Potential applications of thermal energy storage in electric power generation sector (Ⅱ)

简要介绍了储热技术在电力系统中最有潜力的四种具体应用技术,包括太阳能热发电,压缩空气储能,深冷储能,热泵储电,指出了太阳能热发电储热技术在短期内具有很大发展潜力,目前双罐式液体显热储热(储冷)具有较好的整体效率,将在电力系统储热技术中发挥重要的作用.     

Review on combined wind power generation and energy storage systems

储能系统由于能够实现电能的时空平移,具有响应速度快,规模化等优点,是改善风电波动性,提高其并网能力的有效手段,构建风储联合发电系统成为目前研究重点.简单介绍了风电并网对电力系统的影响及不同类型电池储能技术的发展现状,给出了部分国内外风储联合发电系统的示范工程,并分析了平滑风电功率波动,跟踪计划出力曲线和削峰填谷3种主要运行方式,重点阐述了目前风储联合发电系统控制策略和储能容量配置研究现状,对进一步开展风储联合发电系统的研究进行了展望,指出经济性仍然是制约储能技术应用的关键问题之一,提高包含储能单元的风储联合发电系统的经济性是今后的研究重点.     

Utility scale hybrid wind–solar thermal electrical generation: A case study for Minnesota

The performance of a hybrid wind–solar power plant in southwestern Minnesota is modeled for a 2-yr period using hourly wind and solar insolation data. The wind portion of the plant consists of four interconnected wind farms within a radius of 90 km. The solar component of the plant is a parabolic trough solar thermal electric generating system using a heat transfer fluid that drives a steam turbine. The market value of energy produced, retail value of energy produced, and levelized cost of energy of the hybrid plant are compared to those of an energy equivalent wind-only plant. Results show that adding solar thermal electric generating capacity to a wind farm rather than expanding with additional wind capacity provides cost–benefit trade-offs that will continue to change as the two technologies evolve. At the present time, we find that capital cost and levelized cost of energy favor a wind-only plant while electric load matching favors a hybrid wind–solar plant. Regional differences in the solar resource in the US influence the economic viability of the hybrid plant, and a comparison using the present model is made with one location in the Southwest. The hourly data analysis presented here is a possible tool for evaluating the overall economic feasibility and generating characteristics for a hybrid wind–solar thermal electric power plant for any location with available wind, solar, electric load, and price data.     

独立式风光互补发电系统中最大功率控制策略研究

独立风光互补发电系统从能量的角度来看可以分为3部分,即能量获取部分,能量存储部分以及能量消耗部分。主要介绍了能量获取所涉及的风力机最大功率运行和光伏电池最大功率跟踪这2个问题的控制策略,同时对能量存储部分所涉及的蓄电池充放电的控制策略进行了介绍,其中对充电策略的三阶段法做了比较详细的分析。最后对最大功率控制策略的研究方法作了系统的评述并对该领域今后的研究方向作了展望。     

Value analysis of intermittent generation sources from the systemoperations perspective

The objective of this study is to determine the economic and operational impact on energy cost of incorporating large photovoltaic (PV) and wind energy conversion systems (WECS) into the electric utility generation mix. In most cases, PV and WECS power outputs are subtracted from the utility load with the expectation that conventional generation would meet the residual load. This approach is valid for small penetration levels and/or for PV and WECS facilities connected near load centers, However, several constraints such as thermal generation characteristics, fuel supply and delivery, spinning reserve requirements, and hydro availability are not adequately represented in this process. To determine the optimal value of large-scale PV and WECS applications, a new methodology that would take into account the aforementioned constraints as well as a more global penetration is developed. Results indicate that while high hydro availability increases PV penetration levels, high ramping rates can also significantly increase penetration levels     

