What is a PWM Inverter : Types and Their Applications
PWM inverter function on the principle of pulse width modulation technique. The PWM inverter can switch on and off the IGBT at much faster rate. Thus, it is possible to get almost perfect sinusoidal voltage, with a very low harmonic distortion.
Power Inverter is a power electronics device that converts DC signal into AC signal. It is a static device that transforms power from a dc source (like Battery, PV panel) to the AC load. Unlike an AC generator, the inverter is compact in size.
The primary applications of the power converter are for feeding high current and voltage. The circuit used for the same applications in an electronic circuit (lower current and voltage) is called oscillators. The rectifier performs the reverse action of an inverter.
What is a PWM Inverter?
The invention of rectifiers and inverters was a revolutionary in electrical engineering. Further, the invention of the inverter leads to a new era of power generation from PV panels. Nowadays, the inverter is the key controlling device in power generation. The Inverters are widely used for converting solar PV cell DC voltage into AC voltage. Also, PWM inverters are widely used in variable frequency drives.
PWM stands for pulse width modulation. The width of the pulse is varied maintaining an instantaneous magnitude the same as the input. PWM is a switching technique that controls pulse width by tuning switches between supply and load. The frequency of the switching process is very high therefore it does not affect the load. For this reason, the PWM technique is most suitable for the inertial loads(motor).
PWM technique is superior to the other conventional switching techniques. The advantage of using the PWM technique is that we can vary the magnitude and frequency of the output voltage without increasing the number of stages. Therefore, it is possible to eliminate some of the lower order harmonics and thus, this improves the quality of the output waveform reducing the filtering requirements.
Single Pulse Width Modulation
This is a PWM technique in which there is only one pulse present in each half cycle of the output waveform. In this technique, the comparator circuit first compares the carrier and reference signal and outputs the signal for switching of IGBT or power transistor. The frequency of the reference/modulating signal is the deciding factor for the frequency of output voltage.
There are two types of single pulse width modulation techniques depending upon the type of carrier signal.
Type-I
In this type of SPWM(Single Pulse width modulation), the maximum magnitude of the carrier signal coincides with the starting point of the modulating signal. And, the switches get on for the period when AmAc.
Type-II
In this type of SPWM maximum magnitude of the carrier signal coincides with the starting point of the modulating signal. and, the switches get on for the period when Amc.
Here, delta (Δ) can be varied by varying the magnitude of the carrier signal or modulating the signal without changing frequency. The ratio of the amplitude of the reference signal to the carrier signal is called the modulation index.
From Fourier analysis of the output voltage waveform, the output voltage is;
Where n is the number of harmonics. The output voltage is free of even order harmonics because of HWS (Half wave symmetry). To eliminate any specific harmonic value can be adjusted to make Sine term zero.
Multiple Pulse Width Modulation
In multiple pulse width modulation, there is more than one pulse present in each half-cycle. The width of each pulse is the same and can be varied by varying amplitude of carrier signal. The frequency of reference signal decides the frequency of the output signal. In this method, harmonics distortion is less in comparison to the previous one. The carrier frequency decides the number of pulses per half cycle.
The number of pulses per half cycle is
According to the above-given figure,
The total pulse width per each half cycle is
RMS voltage of the output is ;
From Fourier representation of output voltage is;
Sinusoidal Pulse Width Modulation
In this type of technique, the sinusoidal signal is the reference signal, and the triangular signal is the carrier signal. The number of pulses increases in each half cycle which improves the quality of output. Therefore, the lower order harmonics decreases. The higher-order harmonics increase, however, we can easily filter out these harmonic orders. There are three types of Sinusoidal PWM techniques.
Type-I
The zero of the carrier coincides with the zero of a reference signal
In the above figure, the sinusoidal signal is a reference signal, and the triangular signal is a carrier signal.
The number of pulses in each half cycle is;
Type-II
The peak of the carrier coincides with the zero of the reference signal
In this case, the number of pulses per half cycle is;
The output voltage is directly proportional to the modulation index(m=Am/Ac)
The output voltage is directly proportional to the modulation index and input dc voltage, RMS voltage can be varied by varying modulation index and the instantaneous voltage can be varied by changing DC input voltage. Thus, the PWM inverter can vary the output voltage and frequency simultaneously.
