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Abstract: Pumped storage hydroelectric plants are attractive in competitive electricity markets because of their operational flexibility and ability to provide rapid response to change in spot price of electricity. Operating pumped storage plant affects the consumer and producer surplus of the individual market and hence leads to significant changes in energy prices. This paper investigates the impact of pumped storage energy trading on the social welfare of electricity market. A theoretical analysis and intuitive explanation are presented and numerical case study is also illustrated to validate the analytical results developed. Energy trading by pumped storage increases the overall social welfare of the market, when both storing and releasing energy. Further, the implications of pumped storage energy trade are producers benefit more during storage and consumers benefit more during release of stored energy. [Copyright &y& Elsevier]

Abstract: With the integration of increased variable renewable energy generation and advent of liberalized electricity market, much attention has been devoted on the development of pumped hydro energy storage (PHES) as it has many prominent advantages of ensuring the safe and steady operation of power grid. In China, PHES has met a booming periods for the last ten years. Currently, there are 24 PHES stations with an installed capacity of 16.95GW while government''s target of 2020 is 50.02GW. In this paper we provide an overall review of China''s PHES development with a detailed presentation of the installed capacity and distribution of existing and proposed PHES stations, examine 4 typical stations in order to give a good description for the practical functions of PHES in power grid, analyze the management mode and price mechanism of PHES operation and point out the barriers in PHES development in China. State Grid Corporation of China (SGCC), which are making great efforts on China''s PHES development, is discussed as a role model. On that basis we suggest PHES in the fast developing period should be temporarily operated and scheduled by grid companies in terms of exertion of its positive effects, while government should also take responsibility to subsidize on the stations'' operation to relieve the price pressure of the ever-growing integration of renewable energy. [Copyright &y& Elsevier]

Abstract: This paper investigates hydro-pumped storage appraisal and commissioning in Italy and Spain. It argues that analyses to evaluate what is the most cost-efficient flexibility solution, including the possibility of improving existing facilities and regulatory frameworks, should be implemented on a case-by-case basis, as electricity storage is only one out of many possible sources of flexibility. Where pumped hydro is identified as the best solution to provide the ancillary services needed, a market''s ability to deliver it should then be tested, by addressing the major concerns for ex-ante appraisal the paper identifies. Only where a market ‘fails’ to deliver such capacity, a case for commissioning hydro-pumped storage may be justified. The key areas are then: (i) the criteria to define capacity adequacy and (ii) the procedures to select who should build and who should run such facilities. The risks and challenges identified suggest that this solution should be considered with caution. [Copyright &y& Elsevier]

Abstract: Environmental constraints imposed on hydropower operation are usually given in the form of minimum environmental flows and maximum and minimum rates of change of flows, or ramp rates. One solution proposed to mitigate the environmental impact caused by the flows discharged by a hydropower plant while reducing the economic impact of the above-mentioned constraints consists in building a re-regulation reservoir, or afterbay, downstream of the power plant. Adding pumping capability between the re-regulation reservoir and the main one could contribute both to reducing the size of the re-regulation reservoir, with the consequent environmental improvement, and to improving the economic feasibility of the project, always fulfilling the environmental constraints imposed to hydropower operation. The objective of this paper is studying the contribution of a re-regulation reservoir to fulfilling the environmental constraints while reducing the economic impact of said constraints. For that purpose, a revenue-driven optimization model based on mixed integer linear programming is used. Additionally, the advantages of adding pumping capability are analysed. In order to illustrate the applicability of the methodology, a case study based on a real hydropower plant is presented. [Copyright &y& Elsevier]

