Understanding MPPT Solar Charger

Here we try to understand the actual circuit concept of MPPt type of solar charger controllers and learn how do these devices work.

What's MPPT

MPPT stands for Maximum Power Point Tracking, a charger concept specifically intended and designed for acquiring highly efficient solar power harnessing.

Solar panels are excellent devices since they allow us to harness free electrical energy from sun, however the present devices are not very efficient with their outputs. As we all know output from solar panel directly depends the incident rays of the sun, as long as its near perpendicular on  it offers good efficiency, which keeps on deteriorating with slanting rays or dipping sun position.

The above also gets affected with overcast conditions.

Moreover a solar panel output is associated with inconsistent voltage levels which needs proper regulation in order to operate the load which is normally a lead acid battery.

Lead acid batteries or any kind of chargeable battery will require a properly rated input so that it doesn't get damaged and it gets charged optimally. For this we normally involve a charger controller in between the solar panel and the battery.

As a solar panel voltage is never constant and drops with dropping sun light, the current from the solar panel also gets weaker as the sun light intensity gets weaker.

With the above conditions if the solar panel undergoes any kind of loading directly, it's current would further go down producing inefficient outputs.

In other words the efficiency of a panel is maximum when its voltage is near the rated specified value. Therefore, as an example a 18V solar panel will operate with maximum efficiency when it's operated at 18V.

And in case the sun light gets weaker and the above voltage drops to say 16V, yet still we could operate it with maximum efficiency if we could keep the 16V volts intact and derive the output without affecting or dropping this voltage.

The below given graph suggests why and how a solar panel produces maximum efficiency when it's allowed to operate at it's maximum circumstantial voltage output.

What's Maximum Power Point or Knee point

Ordinary solar charger controllers only regulate the solar panel voltage and make it appropriate for charging the connected battery, however these do not carry out the panel regulation correctly.

Conventional charger regulator which employ linear ICs for the regulations are unable to keep the solar panel from getting loaded directly by the connected battery or the inverter or whatsoever may be connected as the load.

The above situation tends to drop the solar panel voltage accordingly making its usage inefficient because now the panel is restricted from producing the rated amount of current to the load.

So why does these linear or PWM regulator chargers are unable to avoid loading of the solar panel despite being extremely advanced, accurate and correct with their operations? How do actual MPPT chargers work?

The answer to the above issues is nowhere addressed comprehensively on the net, therefore I thought it necessary to provide with an in-depth explanation regarding the difference between ordinary charger controllers and actual MPPT.

Coming back to the above question, the answer lies in the fact that in linear regulator chargers the load is directly connected with the panel, with no intermediate buffer stage, causing inefficient power transfer and dissipation.

Whereas in MPPT drivers, the load is connected through an intermediate Buck Boost converter which efficiently alters the power conditions to the load depending upon the sunlight power on the panel, ensuring minimum loading of the panel and maximum power delivery to the load.

Basically MPPTs were developed to ensure that the net input wattage was consistently delivered to the output load regardless of the load compatibility with the panel.

How Buck Boost Topology Help MPPT Controllers to maximize Efficiency

This is primarily achieved with the help of a tracking SMPS buck boost technology.

Therefore we can say that it's the SMPS buck boost technology that forms the back bone of all MPPT designs and has provided with an extremely efficient option of configuring power regulation and supplying devices.

In MPPT charger controllers, the solar panel voltage is first converted into a high frequency equivalent pulsating voltage.

This voltage is applied into the primary of a well dimensioned compact ferrite transformer, which generates the required level of current at its secondary winding, matching the specified charging rate of the battery.

The voltage however may not be matching the battery charging voltage, therefore here an ordinary linear regulator is incorporated for fixing the voltage level correctly.

With the above set up the battery stays completely isolated from the solar panel, and gets efficiently charged even under bad weather conditions, since now the solar panel is allowed to operate without affecting or dropping its available instantaneous voltage under any given condition.

This helps to implement the intended maximum power point tracking effect, which is nothing but allowing the panel to operate under minimal loading yet making sure that the connected load gets the complete power required for its optimal performance.

It would be interesting to know how an SMPS prevents the panel or any source from getting loaded directly by the load.

The secret lies behind the use of the ferrite technology. Ferrite transformers are extremely efficient magnetic devices which saturate effectively to generate an efficient conversion from input to output.

Take the example of an ordinary 2 amp iron core transformer power supply and a 2amp SMPS.   If you load the two counterparts with full current that is with 2amps, you will find the iron core voltage dropping substantially whereas the SMPS voltage dropping only marginally or rather negligibly....so this is the secret behind the effectiveness of an SMPS based MPPT compared to a linear IC based MPPT charger controller.