Type-III
In this type of PWM technique, we maintain the modulation index greater than one, for which AC output voltage remains almost constant. The output waveform looks like a simple square wave. This is also called a case of Overmodulation (m 1).
The Definitive Guide to Solar Charge Controllers: MPPT and PWM Charge Controllers in Off-Grid Solar Power Systems
A solar charge controller, also known as ‘charge regulator’ or solar battery maintainer, is a device that manages the charging and discharging of the solar battery bank in a solar panel system.
Preventing the battery from overcharging is important merely because the voltage generated by even a 12V solar panel is actually higher – between 16 and 20V.
Such voltages are too high for 12 V batteries (which get fully charged at voltages around 14-14.5V), since they can reduce the battery lifespan and even damage the battery.
Thus, in case of a solar array of a higher voltage (by using a 24V panel or by connecting two 12V solar panels in series), the solar charge controller is a must.
Here are listed the main functions of the charge controller in a solar panels system:
– Taking care that the battery bank is not getting overcharged during the day.
– Preventing the electricity stored in the battery to get back to the solar array at night.
– Managing how much power is drained from the battery by the appliances connected to it, and if necessary, disconnecting these loads from the battery, again to prevent it from overdischarging.
To summarize, the charge controller is the manager of the battery power.
Here are other important features of solar charge controllers:
– Regulating the power sent from the solar array to the battery according to the battery state of charge. This extends battery life.
– Low-voltage disconnect (LVD) – disconnecting the load(s) plugged in case of a low battery state of charge and reconnecting the loads when the battery is charged again. The LVD function is ideal for the relatively small loads that are used in RV solar systems.
– Reverse current protection – preventing the battery from being drained by the solar panels at night when the panels cannot charge the battery.
– Control display panel – showing the battery bank voltage and state of charge, as well as the current coming from the solar array.
Which types of solar charge controllers are the most widely used?
There are two main types of charge controllers – PWM (‘Pulse Width Modulation’) and MPPT (‘Maximum Power Point Tracking’) ones.
They are very different from each other since they are based on different principles of operation.
In general, while PWM controllers cost less and are used in small solar panel systems, MPPT charge controllers are used in larger solar power systems, are more advanced, and cost more.
What is a PWM charge controller?
PWM controllers make a direct connection between the solar array and the battery bank.
PWM controllers use Pulse Width Modulation to charge the battery.
A PWM controller does not send a steady output but rather a series of short charging pulses to the battery.
Depending on the battery’s current state of charge, the controller decides how often to send such pulses and how long each one of them should be.
For a nearly fully charged battery, the pulses will be short and rarely sent, while for a discharged battery they will be long and almost constantly sent.
PWM controllers are suitable for small off-grid solar panel systems, of low powers and low voltages – that is, where you have less to use as power and efficiency. These solar controllers are often used in 12V RV solar power systems as a cost-efficient RV solar battery maintainer as well.
PWM solar charge controllers are less expensive than their more advanced MPPT counterparts but they have a distinctive drawback – they create interference to radio and TV equipment due to the sharp pulses generated for the battery bank charging.
In the daytime, when the battery is being charged by the solar panels, the PWM controller brings down the solar array generated voltage down to the battery voltage, which for most typical off-grid systems is as less as 12V DC.
The solar generated voltage of a 12V DC solar panel should be higher, in order to be able to charge the battery, and it is about 17-18V. 24V DC solar panels, however, generate a voltage of 36V DC.
If you connect 24V DC solar panels to a 12V DC battery, a PWM charge controller is going to bring down the voltage to as low as 12V DC, which means that you lose a part of your solar-generated electricity in the charge controller.
If you need to feed a voltage from 24V DC solar panels to a 12 VDC battery without thereby losing of what has been generated, you need a ‘step-down’ feature offered by the MPPT charge controllers.
Most PWM charge controllers do not offer such a step-down feature.
So, with a PWM controller, if the output voltage of the solar array is 24V (which can be achieved either by a single 24V solar panel of by two 12V solar panels wired in series), the voltage of your battery bank should also be 24V, since:
– If you use a battery bank of a lower voltage (e.g. 12V), you are going to lose a half of the solar-generated electricity;
– If you use a battery bank of a higher voltage, you will use all the potential of the solar array without being clear whether it’ll anyway be able to fully charge the battery in due time.