Abstract: This paper presents a power production system for the isolated insular power system of the islands Karpathos and Kasos. Karpathos and Kasos are two small islands, located in the South-East Aegean Sea (Dodecanese complex) that are not connected to the main power distribution network. Energy production is based exclusively on an autonomous thermal power plant and a small wind park, installed on the island of Karpathos. The maximum annual power demand has been estimated to exceed 12MW by 2014. The mean specific annual energy production cost from the existing system has been calculated at 0.249€/kWh in 2008. The proposed system aims at the maximisation of wind energy penetration and the minimisation of imported fossil fuel use for the production of electricity. The proposed system consists of a wind park and a pumped storage system (PSS). The introduced power system aims to guarantee power production for certain hours per day. A thorough sitting of the system is accomplished. Three different sites for the PSS installation are examined before the optimum is selected. The available wind potential of the islands was evaluated using a wind mast installed within the frame of the examined project’s feasibility study. The annual mean wind velocity at the wind park’s installation site was measured to be higher than 11.5m/s. The introduced system’s set-up, and operation & maintenance cost parameters have been estimated. The dimensioning of the system aims mainly at optimising the project’s economic indexes, following the existing legislative framework. The annual guaranteed energy production has also been maximised. An economic sensitivity analysis is performed. It is estimated that the proposed project can exhibit attractive economic indexes, regardless of the availability of a subsidy, on the condition that the selling price of energy should be configured at 0.3552€/kWh and the selling price of guaranteed power should be 127€/kWyear. Under the above mentioned prerequisites, the project payback period is estimated at 5–6years. The present paper proves the economic feasibility of small scale wind powered pumped storage systems, not taking into account the undoubted environmental benefits. [Copyright &y& Elsevier]

Abstract: Energy storage constitutes an effective way to manage excess RES production, and pumped storage is a suitable and mature solution for large storage capacities. The present study aims to investigate the performance of a pumped storage unit introduced in a conventional Hydroelectric Power Plant in Greece. At first, the plant operation and the electric grid data for a reference period of one year are used to compute the time variation of water inflow into the dam, and to estimate the RES production rejections depending on the installed power. Next, a pumping station powered by the rejected RES production and raising water from an adjacent downstream reservoir is modeled. Various scenarios concerning the pumping station power rate and feeding program are examined. The operation of the combined system is simulated in detail and the energy results are analyzed. Also, an economic evaluation is carried out based on current financial conditions in Greece. The results showed that a considerable amount of excess RES production can be stored, but the economic viability of the investment depends on some critical parameters, which are identified. Certain guidelines concerning the optimum sizing and operation strategy of the pumped storage scheme are finally extracted. [Copyright &y& Elsevier]

Jordan's energy balance is largely dominated by combustible fuels. However, the country is well endowed with solar, wind and oil shale resources, in addition to large and small-scale hydropower projects. Based on available data and the current analysis, it is believed that there are at least 6-10 candidate sites in the western part of Jordan and 2-3 locations in the eastern plateau, which could be developed as small hydro plants, with a combined potential of more than 33 MW. At present, only two sites, namely King Talal Dam and Aqaba Thermal Power Plant, have been developed to be operational from 1980's. A major barrier to starting small scale hydro power projects is an understanding of how much the scheme will cost. This paper provides also an overview of the setbacks that inhibit the smooth investment and operation of small hydropower plants in Jordan. It is estimated that installing small hydropower schemes on the most promising existing dams will generate more than 200 GWh/year of electric energy without effecting the natural environment. In addition, there are another few sites, still under study, that may be developed in the future as small hydro plants [ABSTRACT FROM AUTHOR]

A yearly stochastic self-scheduling model for a price-maker hydro producer is presented. In the short term, the producer aims at maximizing profits in the day-ahead market. Residual demand curves model the producer's interaction with his competitors and the load demand. A modification of the residual demand curve is proposed to enable the definition of optimal pumped-hydro bids. Multistage stochastic programming provides hedging against the mid-term uncertainty of inflows, load demand, and competitors' offers. The proposed method models the impact of short-term profit maximization decisions on mid-term scheduling within a compact stochastic mixed integer linear programming (MILP) approach. A test case with a three-stage, 90-scenario stochastic tree and data of the Greek Power System is presented. Results provide insight on both mid-term reservoir management and short-term market-based operation and indicate the feasibility of solving a very large-scale scheduling problem as a unique MILP using a commercial solver. The role of forward contracts in mitigating market power is also analyzed. [ABSTRACT FROM PUBLISHER]

