Simulation of Underground Reservoir Stability of Pumped Storage Power Station Based on Fluid-Structure Coupling

Based on global initiatives such as the clean energy transition and the development of renewable energy,the pumped storage power station has become a new and significant way of energy storage and regulation,and its construction environment is more complex than that of a traditional reservoir.In particular,the stability of the rock strata in the underground reservoirs is affected by the seepage pressure and rock stress,which presents some challenges in achieving engineering safety and stability.Using the advantages of the numerical simulation method in dealing deal with nonlinear problems in engineering stability,in this study,the stability of the underground reservoir of the Shidangshan(SDS)pumped storage power station was numerically calculated and quantitatively analyzed based on fluid-structure coupling theory,providing an important reference for the safe operation and management of the underground reservoir.First,using the COMSOL software,a suitablemechanicalmodel was created in accordance with the geological structure and project characteristics of the underground reservoir.Next,the characteristics of the stress field,displacement field,and seepage field after excavation of the underground reservoir were simulated in light of the seepage effect of groundwater on the nearby rock of the underground reservoir.Finally,based on the construction specifications and Molar-Coulomb criterion,a thorough evaluation of the stability of the underground reservoir was performed through simulation of the filling and discharge conditions and anti-seepage strengthening measures.The findings demonstrate that the numerical simulation results have a certain level of reliability and are in accordance with the stress measured in the project area.The underground reservoir excavation resulted in a maximum displacement value of the rock mass around the caverns of 3.56 mm in a typical section,and the safety coefficient of the parts,as determined using the Molar-Coulomb criterion,was higher than 1,indicating that the project as a whole is in a stable state.

Research on Operation Optimization of Heating System Based on Electric Storage Coupled Solar Energy and Air Source Heat Pump

For heating systems based on electricity storage coupled with solar energy and an air source heat pump(ECSA),choosing the appropriate combination of heat sources according to local conditions is the key to improving economic efficiency.In this paper,four cities in three climatic regions in China were selected,namely Nanjing in the hot summer and cold winter region,Tianjin in the cold region,Shenyang and Harbin in the severe cold winter region.The levelized cost of heat(LCOH)was used as the economic evaluation index,and the energy consumption and emissions of different pollutants were analyzed.TRNSYS software was used to simulate and analyze the system performance.The Hooke-Jeeves optimization algorithm and GenOpt software were used to optimize the system parameters.The results showed that ECSA systemhad an excellent operation effect in cold region and hot summer and cold winter region.Compared with ECS system,the systemenergy consumption,and the emission of different pollutants of ECSA system can be reduced by a maximum of 1.37 times.In cold region,the initial investment in an air source heat pump is higher due to the lower ambient temperature,resulting in an increase in the LOCH value of ECSA system.After the LOCH value of ECSA system in each region was optimized,the heating cost of the system was reduced,but also resulted in an increase in energy consumption and the emission of different pollutant gases.

Optimal capacity planning of combined renewable energy source-pumped storage and seawater desalination systems

As water scarcity is becoming a growing threat to human development, finding effective solutions has become an urgent need. To make better use of water resources, seawater desalination and storage systems using renewable energy sources(RES) are designed and implemented around the world. In this paper, an optimal capacity planning method for RES-pumped storage-seawater desalination(RES-PS-D) system is introduced. The configuration of the RES-PS-D system is clarified first, after which a cost-benefit analysis is performed using all cost and benefit components. A function for determining maximum economic benefits of the RES-PS-D system is then established, and the constraints are proposed based on various limitations. The mixed-integer linear programming algorithm is applied to solve the optimal function. A case study is introduced to validate the feasibility and effectiveness of the method. The conclusion shows that the strategy is suitable for solving the configuration optimization problem, and finally both merits and defects of the method are discussed.

Pumped hydro energy storage and 100 % renewable electricity for East Asia

Rapid cost reductions have led to the widespread deployment of renewable technologies such as solar photovoltaics(PV)and wind globally.Additional storage is needed when the share of solar PV and wind in electricity production rises to 50–100%.Pumped hydro energy storage constitutes 97%of the global capacity of stored power and over 99%of stored energy and is the leading method of energy storage.Off-river pumped hydro energy storage options,strong interconnections over large areas,and demand management can support a highly renewable electricity system at a modest cost.East Asia has abundant wind,solar,and off-river pumped hydro energy resources.The identified pumped hydro energy storage potential is 100 times more than required to support 100%renewable energy in East Asia.

