Bulk Energy Storage Research Articles

Hybrid energy storage system based on supercapacitors and Li-ion batteries

Energy storage systems (ESS) have a wide spectrum of functions. They must provide power quality, shaving of load change, coordination of distributed power systems, bulk energy storage, and end-user reliability, e.g., uninterrupted power supply. In present paper the configuration and design of experimental ESS based on both Li-ion batteries and supercapacitors have been proposed. Such a hybrid energy storage system (HESS) includes three main components: Li-ion batteries, supercapacitors, and grid interconnection consisting of two invertors and control and monitoring system. Energy storage capacity of developed HESS prototype is 100 kWh, nominal power—100 kW, peak power—200 kW. HESS was created and tested within the experimental facility also including 1.5 MW gas turbine power plant, 200 kW controllable active and reactive loads, and control and measurement system. Experimental results showed that HESS successfully provides the following advantages: (i) suppression of voltage, current, and frequency disturbances in the grid; (ii) compensation of reactive power in the circuit; and (iii) uninterrupted power supply. Cost analysis of proposed hybrid system has also been carried out. In comparison with battery ESS without supercapacitors, HESS showed longer life time, lower cost, and higher peak power.

Changes in the economic value of wind energy and flexible resources at increasing penetration levels in the Rocky Mountain Power Area

ABSTRACTWe use a consistent economic framework to estimate the long‐run economic value of wind while including operational constraints for conventional generation and hourly variation in wind and load. Day‐ahead forecast errors in wind are corrected in the real‐time, after commitment decisions for many thermal generators have already been made. The framework is used to estimate the change in the marginal economic value of wind with increasing penetration in the Rocky Mountain Power Area of the USA. We also evaluate the marginal economic benefit to wind energy of implementing several strategies to manage wind energy variability and uncertainty: more flexible conventional generation, real‐time pricing, low cost bulk energy storage, and increased geographic diversity of wind plant siting. Without mitigation, the marginal economic value of wind is found to decrease by $21 MWh (37% of the marginal value of wind at 0% penetration) as wind penetration increases from 0% to 30%. The decline is largely because of the hourly profile of wind output and day‐ahead wind energy forecast errors; factors whose impact is reduced by the mitigation strategies. With mitigation, the marginal value of wind at the 30% penetration level is $6‐$11 MWh greater than the value without the measures (17‐31% increase in value). Although the marginal value of wind energy decreases with increasing penetration in this region, several different types of mitigation strategies are available and should be investigated in more detail. Copyright © 2013 John Wiley & Sons, Ltd.

Global Energy Scenario and Impact of Power Electronics in 21st Century

Power electronics technology has gained significant maturity after several decades of dynamic evolution of power semiconductor devices, converters, pulse width modulation (PWM) techniques, electrical machines, motor drives, advanced control, and simulation techniques. According to the estimate of the Electric Power Research Institute, roughly 70% of electrical energy in the USA now flows through power electronics, which will eventually grow to 100%. In the 21st century, we expect to see the tremendous impact of power electronics not only in global industrialization and general energy systems, but also in energy saving, renewable energy systems, and electric/hybrid vehicles. The resulting impact in mitigating climate change problems is expected to be enormous. This paper, in the beginning, will discuss the global energy scenario, climate change problems, and the methods of their mitigation. Then, it will discuss the impact of power electronics in energy saving, renewable energy systems, bulk energy storage, and electric/hybrid vehicles. Finally, it will review several example applications before coming to conclusion and future prognosis.

A Fast Algorithm for Initial Design of HTS Coils for SMES Applications

Superconducting magnetic energy storage (SMES) is characterized by low-energy density but high-power density, making this an unfeasible approach for bulk energy storage. Nevertheless, there are applications where high amounts of power must be available for a short period of time, like power quality applications. The core element of SMES is the superconducting coil. Different approaches are found in the literature considering the modeling of this component, either for design or simulation purposes. These usually consist of analytical or numerical approaches. The former allows fast results, but only considers geometric effects. The latter provides accurate results, considering, besides electromagnetic, also mechanical and thermal effects. In this paper, a review of these models is performed, and analytical models are used in an algorithm that allows optimizing equivalent inductance for a specified length of tape. Two small prototypes are fabricated, and experimental measurements carried out, in order to validate the models that are in the base of the proposed algorithm.