Abstract: As concerns about global warming grow, societies are increasingly turning to the use of intermittent renewable energy resources, where energy storage becomes more and more important. Pumped-hydro energy storage (PHES) is the most established technology for utility-scale electricity storage. Although PHES has continued to be deployed globally, its development in the United States has largely been dormant since the 1990s. In recent years, however, there has been a revival of commercial interests in developing PHES facilities. In this paper we examine the historical development of PHES facilities in the United States, analyze case studies on the controversies of disputed projects, examine the challenges to and conflicting views of future development in the United States, and discuss new development activities and approaches. The main limiting factors for PHES appear to be environmental concerns and financial uncertainties rather than the availability of technically feasible sites. PHES developers are proposing innovative ways of addressing the environmental impacts, including the potential use of waste water in PHES applications. In some cases, a properly designed PHES system can even be used to improve water quality through aeration and other processes. Such new opportunities and the increasing need for greater energy storage may lead policymakers to reassess the potential of PHES in the United States, particularly for coupling with intermittent renewable energy sources such as wind and solar power. [Copyright &y& Elsevier]

Abstract: In autonomous islands, the wind penetration is restricted due to technical reasons related with the safe operation of the electrical systems. The combined use of wind energy with pumped storage (WPS) is considered as a mean to exploit the abundant wind potential, increase the wind installed capacity and substitute conventional peak supply. In this paper, the experience gained from the analysis of WPS in three specific islands is used towards the estimation of the WPS market in autonomous Greek islands. Parameterized diagrams and a methodology towards the pre-dimensioning and initial design of the WPS are proposed and used towards the estimation of the market in autonomous Greek islands. The objective is to make an initial general prefeasibility study of WPS prospects in the autonomous Greek islands. Results show that there is a significant market for WPS in Greece and the development cost of WPS is competitive to the fuel cost of local power stations in autonomous islands. [Copyright &y& Elsevier]

Pumped storage is generally viewed as the most promising technology to increase renewable energy source penetration levels in power systems and particularly in small autonomous island grids, where technical limitations are imposed by the conventional generating units. The Hybrid Power Station (HPS) of Ikaria Island, Greece, which is currently in the construction stage, will be one of the first wind-hydro-pumped-storage hybrid stations in the world. In this paper, the HPS is described and a suitable operating policy is introduced, both for the HPS and the overall generation system of Ikaria, taking into consideration the existing regulatory framework for HPS in isolated island grids. Based on the proposed policy, the operation of the Ikaria Island system is simulated on an annual basis, in order to quantify the expected benefits from the operation of the HPS. [ABSTRACT FROM PUBLISHER]

Abstract: The aim of this work is to investigate in detail the optimum design and operation strategy of a stand-alone hybrid desalination scheme, capable to fulfill the fresh water demand of an island or other remote coastal regions. The scheme consists of a reverse-osmosis desalination unit powered by wind and solar electricity production systems and by a pumped storage unit. A specific computer algorithm is developed to simulate in detail the entire plant operation and also to perform economic evaluation of the investment. A stochastic optimization software based on evolutionary algorithms is implemented to accomplish design optimization studies of the plant for various objectives, like the minimization of fresh water production cost or the maximization of water needs satisfaction. Miscellaneous parametric studies are also conducted in order to analyze the effects of various critical parameters, as population, water pricing, water demand satisfaction rate and photovoltaics cost are. The results demonstrate not only the performance, the role and the contribution of each subsystem but also the production and economic results of the whole plant. An optimally designed scheme is found to be economically viable investment, although energy rejections are significant and there is a clear need for better exploitation of renewable energy production surplus. [Copyright &y& Elsevier]

