Pumped Storage Hydropower Plants Research Articles

Systems Accounting for Carbon Emissions by Hydropower Plant

Hydropower is the largest renewable source of electricity generation, the carbon emissions of which have attracted a lot attention. However, the system boundaries of existing studies are either incomplete or inaccurate. Therefore, this study provides a systems accounting framework for evaluating both the direct and indirect carbon emissions from a hydropower plant. It is based on the hybrid method as a combination of the process analysis and the input-output analysis. To demonstrate the framework, a case study for a typical pumped storage hydropower plant (NPSHP) is carried out. The total carbon emissions are estimated as 5828.39 kt in the life-cycle of the case system. The end-of-use stage causes the largest carbon emissions (38.4%), followed by the construction stage (34.5%), the operation stage (25.6%), and the preparation stage (1.5%). The direct carbon emissions are mainly released from sediments in the end-of-use stage and the surface of reservoirs in the operation stage (94.8%). The indirect carbon emissions are 2.8 times higher than the direct carbon emissions. The material, machinery, energy, and service inputs respectively account for 7.1%, 14.7%, 15.9%, and 62.3% of the total indirect carbon emissions by the case system. The indicator of EGOC (electricity generation on carbon emission) for the NPSHP is calculated as 26.06 g CO2-eq./kWh, which is lower than that of most other power plants.

INTEGRATION OF VARIABLE ENERGY SOURCES IN ENERGY SYSTEMS

The main global concern in the energy sector is the substitution of fossil fuels and the mitigation of climate change – the transition to the carbon neutrality of the economy. For the power sector, the main solution for this transition is to use hydro, wind and solar energy sources, which have a high energy potential, including in the Republic of Moldova. Variable renewable energy sources, wind and solar, due to their intermittent nature have a significant impact on the power system and the quality of electricity. The necessary measures to reduce the impact of the variability of these sources are presented. The most appropriate measure would be to use pumped storage hydropower plants. The water losses from their accumulation lakes were appreciated. That constitutes approx. 1 … 2 m3/MWh which is considerably lower than the losses from the Thermal Power Plants with steam turbines.

Optimizing pumped storage hydropower for multiple grid services

As an energy storage technology with the largest installed capacity, pumped storage hydropower (PSH) supports various aspects of power system operations. Determining the value of PSH plants for providing various services and contributions to the power system has been a challenge. Despite the large potential benefits, it is often difficult to accurately model and assess all available value streams considering their trade-offs. To address the challenge, this paper presents a method to model and optimize small-scale PSH facilities at the unit level for stacked value streams from a broad range of grid services. The proposed method is generic and applicable to both fixed- and adjustable-speed technologies with different configurations, including separate and reversible pump/turbine as well as ternary sets. An innovative optimal dispatch is developed to optimally utilize the long-duration energy storage capability. Case studies of a small modular PSH system are designed and used to demonstrate and validate the proposed method. Case studies showed that the proposed methodology can effectively maximize the total benefits from stacked value streams. In particular, adjustable-speed and hydraulic short-circuit technologies can significantly increase the flexibility of a PSH plant in providing ancillary services.

Optimum daily operation of a wind-hydro hybrid system

Due to the negative effects of fossil fuels on the environment and health, energy supply is shifting towards renewables. The integration of renewable energy systems is challenging due to the intermittent nature of renewables, however this can be mitigated through storage. Uncertainty in electricity prices in spot markets further complicates the operation of these systems. Pumped storage hydropower is currently the most viable form of large-scale energy storage, and operation of renewable energy systems together with pumped storage hydropower plants is highly efficient. In this study, optimum daily operation strategies are developed for a wind-hydro hybrid system. A long short-term memory network to forecast electricity prices in the day-ahead spot electricity market is coupled with an optimization model to maximize daily revenue. Various scenarios are considered to investigate the benefits of future electricity price estimations. For the wind-hydro hybrid system with 25 MW wind turbine, the net revenue for one-year test period increased 3.5% when forecasted electricity prices with the proposed long short-term memory network is used instead of electricity prices of the previous day. It is observed that increasing the installed capacity of wind turbines compensates for the loss resulting from the poor forecasting of electricity prices; however, the operation schedules of the pump and the hydro turbine do not change when the optimization model uses a simulation duration of one day with hourly time steps.