What is an MPPT charge controller?
The Maximum Power Point Tracking feature enables the input power of an MPPT controller to be equal to its output power.
Therefore, if the output voltage of the solar array (24V, 48V or more) is higher than the battery bank voltage (which is usually 12V), an MPPT controller brings it down to 12V but compensates the ‘drop’ by increasing the current, so that the power remains the same.
Since you don’t lose the solar-generated power, MPPT controllers provide you with the flexibility to connect many solar panels in series thus increasing the total voltage of the array without being afraid of losing a part of the solar-generated power.
The principle of MPPT is squeezing the maximum possible solar-generated power from a solar panel by making it operate at the most efficient combination of voltage and current, also known as ‘maximum power point’.
An MPPT charge controller converts the solar-generated voltage into the optimal voltage so as to provide the maximum charging current to the battery.
The main purpose of the MPPT solar charge controller is not only to prevent your solar power system from losing from the solar-generated power but also to get the maximum power from the solar array.
An MPPT solar charge regulator forces a solar panel to operate at a voltage close to its maximum power point.
Another benefit of an MPPT controller is that it reduces the wire size (gauge) needed for the wires connecting the solar array to the controller.
This is due to the wide input voltage range which allows you to connect many solar panels in series, which increases the voltage but the amps stay the same.
MPPT controllers are more expensive than PWM ones but also more efficient in terms of adding additional losses to the system.
Lots of MPPT controllers available on the market add just 2% to the overall losses of your off-grid system.
What happens when you connect higher voltage panel(s) to a non-MPPT charge controller?
If you connect a 24V solar panel (where maximum voltage can be as high as up to 36V), the non-MPPT (also known as ‘standard’) charge controller brings the solar generated voltage down to the 12V battery charging voltage, which is 13.5-14.5V.
Thus, however, you are going to lose a lot of power, as reducing the solar generated voltage would not result in increasing the solar-generated current.
For example, if you have a 100Wp solar panel generating nominal voltage 36V and nominal current 2.78 A (36V x 2.78A = 100W), after connecting it to a standard (let’s say a PWM) controller, it brings the voltage down to 14V, while the amps will be the same, as a standard controller cannot do MPPT tracking (as MPPT solar charge regulators can). Therefore, at the output of such a controller, your solar power will be as low as 2.78A x 13.5V = 37.5W, which is a significant loss of almost 64%!
So, to get the full power generated by the solar array, you need an MPPT controller.
What you get as a bonus is that MPPT controllers have a wide enough range of the input voltage – up to 120-150V DC, which enables you to connect a larger number of panels in series.
In off-grid systems, this is usually done for the sake of working with low amps and wires of a smaller gauge for connecting the solar panels. If we consider the above example, an MPPT controller will reduce the voltage to 13.5V but increases the current up to 100W / 13.5V = 7.4 amps.
Here is when MPPT controllers are the most effective:
– In case of long wire runs between the solar panels and the battery.
Long wires always mean higher voltage drop and loss of power, which could make charging a 12V battery from a solar array of just 12V output voltage a challenging task. A way to overcome this is to use a larger cross-section wire (low wire gauge), which is always expensive.
If you, however, connect four solar panels in series, the overall voltage of the solar array would increase (from 12V to 48V), so what comes to the controller as voltage would still be high enough to charge the battery.
– In extreme (i.e. either cold or very hot) weather – low temperatures are better for the solar panels to work at but without an MPPT controller, you cannot take advantage of this.
– Under low irradiance, where the output voltage of the solar array can drop dramatically.
– Upon low battery state of charge – a lower battery voltage means a higher charging current provided by the MPPT controller to the battery so that it can get fully charged within a short time.
Do you always need a solar charge controller?
As mentioned above, the lack of a solar battery maintainer would expose the battery bank to frequent overcharges and overdischarges, which would dramatically reduce its lifespan.
This is especially valid for sealed batteries, where the charge controller is really a must.
Otherwise, such a sealed battery can either get damaged or become a safety hazard.
However, you do not need a solar battery maintainer, if you have a solar panel of very low power – below 10Wp – and a battery of 100 amp-hours of capacity or greater.