Agricultural microgrid provides a promising solution for energy supply of rural areas in a cost-effective way. In this paper, the principle of wind-pumped storage integrated agricultural microgrid to fulfill both the electric and water load demand is explored. From the perspective of risk aversion, the indexes of expected power not served (EPNS) and expected power curtailment (EPC) are derived to evaluate the uncertain wind power. Then, a stochastic day-ahead scheduling model of wind-pumped storage power system and irrigation system is proposed to minimize the total operation cost whilst achieve the peak load shaving by taking the advantage of wind-pumped storage compensation. The proposed model is a complex optimization problem that takes into account distributed generations, electrical and water demand, turbine flow rate, and irrigation time and volume. We propose a intraspecific competition (IC) based evolutionary predator and prey strategy (EPPS) to solve the model. Finally, simulation results conducted on an agricultural microgrid have verified that, compared to previous works in the literature, the proposed model can effectively improve the utilization of wind power, reduce the operation cost of microgrid as well as smooth load curve. Additionally, the proposed algorithm can get a more competitive solution than other recently developed algorithms. • A stochastic agricultural microgrid is established with power and irrigation systems. • The indexes of EPNS and EPC are derived from the perspective of risk aversion. • An IC based EPPS is proposed to solve complexity optimization problems. • Comprehensive studies have been conducted on the proposed model and algorithm. [ABSTRACT FROM AUTHOR]

Although the local people agreed to the Lam Ta Khong project before implementation, they complained about project impacts and demanded compensation after 70% of the construction was completed. In evaluating the environmental impact mitigation plan (EIMP) for the project, we find a number of weaknesses in implementation. These include insufficient monitoring records and lack of proper channels of appeal; an ineffective approach to mitigating the adverse effects of land occupation; and poor management of the cooperative. We propose an EIMP management system to address these problems and make a number of recommendations aimed at avoiding problems such as those encountered at Lam Ta Khong. [ABSTRACT FROM AUTHOR]

Photovoltaic driven decentralized reverse osmosis plants for brackish water desalination offer a sustainable and low-emission solution for water deficiency problems, especially in arid and semi-arid regions. However, the primary challenge for this combination is how a brackish water reverse osmosis desalination (BWRO) plant based on photovoltaics (PV) can be operated continuously with high energy efficiency. Therefore, this study presents an innovative concept for a BWRO plant operated 24 h/d with a constant drinking water production capacity based on PV and pumped storage as hydraulic energy storage. The latter is used to cover the hydraulic energy consumption of the BWRO process completely or partially in times when the necessary electrical power cannot be provided by the PV plant due to missing solar radiation. During the course of the year, only 2% of the hydraulic energy to be stored in the pumped storage is lost during charging and discharging. The overall efficiency (from PV electricity to used hydraulic energy) of the pumped storage in the investigated innovative system is 78.4%. This value is 2.4% higher than the overall efficiency for a battery system with a high pressure pump in the current designs for BWRO based on PV and battery. • Innovative concept for a decentralized BWRO plant based on PV and pumped storage • The pumped storage is used as a hydraulic energy storage, minimizing energy losses. • Analysis of two energy supply variants for system operation, with or without grid • Only a small electricity storage is needed for the off-grid system. • Only 2% of the hydraulic energy to be stored in the pumped storage is lost. [ABSTRACT FROM AUTHOR]

According to South Africa's national energy policy, network penetration of variable renewable energy (VRE) generation will significantly increase by 2030. Increased associated network uncertainty creates the need for an additional flexible generation. As the planned VRE is mostly non-synchronous PV and wind generators, additional ancillary services will also be required. Pumped Storage (PS), which is a well-established flexible generation technology with fast ramping capability and the ability to contribute various ancillary services, could help integrate increased VRE penetration on the South African network. However, in the latest revision of South Africa's energy policy, PS was left out in favor of gas turbines and batteries as favored flexible generation options. This paper explores the two-part hypothesis that PS was disadvantaged in the formulation of a national energy mix due to: (a) ancillary services provided by PS not being explicitly monetized in energy modeling software; (b) the uncertainties associated with project costing assumptions. The value of PS in terms of providing ancillary services is firstly explored using the international literature. Secondly, the impact of input-cost uncertainties is demonstrated by comparing pumped storage, gas turbines, and batteries using levelized cost of energy (LCOE) curves and the Tools for Energy Model Optimization and Analysis (Temoa), North Carolina State University, USA, optimization software. Based on LCOE calculations using revised cost assumptions, it is found that PS may indeed be preferential to gas turbines or batteries, particularly at large load factors. The authors hope that this research contributes to the scientific understanding of the role that PS can play in supporting the integration of generation from renewable sources for effective grid operations. [ABSTRACT FROM AUTHOR]

