Development of Innovative Performance Points for PV Water Pumping Systems

Overview

Three-year hourly field data (based on 2 seconds sampling rate) for eight installed systems in Jordan have been thoroughly investigated and analyzed. Five insolation conditions describing system performance under actual field conditions are defined and determined. Performance behaviors and outputs are accordingly defined and concluded

Discussion

For a particular system, the following may influence the PV array power of the system and thus the performance point values: (i) increasing ambient temperature decreases PV output power: for two measurements of similar insolations but different ambient temperatures, PV output powers will be different and thus input powers to the pump are different. Thus, at higher temperatures higher insolation is needed to deliver a certain amount of PV power, (ii) dust accumulated on the surface of the PV array adversely affects its performance: more dust means less power output and thus more insolation is needed to give a certain amount of PV power and (iii) increasing wind speed causes a cooling effect on the PV array thus increasing PV power output. So, even at the same insolation and ambient temperature but different wind speeds, PV power may be different.

 

For different systems there are other factors, in addition to those mentioned above, which affect the determination of the performance points such as: (i) PV array size: a system may reach its maximum capacity and its maximum efficiency at very low insolation if the PV array is too large. Conversely, a system of small PV array size requires high insolation to reach maximum capacity and efficiency, (ii) inclination angle of the PV array: two systems installed in the same location but with different tilt angles may have different insolation reaching the surface of the PV array and thus may produce different powers, (iii) pumping head: two systems of identical components but different pumping heads may require different powers and thus different insolation to start water pumping and to reach maximum subsystem or system efficiencies, (iv) the type of PV module: efficiency of PV modules varies with type and manufacturer, (v) the arrangement of PV modules in the string: (vi) the components efficiencies especially at part load, (vii) type of inverter: different types of tracking inverters may have different power outputs, (viii) matching between components: mismatch of system components reduces PV array power and (ix) matching between the pump characteristics and the well system characteristics:  a good match increases pump’s efficiency and thus decreases PV power value for a particular water output.

 

Concerning the developed performance points, designers should follow a careful design and optimization process in determining insolation points I₁, I₂, I₃ and I₄. In some cases, decreasing I₁ reduces the unused threshold energy which positively affects the daily system performance. However, in most cases decreasing I₁ may decrease I₂ thus increasing the unused amount of energy at high insolation. Moreover, the effect of solar energy on system performance is different at low and high insolation levels. System efficiency at high insolation is higher than that at low insolation.

 

The differing performance characteristics of the systems show that there is a real need for a validated technical model that can be used as guidelines for system sizing and optimization process and an economic model is also needed to determine the techno-economic optimum configurations.