It is sure that such a low-power panel is not capable of overcharging such a high capacity battery.
On the other hand, a large battery capacity guarantees that the battery bank is never fully discharged.
This is only valid if the load is always connected to the above mentioned solar configuration – a 10W solar panel and a 100 Ah battery bank.
In practice, if this configuration is installed at a boat or recreational vehicle (RV), it’s very probable that the load might be turned off for weeks, and there is a risk of possible overcharging.
So, if you have a boat or a RV, or for whatever reason you turn off the loads from the solar system with a high capacity bank for a very long time, you should consider using a solar charge regulator.
Which solar charge controller is the best?
Selecting the ‘right’ type of charge controller does not mean to decide which charge controller technology is better – the PWM one or the MPPT one – but rather to estimate which type of these would be more suitable for your solar system.
The idea is not only to avoid building a system that will not perform well but also save money on buying a costly device that you don’t actually need.
Which charge controller is the best?
How to select your solar charge controller?
Upon selecting a solar panel charge controller regulator, you should consider mainly:
What kind of solar battery maintainer to choose depends on the specific case and is a tradeoff between maximizing the solar generated power and extending the battery life.
PWM controllers are less expensive.
They are very suitable for small wattage solar electric systems.
Furthermore, their efficiency is similar to the MPPT solar panel battery regulator charge controller in hot climates.
An improperly selected charge controller can result in a 50% loss of the solar generated power in a mobile solar panel.
This is a common mistake usually made with charge controllers by owners of caravans, campers, RV and motorhomes.
They get a high voltage solar panel at the lowest cost per Watt and connect this solar panel or these solar panels to a PWM charge controller, and subsequently lose almost 50% percent of the available solar power.
Here is an example of how such a situation can occur.
Let’s consider a 220Wp solar panel with:
Let’s assume such a solar panel connected to a simple mobile solar power system consisting of a solar panel charge controller and a 12V battery bank.
A PWM charge controller is sized in regard to the current delivered by the solar array.
This means that the PWM charge controller delivers a charging current of 7.56A to a 12V battery bank.
If you neglect all the losses of the components of this solar power system, the PWM will only deliver 7.56 x 12V = 90W of power to the battery bank.
Thus you can lose about 130W of the available solar panel’s 220W power!
If you use a Maximum Power Point Tracking (MPPT) charge controller, the current provided to the battery bank increases up to 220W / 12V = 18.3A by such controller.
Such a boost in amps is produced by a current booster, which is an embedded part of every MPPT charge controller.
In this case, the battery bank receives 18.3A x 12V = 220W of power.
In an ideal case with no component losses, all solar panel generated power will be stored in the battery bank.
Therefore, if you want to minimize the power losses with a PWM charge controller, you should always connect a solar panel with maximum power point voltage Vmpp voltage closer to the battery bank’s voltage.
The second option is to consider the usage of an MPPT charge controller.
Although being the most expensive, its high efficiency will pay off in the long run.
Charge controller sizing
The main task of sizing the charge controller is calculating the solar array’s voltage and current, and use the calculated values to select the matching model.
Above all, however, you should determine what type of solar charge regulator would be optimal for your system, so that you neither pay more money than you actually need, neither buy a device that could possibly make your system underperform or even damage any of the other components.
When sizing the charge controller, a safety factor of 1.25 should be used.
By this factor, the maximum input voltage and current of the controller are additionally increased by 25%, so that the controller would be able to meet some sporadic increases in voltage and current due to high temperature, light reflection, etc.
1) Sizing a PWM charge controller
When sizing a PWM power controller, here are some basic principles to follow:
- If the nominal voltage of a PWM charge controller is not equal to the nominal voltage of the solar array and the battery bank, you are going to lose a part of the solar generated power.
- The solar charge regulator must sustain the maximum current of the solar array at the maximum ambient temperature.
- The maximum voltage of the solar array must be lower than the maximum input DC voltage of the controller. Otherwise, the controller might get damaged at the lowest ambient temperature.
- The DC voltage of the solar array must always be higher than the controller’s minimum DC voltage; this rule will ensure that the PWM controller will always work and track the solar array at the highest ambient temperature.