A Novel Pumped Hydro Combined with Compressed Air Energy Storage System

A novel pumped hydro combined with compressed air energy storage (PHCA) system is proposed in this paper to resolve the problems of bulk energy storage in the wind power generation industry over an area in China, which is characterised by drought and water shortages. Thermodynamic analysis of the energy storage system, which focuses on the pre-set pressure, storage volume capacity, water air volume ratio, pump performance, and water turbine performance of the storage system, is also presented. This paper discovers how such parameters affect the performance of the whole system. The ideal performance of this novel system has the following advantages: a simple, highly effective and low cost structure, which is comparable to the efficiency of a traditional pumped hydro storage system. Research results show a great solution to the current storage constraints encountered in the development of the wind power industry in China, which have been widely recognised as a bottleneck in the wind energy storage industry.

Optimal sizing of the CAES system in a power system with high wind power penetration

The compressed air energy storage (CAES) system is a mature and reliable bulk energy storage technique with promising potential to accommodate high wind power penetration in power systems. This paper proposes an optimization model to decide the rated power and capacity of a CAES system, which is crucial to maximizing economical profits. This methodology involves several steps. Firstly, the constraints of the CAES system’s rated power are considered, which include the CAES system’s compensation for power shortages during peak load period, the influence of the operation on power flow and the impact on the system when CAES is switched. Secondly, an exponential distribution is adopted to calculate wind power curtailment at night, based on which the benefits from recovering wind power curtailment can be estimated. Finally, the economical profits are optimized according to the CAES investment cost, operation cost and turnout. The results show that the proposed methodology can provide a referential guidance for CAES sizing according to different situations in practice.

Presentation of a stochastic model estimating the wind energy contribution in remote island electrical networks

The electrification in remote islands whose electricity distribution network is not connected to the mainland’s grid is mostly based on Autonomous Power Stations (APSs) that are usually characterized by a considerably high electricity production cost, while at the same time the contribution of Renewable Energy Sources (RES) in these regions accounts for less than 10% of the total electricity generation. This actually results from the fact that despite the excellent wind potential of most of these islands, the wind energy contribution is significantly restricted from limits imposed to protect the remote electrical grids from possible instability problems, due to the stochastic wind speed behavior and the variable electricity consumption. On the basis of probability distribution of the load demand of a representative Greek island and the corresponding data related to the available wind potential, the present study estimates the maximum – acceptable by the local grid – wind energy contribution. For that reason, an integrated computational algorithm has been developed from first principles, based on a stochastic analysis. According to the results obtained, it becomes evident that with the current wind turbine technology, wind energy cannot play a key role in coping with the electrification problems encountered in many Greek island regions, excluding however the case of introducing bulk energy storage systems that may provide considerable recovery of the remarkable wind energy rejections expected.

Seasonal energy storage system based on hydrogen for self sufficient living

SELF is a resource independent living and working environment. By on-board renewable electricity generation and storage, it accounts for all aspects of living, such as space heating and cooking as well as providing a purified rainwater supply and wastewater treatment, excluding food supply. Uninterrupted, on-demand energy and water supply are the key challenges. Off-grid renewable power supply fluctuations on daily and seasonal time scales impose production gaps that have to be served by local storage, a function normally fulfilled by the grid. While daily variations only obligate a small storage capacity, requirements for seasonal storage are substantial. The energy supply for SELF is reviewed based on real meteorological data and demand patterns for Zurich, Switzerland. A battery system with propane for cooking serves as a reference for battery-only and hybrid battery/hydrogen systems. In the latter, hydrogen is used for cooking and electricity generation. The analysis shows that hydrogen is ideal for long term bulk energy storage on a seasonal timescale, while batteries are best suited for short term energy storage. Although the efficiency penalty from hydrogen generation is substantial, in off-grid systems, this parameter is tolerable since the harvesting ratio of photovoltaic energy is limited by storage capacity.