A general model of optimal energy storage operation in the market conditions

In liberalized electricity markets, energy storage devices, especially those with high capacity, can generate income through multiple services. In this paper, a general model of energy storage operation, suitable for different optimizations and comparisons of various storage technologies in market-oriented power systems, is presented. The objective function maximizes the possible income of storage units (based on the daily operation cycle) earned from energy arbitration and several ancillary services, considering various constraints and market rules for service providers. The mixed integer linear programming (MILP) optimization technique is used to solve the objective function. In numerical examples, the optimal operation modes and possible incomes for typical battery and typical pumped storage hydropower plant (PSHP), using the achieved electricity market prices of energy and the ancillary services (regulation-up, regulation-down and spinning reserve services) in one year, were compared. The influence of the efficiency coefficient, as well as the influence of various PSHP inflows on storage policy, were investigated. The proposed model has proven robust and applicable for various analyses of storage unit operations. The performed numerical calculations have shown that with the decreasing of storage device efficiency coefficient, the incomes generated through ancillary services become more significant.

Reserve-Constrained Unit Commitment Considering Adjustable-Speed Pumped-Storage Hydropower and Its Economic Effect in Korean Power System

The Korean government has declared the goal of net-zero-carbon emissions with a focus on renewable energy expansion. However, a high proportion of baseload generators and an increasing proportion of variable renewable energy (VRE) may cause problems in the power system operation owing to the low cycling capability of baseload generators and variability of VRE. To maintain system reliability, the government is planning to construct pumped-storage hydropower (PSH) plants, which can provide flexibility to the system. This study evaluated the operating cost savings obtained by different types of PSH: the adjustable-speed PSH (AS-PSH) and fixed-speed PSH (FS-PSH), based on the duck-curve phenomenon and the increase in spinning reserve requirement. In this study, the reserve-constrained unit commitment was formulated using a mixed-integer-programming considering the operational characteristics of AS-PSH and conventional generators. To consider the duck-shaped net-load environment, the projected VRE output data were calculated through physical models of wind turbines and photovoltaic modules. The operating costs for the non-PSH, FS-PSH, and AS-PSH construction scenarios were KRW 43,129.38, 40,038.44, and 34,030.46, respectively. The main factor that derived this difference was determined to be the primary reserve of AS-PSH’s pumping mode.

Influence of Temperature and Transmitted Power on Losses in Particular Transmission System

Innovations and trends has been significantly increased during modern theory and practical realizations in the field of energetic. In the Czech Republic, the research of predictions of technical losses on the transmission system can be considered as novel and important topic. Using software possibilities can be appropriately utilized in the frame of estimations of the technical losses. While they cannot be eliminated, they may be minimized. Losses can be measured or calculated using transmission-line parameters. This causality is considered in the form of the presented and proposed mathematical equations including real measured data of the atmospheric temperatures achieved on the substations selected in the Moravian-Silesian region. In this contribution, results of proposed calculations of technical losses based only on line parameters considering the ambient temperature are being compared in relation to a particular transmission system using prediction software. Particularly, technical losses caused by a configuration change of a selected part of a transmission system are considered related to the operation of Dlouhe Strane pumped storage hydro power plant. As can be conclude, after the resulted comparisons using by the proposed mathematical models in software and the obtained real measured data, general minimization of the losses is necessary to create the most accurate models of the states that might occur in the future and to propose required modifications of the given part of the transmission system. Future bounded research can be focused on the sensors situated on the transmission lines instead of the substations.

An efficient, robust optimization model for the unit commitment considering renewable uncertainty and pumped-storage hydropower

This paper presents a new model for allocating pumped-storage hydropower units in the unit commitment program's next day's market. Because the market prices of the next day are highly volatile and have high uncertainty, the time series Autoregressive integral Moving Average (ARIMA) and Stationary Autoregressive integral Moving Average (SARIMA) have been used to predict the market price of the next day. A triple scenario tree is also used to cover electricity market uncertainties. The problem of allocating pumped-storage hydropower plants is planned as a mixed-integer linear programming (MILP) to maximize the power plant profit on a certain operating horizon. Because the variable nature of wind farms is also difficult to accurately estimate the output power of these power plants, the proposed method can be proposed on MNHPSO to consider wind power plant uncertainties with the presence of pumped-storage hydropower plant storage in the unit commitment program. The proposed strategy is simulated in MATLAB software. The simulation results show that in this paper while considering an accurate model for various uncertainties, in the unit commitment planning, it shows that SARIMA can predict the daily prices of the next day market with acceptable accuracy.