Heating with wind: Economics of heat pumps and variable renewables

With the growth of wind and solar energy in electricity supply, the electrification of space and water heating is becoming a promising decarbonization option. In turn, such electrification may help the power system integration of variable renewables, for two reasons: thermal storage could provide low-cost flexibility, and heat demand is seasonally correlated with wind power. However, temporal fluctuations in heat demand may also imply new challenges for the power system. This study assesses the economic characteristics of electric heat pumps and wind energy and studies their interaction on wholesale electricity markets. Using a numerical electricity market model, we estimate the economic value of wind energy and the economic cost of powering heat pumps. We find that, just as expanding wind energy depresses its €/MWh_el value, adopting heat pumps increases their €/MWh_el cost. This rise can be mitigated by synergistic effects with wind power, “system-friendly” heat pump technology, and thermal storage. Furthermore, heat pumps raise the wind market value, but this effect vanishes if accounting for the additional wind energy needed to serve the heat pump load. Thermal storage facilitates the system integration of wind power but competes with other flexibility options. For an efficient adoption of heat pumps and thermal storage, we argue that retail tariffs for heat pump customers should reflect their underlying economic cost.     

Turbine inlet cooling with thermal energy storage

Turbine inlet cooling (TIC) is a common technology used to increase combustion turbine power output and efficiency. The use of mechanical or absorption chillers for TIC allows for more air cooling than evaporative methods and also imposes a significant parasitic load to the turbine. Thermal energy storage (TES) can be used to shift this load to off‐peak hours. Use of thermal storage increases the flexibility of turbine power output, which benefits from the application of optimization tools. This paper explores the effect of combining TIC with TES to enhance the performance of a district cooling system that includes a gas turbine for power generation. The work illustrates how the system's performance can be enhanced using optimization. Application of multi‐period optimization to the system that includes TES brings significant operational cost savings when compared with a system without thermal storage. It is also shown how TES provides demand‐side energy management in the district cooling loop and supply‐side management through the use of TIC. In addition to the optimization study, a thorough literature review is included that describes the current body of work on combining TIC with TES. Copyright © 2013 John Wiley & Sons, Ltd.     

Evaluating energy storage technologies for wind power integration

In this paper we perform a cost analysis of different types of energy storage technologies. We evaluate eleven storage technologies, including lead-acid, sodium–sulfur, nickel–cadmium, and lithium-ion batteries, superconducting magnetic energy storage, electrochemical capacitors, flywheels, flow batteries, pumped hydro and compressed air energy storage systems. We perform economic analysis for key applications associated with a wind farm integrated into the electric grid, including load shifting, frequency support, and power quality. We identify the key characteristics that affect the economic viability for these technologies, perform sensitivity analyses based on key performance criteria and find improvement areas that could make them more competitive in the near future.     

Development of the all‐vanadium redox flow battery for energy storage: a review of technological,financial and policy aspects

The commercial development and current economic incentives associated with energy storage using redox flow batteries (RFBs) are summarised. The analysis is focused on the all‐vanadium system, which is the most studied and widely commercialised RFB. The recent expiry of key patents relating to the electrochemistry of this battery has contributed to significant levels of commercialisation in, for example, Austria, China and Thailand, as well as pilot‐scale developments in many countries. The potential benefits of increasing battery‐based energy storage for electricity grid load levelling and MW‐scale wind/solar photovoltaic‐based power generation are now being realised at an increasing level. Commercial systems are being applied to distributed systems utilising kW‐scale renewable energy flows. Factors limiting the uptake of all‐vanadium (and other) redox flow batteries include a comparatively high overall internal costs of $217 kW^?1 h^?1 and the high cost of stored electricity of ≈ The commercial development and current economic incentives associated with energy storage using redox flow batteries (RFBs) are summarised. The analysis is focused on the all‐vanadium system, which is the most studied and widely commercialised RFB. The recent expiry of key patents relating to the electrochemistry of this battery has contributed to significant levels of commercialisation in, for example, Austria, China and Thailand, as well as pilot‐scale developments in many countries. The potential benefits of increasing battery‐based energy storage for electricity grid load levelling and MW‐scale wind/solar photovoltaic‐based power generation are now being realised at an increasing level. Commercial systems are being applied to distributed systems utilising kW‐scale renewable energy flows. Factors limiting the uptake of all‐vanadium (and other) redox flow batteries include a comparatively high overall internal costs of $217 kW^?1 h^?1 and the high cost of stored electricity of ≈ $0.10 kW^?1 h^?1. There is also a low‐level utility scale acceptance of energy storage solutions and a general lack of battery‐specific policy‐led incentives, even though the environmental impact of RFBs coupled to renewable energy sources is favourable, especially in comparison to natural gas‐ and diesel‐fuelled spinning reserves. Together with the technological and policy aspects associated with flow batteries, recent attempts to model redox flow batteries are considered. The issues that have been addressed using modelling together with the current and future requirements of modelling are outlined. Copyright © 2011 John Wiley & Sons, Ltd.     

