Energy efficiency analysis and impact evaluation of the application of thermoelectric power cycle to today’s CHP systems

High efficiency thermoelectric generators (TEG) can recover waste heat from both industrial and private sectors. Thus, the development and deployment of TEG may represent one of the main drives for technological change and fuel substitution. This paper will present an analysis of system efficiency related to the integration of TEG into thermal energy systems, especially Combined Heat and Power production (CHP). Representative implementations of installing TEG in CHP plants to utilize waste heat, wherein electricity can be generated in situ as a by-product, will be described to show advantageous configurations for combustion systems. The feasible deployment of TEG in various CHP plants will be examined in terms of heat source temperature range, influences on CHP power specification and thermal environment, as well as potential benefits. The overall conversion efficiency improvements and economic benefits, together with the environmental impact of this deployment, will then be estimated. By using the Danish thermal energy system as a paradigm, this paper will consider the TEG application to district heating systems and power plants through the EnergyPLAN model, which has been created to design suitable energy strategies for the integration of electricity production into the overall energy system.     

Ancillary services and the integration of substantial quantities of wind power

Denmark has the World’s highest penetration of grid connected wind power in electricity generation with a share of 15.0% of total domestic demand in 2002 [Danish Energy Authority. Rapport fra arbejdsgruppen om kraftvarme- og VE-elektricitet. Bilagsrapport. Copenhagen: Danish Energy Authority; 2001]. This is unevenly distributed in the two separate electricity systems comprising Denmark, giving a 2003 share as high as 21% in Western Denmark [Eltra. http://www.Eltra.dk. Skærbæk: Eltra; 2004] compared with a more modest 8% in the more densely populated Eastern Denmark [Elkraft System. Miljøberetning 2004. Ballerup: Elkraft System; 2004]. At the same time, Denmark has other forms of distributed generation, e.g., extensive cogeneration of heat and power (CHP) plants for district heating or for covering industrial heat demands. This results in a high fuel-efficiency but also in a technically complex energy system. This combination of wind power and CHP is a challenge for system operators but also gives opportunities. This article analyses the possibilities for integrating even more wind power using new power balancing strategies that exploit the possibilities given by the existence of CHP plants as well as the potential impact of heat pumps used for district heating and installed for integration purposes. The analyses are made with particular focus on grid stability and delivery of ancillary services (required to control voltage and frequency) and demonstrate that it is possible to accommodate 50% or more wind power without having to rely on import or export for power balancing. Relying on import and export sets demands on the neighbouring countries which may not be met. Compulsion to export or import furthermore gives a poor bargaining position on the electricity market. However, in order to reach such high levels of wind power, the generating equipment must be able to supply ancillary services in contrast to their present abilities.     

Dynamic modeling and evaluation of solid oxide fuel cell - combined heat and power system operating strategies

Operating strategies of solid oxide fuel cell (SOFC) combined heat and power (CHP) systems are developed and evaluated from a utility, and end-user perspective using a fully integrated SOFC-CHP system dynamic model that resolves the physical states, thermal integration and overall efficiency of the system. The model can be modified for any SOFC-CHP system, but the present analysis is applied to a hotel in southern California based on measured electric and heating loads. Analysis indicates that combined heat and power systems can be operated to benefit both the end-users and the utility, providing more efficient electric generation as well as grid ancillary services, namely dispatchable urban power.Design and operating strategies considered in the paper include optimal sizing of the fuel cell, thermal energy storage to dispatch heat, and operating the fuel cell to provide flexible grid power. Analysis results indicate that with a 13.1% average increase in price-of-electricity (POE), the system can provide the grid with a 50% operating range of dispatchable urban power at an overall thermal efficiency of 80%. This grid-support operating mode increases the operational flexibility of the SOFC-CHP system, which may make the technology an important utility asset for accommodating the increased penetration of intermittent renewable power.     

