An experiment was conducted at the National Renewable Energy Laboratory (NREL) comparing the time required to charge a fully discharge 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 61percent 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 100percent 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.
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