Directly connecting a solar panel or array to a battery can be catastrophic as solar panels can output a wide voltage range. As an example, a nominal 12 volt rated panel can output anything up to 22volts during an average sunny day. A solar charge controller between the panel and the battery ensures the battery receives the correct output voltage and current from the panel to minimise the risk of the battery being overcharged or discharging back into the panels. Charge controllers come in a variety of types which give different performance and can be matched to simple recreational applications all the way up to complex high power solar array installations.
SWITCHING: Simple switching controllers connect the panel to the battery when the panel is providing power & the battery is not fully charged. This type of controller is low cost and only good for basic solar equipment setups such as standby lighting, etc. where the panel yield is far higher than the load requires. PWM: Pulse width modulated (PWM) controllers continually apply voltage pulses to the battery whenever the panel is providing sufficient voltage. The pulse width (or duration) is varied by the controller depending on the charge state of the battery to ensure the correct amount of charge is harvested from the panel whenever it is available. As a result, PWMc ontrollers provide a much higher power yield than simple switching controllers.
MPPT: Maximum power point tracking (MPPT) controllers maximize power conversion between the panel output and the battery input by using a DC to DC switchmode power converter. By continuously tracking the panel output and adjusting the converter they yield the maximum amount of power under widely varying solar conditions. MPPT controllers give the best solar system efficiency and improve solar system power yield by a significant percentage. Both PWM and MPPT controllers are available with display panels which allow you to track performance of the solar system. Panel voltage, battery voltage, charging current, and total charge supplied can be easily displayed so you can ensure the system is running correctly. More complex models also include integration functions to remotely control other equipment or be linked into advanced systems.