Coupling of a volumetric pump to a photovoltaic array

Abstract

Although the volumetric pump is not preferred for pumping water from shallow wells where centrifugal pumps are better adapted to coupling with photovoltaic arrays, its use is recommended for deep wells and for reverse osmosis water desalination plants because of the technical problems associated with the use of centrifugal pumps for such applications. It should be noted that multistage centrifugal pumps can be employed for pumping water from deep wells (with magnetic mechanical coupling to an immersed sealed d.c. motor or with an a.c. motor powered through a d.c.-to-a.c. variable frequency inverter) although technical problems do exist. The volumetric pump generally drives a constant load. The matching efficiency between a constant load and a photovoltaic array is relatively poor. To improve the matching efficiency, either a d.c.-to-d.c. converter or a storage battery has to be used. In this work analyses for both direct coupling and coupling through a battery are presented. The simplified model developed herein with the object of computing the optimum size for the photovoltaic system is restricted to tropical climates where solar radiation is abundant and cloud occurrence is relatively rare. A significant improvement in system performance is attainable if storage batteries are used.