Hydropower Generation Through Pump as Turbine: Experimental Study and Potential Application to Small-Scale WDN

Abstract

Pump-As-Turbine (PAT) technology is a smart solution to produce energy in a sustainable way at small scale, e.g., through its exploitation in classical Water Distribution Networks (WDNs). PAT application may actually represent a suitable solution to obtain both pressure regulation and electrical energy production. This technology enables one to significantly reduce both design and maintenance costs if compared to traditional turbine applications. In this work, the potential hydropower generation was evaluated through laboratory tests focused on the characterization of a pump working in reverse mode, i.e., as a PAT. Both hydrodynamic (pressure and discharge) and mechanical (rotational speed and torque) conditions were varied during the tests, with the aim to identify the most efficient PAT configurations and provide useful hints for possible real-world applications. The experimental findings confirm the good performances of the PAT system, especially when rotational speed and water demand are, respectively, larger than 850 rpm and 8 L/s, thus leading to efficiencies greater than 50%. Such findings were applied to a small municipality, where daily distribution of pressure and discharge were recorded upstream of the local WDN, where a Pressure Reducing Valve (PRV) is installed. Under the hypothesis of PRV replacement with the tested PAT, three different scenarios were studied, based on the mean recorded water demand and each characterized by specific values of PAT rotational speed. The best performances were observed for the largest tested speeds (1050 and 1250 rpm), which lead to pressure drops smaller than those actually due to the PRV, thus guaranteeing the minimum pressure for users, but also to mechanical powers smaller than 100 W. When a larger mean water demand is assumed, much better performances are reached, especially for large speeds (1250 rpm) that lead to mechanical powers larger than 1 kW combined to head drops a bit larger than those observed using the PRV. A suitable design is thus fundamental for the real-world PAT application.

A Computer Program to Support the Selection of Turbines to Recover Unused Energy at Hydraulic Networks

“…is the efficiency of the hydraulic machine (an average value of 85% is considered for Pelton, Francis, Kaplan, and Turgo turbines, 76% for the Banki turbine, and 70% for the pumps working as PAT turbines) [18][19][20][21][22], and…”

“…where Q is the flow rate that is transferred by the hydraulic machine, H is the net head, ŋ is the efficiency of the hydraulic machine (an average value of 85% is considered for Pelton, Francis, Kaplan, and Turgo turbines, 76% for the Banki turbine, and 70% for the pumps working as PAT turbines) [18][19][20][21][22], and ɣ is the specific weight of water (9810 N/m 3 ). In our case, we are going to consider 85% efficiency because in the selected location we can place turbines that have 85% efficiency (Figure 1).…”

“…As we can see in Figure 5, we obtained the same results as previously mentioned. The computer program says that we can use five types of turbines with the efficiency of each one of them, which are PATs (70%), Turgo (85%), Pelton (85%), Francis (85%), and Banki (76%) [18][19][20][21][22]. These have a power of 50 kW, with the exception of PATs, which, due to their low efficiency, would be 40 kW.…”

Application of Innovative Technologies for Active Control and Energy Efficiency in Water Supply Systems

“…The first approach was used for Multistage Submersed Pumps [26], while the second is proposed by [19] with an extension of Derakhshan and Nourbakhsh model [27] New and reliable data of PAT are useful for the design of future micro hydro power plants. An interesting procedure for the selection is suggested in [20], where the lack of reliable data from the pump manufacturers is overcome by direct pump testing in inverse mode on a new experimental rig, Figure 11. Based on the daily distribution of flow rate and pressure head in the dissipation node, the choice of the best PAT speed can be performed by specific tests, and the daily distribution of pressure drop can be exactly evaluated, Figure 12.…”

“…Figure 12.Measured PAT curves and daily distribution of the head drop for variable impeller speed[20].…”