Evaluating the limits of solar photovoltaics (PV) in electric power systems utilizing energy storage and other enabling technologies

In this work, we evaluate technologies that will enable solar photovoltaics (PV) to overcome the limits of traditional electric power systems. We performed simulations of a large utility system using hourly solar insolation and load data and attempted to provide up to 50% of this system's energy from PV. We considered several methods to avoid the limits of unusable PV that result at high penetration due to the use of inflexible baseload generators. The enabling technologies considered in this work are increased system flexibility, load shifting via demand responsive appliances, and energy storage.     

Analysing the benefits of hybridisation and storage in a hybrid solar gas turbine plant

ABSTRACT

A dynamic model of a tower-driven, hybrid solar gas turbine power plant is presented to highlight the benefits of hybrid operation as well as the development a novel plant configuration to improve solar fraction by leveraging a packed-bed thermal energy storage (TES). Relative to solar-only plant, hybridisation increases solar-to-electric efficiency (STE) by 30%. Introduction of a passive packed-bed TES only leads to slight improvement in solar energy utilisation and displacement of solar load. A novel plant configuration, which utilises a recycle stream to charge TES, is presented to improve solar energy utilisation. The recycle stream gives freedom to manipulate the thermal capacity of flow in the tower collector to control collector exit temperature and direct excess solar energy to TES. Employment of the proposed plant configuration leads to a 10.8% and 11.3% improvement in yearly STE and solar fraction, respectively, relative to a plant not utilising such a control scheme.     

考虑退役动力电池衰减特性的新能源场站群共享储能长期规划配置

为最大化利用退役动力电池的全生命周期价值、解决共享储能在电力系统扩展规划方面需兼顾多方利益的经济性难题,计及逐渐增加的新能源装机容量与负荷需求,提出考虑退役动力电池衰减特性的发电侧共享储能长期规划模型。首先,设计基于退役动力电池的发电侧共享储能运营模式以打破能量共享壁垒,使其既能服务于自身新能源场站又可实现多个新能源场站间的能量互济、必要时还能参与电网的动态调频。其次,考虑退役动力电池衰减特性构建多个新能源场站自配并共享储能的长期规划模型,模型基于合作博弈以应对多方利益诉求冲突给资源优化配置带来的经济性挑战。最后以算例仿真验证所提发电侧共享储能运营模式及长期规划模型的可行性。     

Constructing an innovative Bio-Hydrogen Integrated Renewable Energy System

Hybrid Renewable Energy Systems (HRES) offer alternative energy options that deliver distributed power generation for isolated loads. However, the production of energy from both wind turbines and solar PV systems is weather-dependent. In this study, we developed an innovative Bio-Hydrogen Integrated Renewable Energy System (BHIRES) based on the integration of hydrogen generation from biomass fermentation, renewable energy power generation, hydrogen generation from water electrolysis, a hydrogen storage device, and a fuel cell providing combined heat and power. BHIRES can provide electric power, thermal energy, and hydrogen, with the additional function of processing biomass waste and wastewater. As indicated by results of the economic analysis conducted in this study, the cost of electricity and the average energy cost of using BHIRES are both lower than those for wind/PV/hydrogen HRES. Therefore, this system is ideal for users in remote areas such as islands, and farms in mountainous areas.     

