Dynamic behavior of water wells coupled to PV pumping systems

Evaluation of a water supply system requires an overall analysis of its behavior, including the well performance and drawdown characteristics. The response of the water well is usually characterized by a single relationship between water level and water flow, representing its quasi-equilibrium behavior. However, for days with large and rapid variations of irradiance this relationship does not correspond to the well-equilibrium curve. In order to simulate the well behavior it has been developed a model that takes into account the variation of water level, pressure at the entrance of the well and static pressure of the aquifer, all of them related to the water flow. The model also considers the energy conservation equation of the system through the relationship among hydraulic load, water flow, and collected irradiance. Results of simulations show that, for days with large variations in solar irradiance, the static and dynamic analysis exhibit large differences in the instantaneous water head. The dynamic analysis shows that the water well tends to attenuate the fluctuations of the water head through a negative feedback mechanism. The model helps to understand some facts observed in the field. For example, the dispersion of points in the flow rate versus solar irradiance curves. The maximum drawdown obtained with the dynamic model is considerably smaller than the one predicted with the quasi-equilibrium analysis. That difference can represent some savings in terms of water well hardware (drilling, wiring, and piping) for programs involving the installation of a large number of systems. The slowdown of water column variations, shown by the dynamic model, signifies that the motor-pump system is not so intensively demanded as the quasi-equilibrium analysis would suggest, resulting in longer lifetime prospects. Copyright © 2007 John Wiley & Sons, Ltd.