Author(s): Daniele Novara; Miguel Crespo Chacon; Angeliki Parisi-Ploumpi; Aonghus Mcnabola

Linked Author(s): Daniele Novara, Aonghus McNabola

Keywords: Micro Pumped Hydro Energy Storage (u-PHES); Pump as Turbine (PAT); Experimental Data; Energy storage; Smart Grid

Abstract: Pumps As Turbines (PATs) consist of hydraulic turbines derived from standard water pumps working in reverse, allowing them to generate electricity from pressurized flows. Despite the lower efficiency compared to conventional hydraulic turbines, the mass manufacturing process makes PATs several times less expensive to purchase and operate. Given their ability to work alternatively in both pump and turbine mode, PATs are ideal for Micro Pumped Hydro Energy Storage (µ-PHES) schemes which are characterized by an installed capacity lower than 100 kW. A single PAT can operate cyclically to pump a volume of water to an upper reservoir using excess available electricity and then releasing the same volume of water into the lower reservoir while acting as turbine. The principle is well understood and successfully applied for grid-size energy storage, whereas its miniaturization and application on a µ-PHES scale is matter of ongoing research. In fact, the main energy storage technology currently available in the sub-100 kW capacity market consists of Lithium-Ion batteries to which significant environmental burdens are associated. The only µ-PHES pilot scheme available in the literature makes use of a conventional “dry” PAT and generator, which requires significant civil works since in order to avoid cavitation the powerhouse must be located below the water level of the lower reservoir. Instead, the authors propose the adoption of submersible PATs for µ-PHES projects. The main advantage of this approach is the simplification of the installation layout since a submersible PAT can be conveniently lowered down to the bottom of the lower reservoir while the rest of the electric equipment can be placed at a different nearby location above ground. In order to determine the performance of submersible PATs, a 3 kW prototype was tested on a hydraulic test rig and the results showed a turbine mechanical efficiency comparable to that in pump mode (56%), which is an important result given the small size of the device. A case study of the application of this technology was assessed comprising a hybrid scheme including a PV array for an estate located in Ireland. The aim of the case study was to minimise the electricity imported by the estate, targeting the net-zero carbon emissions. The site already had an existing water pond of about 2,200m3 used for an old hydro system, and a 30 kWp PV array. Installing a submersible PAT would allow the use of the excess PV energy not consumed to boost water to the pond for storage. This could be then transformed into electricity as per the estates needs. The results showed that an 18-kW submersible PAT in combination with the existing PV array would decrease the energy imports by around 40%, and therefore the electricity bill and CO2 emissions.

DOI: https://doi.org/10.3850/IAHR-39WC252171192022779

Year: 2022