A feasibility study of using thermal energy storage in a conventional air‐conditioning system

An Erratum has been published for this article in International Journal of Energy Research 2004; 28 (13): 1213. This paper deals with the simulation of thermal energy storage (TES) system for HVAC applications. TES is considered to be one of the most preferred demand side management technologies for shifting cooling electrical demand from peak daytime hours to off peak night hours. TES is incorporated into the conventional HVAC system to store cooling capacity by chilling ethylene glycol, which is used as a storage medium. The thermodynamic performance is assessed using exergy and energy analyses. The effects of various parameters such as ambient temperature, cooling load, and mass of storage are studied on the performance of the TES. A full storage cycle, with charging, storing and discharging stages, is considered. In addition, energy and exergy analysis of the TES is carried out for system design and optimization. The temperature in the storage is found to be as low as 6.4°C after 1 day of charging without load for a mass of 250 000 kg. It is found that COP of the HVAC system increases with the decrease of storage temperature. Energy efficiency of the TES is found to be 80% for all the mass flow rate of the discharging fluid, whereas exergy efficiency varies from 14 to 0.5%. This is in fact due to the irreversibilities in a TES process destroy a significant amount of the input exergy, and the TES exergy efficiencies therefore become always lower than the corresponding energy efficiencies. Copyright © 2004 John Wiley & Sons, Ltd.     

Modeling of hydrogen and electrical energy storages in wind/PV energy system on the Lake Baikal coast

The paper presents a research on a green power supply system (producing no carbon dioxide and other harmful emissions) in the area of Baikal Lake, for the maximum loads of 10 kW and 100 kW. The system includes photovoltaic converters, wind turbines, batteries for electric energy storage and a system for hydrogen production, storage and energy use. Calculations based on the optimization mathematical model demonstrated the efficiency of the combined use of wind and solar energy in the considered areas, as well as the simultaneous storage of electric energy and hydrogen. The electric energy storage is most efficient for short-term time intervals whereas an increase in the duration of continuous energy “standstills” up to several days makes the storage of hydrogen more cost-effective.     

Optimum energy storage techniques for the improvement of renewable energy sources-based electricity generation economic efficiency

The high wind and solar potential along with the extremely high electricity production cost met in the majority of Greek Aegean islands comprising autonomous electrical networks, imply the urgency for new renewable energy sources (RES) investments. To by-pass the electrical grid stability constraints arising from an extensive RES utilization, the adaptation of an appropriate energy storage system (ESS) is essential. In the present analysis, the cost effect of introducing selected storage technologies in a large variety of autonomous electrical grids so as to ensure higher levels of RES penetration, in particular wind and solar, is examined in detail. A systematic parametrical analysis concerning the effect of the ESSs’ main parameters on the economic behavior of the entire installation is also included. According to the results obtained, a properly sized RES-based electricity generation station in collaboration with the appropriate energy storage equipment is a promising solution for the energy demand problems of numerous autonomous electrical networks existing worldwide, at the same time suggesting a clean energy generation alternative and contributing to the diminution of the important environmental problems resulting from the operation of thermal power stations.     