Mind that if the solar array only consists of solar panels wired in parallel, the solar array voltage is equal to the voltage of a standalone solar panel, while the solar array current will be a sum of the currents of the standalone panel.
Upon sizing the charge controller, here are the essential parameters of a single solar panel that are to be considered:
– Voc – the maximum open-circuit solar panel voltage at the lowest ambient temperature and the minimum open-circuit voltage at the highest ambient temperature.
– Isc – the solar panel short-circuit current at the highest ambient temperature.
In our book ‘Off Grid and Mobile Solar Power For Everyone: Your Smart Solar Guide’ you can find the details on PWM controller sizing, both for a residential and a mobile solar panel system.
You can use our free PWM solar charge controller calculator to select the best PWM charge controller for your system as well.
Please don’t forget to read the help file below the calculator along with accompanying demo examples.
2) Sizing an MPPT charge controller
Most common charge controllers have an output voltage of 12V, 24V or 48V.
The input voltage and current ratings are typically up to 60V and up to 60 A, accordingly.
With MPPT controllers, however, the input voltage range can boost up to 150V, which gives you more freedom to connect many solar panels in series, especially in larger solar panels systems.
Here are some simple steps how to select the MPPT charge controller size for your off-grid system:
– Find out the installed solar power Wp of the solar array.
– Find out the charge current Ic by dividing the Wp by the system voltage. For off-grid solar panels systems, it is often 12V.
– Find out the maximum charge current Icmax by multiplying the Ic by 1.2 (the NEC safety factor mentioned above).
– Find out the nominal voltage of the solar array Vmp_array. What matters here is how many panels are connected in series. You get the Vmp_array by multiplying the voltage of a single panel
Vmp_panel by the number of panels connected in series. For the controller to be able to handle the solar array, the Vmp_array should be within the input voltage range of the controller.
– Check out that the maximum voltage of the solar array Voc_array does not exceed the maximum input voltage of the controller.
Similarly to the above, you get Voc_array by multiplying the open circuit voltage of a solar panel Voc_panel by the number of panels connected in series.
It should be noted that solar manufacturers offer sizing tools for solar charge controllers. These tools can help you select the right size of the charge controller for your off-grid system.
You can find a step-by-step guide on how to size an MPPT charge controller, along with all formulas needed, in our book ‘The Ultimate Solar Power Design Guide: Less Theory Practice’.
Commonly made mistakes during charge controller installation
Let’s assume you’ve found the right type and size of charge controller for your off-grid residential or mobile solar power system. Your next step is to plug it into the system together with the other components.
As you know, wires and connections are the veins of every solar panel system. Here are some common rules you must keep while plugging your charge controller:
- Only DC loads should be connected to the charge controller’s output. AC loads should be connected to the inverter’s output.
- Certain appliances, such as low-voltage refrigerators, must be connected directly to the battery.
- In a small DC system with a charge controller, you do not need any fuses other than the one embedded in the charge controller. In larger DC systems, you need to provide a fuse on the positive terminal of the battery.
- The charge controller should always be mounted close to the battery since precise measurement of the battery voltage is an important part of charge controller’s functions. Therefore, even the smallest voltage drops must be avoided.
- A common charge controller has three terminal connections – for the array, for the battery, and for the DC loads. The charge controller disconnects the battery to prevent it from overcharging and disconnects the DC loads connected to the controller ‘DC load’ terminal to prevent the battery from overdischarging.
- Every device connected directly to the battery instead of the ‘DC load’ terminal of the charge controller renders the charge controller battery’s overdischarching prevention function useless.
- The inverter should be directly connected to the charge controller ‘DC load’ terminal.
- When connecting the inverter to the charge controller ‘DC load’ terminal, check in the charge controller data sheet whether this terminal is powerful enough to provide the input current to the inverter. Otherwise, connect the higher power inverter directly to the battery bank. In such a case, you will render the charge controller’s function that prevents the battery from overdischarging useless.
Cheap charge controllers have a low-current ‘DC load’ terminal.
Therefore, their only function is preventing the battery from overcharging.
You can only connect a low-power 12V lamp or other low-power DC device to this terminal.
This terminal switches off to prevent the battery from overdischarging.
In such a case, you should connect the rest of the DC loads directly to the battery, as there is no way to disconnect them from the battery in case of overdischarging.
