Monitoring and charge-control of lead-acid batteries in photovoltaic applications

This work presents a microcontroller-based charge controller suitable for photovoltaic applications. The controller performs temperature-compensated charge control. It also monitors and stores those parameters that provide an indication of batteries' state of charge and state of health: Panel's voltage, battery's voltage and current, current demanded by a load and temperature. The controller has serial communication capabilities that make possible the interface to a personal computer or central station. By using a local industrial network or remote links via radio, multiple remote controllers can be monitored by a central station running a battery management program. The information collected from all the controllers in the system is analyzed to determine the state of charge of individual batteries and, if required, command the appropriate controller to perform special procedures like, for example, thorough diagnostics or equalization. Preliminary field-test results of a controller installed in a high-way emergency bay are presented in the paper. It is shown that protection against deep discharges is achieved, which contributes to extend the battery useful life.