What is Solar Charge Controller : Working with MPPT Technology

The amount of electrical energy requirement is increasing rapidly with the population growth and technology development. There are ways for generating electrical energy using renewable and non-renewable energy sources. Multiple advantages of solar energy are the key factors behind the usage of solar energy for various purposes. It can be used for generating electrical power with the help of solar panels and for storing the electrical energy by charging the batteries or feeding into loads. Maximum Power Point Tracking technology (MPPT) is a most efficient method among various solar charge controllers such as simple 1 or 2 stage controls, PWM control and MPPT charge controller.

What is Solar Charge Controller

Primarily consider a non-MPPT solar charge controller and don’t get confused with sun tracking solar panel and solar charge controller. The sun tracking solar panel is used to track the sun by mounting the solar panel on a motor board such that maximum solar energy can be used during the day time. By using this sun tracking solar panel system, we can increase the output by 15% in winter and 35% in summer. The blow figure shows the block diagram of sun tracking solar panel that consists of a dummy solar panel, a power supply circuit, a microcontroller for controlling ULN2003A driver and stepper motor for rotating the solar panel.

The block diagram of the solar charge controller consists of different blocks: the solar panel that produces electrical power using solar energy; a charging to switch on and off the charging; a load switch to connect or disconnect load; an indicator for indication purposes; battery for storing energy; and a comparator for comparing and generating control signals. The solar panel charge controller is controlled by a charging mechanism to protect the batteries from under charge, over load and deep discharge conditions. A set of green and red LEDs are used for indicating fully charged condition and under or over or deep discharge condition, respectively. In case of red LEDs’ indication the solar charge controller circuit consists of MOSFET, which is used as power semiconductor switch to turn off the load during an overload or low battery condition.

Why do we use MPPT technology?

Here even though a non-MPPT solar charge controller can facilitate the protection of batteries from undesired charging conditions, but it is unable to increase the efficiency of the system. Generally PV panels are built for 12V and are used to put output in the range of 16 to 18V. But the actual value of the 12V batteries is in the range of 10.5 to 12.7V based on the state of the charge. Consider a 130watt rated solar panel at a particular voltage and current, suppose the current rating is 7.39 amps at 17.6 volts.

If we connect this 130 watt solar panel to a battery using a non-MPPT solar charge controller, then we can get a power which is equal to the product of current of the solar panel: 7.4 amps and voltage of the battery: 12 volts, and is about 88.8 watts. Thus, we get a loss of 41 watts (130-88.8=41.2 approximately), this is due to a poor match between the solar panel and the battery. So, if we use MPPT solar charge controller, then we can increase the power gain by 20 to 45% but primarily we must know about MPPT technology, which is used in the solar panel charge controller.

MPPT Solar Charge Controller

MPPT technology is usually a digital electronic tracking that tracks and compares the battery voltage with the solar panel voltage such that best power at which the battery can be charged using solar panel can be figured out. Notice that while charging the battery the amperes are considered. So, to get maximum amperes into the battery, the compared voltage is converted into its best voltage using modern MPPT technology having 93 to 97% conversion efficiency.

Working of MPPT Solar Charge Controller

The solar panel voltage 17.6V at 7.6A is converted down by MPPT to match the 12V battery. Thus, the battery gets 12V at 10.8A making the total power almost equal to 130W. For charging the battery a high voltage helps to force the current in. In fact, practically, the output of the MPPT solar charge controller varies continuously to get maximum amperes into the battery.

Power point tracker is a high frequency DC to DC converter that takes DC input from the solar panels, then converts the DC into high-frequency AC and, again the AC will be converted back into a different DC voltage and a current to accurately match the batteries and panels. Generally MPPTs operate at frequency ranging from 20-80 kHz (very high audio frequency range). Hence, very high efficiency transformers and small components can be used to design these high frequency circuits.

Non-digital or linear MPPTs are easy and cheap to build compared to the digital MPPTs. But, while using the linear MPPTs, even though efficiency improves a bit, but the overall efficiency varies in a wide range as the linear MPPTs lose their tracking in some cases. For example, if a cloud passes over the linear MPPT circuit, then the linear circuit takes more time to search for next best point.

Major features of MPPT Solar Charge Controller

• MPPT solar charge controller is used for correcting and detecting variations in the current-voltage characteristics of solar panel and as shown in the above figure.
• It is necessary for any solar power systems required to pull out a maximum power from PV module as it forces PV module for operating at voltage close to maximum power point to with draw maximum available power.
• By using MPPT solar charge controller, we can use solar panel with a voltage output greater than the battery system operating voltage.
• System’s complexity can be reduced by using MPPT solar charge controller as it has high efficiency.
• It can be applied for using with multiple energy sources such as water turbines or wind-power turbines, and so on. The solar panel’s output power is used for controlling DC-DC converter directly.

MPPT Solar Charge Controller Integrated with LED Driver

Recent trend in the lighting and illumination frequently uses high brightness LEDs that have long life span with low maintenance cost and high efficiency, but requires a power driver to maintain constant current. This can be facilitated by a DC-DC step-up or step-down converter. The below figure shows the block diagram of an integrated maximum power-point tracking solar charge controller and LED driver built on Programmable System on Chip (PSoC) devices, controllers, drivers, analog and digital peripherals are used for measuring, conditioning and controlling the signal.

MPPT technology is flexible and strong in taking voltage and current from the solar panel to search the peak power by adjusting control signals to operate solar panel at its peak power. Control signal generated from the PSoC is used in driving a synchronous buck converter that converts solar panel power to charge battery. The system is also used to control battery charging process and drive LEDs.

We hope this article has provided a brief account of the advanced solar charge controller using MPPT technology. For more information regarding the solar charger controllers and their detailed working, you can contact us by posting your queries in the comments section below.