoto Protocol the absence of Green House Gases (GHGs) commitments of developing countries (non-Annex I) and the more flexible terms of implementation which are allowed to countries shifting toward a market economy (transition economies) naturally lead to the absence or to less constraining national measures and policies of reduction of the GHGs emissions which, in turn, may determine a comparative advantage in the production of the highest energy/carbon intensive commodities for these countries. These arguments are valid also considering the future implementation of the European Emission Allowance Trading Scheme (EATS). Thus, developing countries may become a haven for the production of not environmental-friendly commodities; in this case, the so-called Pollution Haven Hypothesis, stating that due to freer international trade the comparative advantage may change the economic structure and consequently the trade patterns of the countries linked by trade relationships, could occur. This would lead to the increase of the transfers of energy and carbon embodied in traded commodities from developing countries and transition economies toward Kyoto or EATS constrained countries.     

Economics of electric energy storage for energy arbitrage and regulation in New York

Unlike markets for storable commodities, electricity markets depend on the real-time balance of supply and demand. Although much of the present-day grid operates effectively without storage, cost-effective ways of storing electrical energy can help make the grid more efficient and reliable. We investigate the economics of two emerging electric energy storage (EES) technologies: sodium sulfur batteries and flywheel energy storage systems in New York state's electricity market. The analysis indicates that there is a strong economic case for EES installations in the New York City region for applications such as energy arbitrage, and that significant opportunities exist throughout New York state for regulation services. Benefits from deferral of system upgrades may be important in the decision to deploy EES. Market barriers currently make it difficult for energy-limited EES such as flywheels to receive revenue for voltage regulation. Charging efficiency is more important to the economics of EES in a competitive electricity market than has generally been recognized.     

基于等效焓降法的低压省煤器系统经济性分析

降低排烟温度对于节能降耗、提高锅炉的安全可靠性具有重要的实际意义,低压省煤器系统在降低排烟温度和提高机组热经济性中具有现实可行性.结合某电厂330 MW的发电机组,对低压省煤器热经济性原理和等效焓降法在低压省煤器中的应用进行分析,在保证机组经济安全运行和最优经济性下,理论分析低压省煤器的分水流量、进水温度和引出口位置的...     

On cost‐effective technical measures to avoid environmental damages of regional energy systems

The production of heat and electricity can cause large environmental impacts and, hence, large costs for society. Those are costs that are seldom taken into consideration. An important question is how the future technical energy systems should be formed if environmental costs were considered as any other good or service, such as raw material, capital and labour. This study comprises cost‐effective technical measures when monetary values of external effects are included in an energy system analysis. It is an analysis of how the present energy system can for society be cost‐effectively reconstructed to be more sustainable. A regional energy system model has been developed to perform the study and it concentrates upon production of heat in single‐family houses, multi‐dwelling buildings, non‐residential premises and district heating systems. The analysis adopts a business economic perspective, using present prices of energy carriers, and a more socio‐economic perspective, in which external costs are included. The result of the analysis is the optimal mix of energy carriers as well as new and existing heating plants that minimizes the costs of satisfying a demand for heat. The results show that it is profitable to invest in new heating plants fuelled with woody biomass. Furthermore, the external costs arising with satisfying the demand for heat can decrease substantially, 60%, by carrying through with the investments that are cost‐effective according to the institutional rules valid today. When monetary values of external costs are taken into consideration, this number is additional 5‐percentage points lower. It is shown that if environmental costs are included it is more expensive to continue with business as usual than it is to reconstruct and run a more sustainable energy system. Copyright © 2002 John Wiley & Sons, Ltd.     

Characterization and visualization of industrial excess heat for different levels of on‐site process heat recovery

Increased utilization of industrial excess heat (or waste heat) can reduce primary energy use and thereby contribute to reaching energy and climate targets. To estimate the potential availability of industrial excess heat, it is necessary to capture the significant heterogeneity of the industrial sector. This requires the development of methodologies based on case study assessments of individual plants, adopting a systematic approach and consistent assumptions. Since the recovery of excess heat for power generation or off‐site delivery competes with internal recovery for on‐site fuel savings, a well‐founded approach should enable a comparison of the excess heat availability at different levels of internal process heat recovery. To determine the best solution for excess heat utilization for a given process, there is a need for easy screening of various options, while considering that some techniques require heat at a constant temperature while others can exploit a nonisothermal heat supply. This paper presents a new tool, the excess heat temperature (XHT) signature, for exploring the potential heat availability and trade‐offs for excess heat utilization by weighting the heat according to predefined temperature levels and ranges. A set of reference conditions are defined, and an energy targeting approach is proposed that can be used for characterizing the Theoretical XHT signature, which represents the unavoidable excess heat that can be recovered after maximized internal process heat recovery and ideal integration of a power generation steam cycle. The Theoretical XHT signature is contrasted with the Process Cooling XHT signature, which represents the excess heat that can be recovered given the current design and operation of the process and its utility system. The XHT signature curves provide a consistent representation of the excess heat, enabling comparison between sites and aggregation of results from different case studies.