Making better use of parallel battery strings at solar sites by the inclusion of a simple monitoring module

With parallel battery strings there is often a concern that, as the batteries reach the end of their life, it may be difficult to determine when one or more strings have reduced capacity. This is more so when batteries are in high ambient temperatures and are subject to varying cyclic charge and discharge conditions. Good examples of such a situation are remote solar sites. Routine visits to these sites to check battery health can be costly. This paper describes the development of a cost-effective module, which monitors the individual current in each of the parallel strings in order to give an early warning of a failing string. In this case the battery being monitored consists of four parallel strings of 12-volt VRLA batteries. This battery is housed in an outdoor solar shelter and is subjected to the extremes of temperature in the remote locations where these shelters are required. Design criteria for the module are described together with prototype tests and preliminary field trial tests. Strategies for the replacement of batteries are proposed