Developed Transfer Function Allows Hydro Generators to Enter the Full Range of Ancillary Services Market

As the number of available renewable energy sources has increased annually, there has been a corresponding rise in the levels of pollution created by traditional electricity generation, ultimately contributing to breaking down the stability of the electrical system at large. Therefore, there is an increasing need to integrate the use of nonpolluting electricity sources, such as pumped storage hydropower plants (PSHP), to ensure the stability of the power system and to maintain the frequency of the system from year-to-year. This paper addresses the issue of PSHP being unsuitable for providing Frequency Containment Reserve (FCR) services and proposes real measurements of the aggregation approach to obtain different data arrays. Based on this, the proposed methodology is orientated toward obtaining transfer functions that were developed using the parametric identification models, and the efficiency of these functions was thoroughly investigated. The proposed transfer function in this paper, in combination with battery energy storage system (BESS) technologies, would allow PSHP technologies to occupy a space in the ancillary services market by providing FCR, Frequency Restoration Reserve (FRR), and Replacement Reserve (RR) services. The performance of the function activated in the BESS is positively validated using the Simulink modeling environment.

On Secured Spinning Reserve Deployment of Energy-Limited Resources Against Contingencies

Featured with fast response abilities and high ramp rates, energy storage systems (ESS), such as pumped-storage hydropower (PSH) plants and battery storage systems (BSS), are considered as key first-responders to provide spinning reserve in response to system contingencies. However, ESSs are energy-limited resources, and their sustained spinning reserve deployment is restricted by the stored energy and available capacity. Indeed, the spinning reserve deployment against contingencies may deviate actual state-of-charge (SOC) from the scheduled value, inducing potential SOC boundary violations and non-dispatchability in later hours. This paper proposes the post-contingency operation model and the spinning reserve secure constraints to address these issues. The post-contingency operation model describes that spinning reserve from ESSs is promptly deployed when contingency occurs, and then gradually substituted by quick-start units when they are switched online. By leveraging this operation strategy, spinning reserve secure constraints in terms of SOC headrooms are adopted to guarantee its deployability. A modified IEEE 118-bus system with multiple PSHs and BSSs is used to verify the proposed approach.

Study on the Influence of Moisture Dissipation on the Thermal and Humidity Environment in the Turbine Floor of Underground Pumped Storage Hydropower Plants

The turbine floor of the main plant is an important part in an underground pumped storage hydropower plants.The health of personnel and the safe operation of equipment are endangered due to high space humidity and water seepage through the walls. In this paper, numerical simulations were used to study the thermal and humidity environment of the main plant turbine floor in summer. Two working conditions with and without the dissipation of humidity are computed and compared. The psychrometric chart was also used to analyze the air treatment process in the turbine floor. Results show that the air temperature decreases by 28% and the relative humidity increases by 34% when considering the effect of the moisture dissipation source. The results of temperature and humidity analyzed by the psychrometric chart are similar to those of numerical simulation. And validition of the numerical method is conducted . The research results have a reference significance for predicting the relative humidity distribution of the turbine floor and the arrangement of dehumidification devices at design stage .

Location of seawater pumped storage hydropower plants: Case of Morocco

Energy transition consists of developing new energy strategies to diversify the power grid portfolio. However, these strategies depend in one hand to the available energy sources and technology maturity. Energy storage is one option to manage the power flow, grid interconnections and increase the social welfare for communities. Marine energy not yet well deserved to produce energy in Africa. In this potential study, we focus to locate suitable sites for seawater pumped storage systems in Morocco. The results were promising with high energy storage potentials. For medium hydropower storage plants, 11 sites were selected and for very high heights, 4 sites were selected. The available energy storage is at about 300 MWh depending on site geography and the chosen surface. The main tool used for this work, is the GIS with the open-source software QGIS and the academic version of Visual PROMETHEE software. Energy storage ranking showed that hydrogen can be a good option to store energy in the coming decades where flywheel has a cost competitive advantage regarding the other options. Compressed air and pumped storage stay on the middle of GAIA results.