MOEA based design of decentralized controllers for LFC of interconnected power systems with nonlinearities, AC–DC parallel tie-lines and SMES units

A new design of Multi-Objective Evolutionary Algorithm based decentralized controllers for load–frequency control of interconnected power systems with Governor Dead Band and Generation Rate Constraint nonlinearities, AC–DC parallel tie-lines and Superconducting Magnetic Energy Storage (SMES) units, is proposed in this paper. The HVDC link is used as system interconnection in parallel with AC tie-line to effectively damp the frequency oscillations of AC system while the SMES unit provides bulk energy storage and release, thereby achieving combined benefits. The proposed controller satisfies two main objectives, namely, minimum Integral Squared Error of the system output and maximum closed-loop stability of the system. Simulation studies are conducted on a two area interconnected power system with nonlinearities, AC–DC tie-lines and SMES units. Results indicate that the proposed controller improves the transient responses and guarantees the closed-loop stability of the overall system even in the presence of system nonlinearities and with parameter changes.

A Family of Single-Stage Resonant AC/DC Converters With PFC

A family of novel, single-stage, isolated, resonant-based AC/DC power supply circuits with inherently high power factor is presented in this paper. The three topologies in the family are transformer isolated; they contain a bulk energy storage capacitor to enable output voltage holdup, and they also contain a resonant circuit in which a resonant capacitor is connected directly across the mains input rectifier. The presence of this resonant circuit results in AC line current being drawn over much of the line cycle, as well as in soft switching of the power devices. The rectifier-compensated fundamental-mode approximation (RCFMA) method is used to provide an accurate yet simple analysis of the circuit. Experimental results for closed-loop operation of two of the topologies are also presented. This family of single-stage, high-power-factor converters provides for simple control and high-frequency operation, due to the resonant configuration of the power circuit, without the excessive conduction loss of fully resonant techniques.

Modelling electricity storage systems management under the influence of demand-side management programmes

Electricity storage systems (ESS) for bulk energy storage are principally used for load levelling purposes or for relieving the intermittency of renewables. Another use is electricity arbitrage through the rule of ‘buy low, sell high’. This operation tracks the market-clearing price (MCP) profiles and produces profit by exploiting the differences between peak and off-peak prices. The profits made in this way depend on technology characteristics and the market competition level. We investigate the influence of demand-side management (DSM) on ESS profitability when the only income is from provision of electricity arbitrage services, by optimizing the time allocation of the charge and discharge operations. Two scenarios of DSM in the market have been selected for two management periods (MP): 1 day and 3 days. The longer MP is examined in order to investigate the potential for higher economic value when energy transfer to the next day is permitted. The key finding is that a very small load shifting from peaks to off-peaks, due to DSM, significantly affects the ESS profit. The significant profit losses the ESS showed are a result of the high capital costs and the small difference of the peak and off-peak electricity prices in the Greek market. Therefore, under the assumptions we have made for this research, any attempt to use ESS in ‘buy low, sell high’ operation is not profitable. Copyright © 2008 John Wiley & Sons, Ltd.

Value of Bulk Energy Storage for Managing Wind Power Fluctuations

This paper considers the impact of uncertain wind forecasts on the value of stored energy (such as pumped hydro) in a future U.K. system, where wind supplies over 20% of the energy. Providing more of the increased requirement for reserves from standing reserve sources could increase system operation efficiency, enhance wind power absorption, achieve fuel cost savings, and reduce CO2 emissions. Generally, storage-based standing reserve's value is driven by the amount of installed wind and by generation system flexibility. Benefits are more significant in systems with low generation flexibility and with large installed wind capacity. Storage is uniquely able to stock up generated excesses during high-wind/low-demand periods, and subsequently discharge this energy as needed. When storage is combined with standing reserve provided from conventional generation (e.g., open-cycle gas turbines), it is valuable in servicing the highly frequent smaller imbalances

Bulk energy storage potential in the USA, current developments and future prospects

Stored energy can provide electricity during periods of high demand, as currently demonstrated with bulk storage systems such as pumped hydro storage (PHS), which accounts for only 2.5% of the current installed base load in the USA. Sites for future developments have become less available, and environmental siting issues, as well as high costs have stopped further prospects. This paper looks at the potential beyond PHS, with bulk storage systems such as compressed air energy storage (CAES) flow-batteries and 1 MW flywheel systems that can provide system stability/support at the grid, substations and distributed level. Current developments in bulk energy storage will be reviewed as well as some storage project developments incorporating wind energy and the impact on base-loaded coal and natural gas fired GT combined cycle plants. The large potential and the economic benefits for energy storage in the US will be examined.