Corrosion behavior of Q235B carbon steel in simulated seawater pumped storage system under operational conditions

Seawater pumped storage systems have bright prospect for energy storage in the coming years.The operational conditions of seawater pumped storage system are complex and harsh,where metal materials suff er from severe general and local corrosion.The corrosion behavior of Q235B carbon steel in simulated seawater pumped storage system under operational conditions was studied by potentiodynamic polarization,cyclic potentiodynamic polarization,and scanning electron microscope(SEM).The results confi rm that the working pressure aff ected the corrosion resistance of Q235B carbon steel during the whole immersion period.The pressure promoted the electrochemical reaction of corrosion process and the corrosion rate increased with pressure at the initial immersion period.However,the stable rust layer formed after longtime immersion at diff erent pressures increased the corrosion resistance of carbon steel,and decreased the corrosion degree of carbon steel.Meanwhile,the working pressure aff ected the pitting corrosion behavior of Q235B carbon steel during the whole immersion period.The pitting corrosion potential was more negative and the tendency of pitting corrosion was higher at 4 MPa during the whole immersion period.However,pressure also accelerated the formation rate of protective rust layer on the steel surface.Q235B carbon steel has higher susceptibility to pitting corrosion at 4 MPa in the static seawater.

Present status of pumped hydro storage operations to mitigate renewable energy fluctuations in Japan

This paper focuses on pumped hydro energy storage(PHES)plants’current operations after electricity system reforms and variable renewable energy(VRE)installations in Japan.PHES plants have historically been developed to create electricity demand at night in order to operate base load power plants,such as nuclear power plants,in stable conditions.Therefore,many PHES plants are located midway between nuclear power plants and large demand areas.However,all nuclear power plants had to–at least temporarily–shut down after the Great East Japan Earthquake followed by a nuclear accident at Fukushima Daiichi in 2011,and renewable energy power plants have been deployed rapidly after the introduction of a feed-in-tariff(FIT)scheme.Therefore,PHES plants are being used to mitigate fluctuations of VRE,especially in areas where renewable energy has been significantly installed.The daily highest capacity ratio of PHES plants in Kyushu area has recorded three times higher than it in the other areas where the past operating mode is still conducted.But those operations on PHES plants are simply followed as a dispatch rule of the Organization for Crossregional Coordination of Transmission Operators(OCCTO),market-based operations have not been conducted enough yet.The market design shall be changed to harmonize VRE installation and PHES plants’operations are necessary to make the transition from the past operating mode of PHES plants across Japan.

Prospect of new pumped-storage power station

In this paper, a new type of pumped-storage power station with faster response speed, wider regulation range, and better stability is proposed. The operational flexible of the traditional pumped-storage power station can be improved with variable-speed pumped-storage tech no logy. Combined with chemical en ergy storage, the failure to achieve sec on d-order response speed and the insufficient safety and reliability of pumped-storage power units could be solved. With the better solar en ergy and site resources, the in teg rated performance can be improved by an optical storage system in stalled in future pumped-storage stations. Through the characteristics analysis of the new type of pumped-storage power station, three types of optimal station locations are proposed, namely, the load concentration area, new energy concentration area, and ultrahigh- voltage direct current receiver area. Taking the new pumped-storage power station as an example, the advantages of multi-energy cooperation and joint operation are analyzed. It can be predicted that the frequency and load regulation of the power grid will be more flexible, and the service capacity to the main power grid will be much stronger in the future.

Pumped-Storage Solution towards Energy Efficiency and Sustainability: Portugal Contribution and Real Case Studies

This paper aims at presenting different pumped-storage solutions for improving the energy efficiency and economic sustainability of water systems. The assessment of pumped-storage solutions, either using fresh water or sea-water, is seen as a viable option to solve problems of energy production, as well as in the integration of intermittent renewable energies, providing system flexibility due to energy loads’ fluctuation, as long as the storage of energy from intermittent sources. Pumped-storage is one of the best and most efficient options in terms of renewable resources as an integrated solution allowing the improvement of the energy system elasticity and the global system efficiency. Two real case studies are presented: a fresh water system installed in a river dams—the Alqueva system, in Portugal—and a sea-water system in an arid region of the Cape Verde Islands in Africa. These cases demonstrate the benefits associated to pumped-storage solutions, depending on the storage volume capacity, operational rules and energy tariffs.

Study on integrated development and hybrid operation mode of nuclear power plant and pumped-storage power station

The nuclear power plant is suitable for base-load operation, while the pumped-storage unit mainly gives play to capacity benefit in the electric power system;hence, the integrated development and hybrid operation mode of the two can better meet the needs of the electric power system. This article first presents an analysis of the necessity and superiority of such mode, then explains its meaning and analyzes the working routes. Finally, it proposes the business modes as follows: low price pumping water electricity plus nuclear power in the near term;nuclear power shifted to pumped storage power participating in market competition in the middle term;and, in the long term, nuclear power shifted to pumped storage power as primary and serving as an electric power system when needed.

