The Solar Power Controller

The Solar Power Controller has integrated circuits containing an algorithm which determines the power state of the solar panels and of the batteries.  It uses the state knowledge to assess the battery and current power being produced by the solar power subsystem and it determines how to adjust the mode of power transfer to the batteries for optimum power use, conservation, and battery performance.  Renogy, a leading retailer of solar panel technology describes the functions of their Rover Series charge controllers as follows:

"Four Charging Stages
The Rover [maximum power point tracker] MPPT charge controller has a 4-stage battery charging algorithm for a rapid, efficient, and safe battery charging. They include: Bulk Charge, Boost Charge, Float Charge, and Equalization.

Bulk Charge: This algorithm is used for day to day charging. It uses 100% of available solar power to recharge the battery and is equivalent to constant current. In this stage the battery voltage has not yet reached constant voltage (Equalize or Boost), the controller operates in constant current mode, delivering its maximum current to the batteries (MPPT Charging).

Constant Charging: When the battery reaches the constant voltage set point, the controller will start to operate in constant charging mode, where it is no longer MPPT charging. The current will drop gradually. This has two stages, equalize and boost and they are not carried out constantly in a full charge process to avoid too much gas precipitation or overheating of the battery.

Boost Charge: Boost stage maintains a charge for 2 hours by default. The user can adjust the constant time and preset value of boost per their demand.

Float Charge: After the constant voltage stage, the controller will reduce the battery voltage to a float voltage set point. Once the battery is fully charged, there will be no more chemical reactions and all the charge current would turn into heat or gas. Because of this, the charge controller will reduce the voltage charge to smaller quantity, while lightly charging the battery. The purpose for this is to offset the power consumption while maintaining a full battery storage capacity. In the event that a load drawn from the battery exceeds the charge current, the controller will no longer be able to maintain the battery to a Float set point and the controller will end the float charge stage and refer back to bulk charging.

Equalization: Is carried out every 28 days of the month. It is intentional overcharging of
the battery for a controlled period of time. Certain types of batteries benefit from periodic
equalizing charge, which can stir the electrolyte, balance battery voltage and complete
chemical reaction. Equalizing charge increases the battery voltage, higher than the standard
complement voltage, which gasifies the battery electrolyte."

The nice thing about this charge controller functionality is it manages the charge distribution automatically.