A solar controller is an electronic device that controls the circulating pump in a solar hot water system to harvest as much heat as possible from the solar panels and protect the system from overheating. The basic job of the controller is to turn the circulating pump on when there is heat available in the panels, moving the working fluid through the panels to the heat exchanger at the thermal store. Heat is available whenever the temperature of the solar panel is greater than the temperature of the water in the heat exchanger. Overheat protection is achieved by turning the pump off when the store reaches its maximum temperature and sometimes cooling the store by turning the pump on when the store is hotter than the panels.
When a battery reaches full charge, it can no longer store incoming energy. If energy continues to be applied at the full rate, the battery voltage gets too high. Water separates into hydrogen and oxygen and bubbles out rapidly. (It looks like it's boiling so we sometimes call it that, although it's not actually hot.) There is excessive loss of water, and a chance that the gasses can ignite and cause a small explosion. The battery will also degrade rapidly and may possibly overheat. Excessive voltage can also stress your loads (lights, appliances, etc.) or cause your inverter to shut off.
Preventing overcharge is simply a matter of reducing the flow of energy to the battery when the battery reaches a specific voltage. When the voltage drops due to lower sun intensity or an increase in electrical usage, the controller again allows the maximum possible charge. This is called "voltage regulating." It is the most essential function of all charge controllers. The controller "looks at" the voltage, and regulates the battery charging in response.
A circuit is overloaded when the current flowing in it is higher than it can safely handle. This can cause overheating and can even be a fire hazard. Overload can be caused by a fault (short circuit) in the wiring, or by a faulty appliance (like a frozen water pump). Some charge controllers have overload protection built in, usually with a push-button reset.
Built-in overload protection can be useful, but most systems require additional protection in the form of fuses or circuit breakers. If you have a circuit with a wire size for which the safe carrying capacity (ampacity) is less than the overload limit of the controller, then you must protect that circuit with a fuse or breaker of a suitably lower amp rating. In any case, follow the manufacturer's requirements and the National Electrical Code for any external fuse or circuit breaker requirements.
So, 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.
However, this is not enough, some people need higher efficiency, which is not normal solar controller can perform, MPPT solar controller comes. MPPT means maximum power point tracking, 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 up to about 28 volts to fully charge it. When the battery being charged is in a fairly low state, it's voltage may be 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, so they are designed to produce at least 24 volts in those conditions. In bright sunshine time, these panels may be cable of producing 40 volts. In-fact, they are likely to produce their rated output power at 32 - 34 volts.
When the battery is at 24 volts, it will be pulling the panel voltage down to 24. This results in the panels producing significantly less than their rated output and therefore there is a loss in efficiency.
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.
So, MPPT solar controller is really necessary for higher working efficiency, however, finding a good MPPT solar controller is not easy. Luckily, Wuhan Wellsee is a professional player in Solar PV systems, Wellsee MPPT solar controller will be your trustworthy choice.