Verification of Computer Sizing of Photovoltaic Power Systems

There are no generally accepted computer sizing programs for stand-alone photovoltaic power systems, including the array and the battery, which have been verified for an extended period of time. In order to test the performance and the reliability of stand-alone photovoltaic power systems a computer sizing program for the solar array and battery has been developed. The program covers both vented low antimony and maintenance free lead-acid batteries as well as pocket plate nickel cadmium batteries. The sizing program has been verified in a one year full scale testing including four different types of batteries taking into consideration charge efficiency versus state of charge, aging, temperature, insulation, depth of discharge, type of load, catalytic vents and water consumption. The conclusion drawn from the test is that a pocketplate nickel cadmium battery with property balanced electrode capacity has extremely good charging efficiency in the actual current range. There has been no aging during the 12 months test and the retained capacity is better than for lead acid batteries. The so called maintenance free lead acid battery did not show satisfactory performance in this application.