Reducing Intermittence of Renewable Energy Sources with Seasonal-Pumped-Storage Plants

This paper presents a computational method to model and evaluate if Pumped Storage Plants (PSP) have the potential to reduce the intermittency of wind generation from different sites in Brazil and to improve the operation efficiency of hydroelectric plants when operating in cascade. Since the problem to be solved does not have a defined analytic solution, a Stochastic Optimization Algorithm was implemented to reach an optimal solution to the set of equations, inputs and proposed scenarios. A case study was developed based on the Paraná River Basin and the results shows that the model can operate in a variety of different operational patterns, making feasible the evaluation of different hydrological and wind scenarios. Given the Model support, it is easy to assume different PSP storage and generation capacities, allowing the comparison between the efficiency improvement of a conventional Pumped-Storage and a Season-al-Pumped-Storage in the same scenario. The study concludes that a PSP can effectively reduce the intermittency of wind and solar sources and contribute to the optimization of the Brazilian electricity sector.

Equivalent Substitution Based Method for Calculation of Best Installed Capacity of Pumped Storage Power Station

This paper proposes a novel method to calculate the best installed capacity of pumped storage power station. First, we choose the day with maximum load as the typical day for every month and simulate the system running in two cases of whether the pumped storage power station is put into operation. The difference of the total coal consumption between the two cases is the peak load shifting benefit. Furthermore, we build load model and power generation model to calculate the benefit of emergency use and frequency modulation, which are the major projects of dynamic benefits. At last, on the premise of ensuring the system requirements, the developed method employs the maximum benefit of the unit capacity as the objective function to get the best installed capacity of pumped storage power station by simulations. Tests on a provincial power grid have shown that the developed method which combines of load characteristics, electric structure and other factors can get the best installed capacity of pumped storage power station easily and has a certain guiding significance for the planning and construction of the pumped storage power station.

Study of Local Structural Changes on Air Cooling at the End of Rotor Windings for Variable Speed Pumped Storage Generator-Motor

The shrink fit retaining ring is currently the easiest to install and the most widely used end fixed for structure AC excitation variable speed generator-motor rotor end windings.However,the current research on the effect of high strength sealing on the ventilation and heat dissipation performance of the end is not enough.In this paper,based on the actual structural parameters and periodic symmetry simplification,the three-dimensional coupled calculation model of fluid field and temperature field is established.After solving the fluid and thermal equations,the influence of the length of rotor support block,the height of rotor support block,and the number of rotor support block on the fluid flow and temperature distribution in the rotor end region of generator-motor is studied using the finite volume method.The rheological characteristics of the air in the rotor domain,such as velocity and inter-winding flow,are analyzed.The law of temperature variation with local structure in the computational domain is studied.The variation law of cooling medium performance inside the large variable speed power generator motor is revealed.

Utilization of cross-regional interconnector and pumped hydro energy storage for further introduction of solar PV in Japan

The amount of solar PV installed capacity has steadily increased to 44.5 GW at the end of FY2017,since the introduction of the Feed in Tariff(FiT)to Japan in 2012.On the other hand,since the first curtailment of solar PV was conducted on October 13th,2018 in the Kyushu area,the curtailment has been frequently executed including wind power after that.In this study,cross-regional interconnector and pumped hydro energy storage(PHES)are focused on mitigating curtailment.In Japan,there are 9 electric power areas which connected each other by cross-regional interconnectors.According to the historical operation,cross-regional interconnectors were secured as emergency flexible measures,but after the implicit auction was started from October 2018,it is used on merit order.Regarding a PHES in Japan,they have been built with nuclear power plants for several decades.Because the output of nuclear power generation is constant,so the PHES is used to absorb the surplus at nighttime when the demand declines.All nuclear power plants in Japan have been shut down after the accident at the Fukushima Daiichi Nuclear Power Plant following the Great East Japan Earthquake that occurred on March 11th,2011.There are several nuclear power plants that have been restarted(9 reactors,as of August 2019).In this study,the amount of curtailment for solar PV in the Kyushu area is sent to the Chugoku area using the cross-regional interconnector(Kanmon line).Then,the PHES in the Chugoku area is pumping with low price.Because the spot price in the market is low when the curtailment is executed.After that,the PHES is generating at night with high price when the solar PV is not generating.It makes a profit by the deference for the cost of pumping and the revenue of generating by the PHES.As a calculation result,for one week from May 2nd to 8th,2019,a profit becomes 152.2 million JPY(about 1.22 million EUR).For this purpose,it is necessary to raise the operation capacity of the cross-regional interconnector up to the rated capacity with the frequency control function of solar PV instead of the capacity to keep frequency in the event of an accident.This will allow the further introduction of solar PV in Japan.

