Juan I. Pérez-Díaz

Optimal short-term operation and sizing of pumped-storage power plants in systems with high penetration of wind energy

In this paper the short-term optimal operation of an electric system comprising several thermal power plants and one pumped storage plant is studied in several scenarios of power demand and wind penetration in order to draw conclusions about the contribution of the pumped storage plant to system operation costs. A mixed integer linear programming model is used to obtain the optimal hourly thermal, hydro and pumping powers so that the production cost of the entire system is minimized. An aggregated piecewise linear hourly production cost curve is used to represent the thermal generation; the marginal production cost varying as a function of the power generated according to the slope of each piecewise linear segment. Main design parameters of the pumped storage plant are not considered fixed in the model but rather they are obtained in the solution with the purpose of drawing conclusions about the plant optimal sizing.

Optimal operation of variable speed pumped storage hydropower plants participating in secondary regulation reserve markets

Pumped storage hydropower plants can contribute to a better integration of intermittent renewable energy and to balance generation and demand in real time by providing rapid-response generation. In order to invest in a new pumped storage plant, it is necessary to assess carefully the profitability of the project as the recovery of investment costs could be jeopardised by many factors. Apart from participating in the day-ahead market, ancillary services can also play an important role when determining the incomes. The aim of this paper is to make a preliminary comparison of pumped storage plants market incomes with and without ability to regulate power in pumping mode through variable speed technology. A deterministic mixed-integer programming model is proposed to calculate power bids for the day-ahead and secondary regulation markets. The model considers the hourly day-ahead and secondary reserve market prices as well as usage and prices of secondary regulation-up and down energy requested by the Spanish System Operator.

Optimal Energy and Reserve Scheduling of Pumped-Storage Power Plants Considering Hydraulic Short-Circuit Operation

This paper presents a mixed-integer model for the hourly energy and reserve scheduling of a price-taker and closed-loop pumped-storage hydropower plant operating in hydraulic short-circuit mode. The plant participates in the spot market and in the secondary regulation reserve market, taking into account the regulation energy due to the real-time use of the regulation-up and -down reserves. The proposed model is used to compare the maximum theoretical income of the plant with and without considering hydraulic short-circuit operation. Numerical results demonstrate that the operation in hydraulic short-circuit mode could help significantly to enlarge the income of the power plant and that the secondary regulation reserve market might be the main source of revenue in a realistic setting characterized by a high level of renewable energy sources in the generation mix.

Stability Analysis of a Run-of-River Diversion Hydropower Plant with Surge Tank and Spillway in the Head Pond

Run-of-river hydropower plants usually lack significant storage capacity; therefore, the more adequate control strategy would consist of keeping a constant water level at the intake pond in order to harness the maximum amount of energy from the river flow or to reduce the surface flooded in the head pond. In this paper, a standard PI control system of a run-of-river diversion hydropower plant with surge tank and a spillway in the head pond that evacuates part of the river flow plant is studied. A stability analysis based on the Routh-Hurwitz criterion is carried out and a practical criterion for tuning the gains of the PI controller is proposed. Conclusions about the head pond and surge tank areas are drawn from the stability analysis. Finally, this criterion is applied to a real hydropower plant in design state; the importance of considering the spillway dimensions and turbine characteristic curves for adequate tuning of the controller gains is highlighted.

Economic Viability of Pumped-Storage Power Plants Equipped with Ternary Units and Considering Hydraulic Short-Circuit Operation

This paper analyses the economic viability of pumped-storage hydropower plants equipped with ternary units and considering hydraulic short-circuit operation. The analysed plant is assumed to participate in the day-ahead energy market and in the secondary regulation service of the Spanish power system. A deterministic day-ahead energy and reserve scheduling model is used to estimate the maximum theoretical income of the plant assuming perfect information of the next day prices and the residual demand curves of the secondary regulation reserve market. Results show that the pay-back periods with and without the hydraulic short-circuit operation are significantly lower than their expected lifetime and that the pay-back periods can be reduced with the inclusion of the hydraulic short-circuit operation.

Neural networks for optimal operation of a run-of-river adjustable speed hydro power plant with axial-flow propeller turbine

This paper analyzes the regulating capabilities of both turbine speed and guide vanes position in an axial-flow propeller turbine. Two neural networks are implemented in order to simulate the turbine behavior and the turbine efficiency. A maximum-efficiency-tracking algorithm is developed to set the guide vanes position. An experimental power plant built in the Hydraulics Laboratory is described. In order to validate the proposed operation control, the dynamics of this run-of- river pilot plant has been simulated. Substantial increases in the turbine efficiency have been found.

Simulation model of a variable-speed pumped-storage power plant in unstable operating conditions in pumping mode

This paper presents a dynamic simulation model of a laboratory-scale pumped-storage power plant (PSPP) operating in pumping mode with variable speed. The model considers the dynamic behavior of the conduits by means of an elastic water column approach, and synthetically generates both pressure and torque pulsations that reproduce the operation of the hydraulic machine in its instability region. The pressure and torque pulsations are generated each from a different set of sinusoidal functions. These functions were calibrated from the results of a CFD model, which was in turn validated from experimental data. Simulation model results match the numerical results of the CFD model with reasonable accuracy. The pump-turbine model (the functions used to generate pressure and torque pulsations inclusive) was up-scaled by hydraulic similarity according to the design parameters of a real PSPP and included in a dynamic simulation model of the said PSPP. Preliminary conclusions on the impact of unstable operation conditions on the penstock fatigue were obtained by means of a Monte Carlo simulation-based fatigue analysis.

Value of perfect information of spot prices in the joint energy and reserve hourly scheduling of pumped storage plants

The value of perfect information of the day-ahead energy prices is studied in the context of the operation of a closed-loop and daily-cycle pumped-storage hydropower plant, participating in the spot market as a price-taker and in the secondary regulation reserve market as a price-maker, and also considering the secondary regulation energy due to the real-time use of reserves. Results show that the percentage of the profit loss with respect the maximum theoretical income due to the errors in forecasting the spot prices in the Iberian electricity market decreases if the plant also participates in the secondary regulation service.

Economic impact of forecasting errors in residual reserve curves in the day-ahead scheduling of pumped storage plants

The economic impact of forecasting errors in the residual demand curves of the secondary regulation reserve market is analysed in the context of the operation of a closed-loop and daily-cycle pumped-storage hydropower plant. The plant participates in the day-ahead energy market as a price-taker and in the secondary regulation reserve market as a price-maker. The secondary regulation energy due to the real-time use of the committed reserves is also considered in the optimization model. The results show that profit is significantly more sensitive to forecast errors in the day-ahead energy market prices than in the residual demand curves of the secondary regulation reserve market.