A Solar charge controller, or solar regulator is similar to the voltage regulator in your car. It regulates the voltage and current coming from the solar panels going to the battery. Most "12 volt" panels put out about 16 to 20 volts, so if there is no regulation the batteries will be damaged from overcharging. Most batteries need around 14 to 14.5 volts to get fully charged.
Not always, but usually. Generally, there is no need for a Solar charge Controller with the small maintenance, or trickle charge panels, such as the 1 to 5 watt solar panels. A rough rule is that if the panel puts out about 2 watts or less for each 50 battery amp-hours, then you don't need one.
For example, a standard flooded golf car battery is around 210 amp-hours. So to keep up a series pair of them (12 volts) just for maintenance or storage, you would want a panel that is around 4.2 watts. The popular 5 watt panels are close enough, and will not need a controller. If you are maintaining AGM deep cycle batteries, such as the Concorde Sun Xtender then you can use a smaller 2 to 2 watt panel.
The most PWM Solar controller simply monitors the battery voltage and opens the circuit, stopping the charging, when the battery voltage rises to a certain level. Quite a few charge controls have a "PWM" mode. PWM stands for Pulse Width Modulation. PWM is often used as one method of float charging. Instead of a steady output from the controller, it sends out a series of short charging pulses to the battery – a very rapid "on-off" switch. The controller constantly checks the state of the battery to determine how fast to send pulses, and how long (wide) the pulses will be. In a fully charged battery with no load, it may just "tick" every few seconds and send a short pulse to the battery. In a discharged battery, the pulses would be very long and almost continuous, or the controller may go into "full on" mode. The controller checks the state of charge on the battery between pulses and adjusts itself each time.
In any applications which PV module is energy source, MPPT solar controller is used to correct for detecting the variations in the current-voltage characteristics of solar cell and shown by I-V curve.
MPPT solar controller is necessary for any solar power systems need to extract maximum power from PV module; it forces PV module to operate at voltage close to maximum power point to draw maximum available power.
MPPT solar controller allows users to use PV module with a higher voltage output than operating voltage of battery system.
For example, if PV module has to be placed far away from charge controller and battery, its wire size must be very large to reduce voltage drop. With a MPPT solar controller, users can wire PV module for 24 or 48 V (depending on charge controller and PV modules) and bring power into 12 or 24 V battery system. This means it reduces the wire size needed while retaining full output of PV module.
MPPT solar controller reduces complexity of system while output of system is high efficiency. Additionally, it can be applied to use with more energy sources. Since PV output power is used to control DC-DC converter directly.
MPPT solar controller can be applied to other renewable energy sources such as small water turbines, wind-power turbines, etc.
Another area that is enhanced by an MPPT charge controller is power loss. Lower voltage in the wires running from the solar panels to the charge controller results in higher energy loss in the wires than higher voltage. With a PWM charge controller used with 12v batteries, the voltage from the solar panel to the charge controller typically has to be 18v. Using an MPPT controller allows much higher voltages in the wires from the panels to the solar charge controller. The MPPT controller then converts the excess voltage into additional amps. By running higher voltage in the wires from the solar panels to the charge controller, power loss in the wires is reduced significantly.
MPPT charge controllers are more expensive that PWM charge controllers, but the advantages are worth the cost. If you can afford it, you should definitely use an MPPT solar charge controller.
The final function of modern solar charge controllers is preventing reverse-current flow. At night, when solar panels aren't generating electricity, electricity can actually flow backwards from the batteries through the solar panels, draining the batteries. You've worked hard all day using solar power to charge the batteries, you don't want to waste all that power! The charge controller can detect when no energy is coming from the solar panels and open the circuit, disconnecting the solar panels from the batteries and stopping reverse current flow.
