Comparison of time required to charge a battery in a stand-alone photovoltaic system using different charge-controller types

An experiment was conducted at the National Renewable Energy Laboratory (NREL) comparing the time required to charge a fully discharged valve-regulated lead-acid battery in a photovoltaic (PV) system using on/off-shunt and pulse-width-modulated (PWM) charge controllers. In one system configuration, an on/off-shunt charge controller was only able to charge the battery to 61% of its rated capacity after 16 days. In a subsequent test, a different on/off-shunt controller in a different PV system configuration readily charged its battery to 100% rated capacity in less than 6 days. It charged its battery as quickly as a couple different PWM charge controllers did in identical systems in a side-by-side comparison.