Environmental impacts of natural gas distribution networks within urban neighborhoods

This study uses the life cycle assessment methodology to analyze the type and origin of environmental impacts related to natural gas distribution networks in high and low density neighborhoods, and compares the environmental performance of two infrastructures in low density neighborhoods: a standard natural gas grid and a discontinuous system based on propane tanks. The results show that the impact per dwelling in the environmental categories studied is between 1.9 and 4.8 times higher in a low density neighborhood, depending on the impact category. Besides, in high density areas the main impact originates from components and materials related to the buildings and dwellings, whereas in low density areas the main impact originates on the neighborhood network. Given this last result, the advisability of substituting the neighborhood network by a discontinuous system based on propane tanks has been evaluated, obtaining as a result that when a single neighborhood pipe, longer than 1 km, is required to reach one user, it is environmentally preferable for all the studied environmental categories to use the propane tank system.     

Design and analysis of a waste gasification energy system with solid oxide fuel cells and absorption chillers

Energy saving is an open point in most European countries where energy policies are oriented to reduce the use of fossil fuels, greenhouses emissions and energy independence, and to increase the use of renewable energies. In the last several years, new technologies have been developed and some of them received subsidies to increase installation and reduce cost. This article presents a new sustainable trigeneration system (power, heat and cool) based on a solid oxide fuel cell (SOFC) system integrated with an absorption chiller for special applications such as hotels, resorts, hospitals, etc. with a focus on plant design and performance. The proposal system is based on the idea of gasifying the municipal waste, producing syngas serving as fuel for the trigeneration system. Such advanced system when improved is thus self-sustainable without dependency on net grid, district heating and district cooling. Other advantage of such waste to energy system is waste management, less disposal to sanitary landfills, saving large municipal fields for other human activity and considerable less environmental impact. Although plant electrical efficiency of such system is not significant but fuel utilization factor along with free fuel, significant less pollutant emissions and self-sustainability are importance points of the proposed system. It is shown that the energy efficiency of such small tri-generation system is more than 83% with net power of 170 kW and district energy of about 250 kW.     

高级量测体系及其在需求响应中的应用

针对智能电网用电环节建设的主要内容,概述了高级量测体系中智能电表、双向通信网络、量测数据管理系统和用户信息显示平台四大组成部分,着重介绍了通信网络的分层布局.调研了国外高级量测体系在需求响应中的应用情况,并归结为基于电价的需求响应、基于用电信息的需求响应和家庭智能设备的远程控制三类,为我国智能电网用电环节建设提供了参考.     

Potential of power-to-heat from excess wind energy on the city level

ABSTRACT

This study discusses the potential of power-to-heat (P2H) as an effective option to reduce greenhouse gas emissions in the heating sector and energy curtailment. P2H promotes the integration of electricity from renewable energy sources into the power grid by utilizing otherwise unused electricity (excess energy) for space heating. To estimate the contribution of this effect from a techno-economic perspective, a linear problem is defined by minimizing the overall heating costs and solved by an open source model generator. Four different scenarios are modeled on a city level, using real heat demand data from a case study regarding the municipality of Greifswald, a region with dominant wind-energy. Results indicate that district heating networks are an important technology for coupling power and heat to meet CO₂ reduction targets. In addition, further integration of renewable energy is promoted to reduce overall emissions and achieve Germany’s climate protection goals by 2050.     

Grid of the future

Many believe the electric power system is undergoing a profound change driven by a number of needs. There's the need for environmental compliance and energy conservation. We need better grid reliability while dealing with an aging infrastructure. And we need improved operational effi ciencies and customer service. The changes that are happening are particularly signifi cant for the electricity distribution grid, where "blind" and manual operations, along with the electromechanical components, will need to be transformed into a "smart grid." This transformation will be necessary to meet environmental targets, to accommodate a greater emphasis on demand response (DR), and to support plug-in hybrid electric vehicles (PHEVs) as well as distributed generation and storage capabilities. It is safe to say that these needs and changes present the power industry with the biggest challenge it has ever faced. On one hand, the transition to a smart grid has to be evolutionary to keep the lights on; on the other hand, the issues surrounding the smart grid are signifi cant enough to demand major changes in power systems operating philosophy.     

