A Primer On Charge Controllers

Charge controllers are critical components in solar PV systems with batteries, as they regulate, or “control”, the amount of the charge (current) that the PV modules send to the system’s battery pack.

Why is that important? Because batteries are manufactured to operate within certain limits of charge capacity. Overcharge or undercharge your batteries and you are quite likely to damage them.

How Charge Controllers Work

Charge controllers function in 3 stages:

A) Bulk charging: This occurs when the batteries are depleted of charge (usually in the morning after being used at night). The charge controller allows maximum current into the batteries, thus charging them up to the manufacturer specified “voltage set point for bulk charging” (which is usually about 80% of full charge).


B) Absorption Charging: To top off the battery’s charge to 100%, the charge controller holds the input voltage constant while it gradually reduces the current, till full battery charge is achieved.

Absolption charging is so designed because, if the input current is not limited after reaching the bulk charging voltage set point, the battery pack may get overcharged – leading to excessive heat and gas production. This would be extremely harmful to the batteries.

C) Float Charging: This mode of charging keeps the battery in full state of charge (as long as the sun or an alternate source of energy, such as a diesel generator set is available). Float charging is always activated only after the first two stages have been completed.

In winter, under shorter sunlight hours, float charging may not be activated at all. On the other hand, in summer, float charging may be employed by the charge controller for the majority of the day.

In the next post, we will delve into more advanced topics on charge controllers.

To read more about the performance of rooftop PV systems, click here.


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Aniruddha Bhattacharjee
Aniruddha Bhattacharjee
Aniruddha has been a renewable energy researcher and report writer for over 3 years. He has also been a content developer for multiple websites, including portals on travel and tourism, restaurants and personal finance. He holds a bachelor's degree in mechanical engineering and a master's in endangered species conservation. Apart from renewable energy, Aniruddha is a keen motor sports and aviation enthusiast, and a beginner in photography.
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