Comparison and Influence of Flywheels Energy Storage System Control Schemes in the Frequency Regulation of Isolated Power Systems

Increased renewable energy penetration in isolated power systems has a clear impact on the quality of system frequency. The flywheel energy storage system (FESS) is a mature technology with a fast frequency response, high power density, high round-trip efficiency, low maintenance, no depth of discharge effects, and resilience to withstand continuous charge-discharge cycling without lifetime degradation. These FESS properties allows to effectively address the frequency quality problem. This study analyzes the contribution of a FESS to reducing frequency deviations in an isolated system that combines a diesel plant, wind farm, and pump-storage hydropower plant based on the El Hierro power system. This study approaches this analysis by comparing six different FESS governor control schemes (GCSs). Of these six GCSs, the nonlinear proportional variant (NLP <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\mathrm {V}}$ </tex-math></inline-formula> ) is a singular contribution based on the NLP scheme previously developed by the same researchers. Different governor’s parameter settings for the FESS GCSs were also compared, obtained from the proposed tuning methodology that considers the renewable energy generation distribution, frequency impact, and lifetime degradation of diesel, hydraulic groups, and flywheels. The GCSs were compared in terms of average frequency deviation, Zenith and Nadir frequency difference, wear and tear of diesel electromechanical elements and Pelton turbine nozzles, flywheels cycles per hour, and FESS average state of charge. The results show that including a FESS plant considerably improves frequency regulation. The tuning criteria and GCSs have a clear influence on the results, with NLP and NLP <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</sub> GCSs offering relevant improvements in frequency deviations.

Analysis of Prosumer Behavior in the Electrical Network

This article deals with the prosumer behavior, specifically on an on-grid electrical network that is connected to a larger synchronous electrical network, as well as an off-grid system. In the Simulink (Matlab) application, two models were constructed for this purpose. The modeling of the operation of the electrical network’s on-grid system takes place in one of the models. The simulation of the operation of the electrical network’s off-grid system takes place in the other. We examined the model’s behavior in the provided simulated period from the standpoint of transient states and qualitative indicators of electrical energy under various connection configurations in both systems. The simulations resulted in the possibility of incorporating new sources of energy accumulation, such as pumped storage hydropower plants based on energy storage systems (ESSs), and modifying the model to the user’s needs.

Making the most of hydropower storage

Pumped hydro storage plays a critical role as a clean, low-cost and renewable energy storage system. Should a more rigorous approach be undertaken to improve the efficiency at pumped storage hydropower plants in the long term, rather than simply maintaining key hydropower equipment?

Evolution mechanism of a prototype pump turbine after pump power-off

This study aimed to analyze the time–frequency characteristics of pressure fluctuations and reveal their underlying flow mechanisms during the unavoidable guide vane closing process after a pump power-off in a pumped-storage hydropower plant. In this study, the weak compressibility model, one- and three-dimensional (1D–3D) coupling simulation method, and dynamic mesh technology were adopted simultaneously to accurately simulate the transient flow in a prototype pump turbine during the guide vane closure process after the pump power-off. According to the analysis results of the short-time Fourier transformation for the pressure fluctuations, apart from the familiar runner blade passing frequency and its harmonics, this study found a new component that is five times the runner rotation frequency as well as components that are lower than 4.5 times the runner rotation frequency and correspond to severe fluctuations in the pressure. Internal flow analysis suggests that the former is induced by unstable vortices near the trailing edges of the runner blades, whereas the latter ones are induced by local backflow vortices near the runner inlet. Additionally, these severe pressure fluctuation components were significantly large closer to the maximum reverse discharge of the pump brake mode. This finding indicates that these severe unsteady pressure fluctuation components can be suppressed by optimizing the reduction in the maximum reverse discharge in the pump brake mode.

