Feasibility of CHP-plants with thermal stores in the German spot market

The European Energy Exchange (EEX) day ahead spot market for electricity in Germany shows significant variations in prices between peak and off-peak hours. Being able to shift electricity production from off-peak hours to peak hours improves the profit from CHP-plant operation significantly. Installing a big thermal store at a CHP-plant makes it possible to shift production of electricity and heat to hours where electricity prices are highest especially on days with low heat demand. Consequently, these conditions will have to influence the design of new CHP-plants. In this paper, the optimal size of a CHP-plant with thermal store under German spot market conditions is analyzed. As an example the possibility to install small size CHP-plant instead of only boilers at a Stadtwerke delivering 30,000 MW h-heat for district heating per year is examined using the software energyPRO. It is shown that, given the economic and technical assumptions made, a CHP-plant of 4 MW-el with a thermal store participating in the spot market will be the most feasible plant to build. A sensitivity analysis shows to which extent the optimal solution will vary by changing the key economic assumptions.     

Exploration of economical sizing of gas engine and thermal store for combined heat and power plants in the UK

There has been discussion about the extent to which combined heat and power (CHP) plants with thermal stores are suitable for sustainable energy production. At the moment, in the UK the development of this type of plant is limited. This paper analyses the economics and optimum size of CHP operating with gas engines and thermal stores in British market conditions. This is achieved using energyPRO software. It is shown that, due to the big differences in electricity prices between day and night, the use of thermal stores could be profitable in the UK. The economical size of CHP plant for a district or community heating load of 20,000 MWh per year is found to be a 3 MWe gas engine with a 7.8 MWh thermal store. In this case the analysis reveals that the use of a thermal store more than doubles the return on investments (as measured in net present value) compared with the same size of a plant without a thermal store. It is concluded that thermal stores can improve the overall economics of CHP plants in present British circumstances.     

Do liberalised electricity markets help or hinder CHP and district heating? The case of the UK

This paper investigates whether and how Danish-style combined heat and power (CHP) and district heating (DH) can be implemented in the UK in the context of a liberalised electricity market. There is currently an absence, in the UK, of the Danish system of planning rules and also good tariffs for CHP electricity exports to the grid that led to the development of the Danish system of CHP and DH. However, there are some changes in UK planning practice that may help CHP and DH. These would need to be strengthened, but it is also the case that the way the liberalised electricity market operates in the UK effectively discriminates against small CHP plant selling their electricity to the grid. A Danish system of ‘aggregating’ CHP–DH plant using thermal stores could help to overcome this problem. However, an alternative strategy would be to establish feed-in tariffs for CHP units that are linked to DH modelled on the Danish ‘triple tariff’. This could help the UK's long-term objective of absorbing high levels of fluctuating renewable energy sources.     

Exergetic comparison of efficiency indicators for combined heat and power (CHP)

Legislative regulations in favor of combined heat and power (CHP) production have been implemented in many countries. Although these regulations put different emphasis on power production vs. process heat production, they are based on energy quantities and not on exergy. In order to analyze and compare the exergetic consequences of the various legislations, a relative avoided irreversibility (RAI) is defined. This can be regarded as the exergy loss that is avoided when reference plants with separate production are replaced by an actual CHP plant. Some series of industrial and district heating CHP plants, under varying operational conditions, are used as test cases. It is seen that some, but not all, CHP cases are exergetically beneficial to separate generation. Comparison with the RAI allows a quantitative assessment of the various performance indicators. It is seen that exergetic improvements were only captured to a limited degree by the various energy-based efficiency indicators. Some legislatively defined indicators even appear to discourage thermodynamic improvements.     

