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

Matteo Postacchini,Elisa Di Giuseppe,Fiorenza Finizio,Luciano Soldini,Giovanna Darvini,Leonardo Pelagalli

doi:10.3390/w12040958

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.

Highlights

Nowadays, the need to produce energy in a sustainable way is an important issue to tackle to both improve environment quality and human life
Since international agreements and incentive policies by governments suggest that water use and reuse in our society are of primary importance, a significant contribution may come from small hydropower plants based on the exploitation of centrifugal pumps operating in reverse mode, called Pumps As
The first aim of the experimental tests was that of finding such curves, which represent the evolution of the head drop ∆H with the discharge Q at specific rotational speeds, imposed through the test bench

Summary

Introduction

The need to produce energy in a sustainable way is an important issue to tackle to both improve environment quality and human life. To this effort, new energy systems, exploiting different available natural sources such as water, have been developed over time to reduce carbon emissions and produce energy in a renewable way (e.g., [1,2,3,4,5,6,7]). Since international agreements and incentive policies by governments suggest that water use and reuse in our society are of primary importance, a significant contribution may come from small hydropower plants based on the exploitation of centrifugal pumps operating in reverse mode, called Pumps As. Turbines (PATs) [2,4].

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Conclusion