Flow instability transferability characteristics within a reversible pump turbine (RPT) under large guide vane opening (GVO)

Reversible pump turbines (RPT), though praised for their operational flexibility within pumped storage hydropower plants, suffer from large flow instabilities that take source from frequently imposed off-design operating conditions, where the vaneless space (VS) between the runner and guide vanes is claimed to be the base. This study therefore intends to investigate the VS flow instability development mechanism, and the effect of both the machine influx and runner blade number on its transferability to other flow zones. CFD-backed simulations are conducted on ten flow conditions spanning from turbine zone through runaway vicinities to turbine brake, using three runner models with 7, 8, and 9 blades respectively. Results have shown that, while VS pressure pulsation amplitude increased with the decreasing runner blades number, a continuous decrease of machine influx led to a correspondingly dropping VS pressure pulsation level within the Turbine zone before gradually increasing to Runaway and dropping again back to deep turbine brake operating zone. The effect of machine flow conditions and runner blade number on VS flow instability propagation mode to upstream flow zones is more remarkable than the downstream flow zones. This study contributes to a thorough understanding of RPT flow dynamics, especially under off-design operating conditions.

Simplified Model for Evaluation of Hydropower Plant Conversion into Pumped Storage Hydropower Plant

Abstract Increasing capacity of intermittent generation brings new challenges to balance demand and supply in power systems. With retirement of conventional fossil generation, the role of energy storage is increasing. One of the most competitive storage technologies is pumped storage hydropower plant (PSHP). Usually, such PSHPs are constructed as green field solutions, but in some cases conversion of a hydropower plant into a pump storage hydropower plant by building a pump station is possible. To evaluate the feasibility of such modernisation it is necessary to estimate the benefits of PSHP operation. The simplified model was developed for simulation of charging and discharging cycles of PSHP in Latvian power system and trading electricity in Nord Pool power exchange. The nature of this task is stochastic as the price volatility has a trend to increase with expansion of wind and solar power plant capacity. Results of PSHP operation simulation were then used in the economic model to evaluate the feasibility of the proposed conversion.

Secured Reserve Scheduling of Pumped-Storage Hydropower Plants in ISO Day-Ahead Market

Due to their fast response ability and high ramping rates, pumped-storage hydropower (PSH) plants are playing an increasingly critical role in mitigating power generation fluctuations induced by the growing proliferation of renewable energy resources. However, because they are energy-limited resources, actual reserve deployment from PSHs would cause the deviation of state-of-charge (SOC) from the scheduled value, which, once accumulated over time, could induce potential violations of SOC limits and cause non-dispatchability of PSHs. In recognizing this potential issue, it can become important to securing the reserve schedule of PSHs and other energy limited resources preventively in the day-ahead market clearing. To ensure reserve dispatchability of PSHs despite SOC deviations, this paper proposes the reserve secure constraints, which are cast as a distributionally robust chance-constrained formulation by judiciously introducing random parameters to describe deployment ratios of scheduled regulation reserve from PSHs. These constraints are converted into tractable second-order cone constraints, and further approximated as linear constraints to be compatible with the current ISO day-ahead market clearing model. A modified IEEE 118-bus system with multiple PSHs is adopted to verify the proposed approach.

Cost-reliability analysis of hybrid pumped-battery storage for solar and wind energy integration in an island community

This paper presents a mathematical model for estimating the optimal sizing and assessing a standalone hybrid power system's performance entirely based on variable renewable energy sources and coupled with a hybrid energy storage system. This study evaluates how different levels of the main components' capital cost and the loss of power supply probability would affect the cost of energy and the power system's optimal sizing. The case study selected for this study was Ometepe Island in Nicaragua, where the crater lake of an extinct volcano was considered a feasible upper reservoir of a pumped storage hydropower plant, reducing the investments associated with this component. The mathematical formulation considers energy storage losses and gains, and the Pareto efficient solutions of the multi-objective optimization model simultaneously increase reliability, reduce the cost of energy, and minimize curtailment energy. By employing time-series with an hourly resolution, the model allows assessing the impact of the interannual variability of renewable energy sources on the system's performance. As for the case study, the cost of energy obtained from the model results ranges between €0.047/kWh and €0.095/kWh, based on international reference values, and these values match the information available in the literature and other databases.