中国电网技术成就、挑战与发展

电网作为电力传输的基本途径,是重要的能源基础设施,关系到国民经济命脉和国家能源安全。文章首先介绍了中国交、直流输电电压等级的演变历程和电网技术发展取得的成就,其次从大型能源基地输送需要、分布式能源接入的挑战、节能环保及资源约束、智能化与信息化潮流、用电侧的新要求和电网技术“走出去”等方面分析了当前中国电网技术面临的挑战。最后从大容量远距离输电技术、智能电网、柔性输电、分布式能源接入和配用电及微电网、新形势下的先进调度、设计施工与运维的信息化、节能环保与资源高效利用、设备国产化与标准的国际化等八个方面探讨了现代电网技术的发展方向。     

Sustainability assessment of cogeneration sector development in Croatia

The effective and rational energy generation and supply is one of the main presumptions of sustainable development. Combined heat and power production, or co-generation, has clear environmental advantages by increasing energy efficiency and decreasing carbon emissions. However, higher investment cost and more complicated design and maintenance sometimes-present disadvantages from the economical viability point of view. As in the case of most of economies in transition in Central and Eastern Europe, Croatia has a strong but not very efficient co-generation sector, delivering 12% of the final energy consumption. District heating systems in the country's capital Zagreb and in city of Osijek represent the large share of the overall co-generation capacity. Besides district heating, co-generation in industry sector is also relatively well developed. The paper presents an attempt to assess the sustainability of Croatian co-generation sector future development. The sustainability assessment requires multi-criteria assessment of specific scenarios to be taken into consideration. In this respect three scenarios of Croatian co-generation sector future development are taken into consideration and for each of them environmental, social and economic sustainability indicators are defined and calculated. The assessment of complex relationships between environmental, social and economic aspects of the system is based on the multi-criteria decision-making procedure. The sustainability assessment is based on the General Sustainability Index rating for different cases reflecting different criteria and their priority. The method of sustainability assessment is applied to the Croatian co-generation sector contributing to the evaluation of different strategies and definition of a foundation for policy related to the sustainable future cogeneration sector development.     

Thermodynamic analysis of a novel solar and geothermal based combined energy system for hydrogen production

The present study develops a new solar and geothermal based integrated system, comprising absorption cooling system, organic Rankine cycle (ORC), a solar-driven system and hydrogen production units. The system is designed to generate six outputs namely, power, cooling, heating, drying air, hydrogen and domestic hot water. Geothermal power plants emit high amount of hydrogen sulfide (H₂S). The presence of H₂S in the air, water, soils and vegetation is one of the main environmental concerns for geothermal fields. In this paper, AMIS(AMIS® - acronym for “Abatement of Mercury and Hydrogen Sulphide” in Italian language) technology is used for abatement of mercury and producing of hydrogen from H₂S. The present system is assessed both energetically and exergetically. In addition, the energetic and exergetic efficiencies and exergy destruction rates for the whole system and its parts are defined. The highest overall energy and exergy efficiencies are calculated to be 78.37% and 58.40% in the storing period, respectively. Furthermore, the effects of changing various system parameters on the energy and exergy efficiencies of the overall system and its subsystems are examined accordingly.     

Conflicting strategies towards sustainable heating at an urban junction of heat infrastructure and building standards

Approaches to ‘sustainability transitions’ stress the possibility of aligning actors around a shared vision of the future, e.g. at the scale of a city. Empirical accounts reveal how difficult such coordination often is due to contradictory views involved. How can we better understand related processes of searching and negotiation? What does this mean for the organization of decision making processes regarding long-term infrastructural change?We analyze a conflict which erupted in Freiburg, Germany when two strategies of reducing environmental impacts of space heating were to be applied in the Vauban ‘model district’: A) Efficient co-generation of heat and power (CHP) combined with district heating systems (DHS), and B) Reducing heat demand by low-energy designs and ambitious energy standards (‘passive house standard’). In order to understand the politics of infrastructure development, we unravel 1) enabling factors and driving forces of the conflict, 2) normative content of opposing viewpoints, 3) resources tapped into for settling the disagreement, and 4) the institutional setup of such decision making about energy policy priorities in the municipality.We reflect on implications of such a perspective on how policies and how governance arrangements should ideally be shaped and take a brief outlook on further research needed.     

