MPPT stands for Maximum Power Point Tracking in Solar inverters. Solar inverters are the essential apparatus in a Solar power system that converts the DC power into AC.
The photovoltaic modules or PV modules in Solar panels produce DC power by absorbing sun rays. But most of the modern appliances run on AC. We need to convert the DC solar power into AC to run our lives. Here comes the solar inverter that does this job for us.
The inverter runs the energy produced by the PV system through a transformer to generate an AC supply. You may think this conversion is the only function of a solar inverter but wait!
Solar inverters show a lot more capability with Maximum Power Point Tracking (MPPT). If you don’t yet know what MPPT is or want to know more about it? This article is just for you!
Why Are Solar Inverters Essential?
Solar Power Systems consist of many components like PV panels, batteries, distribution lines, inverters, etc. Solar inverters are often referred to as PV inverters. They are considered as the brains of a Solar power project.
Inverters are one of the most particular constituents without which a modern-day Solar Power System cannot work. As the energy produced by the solar panels is DC, we need to somehow change it to consumable alternating current (AC) for residential or commercial use.
Inverters are used for this operation. DC energy generated by the Solar Panels comes to inverters and becomes easily usable AC. A body cannot exist without a brain. You will not be able to set up a fully functioning autonomous solar power system without an inverter.
What is MPPT in Solar Inverters?
Maximum Power Point Tracking or MPPT offers us maximized energy extraction from sources with variable energy. This method is invariant of any constraints.
Solar panels are made of photovoltaic cells or PV cells that generate electrical energy out of solar energy. But throughout the day, the Sun doesn’t shine equally, which means your solar panels do not get adequate sunlight to produce electricity that can meet up your needs.
Also, the solar panel and battery voltage changes as per weather conditions, resulting in deviation in power output efficiency. This problem can be addressed by an MPP tracker (Maximum Power Point Tracker).
An MPPT circuit constantly monitors and finds the optimal voltage-current array for which you can get maximum power all the time.
Role of Solar Inverters in Your Solar System:
Sunlight containing high-energy photons falls on the photovoltaic (PV) cells of the solar panels. Solar panels thus produce electric energy. If you look at the mechanism, it seems simple but superb! PV cells are typically made of extrinsic semiconductors like Silicon Arsenide (SiAs) or Gallium Arsenide (GaAs).
These doped semiconductors contain holes (positively charged) and electrons (negatively charged) in crystalline lattice space. When sunlight falls on the PV cells, these semiconductors absorb energy. When the charged carriers get enough energy, they come into motion. The motion of charged carriers (electrons or holes) is what we call electricity.
This free flow of charge generates Direct Current (DC). Once DC energy is produced, it goes to the inverters that transform it into AC. Else it is stored in Solar batteries for later use.
In our home workspace, we need AC to run all our appliances. Inverters pass the DC input to a transformer that discharges AC output. Inverters run direct current through two or more transistors that on-off very fast and feed the transformer’s two varying sides.
So, you can see how powerful solar inverters are in the Solar Power System. If we get an idea of MPPT in inverters, we can boost its functionalities.
How Does MPPT Work?
MPPT checks the best power output that your PV system can offer. Then MPPT adjusts the battery voltage and fixes the best voltage to get maximum current. MPPT sets the optimal array voltage-current ratio for grid-tied systems that give out maximum power to the inverters. The best favorable conditions for MPPT to do its job remarkably are-
- When the sky is cloudy or, low sunlight is falling on the earth
- When the battery charge is very low.
If excess voltage is available from the PV, MPPT converts it to the current fed to the batteries.
Get to know more about MPPT vs. PWM in our other post!
Understand the Voltage-Current Graph
Now you see the voltage of the solar panels varies with external factors like weather, temperature. Current through the panels also changes with variable voltage. We can draw an I-V curve to get a visual of it.
The above graph is a standard example of how voltage-current characteristic works. Here the maximum power point lies at the bending of the curve. Generally, the maximum power point means the optimal value of voltage and current that drives the panels’ maximum power are different throughout the day.
The Maximum Power Point Tracker (MPPT) fixes those optimal values.
Keeping up the Maximum Power Point
So, your MPPT successfully finds out the maximum power point that is the best combination of voltage-current that provides you maximum power out of your Solar system. But that is not enough.
Finding the values doesn’t do the job. It has to constantly trick the panels by varying inverter resistance to maintain the desired voltage. It is an unstoppable full-time job.
You know the panel voltage changes continuously with solar irradiance and temperature, right? Then imagine how occupying MPPT’s job is! It actually deals with an infinite number of sets of current-voltage (I-V) for different irradiance and temperature. But it never fails to give you the maximum power out of your system appreciating the MPPT technique.
Dual vs. Single MPPT
We can already see the benefits of the MPPT technique. Using more than one MPPT is always better. Dual MPPT allows you to use multiple arrays with different azimuths and angles and is less susceptible to partial shading. You don’t need a second inverter if you use a dual MPPT inverter. It allows solar panels to work at their highest potential.
A single MPPT inverter will become highly inefficient to work for more arrays with different azimuths. So simply for systems involving two or more strings, dual MPPT is more convenient.