There is a strict sequence to follow upon introducing the charge controller to the solar electric system while connecting and while disconnecting the wires between the solar panel, charge controller, and battery bank:
If the battery is not connected to the charge controller first, higher solar panel voltage can damage the load.
- Pop MSE, Lacho, Dimi Avram MSE, 2018, Off Grid and Mobile Solar Power For Everyone: Your Smart Solar Guide. Digital Publishing Ltd
- Pop MSE, Lacho, Dimi Avram MSE, 2015, The Ultimate Solar Power Design Guide: Less Theory Practice. Digital Publishing Ltd
- Pop MSE, Lacho, Dimi Avram MSE, 2017, The New Simple and Practical Solar Component Guide. Digital Publishing Ltd
- Pop MSE, Lacho, Dimi Avram MSE, 2016, Top 40 Costly Mistakes Solar Newbies Make: Your Smart Guide to Solar Powered Home and Business, Digital Publishing Ltd
Lacho Pop, Master of Science in Engineering
Lacho Pop, MSE, holds a Master’s Degree in Electronics and Automatics. He has more than 15 years of experience in the design and implementation of various sophisticated electronic, solar power, and telecommunication systems. He authored and co-authored several practical solar books in the field of solar power and solar photovoltaics. All the books were well-received by the public. You can discover more about his bestselling solar books on Amazon on his profile page here: Lacho Pop, MSE Profile
About Me
Lacho Pop, Master of Science in Engineering
Lacho Pop, MSE, holds a Master’s Degree in Electronics and Automatics. He has more than 15 years of experience in the design and implementation of various sophisticated electronic, solar power, and telecommunication systems. He authored and co-authored several practical solar books in the field of solar power and solar photovoltaics. All the books were well-received by the public. You can discover more about his bestselling solar books on Amazon on his profile page here: Lacho Pop, MSE Profile
Blog Table of Contents
- Mixing solar panels – Dos and Don’ts
- Types of Solar Panels – Pros and Cons of the Most Used PV Solar Panels
- How to Choose The Best Solar Panels for Your Solar Power System
- Do Solar Panels Save You Money?
- How Many Solar Panels Do I Need?
- Free Solar Panels: What’s The Catch
- What Are Solar Panels Made Of- How Do Solar Panels Work
- Where Are Solar Panels Used
- Which Solar Panels Are Best For Camping?
- Solar Panels For RV
- Solar Panels For A Caravan: What Is The Best Type
- The Best Solar Panel For a Motorhome
- Solar Panels Mounting Exposed
- Essential Guidelines on Mobile Solar Power for RVs, Caravans, Campers or Boats
- Solar Power Systems For Your Home Or Business
- Solar Power Systems Unveiled: The Definitive Gide
- 15 Blunders That Can Ruin Your Solar Power Project
- Solar Power System Components Demystified
- What Are The Problems With Solar Power
- Solar Energy
- Uses of Solar Energy
- What Is the Cost of Using Solar Energy
- Energy Efficiency and Going Solar
- Solar FAQs
- Can Solar Panels Power a House?
- How to Perform a Solar Site Survey: Costly Solar Mistakes Related to Solar Site Survey
- Preparing For Solar-Important Tips Before Going Solar
- The Ultimate Off-Grid and Mobile Solar Power Bundle: 2 Books in 1
- Off-Grid Solar and RV Solar Power For Everyone
- The Ultimate Solar Power Design Guide: Less Theory Practice
- The Truth About Solar Panels Book
- The New Simple And Practical Solar Component Guide: Your Personal Solar Advisor
- 40 Costly Common Solar Power Mistakes Exposed
- Solar Power Demystified Free Book
- Free Ebook: Solar Panel Basics Exposed
- Free Ebook: Top 20 Solar Mistakes
- The Definitive Guide to MPPT and PWM Charge Controllers in Off-Grid Solar Power Systems
- PWM Charge Controller Calculator
- Solar Battery Monitors Demystified: Battery Monitor For RV And Off-Grid Solar Power Systems
- Solar Load Calculator For Off-Grid and RV Solar Power Systems
- Free Solar Panel Calculator For Off-GridOn Grid Solar Systems
- Free Solar Cable Size Calculator
- Free Solar Battery Calculator: Calculate Fast Easy The Solar Battery Bank Capacity And The Number Of Batteries In Series Or Parallel
- Free PWM Charge Controller Calculator
- Solar Panel Output Calculator- Estimate the Real Energy You Can Get From Your Solar Panels
- Solar Sizing Software
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MPPT vs PWM | The two major types of solar charge controllers are:
As shown in the chart below, PWM controllers tend to be smaller and they operate at battery voltage, whereas MPPT controllers use newer technology to operate at the maximum power voltage. This maximizes the amount of power being produced which becomes more significant in colder conditions when the array voltage gets increasingly higher than the battery voltage. MPPT controllers can also operate with much higher voltages and lower array currents which can mean fewer strings in parallel and smaller wire sizes since there is less voltage drop.