Abstract: The “Energy Tower” (ET) is a power plant project which uses hot dry air and seawater to produce electricity. An optimized design of a system that is a combination of an ET, pumped storage and seawater desalination plant is considered. A model set covering each subsystem, and results of the optimized design for a project in the area of Eilat are presented. The additional benefit from combining the systems comes from an efficient use of the energy in the brine water coming from the desalination process, and from using pumped storage in an unconventional way. The benefits of the combined system lead to an increase of 14% in the annual net profit, compared to the sum of profits from optimally designed stand-alone systems. [Copyright &y& Elsevier]

The article reviews sustainable electrical energy production with wind and pumped storage, status of resynchronization of the two UCTE synchronous zones, and progress of the Mediterranean Ring and the interconnection with North Africa. It considers transmission system developments and interconnections, in addition to implementing technology in power generation in Europe with respect to the Kyoto Protocol. The final part of the article examines technical aspects for interconnecting the largest European power systems of UCTE, NORDEL, and IPS/UPS by back-to-back converters and synchronously. [ABSTRACT FROM AUTHOR]

Abstract: In this paper the results of the application of a model for the technical and economic sizing of the various components that make up medium sized wind-powered pumped hydrostorage systems are discussed. The characteristics and unit energy cost of each technically feasible combination of components are determined by applying the model in the island of El Hierro (Canarian archipelago). This enables the selection of the most viable composition for the system from an economic point of view given certain technical restrictions. The results of the application of the model (developed in Part I) in El Hierro indicate that an annual renewable energy penetration of 68.40% can be achieved. This would mean a diesel oil saving of 7364m3 and a decrease in CO2 emissions of 20.91Gg. Furthermore, the system would be economically competitive with conventional systems if fuel prices were 0.283€/l. [Copyright &y& Elsevier]

Abstract: In this paper a model is presented for the technical and economic sizing of the various components that make up medium sized wind-powered pumped hydrostorage systems. A further aim of this model is the optimisation of the operation of such systems, thereby making full use of the synergy of the unit as a whole. A general model is described for use as an analytical tool in implementing such systems in topographically suitable sites with sufficient wind resources. The general model developed allows for six strategies for the system operating configuration. Each strategy is based on the hypothesis that there is a centralised operator to control all the system components, except for the load systems. The characteristics and unit energy cost of each technically feasible combination of components are determined by applying the model. This enables the selection of the most viable composition for the system from an economic point of view given certain technical restrictions. [Copyright &y& Elsevier]

A conceptual examination of the energy impact of leaks in systems with storage is undertaken. Consideration of how leakage is experienced at the pump is followed by an analysis of how different leakage levels alter energy costs for a rudimentary system with three topological configurations: two with a storage tank located at different points, and one without storage. Additionally, two friction regimes are subsumed in the analysis. EPANET 2 simulations are used to determine system pressures, storage tank levels, energy costs, power consumption, and leakage volumes for all scenarios at five levels of leakage. Leaks increase operating costs in terms of lost water and extra energy consumption for all systems, and when a price pattern is implemented, the financial cost of energy can sometimes be traded off with actual energy consumption. Storage in a system does not guarantee lower energy use relative to direct pumping, and in some cases it may promote higher leakage due to elevated system pressures. The results, though system specific, suggest that the importance of leaks in a system with storage depends on a number of factors, especially the relative locations of system components and the pumping strategy. Thoughtful consideration of the latter can be instrumental in achieving operation that balances financial and energy conservation objectives. To further test key relationships, a representative network is briefly considered. In all cases, the percentage increase in energy cost is greater than percentage leakage when the same pressure requirements are met. [ABSTRACT FROM AUTHOR]