Constraints on the effective utilization of wind power in China: An illustration from the northeast China grid

Even though China's wind power industry has experienced a rapid growth since the beginning of this century, the utilization of wind power is still worrisome. In 2010, about 30% of China's total installed capacity could not get access to the grid. And about 10% of China's total wind power generation was curtailed. The problem of wind power curtailment is more prominent in Northeast-China region. The main particularity of Northeast China Grid is as follows: during the long heating period in winter, combined heat and power thermal plants need to modify the turbine generator's output to meet the heating demand and thus the thermal power peak regulation capacity is reduced, as a result the barriers of wind power consumption are increased. This paper provides a new perspective of the constraints on the effective utilization of wind power in the Northeast China Grid. We argue that there are two categories of constrained factors: structural factor and operational factor. The former includes grid structure, wind source structure, power source structure, and market structure. The latter includes power price mechanism, dispatch mode arrangement, wind power integration codes, and wind power forecast. At last, we make policy recommendations: promote the coordination between wind farm investment and grid construction, strengthen interprovincial power trade mechanism, implement flexible pricing mechanisms as well as improve current dispatch mode, etc.     

Comparing electricity,heat and biogas storages’ impacts on renewable energy integration

Increasing penetration of fluctuating energy sources for electricity generation, heating, cooling and transportation increase the need for flexibility of the energy system to accommodate the fluctuations of these energy sources. Controlling production, controlling demand and utilising storage options are the three general categories of measures that may be applied for ensuring balance between production and demand, however with fluctuating energy sources, options are limited, and flexible demand has also demonstrated limited perspective. This article takes its point of departure in an all-inclusive 100% renewable energy scenario developed for the Danish city Aalborg based on wind power, bio-resources and low-temperature geothermal heat. The article investigates the system impact of different types of energy storage systems including district heating storage, biogas storage and electricity storage. The system is modelled in the energy systems analyses model energyPRO with a view to investigating how the different storages marginally affect the amount of wind power that may be integrated applying the different storage options and the associated economic costs. Results show the largest system impact but also most costly potential are in the form of electricity storages.     

LCA of domestic and centralized biomass combustion: The case of Lombardy (Italy)

This paper analyzes and compares the environmental impacts of biomass combustion in small appliances such as domestic open fireplaces and stoves, and in two types of centralized combined heat and power plants, feeding district heating networks. The analysis is carried out following a Life Cycle Assessment (LCA) approach. The expected savings of GHG (greenhouse gases) emissions due to the substitution of fossil fuels with biomass are quantified, as well as emissions of toxic pollutants and substances responsible for acidification and ozone formation.The LCA results show net savings of GHG emissions when using biomass instead of conventional fuels, varying from 0.08 to 1.08 t of CO₂ eq. per t of dry biomass in the different scenarios. Avoided GHG emissions thanks to biomass combustion in Lombardy are 1.32 Mt year^?1(1.5% of total regional GHG emissions). For the other impact categories, the use of biomass in district heating systems can again cause a consistent reduction of impacts, whereas biomass combustion in residential devices shows higher impacts than fossil fuels with a particular concern for PAH, VOC and particulate matter emissions. For example, in Lombardy, PM10 emissions from domestic devices are about 8100 t year^?1, corresponding to almost one third of the total particulate emissions in 2005.     

锂离子动力电池低温加热策略研究进展

随着新能源产业飞速发展,纯电动汽车的市场渗透率迅速上升。而制约电动汽车使用的一大关键因素,就是环境温度。在低温下,动力电池的功率特性衰减、电池内阻增大、电池可用容量降低。这些负面因素将直接影响电动汽车的续航里程与安全性。基于动力电池低温加热策略的主要产热区域,将目前锂离子电池低温加热策略划分为电池内部加热策略和电池外部加热策略两个大类。分别对这两个大类进行更详细的梳理,对目前的锂离子电池低温加热策略进行了系统的研究。分析了各种加热策略的优点与弊端,并针对存在的问题提出了解决意见。可为后续电动汽车动力电池低温加热策略的研究、锂离子电池低温下热管理系统的设计提供参考。     

