The solar charge controller is a small component in the overall solar power system but it plays a crucial role in the proper functioning of the system.
Its right configuration and type help in producing optimum output and the smooth functioning of the system. Therefore, it is very important to choose the right type of solar charge controller for your home. Before doing so, let's understand its function and working. Definition
A solar charge controller is required in almost all solar systems which require the battery backup.
The solar charge controller is an electronic device when placed between the solar panels and the battery regulates the voltage coming from the solar panels to the battery. Function
i) It regulates the battery voltage and protects it from being overcharged.
The solar charge controller checks the voltage of the battery. When it sees that it is low, it allows full flow of current from the panels to enter into the battery. 
When the battery voltage reaches to the certain level, it reduces the flow of energy to prevent overcharging of the battery.
opens the circuit and the charging of the battery from the panels gets stopped. 
When the voltage of the battery drops due to less sunlight or increase in electrical consumption, the charge controller again allows full flow of energy to enter into the battery.
In this way, it regulates the charging of the battery.
ii) It blocks the reverse current from flowing back to the solar panels.
During night, the solar panels do not produce current and hence are at lower potential with respect to the battery. We all know that current flows from higher potential to the lower (Battery to solar panel in this case). There is a chance that current will leak from the battery to the panels and will drain it. 
But the diode connected inside the solar charge controller allows current to flow in one direction that is from solar panels to the batteries.
It restricts the back flow of the current. Hence, it stops the reverse flow of the current and prevents the draining of the batteries. Types of Charge Controller
The solar charge controllers which are commonly used in the solar power systems are:
The working
The PWM solar charge controller works by adjusting the charge from the solar panels according the battery’s condition and its recharging requirements.
The charging rate is higher and pulses are wider when the battery is nearly discharged and the charging rate and the width of the pulses keeps on decreasing as the battery reaches its maximum charging level . It can keep the battery fully charged state for an indefinite period of time. This helps in avoiding heating and gassing of the battery and results in high charging efficiency with healthy battery life. When sizing the system the voltage specification of the PWM charge controller must match the voltage of the battery. Whereas the normal solar charge controller also called shunt controller, stops charging the battery when it is fully charged and re-charges again when battery drops to the certain level.
Understand the difference with an example
For example: A 140 watt panel at STC (Standard Test Conditions) has the following specifications:
Further assume, this panel is used to charge the 12 volts/100Ah battery. A 12 volts battery generally requires around 14 volts from the panel to charge it. It means, the remaining (17-14) volts( 3 volts) from the panels will get wasted. The power that is going inside the battery is: = 14 volts x 8.24 amperes (Power = Voltage x Current) = 115.4 watts While the panel is producing 140 watts under STC The remaining power of {(140-115.4) watts} 24.6 watts gets wasted. The efficiency of the system is reduced by: = (140 - 115.4)/140 x100 % = 17.6 %. The charging time is: = (12 volts*100 ampere-hr)/ (115.4 watts) = (1200 watt-hr)/ (115.4 watts) = 10.4 hours to charge the battery (assuming the output power from the panel is constant). Here, we saw that even though the PWM charge controller is able to protect the batteries from overcharging but at the same time the efficiency of the system is reduced by 17.6%. We need something that in addition to protecting the batteries from overcharging also keeps the system effective and efficient.
Here comes MPPT (Maximum Power Point Tracking) charge controller in picture.
The basic function of this charge controller is same as that of PWM charge controller (like regulating the voltage, protecting the batteries from overcharging, and preventing the current drain from the batteries). In addition to all this, it provides the maximum power to the batteries and reduce their charging time. Let us take the same case in which the voltage from the solar panel is 17 volts and the current is 8.24 amperes under STC. As the requirement of the battery is 14 volts, the remaining 3 volts are not wasted but are converted into equivalent amount of amperage by the MPPT charge controller. Assuming, the power generated by the panel and the power reaching to the battery for charging is the same i.e. 140 watts. (Ignoring other losses like conversion loss and heat loss). The MPPT charge controller will convert the excess 3 volts into the equivalent amperage, using the equation:
The reduction in the voltage from 17 volts to 14 volts leads to increase in current from 8.24 amperes to 10 amperes, keeping the power same. 
Hence, the battery gets same power (140 watts) despite the difference in the charging voltage and the voltage produced by the panels under STC.
The charging time of the batteries in this case will be: = (12 volts*100 ampere-hr)/140 watts = (1200 watts-hr)/140 watts = 8.6 hours (Assuming the power from the solar panel is constant). Hence the charging time is reduced when compared with the charging time using PWM charge controller. Variable output by Panel
The voltage and the current from the panel is the function of the temperature and the amount of the solar radiation falling on the surface.
As both of these parameters change continuously which cause the output power from the panel to vary throughout the day; the MPPT charge controller detects the maximum power produced by the solar panel and transmits the same to the battery for charging. Even though the MPPT charge controller is expensive than the PWM charge controllers but paying high price is worth in a view of the increased efficiency of the system. Which is the BEST?
However each technology has its own advantages which are based on the site location, temperature, and size of the array with respect to the load, size and the cost of system.
Let us understand their efficiency and the advantages under different set of conditions: a) Location: The angle at which sun rays striking at the solar panels depends on the location and the season. The less amount of energy is absorbed by the solar panel when the sun rays coming at the shallow angle and hence resulted in less output power from the solar panel. Here the MPPT technology is suitable for harvesting the maximum amount of the solar energy. b) Temperature: As the temperature drops the Vmp of the solar module increases causes more differential between the battery voltage and the panel voltage. As MPPT charge controller has the ability to track or detect the excess voltage and covert the difference into the equivalent amperage. Therefore in lower temperature conditions the MPPT technology has better harvesting power than that of PWM technology. c) Increase in the size of array with respect to the load: In a situation where the size of the panels are large enough relative to the power drawn by the load, the battery will remain in the full charge state almost all the time. Here the PWM charge controller is suitable and economical as compared to the MPPT charge controller. d) When the size of the system is small: Small power solar system is better suited to the PWM controller because it operates at the constant harvesting efficiency irrespective of the size of the solar system. Whereas, the harvesting efficiency of the MPPT charge controller is low with small solar power system. So, in low power applications PWM charge controller is better and economical option. e) Cost of the system: PWM charge controllers are less expensive than the MPPT charge controllers. So PWM charge controllers have cost advantage over their counterpart. So, you can decide which type of the solar charge controller is suitable for your solar system by analyzing the above mentioned parameters. Conclusion
Finally, we saw that the right type of solar charge controller
(PWM or MPPT) depends on the location, temperature changes, size of the system, and your budget. An MPPT charge controller may be doing well in one location but is not effective in another. Similarly, PWM charge controller may not suits well in every size of the system. It is you who can decide the best one for your home after considering all the above factors. Thank you!
1 Comment
Charu
4/9/2020 01:09:58 pm
This post covers everything about solar charge controllers. It is very helpful for a person to find all information in a single article. Keep writing... Leave a Reply. |
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