solar charge controller : FAQs

Solar Charge Controller FAQs :

  • What is a solar charge controller?

Solar charge controller is an electronic device which is connected between solar pv panel and the battery. The main function of solar charge controller is to regulate battery charging process using power from the solar panel which includes multiple battery and panel protections for the system.
Solar charge controllers are rated as per maximum input voltage and maximum charging current. These are further divided into two types based on technology used which is PWM or Pulse Width Modulation solar charge controller and MPPT or maximum power point tracker solar charge controller.

  • What is the difference between PWM and MPPT solar charge controllers?

Solar charge controllers are mainly of 2 types, PWM & MPPT.
Pulse Width Modulation (PWM) solar charge controllers draws current out of solar panel just above battery voltage.
Maximum Power Point Tracking (MPPT) solar charge controllers draws current out of solar panel at maximum power voltage. The MPPT charge controllers convert excess voltage into amperage. The voltage from solar PV module will drop down, with a corresponding increase in the current amperage. This increase in current will lead to faster recharge of battery. These MPPT solar charge controllers automatically adjust to derive maximum power from the solar pv panel to charge battery & solar pv panel power losses are significantly reduced.
MPPT provide increase in charging efficiency of upto 30% compared to PWM solar charge controllers. This improvement also varies based on ambient temperature of solar pv panel. A P&O MPPT solar charge controller improves the performance even further compared to conventional MPPT solar charge controller.

  • How is P&O (perturb and observe) MPPT better than OV (open circuit voltage) MPPT solar charge controller?

In open circuit voltage (OV) MPPT method, it’s assumed-

Vmmp = k.Voc, where k is a constant and its value for crystalline silicon is usually to be around 0.7 to 0.8 but the constant k is an approximation & each time the system needs to find the new open circuit voltage (Vout) when the illumination (sunlight) condition changes. This leads to reduced efficiency.

A better method for MPPT solar charge controller is the perturb and observe (P&O) technique which gives excellent results.

The solar panel/PV output power is periodically measured and compared with the previous power. If the output power increases, the same process is continued otherwise perturbation is reversed. Here perturbation is provided to the solar panel/PV module voltage.
When an increase in voltage leads to an increase in power,so further perturbation is required towards the right to reach MPP. Conversely, if an increase in voltage leads to a decrease in power, it means further perturbation towards the left is required to reach MPP.

The results show that the P&O MPPT solar charge controller improves the efficiency of the solar PV panel when compared to OV MPPT solar charge controllers.

  • What protections should be offered by solar charge controllers?

For proper functioning of the solar pv system, the solar charge controllers should offer following protections:

  1. Short circuit/overload protection.
  2. Reverse battery & solar panel protection.
  3. Reverse flow of current from battery to solar panel during night.
  4. Low voltage disconnect & high voltage disconnect to ensure battery doesn’t get over-charged or over-discharged.
  5. Lightning protection which is useful in monsoons.
  6. No battery protection : Solar charge controller should cut off the solar panel supply in absence of battery to protect the load and itself. For this solar charge controller should individually monitor all parameters independently
  • How to select right capacity solar charge controller?

Whether the solar charge controller is PWM or MPPT based, what is important is the peak current (input) from solar panel and maximum current consumption (output) of the load for given nominal voltage system like 12V/24V. It is recommended to have a solar charge controller with atleast 25% more capacity than the input & output current values. Also, it is important to see whether the solar charge controller current rating is for both- input from solar panel as well as output for load or the ratings mentioned on solar charge controller is for solar panel current only. So a 20A PWM solar charge controller should support 20A from solar panel & 20A to load, while incase of MPPT solar charge controller, it should support 20A from solar panel & upto 26A to load because MPPT solar charge controller converts excess solar panel voltage to current.

  • What are the benefits of hybrid solar charge controller over conventional solar charge controller?

In applications when reliability of the performance needs to be extremely high and can’t be dependent on weather or grid supply alone, hybrid solar charge controllers are useful as they have dual power source: solar panel and grid supply. It always has solar priority but incase the battery becomes low, the load is switched to grid supply. This ensures load is on irrespective of absence of any one of the power source. With remote monitoring system, all the parameters can be seen and controlled making the entire solar system even more robust and reliable. As this can be used for smaller load applications also like street lighting, traffic signals etc. it becomes much more cost effective and efficient than using hybrid solar inverters. Our hybrid solar charge controllers too are P&O MPPT based making them even more efficient than PWM or regular MPPT solar charge controllers.

  • What are the advantages of having built-in LED driver in Solar Charge Controllers for Solar Lighting?

Solar charge controller with built-in LED driver for solar lighting gives complete control to the user who can select LED load/wattage, dimming percentage, time settings using on-board links. The LED driver is a constant current drive buck driver which offers higher efficiency and performance across various wattage, from 9W to 200W. And with no additional wiring required between charge controller and LED driver, it improves the overall reliability, elimination of voltage/current drop across the wire in the system. So this solar charge controller acts as all-in-one solution for solar lighting applications.