Thermodynamic analysis of a novel integrated system operating with gas turbine,s-CO2 and t-CO2 power systems for hydrogen production and storage

In this paper, a proposal for a novel integrated Brayton cycle, supercritical plant, trans critical plant and organic Rankine cycle-based power systems for multi-generation applications are presented and analyzed thermodynamically. The plant can generate power, heating-cooling for residential applications, and hydrogen simultaneously from a single energy source. Both energetic and exergetic analyses are conducted on this multi-generation plant and its subsystems in order to evaluate and compare them thermodynamically, in terms of their useful product capabilities. The energetic and exergetic effectiveness of the multi-generation system are computed as 44.69% and 42.03%, respectively. After that, a parametric study on each of the subsystems of the proposed combined system is given in order to provide a deeper understanding of the working of these subsystems under different states. Lastly, environmental impact assessments are provided to raise environmental concerns for several operating conditions. For the base working condition, the results illustrate that the proposed plant has 0.5961, 0.0442, 0.6265 and 1.678 of exergo-environmental impact factor, exergy sustainability index, exergy stability factor and sustainability index, respectively.     

微燃机冷热电联供系统性能的模拟研究

介绍了冷热电联供(CCHP)系统,以上海某示范性微燃机冷热电联供系统为研究对象,通过建立系统主要设备的数学模型,模拟分析了系统在不同环境温度下的性能和系统全年的运行工况。结果表明:微燃机冷热电联供系统的性能受环境温度的影响,系统过渡季节不运行时年平均能源综合利用率可达到70%以上。     

Comparative Life Cycle Assessment of a Thai Island's diesel/PV/wind hybrid microgrid

Hybrid microgrid systems are an emerging tool for rural electrification due in part to their purported environmental benefits. This study uses Life Cycle Assessment (LCA) to compare the environmental impacts of a diesel/PV/wind hybrid microgrid on the island of Koh Jig, Thailand with the electrification alternatives of grid extension and home diesel generators. The impact categories evaluated are: acidification potential (kg SO₂ eq), global warming potential (kg CO₂ eq), human toxicity potential (kg 1.4 DCB eq), and abiotic resource depletion potential (kg Sb eq). The results show that the microgrid system has the lowest global warming and abiotic resource depletion potentials of all three electrification scenarios. The use phase of the diesel generator and the extraction of copper are shown to significantly contribute to the microgrid's environmental impacts. The relative environmental impacts of the grid extension scenario are found to be proportional to the distance required for grid extension. Across all categories except acidification potential, the impacts from the home diesel generators are the largest. Sensitivity analyses show that maximizing the renewable energy fraction does not necessarily produce a more environmentally sustainable electrification scenario and that the diesel generator provides versatility to the system by allowing power production to be scaled significantly before more technology is needed to meet demand. While the environmental benefits of the microgrid increase as the installation community becomes more isolated, the choice of electrification scenario requires assigning relative importance to each impact category and considering social and economic factors.     

Life-cycle assessment of diesel, natural gas and hydrogen fuel cell bus transportation systems

The Sustainable Transport Energy Programme (STEP) is an initiative of the Government of Western Australia, to explore hydrogen fuel cell technology as an alternative to the existing diesel and natural gas public transit infrastructure in Perth. This project includes three buses manufactured by DaimlerChrysler with Ballard fuel cell power sources operating in regular service alongside the existing natural gas and diesel bus fleets. The life-cycle assessment (LCA) of the fuel cell bus trial in Perth determines the overall environmental footprint and energy demand by studying all phases of the complete transportation system, including the hydrogen infrastructure, bus manufacturing, operation, and end-of-life disposal. The LCAs of the existing diesel and natural gas transportation systems are developed in parallel. The findings show that the trial is competitive with the diesel and natural gas bus systems in terms of global warming potential and eutrophication. Emissions that contribute to acidification and photochemical ozone are greater for the fuel cell buses. Scenario analysis quantifies the improvements that can be expected in future generations of fuel cell vehicles and shows that a reduction of greater than 50% is achievable in the greenhouse gas, photochemical ozone creation and primary energy demand impact categories.