We can see this via a table:
Operation with Batteries
All solar power systems do not have batteries in common. For grid-tied PV systems, there is no need to install a battery. So, you simply didn’t buy any. But for off-grid PV systems, it is essential to buy and install a properly sized battery to get an uninterrupted power supply. Here we can look at how MPPT technology operates with batteries and whether MPPT has anything to do with the battery system.
Well, yes, MPPT helps to resolve an issue when batteries are not fully charged. When batteries are fully charged in an off-grid PV system, the voltage stays close to the maximum power point voltage. But when batteries are partially charged (low charge), the voltage gets low. MPPT adjusts the load resistance or the inverter resistance to maintain the maximum power peak.
When batteries are fully charged, and production exceeds load, MPPT can not maintain a power peak as there is no load to absorb the excess power. MPPT shifts the operating point of the I-V (current-voltage) characteristics from the peak value until the production equalizes demand.
In an on-grid system, things are less complicated. The excess production is back-fed to the grid so, MPPT keeps the maximum power point constant.
Multi MPPT Inverters
If you have your solar panels across multiple roofs with different azimuths and various solar tilt angles, solar inverters with multiple MPPT are a prominent choice for you.
In this case, your panels will not get an equal amount of solar energy, so the I-V characteristics for each panel are different. You still intend to get the maximum power out of your system. Don’t worry! A multi MPPT inverter uses one maximum power point tracker for each one of the panel arrays.
Makers of these devices always keep your benefit in mind. Using a multi MPPT inverter, you can continue extracting maximum power and stay benefited.
PV panels show different voltage-current levels under partial shading conditions (PSC). The power vs. voltage curve (P-V) exhibits multiple peaks under PSC.
Global maximum power point (GMPP) tracking is a process to extract maximum power from the solar panels, i.e., photovoltaic cells under any atmospheric condition. But if the panels face shading, the MPP technique tracks the local MPP and fails to track global MPP.
The classical Maximum Power Point Tracking (MPPT) algorithm can’t reach the global MPP under shading conditions. Almost 6% of energy gets lost due to shading and irradiance of sunlight. According to a study in 2019, different PV systems show different efficiency under weather obstructions.
But sometimes, your solar panels can produce 70% less power when they fail to detect the maximum power point. Well, you can handle this situation in two ways. One is to improve the conventional MPPT algorithm by implementing complex programs. Another is to use topologies based on AI and intelligent computing methods.
MPPT vs. PWM
There are mainly two types of solar efficiency controllers, PWM and MPPT. PWM or Pulse Width Modulation is the charge controller that has a direct connection from the solar array to batteries. This device uses a rapid ‘switch’ (transistor) to modulate the battery charging.
After the battery reaches the absorption charge voltage, the open switch starts to open and close hundred times per second to modulate the current and maintain the battery voltage at a fixed value.
The major problem with these PWM devices is the solar panel voltage comes down to match the battery voltage. Because of this, the panel voltage drifts away from the optimum operating voltage (Vmp), hence reducing the power output and the efficiency of your solar panels.
However, for small 12V systems with one or two panels, PWM solar charge controllers are usable. Simple functions like USB charging, camping, or solar lighting can be performed using this type of system.
On the other hand, Maximum Power Point Trackers or MPPTs are based on an advanced technique that helps the solar panels to operate at their maximum power point, i.e., it keeps the panel voltage at a specific value that gives out maximum power. Depending upon the battery voltage and the operating voltage of the solar panel (Vmp), MPPT can help you to acquire almost 30% more efficiency.
The AERL company first introduced MPPT charge controllers in 1985. Today mostly all grid-tied solar inverters and charge controllers use the MPPT technique. So don’t you think MPPT in solar inverters is just the most beneficial thing for your solar power system!
This simple yet stunning technique allows solar panels to work on a preferable voltage and current combination to produce maximum power irrespective of varying degrees of sunlight.
Quick View on MPPT for Everyone
If all these explanations seem a bit heavy, here is an analogy that will help you understand the MPPT concept. Imagine placing your thumb over the open end of a hosepipe.
If you intend to get the maximum power of a water stream to hit something at a distance, all you have to do is cover the hole of the hosepipe with your hand to reduce the size of the hole. Now, if you cover too much, you will get a fine mist of water coming out because of less power, and if you cover less, you will get good water flow, but it’ll not travel far.
Between these two points, there is a point where the water stream coming out of the hosepipe can go a wanted distance. In our case, that is the Maximum Point.
As our analogy, a Maximum Power Point Tracker (MPPT) changes the inverter resistance to maximize the power out of our PV panels. An MPPT in your inverter has to constantly change and adjust the electrical resistance of the solar inverter as the variation of weather, strength of sunlight. So, briefly, MPPT is a feature that ensures maximum power draw out of your Solar panels despite any situational constraints.
If you wish to take a step to make your planet healthier and habitable for many more years, you can start using renewable energy sources. And among all, Solar energy is very famous, you must admit.
Until now, it seems that you got an idea of how important and brilliant the MPPT mechanism is. It makes your solar system intelligent and efficient. It presents you with maximum power out of your renewable energy production system.
As you have to use an inverter to get AC power from the system, why not use an MPPT inverter? The cost of an MPPT inverter is not going to dig a hole in your pocket! Also, all off-grid solar inverters have the MPPT feature in them.