Pumped Hydroelectric Energy Storage (PHES) is the most used bulk Electric Energy Storage (EES) technology with a global installed capacity of 130 GW. This technology combined with wind power creates a power technology named hybrid wind-hydro. A study case on a hybrid wind-hydro power plant is presented, analyzing in detail 2 different cases in which the plant can operate (with excess wind and with no wind). In the first case, the pump group will play the central role, being able to achieve a head of 200 m for the storage of the excess wind in the upper reservoir. A mathematical model is developed for centrifugal pumps using the pump NK 32-125/142 from Grundfos for such purpose. Lab tests are performed using this same pump to collect data for model validation. The impeller of the Grundfos pump has been optimized based on the mathematical model. Lab tests are conducted also for the new impeller to verify the optimization (despite not being presented in this report). Finally, the optimized impeller is up-scaled to suit the requirements of a 1 MW pump which can be used in the hybrid wind-hydro power plant. This last step will verify that the mathematical model is suitable for pumps of diverse size and application.