Abstract
The use of Pumps-as-Turbines (PaTs) to replace hydraulic turbines as energy recovery units in industrial and civil applications is widening the penetration of hydropower in small-scale plants. PaTs show advantages in terms of installation costs and availability of solutions. Water Distribution Networks (WDNs) represent a potential application where PaTs can be installed to recover water pressure energy. In this work, a Matlab–Simulink model of a WDN branch located in South-Tyrol (Italy) was developed. The flow rate of the WDN was assessed though a measurement campaign showing a high daily variability, which negatively affect PaTs performance. To let the machine operate close to the Best Efficiency Point (BEP), four different operating strategies were studied to meet the constraint of a fixed pressure equal to 4 bar downstream the WDN branch, required to supply water to users. A PaT speed control strategy was implemented, granting a better exploitation of flow rates even in presence of high daily fluctuations. The energy recovery was 23% higher than the reference one thanks to an advanced strategy based on controlling the PaT rotational speed when the flow rate is smaller than the design one and operating in off-design conditions when the flow rate is higher than the BEP one.