ABSTRACT
There are many applications for small standalone photovoltaic (PV) and wind powered systems, in areas where it is not possible or economical to connect to the utility electrical network. The battery is ideally required to be low maintenance, have good cycling performance, and be resistant to acid stratification. The maintenance-free valve-regulated lead-acid (VRLA) battery is suitable for use in such applications. This paper describes the development of a VRLA absorptive glass mat (AGM) battery with improved cycling performance, through the use of a newly developed separator material with improved characteristics. This significantly reduces acid stratification, thus prolonging battery lifetime and reducing the overall system lifetime cost. A further innovation is the development of an adaptive charge controller which optimises the recharge time by taking the previous operating conditions of the battery into account, and ensures that the battery is fully recharged whenever possible. Prototype batteries and charge controllers have been designed, tested, and incorporated in a demonstration PV/wind system. The results of laboratory and application testing demonstrate the increased cycling capacity of the batteries, and the improved battery recharge achieved by the charge controller. Bench tests of the new battery indicate a 50% increase in the expected lifetime.