Sub-envelope modulation method to reduce total harmonic distortion of AC∕AC matrix converters

An AC/AC matrix converter is an array of power semiconductor switches that connects directly a three-phase AC source to another three-phase load. It can convert an AC power source with certain voltage and frequency to another AC load with variable voltage and variable frequency directly without a DC-link and bulk energy storage component. Classical modulation methods such as the Venturini method and the space vector modulation method using AC-network maximum-envelope modulation, implement matrix conversion successfully. However, they also cause very high total harmonic distortion (THD). A novel approach, the sub-envelope modulation (SEM) method, is presented to reduce THD of matrix converters effectively. The approach is extended to an improved version of matrix converters and the THD can be reduced further. The algorithm of the SEM method is described in detail. Simulation and experimental results are also presented to verify the feasibility of the SEM approach. The results will be very helpful for industry applications.

Effects of tool/workpiece temperature on tool wear when cutting hard steels : R. Dewes et al. (Universty of Birmingham, Birmingham, UK.)

This paper presents a generic bulk energy storage dispatch model for production costing simulation, and assesses the performance and economics of storage under various system scenarios. The storage model presented captures the dynamic relationship between the reservoir energy status and the storage commitments in energy and ancillary co-optimization market, thereby enabling the dispatch of storage for both energy and cross-market arbitrage opportunities. The paper also presents a methodology to quantify the cycling costs incurred by conventional generating units due to frequent start–shut cycles and ancillary services. The bulk storage technology modeled is compressed air energy storage (CAES), and it is represented within the IEEE 24 bus reliability test system. Simulations are performed to quantify the impacts of bulk energy storage in terms of reduction in market prices, system production and cycling costs, and also to investigate the economic viability of storage projects in terms of payback periods under increasing wind penetration levels.

Large-scale storage of electrical energy

Today, bulk energy storage is economic because it helps cut generation costs by keeping the amount of spinning reserve to a minimum and helping to meet peak demand. In the future, with more nuclear power stations in the system and the increasing contribution of alternative energy supplies, storage will have even greater benefit

A focus for biophysical research in energy problems.

There is widespread agreement that solar energy is the most promising long-range energy source. However, contemporary technology for bulk energy storage is so primitive that full use of the inevitably erratic solar energy flux is severely limited. Biological systems have perfected methods of storing solar energy for later use in periods of darkness, and it is argued in this symposium presentation that there are many frontiers in biophysics related to the solar energy storage problem. Moreover, the conceivable biological storage systems span a wide range of technology, with appropriate applications in societies of widely varying degrees of industrial development. Use of biological systems to produce hydrogen from solar energy may be among the most versatile of these applications. The entire problem of bioconversion of solar energy presents an excellent example of how the needs for basic scientific understanding and application engineering can be very tightly interwoven.

Cost and Size Estimates for a Redox Bulk Energy Storage Concept

Preliminary capital cost and size estimates were made for an electrochemical bulk energy storage concept. The electrochemical system considered was an electrically rechargeable flow cell with a titanium trichloride |titanium tetrachloride ‖ferric chloride|ferrous chloride redox couple. The preliminary calculations were made to help determine whether the redox‐flow‐cell system has an attractive potential as a bulk energy storage system for power load leveling. With the rise in demand for electric power, the problem facing the electric utility industry of meeting peak power demands has been growing more acute. Because present methods of meeting peak power demands are not entirely adequate the electric utility industry has been interested in new methods for meeting peak power demands. On the basis of preliminary capital cost estimates, size estimates, and several other important considerations, the redox‐flow‐cell system emerges as having great promise as a bulk energy storage system for power load leveling. The size of this system would be less than 2% of that of a comparable pumped hydroelectric plant. The capital cost of a 10 MW, 60 and 85 MW‐hr redox system is estimated to be $190–$330 per kilowatt. This cost compares well with that of competing systems, especially when one considers that for many sites a saving in transmission costs (up to $200 per kilowatt) could be realized with the redox system. This saving could be achieved because the redox systems could be built in various sizes and located near the load centers. The other important features of the redox system contributing to its load‐leveling application are its low adverse environmental impact, its high efficiency, its apparent absence of electrochemically related cycle life limitations, and its fast response.