• Proposal of the Enhanced Partial Frequency Variation (EPFV) starting method. • EPFV improves traditional partial frequency variation starting method. • EPFV increases starting torque, don't disturb power grid, limit inrush current. • Design of EPFV for the case study using model-based design approach. • Real plant implementation using digital excitation control systems. • Experimental results from the commissioning tests. The hydroelectric pumped storage is one of the most sustainable solutions to store electrical energy for optimizing the grid operation. However, the pump motor starting may constitute a significant issue for the power plant. Indeed, the motor's large power and the long power lines (needed for connecting remotely located plants to the grid) may prevent a direct-on-line start. On the other hand, constraints as spaces availability in the powerhouse, and time and cost availability (especially for revamping projects) limit the feasibility of other starting methods. In this paper, a novel starting method is proposed for the revamping of a hydroelectric power plant (HPP), where a synchronous machine is used to drive the pump. On the basis of the power plant characteristics, an enhanced version of the synchronous starting with partial frequency variation is proposed, leading to the creation of a startup sequence capable of being integrated into the existing excitation control systems' software (of both the generator and the motor installed in the power plant). Such Enhanced Partial Frequency Variation (EPFV) starting method combines the advantages of back-to-back starting method to the ones of asynchronous starting, without requiring additional equipment in respect to a conventional direct-on-line start solution. This is enabled by the model-based design approach here applied, which allows to determine the correct set of parameters and variables' thresholds required for the machine startup, taking into account the specific characteristics of the HPP in study. The developed starting sequence, implemented into the real HPP by using the capabilities of the existing digital excitation control systems, allowed the correct starting of the motor. This is demonstrated by experimental data obtained during the 5MVA motor starting tests. The results also prove the effectiveness of the model-based design approach in enabling the definition of the pump starting sequence, as well as validating the mathematical model used for the sequence design. [ABSTRACT FROM AUTHOR]

This paper reviews the development of Britain's limited hydropower resources, most of which is concentrated in Scotland producing on average some 4000 GWh per year. The Scottish schemes are dominated by the reservoir storage type although pumped storage plants have been constructed since the 1960s. These latter also occur at two sites in Wales. The performance of existing schemes is examined, with particular reference to environmental aspects, and the potential and prospects for future hydropower development are considered. [ABSTRACT FROM AUTHOR]

This study researches the concept of underground pumped-storage hydro power plants in closed-down underground hard coal mines in Germany. After a review on how this could be realized technically, an economic feasibility analysis is presented, with a particular focus on the costs for the underground storage reservoir. The analysis is performed for different lower (i.e., underground) reservoir sizes and temporal arbitrage potentials (peak/off-peak electricity price spreads), and cost uncertainty is dealt with by means of a Monte Carlo simulation for two distinct head heights. The findings regarding costs and acceptability are compared with those of a classic (on-surface) pumped-storage hydro power plant in a mountainous area. Based on a techno-economic evaluation we conclude that under favorable conditions the realization of underground pumped-storage hydro power (UPSHP) plants seems both technically feasible and economically reasonable. More specifically, an extension of a tubular system seems the most promising option. A UPSHP plant in a mineshaft is probably slightly more expensive than a conventional one, an outcome that depends strongly on the feasible head height. However, the significant reduction of the adverse impacts on the landscape and on local residents, as well as a potentially large number of feasible sites in flat terrain, could make UPSHPs an interesting option for the future energy transition, not just in Germany but worldwide at sites where underground mining is being abandoned. [ABSTRACT FROM AUTHOR]

Abstract: This paper provides a short introduction to the papers in the special section below on economic regulation in infrastructure industries. The papers are from the CCRP Research Workshop held at City University, London in January 2012. The topics covered include (i) supply-side competition for airports (Bilotkatch and Mueller); (ii) resource cost pricing in the water supply industry and how best to establish the value of water (Stern and Mirrlees-Black); and (iii) the role and regulation of hydro pumped storage for electricity in an environment where the role of intermittent renewable generation is growing (Rangoni). [Copyright &y& Elsevier]