高水电比重系统随机电力电量平衡模型与算法

针对高水电比重系统中电力电量平衡问题,首先考虑利用典型周负荷曲线进行电力电量平衡分析,以更好地计及工作日和非工作日不同的负荷曲线对可调水电站库容及火电站开机的影响。为恰当考虑风电场和光伏电站出力的不确定性和波动性,建立了基于随机优化的随机电力电量平衡模型,从概率的角度更好地分析和衡量风光电站对电量平衡的贡献。为方便该模型的求解,对非线性的水电转换函数进行线性化处理,得到混合整数规划模型,采用CPLEX对模型进行求解。以某高水电比重系统作为算例进行仿真分析,验证了所提随机电力电量平衡模型与算法的正确性和有效性,从概率的角度定量分析了风光电站的电量贡献。     

Economic implications of thermal energy storage for concentrated solar thermal power

Solar energy is an attractive renewable energy source because the sun's energy is plentiful and carbon-free. However, solar energy is intermittent and not suitable for base load electricity generation without an energy backup system. Concentrated solar power (CSP) is unique among other renewable energy options because it can approach base load generation with molten salt thermal energy storage (TES). This paper describes the development of an engineering economic model that directly compares the performance, cost, and profit of a 110-MW parabolic trough CSP plant operating with a TES system, natural gas-fired backup system, and no backup system. Model results are presented for 0–12 h backup capacities with and without current U.S. subsidies. TES increased the annual capacity factor from around 30% with no backup to up to 55% with 12 h of storage when the solar field area was selected to provide the lowest levelized cost of energy (LCOE). Using TES instead of a natural gas-fired heat transfer fluid heater (NG) increased total plant capital costs but decreased annual operation and maintenance costs. These three effects led to an increase in the LCOE for PT plants with TES and NG backup compared with no backup. LCOE increased with increasing backup capacity for plants with TES and NG backup. For small backup capacities (1–4 h), plants with TES had slightly lower LCOE values than plants with NG backup. For larger backup capacities (5–12 h), plants with TES had slightly higher LCOE values than plants with NG backup. At these costs, current U.S. federal tax incentives were not sufficient to make PT profitable in a market with variable electricity pricing. Current U.S. incentives combined with a fixed electricity price of $200/MWh made PT plants with larger backup capacities more profitable than PT plants with no backup or with smaller backup capacities. In the absence of incentives, a carbon price of $100–$160/tonne CO_2eq would be required for these PT plants to compete with new coal-fired power plants in the U.S. If the long-term goal is to increase renewable base load electricity generation, additional incentives are needed to encourage new CSP plants to use thermal energy storage in the U.S.     

The thermodynamic effect of thermal energy storage on compressed air energy storage system

With the increasing penetration of renewable energy into energy market, it is urgent to solve the problem of fluctuations of renewable energy sources (RES). Energy storage technology is regarded as one method to cope with the unstable nature of RES. One of these technologies is compressed air energy storage (CAES), which is a modification of the basic gas turbine technology. Electric power supplied by CAES can meet peak-load requirement of electric utility systems. Because there is heat waste in the existing CAES systems during compression process, fossil fuels are used to improve the expansion work to generate peak power. In order to avoid the use of fuels and keep high efficiency of system, CAES system with thermal energy storage (TES) is designed to capture and reuse the compressed air heat. This paper uses a thermodynamic model of a CAES system with TES to analyze the effect of TES on system efficiency. Besides, this paper evaluates the influence of temperature and pressure on the utilization of heat in TES. Results show that even when power efficiency reaches maximum, there is still a proportion of thermal energy left in TES for other use. Meanwhile, the utilization of heat in TES can be affected by pressure in the air storage chamber. With appropriate selection of pressure limits, the utilization of compressed air heat can be optimized.     

储能电池在风光互补发电系统中的容量配置分析

储能电池是分布式发电系统的关键组件。增加储能电池的容量可以提高发电系统的可靠性,但会增加系统的投资和运行费用。基于上海地区全年8 760 h的气象数据,计算了风光互补发电系统在不同储能容量下的负荷缺电率和能量溢出率的变化。对于独立的风光互补发电系统,在满足能量溢出率小于0.3的情况下,如果系统缺电率维持在1%左右时,需要配置3天的储能容量;如果系统缺电率为0,则需要配置5天的储能容量。