Performance improvement of a 70 kWe natural gas combined heat and power (CHP) system

Combined heat and power is the simultaneous production of electricity and heat. CHP plants produce energy in an efficient way. A natural gas CHP system based on an internal combustion engine (ICE) is described, which has been set up at the Building Energy Research Center in Beijing, China. The system is composed of an ICE, a flue gas heat exchanger, a jacket water heat exchanger and other assistant facilities. The ICE generates power on-site, and the exhaust of the ICE is recovered by the flue gas heat exchanger, and the heat of the engine jacket is recovered by the jacket water heat exchanger to district heating system. In order to improve the performance of the system, an absorption heat pump (AHP) is adopted. The exhaust of the ICE drives the AHP to recover the sensible and latent heat step by step, and the temperature of the exhaust could be lowered to below 30 °C. In this paper, the performance of the new system were tested and compared with conventional cogeneration systems. The results show that the new CHP system could increase the heat utilization efficiency 10% compared to conventional systems in winter. All the results could be valuable references for the improvement of the CHP system.     

Design of a biomass power plant for burning date palm waste to cogenerate electricity and distilled water

Date palm trees (Phoenix dactylifera L.) produce approximately 40 kg of burnable waste including dried leaves, spathes, sheaths, and petioles annually. In this paper, the potential of date palm waste as a bioenergy source has been investigated. As a sample project, a power plant has been preliminary designed to simultaneously generate electrical power using a steam Rankine cycle and distilled water by the thermal desalination of seawater using a multiple effect evaporator. The results indicated that a small plant in Bushehr Province in southern Iran which burns 140,000 tons of waste annually can produce approximately 62 GWh of electricity in conjunction with 2.27 million tons of distilled water. This production is equivalent to 75 GWhe/year. Environmental assessments revealed that the use of this amount of biomass leads to a net green-house gas (GHG) reduction of 40,500 tCO₂/year.     

Interaction among competitive producers in the electricity market: An iterative market model for the strategic management of thermal power plants

The liberalization of the electricity sector requires utilities to develop sound operation strategies for their power plants. In this paper, attention is focused on the problem of optimizing the management of the thermal power plants belonging to a strategic producer that competes with other strategic companies and a set of smaller non-strategic ones in the day-ahead market. The market model suggested here determines an equilibrium condition over the selected period of analysis, in which no producer can increase profits by changing its supply offers given all rivals’ bids. Power plants technical and operating constraints are considered. An iterative procedure, based on the dynamic programming, is used to find the optimum production plans of each producer. Some combinations of power plants and number of producers are analyzed, to simulate for instance the decommissioning of old expensive power plants, the installation of new more efficient capacity, the severance of large dominant producers into smaller utilities, the access of new producers to the market. Their effect on power plants management, market equilibrium, electricity quantities traded and prices is discussed.     

国外热电联产发展政策、经验及我国发展分布式小型热电联产的前景

热电联产被公认为2l世纪的清洁能源，工业性的应用已经较为广泛，商业设施和区域供热方面的应用也有很大发展。生产技术上的特殊性造成其发展依然面临着很多困难，需要政策扶持。然而全社会对环保、对能源安全的共识又为其提供了良好的发展机遇。根据联合国亚太经济与社会委员会的相关报告，热电联产事业面临的障碍可以归纳为：1)技术障碍；2)经济激励措施的缺失；3)政策框架尚不完善；4)电力工业的短视；5)对环境保护缺乏重视。另外还有技术和管理人才的缺乏等。这些障碍在中国都不同程度地存在，发展热电联产要从以上各方面共同推进。而西方国家在发展热电联产的过程中，在国家能源结构和供求情况、全球环境政策、电力和燃料市场自由化等国内和国际因素的影响下，能源政策随之变化，热电联产事业也历经起伏。由于他们起步较早，技术和政策方面的基础较强，电力市场化改革也在进行中，它们的经验，会对中国的热电联产事业发展有所启迪。下面我们介绍一些具有代表性的国家发展热电的努力。在文章的最后，我们还将重点讨论热电技术中极有前途的小型分散式热电联产技术。     

Performance comparison between partial oxidation and methane steam reforming processes for solid oxide fuel cell (SOFC) micro combined heat and power (CHP) system

The aim of this research work is to describe in qualitative and quantitative form the performance of a micro Combined Heat and Power system for residential application based on Solid Oxide Fuel Cell fueled by natural gas with two different types of pre-reforming systems, namely Steam Reforming and Partial Oxidation and recirculation of anode and cathode gas.The comparative analysis among the different configurations will lead us to conclude that maximum efficiency is achieved when cathode and anode gas recirculation are used along with steam methane reforming. Further Steam Methane Reforming process produces a higher electrical system efficiency compared to Partial oxidation reforming process.Efficiency is affected when running the system in part load mode mainly due to heat loss, additional natural gas supplied to the burner to satisfy the required heat demand inside the system, and ejector efficiency drop in the recirculation system. Due to high temperature of operation heat loss strongly affects the system efficiency especially at part load operation.     

