Design of a Low-head Shaft Driven Contra-Rotating Reversible Pump Turbine for Pumped Hydro Storage Application

Design of a Low-head Shaft Driven Contra-rotating Reversible Pump Turbine for Pumped Hydro Storage Application

Meeting the Europe’s goal of becoming the first carbon neutral continent by 2050 requires significant reduction of greenhouse gas emissions. An essential step to achieve this is by the decarbonisation of electricity generation, which requires a larger share of renewable energy sources into the power supply. Integration of higher proportion of intermittent renewable energy sources needs an effective balancing measure maintaining grid stability and enhancing grid stability. Energy storage systems are recommended for this purpose. Pumped hydro storage is a natural choice as it is a mature and cheaper technology. But conventional hydroelectric technology is developed for a high-head and are suited for mountainous regions. This cannot be used in low lying countries with flat topographies such as Belgium, Netherlands etc. Hence, it is important to develop a solution to this problem for meeting the ultimate goal. 

ALPHEUS project is a coordinated effort to develop a low to ultra-low head (2-20 [m]) reversible pump turbine technology (RPT) with a target round trip efficiency of 70-80%. Due to long operational lifetime, levelized costs of storage of this solution is expected to be competitive. In addition to this ALPHEUS will also explore a positive displacement RPT due to it being a fish friendly, seawater-robust and low-cost technology.

Due to high specific speeds, reversible Francis turbines are not ideal for this application; Axial Kaplan and propeller-based devices are not optimized as reversible pump-turbines. Based on preliminary assessments, a Shaft-Driven variable-speed Contra-Rotating propeller RPT (SDCRRPT) technology could meet the complex set of requirements. The design of the RPT is carried out in the pump mode, then the performance is assessed in both pump and turbine modes using CFD analysis. The rotors for the SDCRRPT are designed based on 3D inverse design method using ADT’s TURBOdesign 1 software. Initial design is created at a design flow rate of 130[m3s-1] flow rate, rotor 1 speed of 50[rev min-1], rotor 2 to rotor 1 speed ratio of 0.9. The target power of 10[MW] is achieved in turbine mode, at 7.8[m] head with more than 91% efficiency.

The prototype design is scaled down to model scale based on the lab test specifications. A multi-point multi-objective optimization is carried out in the model scale to maximize the performance of the stage at 3 operating points in each mode. The optimization is based on a Design of Experiments (DoE) and surrogate model approach. 21 design parameters covering a wide range of geometry variation are chosen for an initial sensitivity study. Then a full DoE matrix with the variation of 11 sensitive parameters is generated for the optimization. Maximization of power in turbine mode and minimization of power in pump mode are the optimization objectives with head constrained in the required range. The average stage efficiency across 3 operating points is improved by ~2.6% points in pump mode for the best performing candidate. In turbine mode, the average stage efficiency is improved by ~ 1.1% points for the best candidate. Lab tests are conducted to assess the actual performance.