Maximum Power Point Tracker Solar Charge Controllers
A basic charge controller simply performs the necessary function of ensuring that your batteries cannot be damaged by over-charging, effectively cutting off the current from the pv panels (or reducing it to a pulse) when the battery voltage reaches a certain level.
A Maximum Power Point Tracker controller performs an extra function to improve your system efficiency.
The efficiency loss in a basic system is due to a miss-match between voltage produced by the pv panels and that required to charge the batteries under certain conditions.
A 24 volt battery will require upto about 28 volts to fully charge it. When the battery being charged is in a fairly low state, it's voltage (under charge) may only 24 volts.
Our PV panels, which we refer to as 24 volt panels, need to be able to charge the batteries on a bright day (not only in full sunshine) so are designed to produce at least 24 volts in those conditions. In bright sunshine hover, these panels may be cable of producing 40 volts. In-fact, they are likely to produce their rated output power (volts x amps) at 32 - 34 volts.
When the battery is at 24 volts, it will be pulling the panel voltage down to 24 (assuming no voltage drop in your cables). This results in the panels producing significantly less than their rated output and therefore there is a loss in efficiency.
How Does MPPT Help
An MPPT controller, in addition to performing the function of a basic controller, also includes a DC voltage converter, converting the voltage of the panels to that required by the batteries, with practically no loss of power. In other words, they attempt to keep the panel voltage at their Maximum Power Point, while supplying the varying voltage requirements of the battery.
Furthermore, a 24 volt system with an MPPT charge controller may have the panels wired in series to produce 48 volts, maintaining the ability to provide some charging current in dull conditions, when a standard system would not provide any charge.
Manufacturers claim upto 40% power increase from your panels using MPPT, which is most likely to be achieved when battery levels are low and/or light levels are low.