Drillhole high-pressure packer permeability test for underground powerhouse in Pushihe pumped storage hydro-plant

Usually the water head of the pumped storage hydro-plant is high, generally up to 400-500 m, therefore the rock mass under the high-pressure bifurcation pipe have to bear as high as millions Pascal water pressure, in according with the requirements of high water head pumped storage hydro-plant should be 1.2 times of the water head special high-pressure packer permeability test compared with normal to test the permeability of rock and rock cleavage pressure value. The test results on the choice of design options often play a decisive role. Based on the engineering practice, the authors studied the drillhole high-pressure packer permeability test in the pumped storage hydro-plant's underground powerhouse, by the analysis of test results, this article offers a demonstration of the deformation of rock fracture witch under building in the condition of high-pressure water head, it provides a more detailed engineering geological background.

A novel technology for control of variable speed pumped storage power plant

Variable speed pumped storage machines are used extensively in wind power plant and pumped storage power plant. This paper presents direct torque and flux control(DTFC) of a variable speed pumped storage power plant(VSPSP). By this method both torque and flux have been applied to control the VSPSP. The comparison between VSPSP's control strategies is studied. At the first, a wind turbine with the capacity 2.2 k W and DTFC control strategies simulated then a 250 MW VSPSP is simulated with all of its parts(including electrical, mechanical, hydraulic and its control system) by MATLAB software. In all of simulations, both converters including two-level voltage source converter(2LVSC) and three-level voltage source converter(3LVSC) are applied. The results of applying 2LVSC and 3LVSC are the rapid dynamic responses with better efficiency, reducing the total harmonic distortion(THD) and ripple of rotor torque and flux.

Providing Frequency Support of Hydro-Pumped Storage to Taiwan Power System with Wind Power Integration

The combination of wind and pumped storage is a useful method to compensate the fluctuation of wind power generation, which would exploit the abundant wind potential and increase wind power penetration. Taiwan Power Company (TPC) develops renewable energy actively in recent years. Moreover, TPC has started planning a high penetration wind power system and building offshore wind farms around the coast of Zhangbin, Yunlin and Penghu. The target of the offshore wind power installed capacity is up to 3 GW by 2025. However, the integration of the large scale of wind power would give huge challenges to the system operator because wind is randomly characterized. In this study, after high penetration wind power is integrated, the impacts of system frequency and the dispatch of conventional units will be discussed. Additionally, the hybrid system combing wind power with pumped-storage will be planning to reduce the effect of system frequency.

Enhanced Electric Power Adaptability Using Hybrid Pumped-Hydro Technology with Wind and Photovoltaic Integration

The integration of solar and wind energy into the electrical grid has received global research attention due to their unpredictable characteristics.Because wind energy varies across all timescales of utility activity,renewable energy generation should be supplemented and enhanced,from real-time,minute-to-minute variations to annual alterations influencing long-termstrategy.Wind energy generation does not only fluctuate but is also challenging to accurately forecast the timeframes of significance to electricity decision makers;day-ahead and long-term making plans of framework sufficiency such as meeting the network peak load annually.A utility that integrates wind and solar energy into its electricity mix would understand how to adapt to uncertainty and variability in operations while sustaining grid stability.Due to hydropower’s adaptability,a system using hydropower as one of its generating resources could be precisely adapted to absorb the variability of wind and solar energy.The objective of this research study is to create a hybrid system comprising hydro-wind and solar(Hybrid-HWS)integration for power balancing in an isolated electrical network in Klipkop village,Pretoria region,South Africa.The desirability of designing and building goaf storage tank in regard to capability,the fullness of line throughoutwater pumping,dispensing,storage tank spillage,and pressure difference throughout liquid flow within the storage tanks were preliminary assessed using geotechnical and weather forecasting data from a distinctive area of Klipkop town in Pretoria,South Africa.Different facility hours premised on daylight accessibility are scheduled to balance maximum load at early and late hours.However,in the scenario of electrical power,time shift requiring storage for extended periods of time,such as in terms of hours,Hybrid-HWS has been found to have a crucial role.The results of simulations showed a coordinated process design for Hybrid-HWS Energy Storage(ES)to determine everyday strategic planning in reducing the variability of the system resulting from wind-solar-pumped hydro ES output inadequacies and satisfy daily load demands.It could be recommended that by considering the adaptability characteristics,extremely rapidly,ramping,peaking support and maximum stabilizing aid of the system could be archived with pump-hydro into the energy mix which can provide specific guidelines for energy policymakers.