Feed-in tariff and market electricity price comparison: The case of cogeneration units in Croatia

In August 2007, the Government of the Republic of Croatia instituted a feed-in tariff system, requiring the Croatian Electricity Market Operator (HROTE) to off-take the electricity produced from renewable energy sources or cogeneration units fueled by natural gas. Analysis of the off-take electricity price range, which depends on the net electrical output and electricity market trends, indicates that it is more cost effective for cogeneration units greater than 1 MW to sell their electricity on the exchange market. This was confirmed by developing a mathematical model to calculate the cost-effectiveness ratio of a cogeneration unit. This ratio represents the relation between the profit spread, i.e. the difference between the profit generated from selling the electricity on the exchange market and the profit made from dispatching the electricity to HROTE, as well as the total investment costs. The model can be applied for changes in certain parameters, such as the net electrical output, volatility and spot electricity price. The Monte Carlo method is used to obtain the most probable cost-effectiveness ratio and average future electricity price. Together with these two economic parameters and market price analysis, it is possible to calculate and calibrate an acceptable off-take electricity price.     

意大利热电联产现状:能源政策、法规及市场自由化的影响

热电联产在意大利的应用比较普遍，但中小型热电机组的发展则比较缓慢。介绍了意大利的能源政策、法规及市场自由化对热电联产的影响，还介绍了意大利环境方面法规，意大利在热电(冷)联产方面的激励措施等。     

Risk analysis for CHP decision making within the conditions of an open electricity market

Decision making under uncertainty is a difficult task in most areas. Investment decisions for combined heat and power production (CHP) are certainly one of the areas where it is difficult to find an optimal solution since the payback period is several years and parameters change due to different perturbing factors of economic and mostly political nature.     

Cost optimization of the design of CHCP (combined heat,cooling and power) systems under legal constraints

Combined heat, cooling and power (CHCP) systems are interesting for the supply of different energy services in urban districts and in large buildings. CHCP systems utilize a fuel's energy to a greater extent, because the cogenerated heat can be used for heating in winter as well as for cooling in summer with an absorption refrigerator. The use of thermal energy storage (TES) provides the additional advantage of covering variable thermal demands while the production system operates continuously at nominal conditions. Thus, energy supply systems integrating the technologies of cogeneration, absorption refrigeration and thermal storage can provide substantial benefits from economic, energetic and environmental viewpoints. In this paper an optimization model is developed, using mixed integer linear programming (MILP), to determine the preliminary design of CHCP systems with thermal storage. The objective function to be minimized is the total annual cost. Taking into account the legal constraints imposed on cogeneration systems in Spain, the optimization model is applied to design a system providing energy services for a set of buildings constituted of 5000 apartments located in the city of Zaragoza (Spain). The effect of legal constraints in the design and operation of CHCP systems is highlighted in this study.     

Development of an artificial neural network model for the steam process of a coal biomass cofired combined heat and power (CHP) plant in Sweden

The development of a model for any energy system is required for proper design, operation or its monitoring. Models based on accurate mathematical expressions for physical processes are mostly useful to understand the actual operation of the plant. However, for large systems like combined heat and power (CHP) plants, such models are usually complex in nature. The estimation of output parameters using these physical models is generally time consuming, as these involve many iterative solutions. Moreover, the complete physical model for new equipment may not be available. However, artificial neural network (ANN) models, developed by training the network with data from an existing plant, may be very useful especially for systems for which the full physical model is yet to be developed. Also, such trained ANN models have a fast response with respect to corresponding physical models and are useful for real-time monitoring of the plant. In this paper, the development of an ANN model for the biomass and coal cofired CHP plant of Västhamnsverket at Helsingborg, Sweden has been reported. The feed forward with back propagation ANN model was trained with data from this plant. The developed model is found to quickly predict the performance of the plant with good accuracy.     