PWM controllers need to be used with arrays that are matched with the battery voltage which limits what modules can be used. There are many 60 cell modules with maximum power voltage (Vmp) equal to about 30V, which can be used with MPPT controllers but are simply not suitable with PWM controllers.
To answer the question: Which is better, PWM or MPPT? All things being equal, MPPT is a newer technology that harvests more energy. However, the advantages of MPPT over PWM controllers come at a cost, so sometimes a less expensive PWM controller can be the right choice, especially with smaller systems and in warm climates where the MPPT boost is not as significant.
PWM vs. MPPT Solar Charge Controller Comparison
| Array voltage is “pulled down” to battery voltage | Convert excess input voltage into amperage |
| Generally operate below Vmp | Operate at Vmp |
| Suitable for small module configurations | Suitable for large module configurations that have a lower cost per watt |
| Often chosen for very hot climates which will not yield as much MPPT boost | Provide more boost than PWM, especially during cold days and/or when the battery voltage is low |
Every Morningstar PWM and MPPT solar charge controller is listed on the Morningstar Product Series page. Each listed product is hypertext linked to its product page that includes datasheets, operation manuals, and other helpful information.
PWM Charging
Traditional solar regulators featuring PWM (Pulse Width Modulation) charging operate by making a connection directly from the solar array to the battery bank. During bulk charging when there is a continuous connection from the array to the battery bank, the array output voltage is ‘pulled down’ to the battery voltage. The battery voltage adjusts slightly up depending on the amount of current provided by the array and the size and characteristics of the battery.
MPPT Charging
Morningstar MPPT controllers feature TrakStar technology, designed to quickly and accurately determine the Vmp (maximum power voltage) of the solar array. TrakStar MPPT controllers ‘sweep’ the solar input to determine the voltage at which the array is producing the maximum amount of power. The controller harvests power from the array at this Vmp voltage and converts it down to battery voltage, boosting charging current in the process.
Why Choose PWM Over MPPT
The preceding discussion of PWM vs. MPPT may cause some to wonder why a PWM controller would ever be chosen in favor of an MPPT controller. There are indeed instances where a PWM controller can be a better choice than MPPT and there are factors which will reduce or negate the advantages the MPPT may provide. The most obvious consideration is cost. MPPT controllers tend to cost more than their PWM counterparts. When deciding on a controller, the extra cost of MPPT should be analyzed with respect to the following factors:
Low power (specifically low current) charging applications may have equal or better energy harvest with a PWM controller. PWM controllers will operate at a relatively constant harvesting efficiency regardless of the size of the system (all things being equal, efficiency will be the same whether using a 30W array or a 300W array). MPPT regulators commonly have noticeably reduced harvesting efficiencies (relative to their peak efficiency) when used in low power applications. Efficiency curves for every Morningstar MPPT controller are printed in their corresponding manuals and should be reviewed when making a regulator decision. (Manuals are available for download on the Morningstar website).
The greatest benefit of an MPPT regulator will be observed in colder climates (Vmp is higher). Conversely, in hotter climates Vmp is reduced. A decrease in Vmp will reduce MPPT harvest relative to PWM. Average ambient temperature at the installation site may be high enough to negate any charging advantages the MPPT has over the PWM. It would not be economical to use MPPT in such a situation. Average temperature at the site should be a factor considered when making a regulator choice
Systems in which array power output is significantly larger than the power draw of the system loads would indicate that the batteries will spend most of their time at full or near full charge. Such a system may not benefit from the increased harvesting capability of an MPPT regulator. When the system batteries are full, excess solar energy goes unused. The harvesting advantage of MPPT may be unnecessary in this situation especially if autonomy is not a factor.