Engineering analysis of uncertainties in the performance evaluation of CHP systems

From January 1, 2011, in all UE countries the combined production of electric (or mechanical) and thermal energy (also called Combined Heat and Power, CHP, or cogeneration) is recognized as a high efficiency technology only when it is able to ensure a minimum value of energy saving with respect to the separate production of the same energy flows. The Directive 8/2004/EC, and a few successive Decisions of the European Commission, introduced a methodology to establish whether any cogeneration plant, existing or new, can be acknowledged as a high-efficiency CHP plant, and can therefore be supported from the UE member states. In the paper, such methodology, based on the evaluation of a standard Primary Energy Saving (PES) index, is briefly described, and then a metrological analysis is presented, in order to evaluate the uncertainties affecting the field evaluation of such index. Three numerical examples are also presented and discussed, referred to natural gas plants, showing that the evaluation of the PES index can be quite critical, especially for values close to the minimum limit fixed by the Directive, and in particular for small and medium scale CHP units, mainly due to the low accuracy that usually affect, in such cases, the measures of the fuel input.     

Should a small combined heat and power plant (CHP) open to its regional power and heat networks? Integrated economic,energy, and emergy evaluation of optimization plans for Jiufa CHP

The development of industrial ecology has led company managers to increasingly consider their company's niche in the regional system, and to develop optimization plans. We used emergy-based, ecological-economic synthesis to evaluate two optimization plans for the Jiufa Combined Heat and Power (CHP) Plant, Shandong China. In addition, we performed economic input–output analysis and energy analysis on the system. The results showed that appropriately incorporating a firm with temporary extra productivity into its regional system will help maximize the total productivity and improve ecological-economic efficiency and benefits to society, even without technical optimization of the firm itself. In addition, developing a closer relationship between a company and its regional system will facilitate the development of new optimization opportunities. Small coal-based CHP plants have lower-energy efficiency, higher environmental loading, and lower sustainability than large fossil fuel and renewable energy-based systems. The emergy exchange ratio (EER) proved to be an important index for evaluating the vitality of highly developed ecological-economic systems.     

The economic benefit of short-term forecasting for wind energy in the UK electricity market

In the UK market, the total price of renewable electricity is made up of the Renewables Obligation Certificate and the price achieved for the electricity. Accurate forecasting improves the price if electricity is traded via the power exchange. In order to understand the size of wind farm for which short-term forecasting becomes economically viable, we develop a model for wind energy. Simulations were carried out for 2003 electricity prices for different forecast accuracies and strategies. The results indicate that it is possible to increase the price obtained by around £5/MWh which is about 14% of the electricity price in 2003 and about 6% of the total price. We show that the economic benefit of using short-term forecasting is also dependant on the accuracy and cost of purchasing the forecast. As the amount of wind energy requiring integration into the grid increases, short-term forecasting becomes more important to both wind farm owners and the transmission/distribution operators.     

我国建设生物质热电联产项目主要问题研究

本文概要介绍了我国生物质直接燃烧发电项目、以民用供热为主燃煤中小热电联产项目的发展现状和存在问题,分析了我国建设生物质热电联产项目的主要障碍,并提出解决问题的政策建议。     

Regulation strategies of cogeneration of heat and power (CHP) plants and electricity transit in Denmark

Denmark is in a situation with many scattered sources of electricity that are not controlled by the central load dispatch. At the same time, Denmark is being used as an electricity transit corridor between the hydro-based systems of Norway/Sweden and the thermal systems of Germany and continental Europe. Through energy systems analyses and load-flow analyses, it is determined that if geographically scattered load balancing utilising the regulation ability of hitherto locally controlled plants is introduced while also introducing new dispatchable loads in the form of electric vehicles and heat pumps, electricity transit is enabled to a higher degree than if central load balancing is maintained. This is the case of an intact transmission system as well as a system with inoperative transmission lines. With an intact system, the average load of the system is approximately halved when applying scattered load balancing. Utilising the regulating capacity of local plants thus improves the role of the Danish system in the Northern European system.