Why Choose MPPT Over PWM
Increased Energy Harvest:
MPPT controllers operate array voltages above battery voltage and increase the energy harvest from solar arrays by 5 to 30% compared to PWM controllers, depending on climate conditions.
Array operating voltage and amperage is adjusted throughout the day by the MPPT controller so that the array’s power output (amperage X voltage) is maximized.
Less Module Restrictions:
Since MPPT controllers operate arrays at voltages greater than battery voltage, they can be used with a wider variety of solar modules and array configurations. over, they can support systems with smaller wire sizes.
Support for oversized Arrays
Unlike PWM controllers, MPPT controllers can support oversized arrays that would otherwise exceed the maximum operating power limits of the charge controller. The controller does this by limiting the array current intake during periods of the day when high solar energy is being supplied (usually during the middle of the day).
While energy from the array is capped or shaved off during the middle of the day, the oversized array is able to provide more power during teh early and late part of the day compared to smaller non-oversized array.
Download Our PWM vs MPPT White Paper
Please click here to download the Traditional PWM vs Morningstar’s TrakStar™ MPPT Technology white paper. Morningstar’s MPPT charge controllers use the TrakStar advanced control MPPT algorithm to harvest maximum power from a Solar Array’s peak power point. It is generally accepted that even the most basic MPPT controller will provide an additional 10‐15% of charging capability, when compared to a standard PWM regulator. Besides this extra charge capability, there are several other important differences and advantages between MPPT and PWM technologies that are outlined in this whitepaper.
What is the Difference Between PWM and MPPT Solar Charge Controllers?
When do you require a solar charge controller? As the name suggests, a solar charge controller modulates the current amperage (thus, the voltage too) moving towards the batteries from the solar panels. It is a regulator that prevents the batteries from overcharging. Overcharging can cause heating and explosion, posing a safety risk. Heating also reduces the efficiency of the system. over, when the batteries are discharging to provide power to your household, the controller regulates the rate of discharge to match the requirement. Hence, a solar charge controller is an important part of the installation.
Do you need a solar charge controller or not?
Now, if you are wondering whether you need a solar charge controller or not, here is what you should know. Every solar panel instalment needs a solar charge controller. However, the overall system determines whether you need a solar inverter with an inbuilt charge controller or an additional charge controller.
Pulse Width Modulation (PWM)
This Pulse Width Modulation type is cheaper, and hence, commonly used for off-grid solar solutions in households and commercial applications. A 12V solar panel can charge a 12V battery. Two 12V panels wired in series, or a single 24V panel, is needed for a 24V battery bank, and so on.
PWM requires you to match the voltage of the panel array to that of the battery bank. Otherwise, there will be a loss of charging power. And the greater the mismatch, the greater will be the loss of power. So, PWM is cheaper but comes with less flexibility and efficiency.
Advantages: PWM controllers are time-tested as they have been around for long. Cheaper too.
Disadvantages: They do not provide you with much flexibility for system growth. over, the voltage of the battery bank must be matched to the nominal voltage of the solar array.
The more recent technology that is increasing being adopted for charge controllers is:
Maximum Power Point Tracking (MPPT)
MPPT controllers are more expensive, but give greater flexibility in terms of number of panels. The voltage from the PV module will drop down, with a corresponding increase in the current amperage, to match the battery bank. An increase in amperage will lead to faster recharge. These solar charge controllers will automatically adjust as per the P = V x A equation. As a result, you will get more power to charge the battery and there will be no loss, unlike the PWM.
The benefits of MPPT are as follows:
- The MPPT controller allows a panel array to be of higher voltage than the battery bank. This is relevant for areas with low irradiation or during winter with fewer hours of sunlight.
- They provide an increase in charging efficiency up to 30% compared to PWM
- Greater flexibility for system growth. This is relevant for commercial establishments
- They typically come with higher warranty periods than the PWM type
Now that you understand the difference between MPPT and PWM controllers, visit Genus for reliable turnkey solutions for your domestic or commercial applications.