PWM vs MPPT Charge Controllers: What’s the Difference?
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In this guide, I’ll break down the differences between PWM and MPPT charge controllers.
And I won’t just talk about price and efficiency. I’m going in depth to help you understand when you should choose a PWM or MPPT.
I’ll also show you the results of a real-world PWM vs MPPT test I did.
PWM vs MPPT Comparison Table
| Pros | – Cheap (but can lead to increased wiring and equipment costs)– All you need for some small solar power systems | – Efficient (~95% conversion efficiency)– Higher current and PV voltage limits– features (e.g. Bluetooth, custom charging profiles)– Usually better build quality |
| Cons | – Less efficient (~75% conversion efficiency)– Lower current and PV voltage limits– Usually fewer features than MPPT charge controllers– Usually worse build quality | – Expensive– Overkill for some small solar power systems |
| Best for | – Small solar power systems (300-400W or less)– When PV voltage is close to battery voltage | – Larger solar power systems (400W)– When mounting space is limited– When conversion efficiency is a top priority– When series connecting solar panels |
| My favorites | – Renogy Wanderer 30A– Renogy Wanderer 10A– Morningstar SunSaver | – Victron SmartSolar MPPT 100/30– Renogy Rover 40A– EPEver Tracer 4215BN |
| Full review | Best PWM Charge Controllers | Best MPPT Charge Controllers |
4 Main Differences
- MPPT charge controllers are more efficient than PWM charge controllers. The rule of thumb conversion efficiencies are about 75% for PWMs and 95% for MPPTs.
- PWM charge controllers are cheaper than MPPT charge controllers. Many popular PWMs retail for 20-50, while MPPTs start at around 100.
- When connecting multiple solar panels together, PWM charge controllers usually require you to wire them in parallel. Most MPPT charge controllers have high enough PV voltage limits that you can wire them in series. Parallel wiring increases current (amperage), which can require thicker wire and equipment with higher current ratings.
- PWM charge controllers are often best suited for smaller solar arrays of 300-400 watts or less. MPPT charge controllers are often best suited for larger solar arrays of 400 watts or more. MPPTs start to make more sense the greater the size of the solar array.
PWM vs MPPT: How to Choose
Here are the main considerations when deciding between a PWM or MPPT charge controller.
Conversion Efficiency
PWM charge controllers have a rule of thumb conversion efficiency of 75%. If you don’t need to squeeze every possible watt out of your solar panels, a PWM is probably all you need.
MPPT charge controllers have a rule of thumb conversion efficiency of 95%. When conversion efficiency is a top priority, an MPPT is often the best option.
Note: As you’ll see from the results of my real-world test, these conversion efficiencies don’t always hold true. But they’re helpful for conveying average expected efficiency across a number of different scenarios.
Price
PWM charge controllers are cheap. You can find many budget PWMs online for 15-25, though caveat emptor definitely applies when buying one of these. Higher quality ones start around 40-50.
However, the sticker price of a PWM charge controller can be misleading, because — depending on how you build your system — using one can lead to greater downstream costs. For instance, if you want to use multiple solar panels with a PWM, you’ll likely have to wire them in parallel which can lead to increased wire and equipment costs.
MPPT charge controllers are expensive. It’s hard to find one for less than 100. Many popular options fall in the 150-200 price range.
Solar Array Size
PWM charge controllers often have low current and PV voltage ratings, making them best suited for solar arrays of around 300-400 watts or less. For instance, it’s common to see PWM charge controllers with max PV voltages of 25-50 volts (usually 1-2 100W 12V solar panels wired in series), and current ratings of 10-30 amps (usually 2-4 100W 12V solar panels wired in parallel).
MPPT charge controllers are often suited for larger solar arrays, such as 500-1000 watts. This is because they tend to have higher current and PV voltage ratings, such as 30-40 amps and 100-150 volts.
Tip: Use our maximum open circuit voltage calculator to find the maximum voltage of your solar array. Pick a charge controller with a PV voltage limit that is greater than this number.
PV Voltage vs Battery Voltage
PWM charge controllers work best when the incoming PV voltage (i.e. solar panel voltage) is close to the battery voltage. The ideal setup with many PWMs is with a 12V solar array and 12V battery. The greater the difference between PV voltage and battery voltage, the less efficient a PWM charge controller will be.
MPPT charge controllers work well regardless of the difference between PV voltage and battery voltage. For example, with an MPPT, you could efficiently charge a 12V battery with a 36V solar array.
Note: For both types of charge controllers, PV voltage needs to be greater than the battery voltage in order for the battery to charge. The only exception is if you’re using a boost MPPT charge controller, which is capable of boosting the incoming PV voltage to match the battery’s voltage. There is no such thing as a boost PWM charge controller.
Where You Live
PWM charge controllers perform about the same as MPPTs in subtropical to tropical climates, unless you have lots of panels connected in series.
MPPT charge controllers perform better in cold to temperate climates.
Series vs Parallel Connections
PWM charge controllers: When wiring multiple solar panels to a PWM, you’ll usually have to wire them in parallel. This is because many PWMs have low PV voltage limits (e.g. 25V or 50V), which is enough for only one or two 12V solar panels in series.
MPPT charge controllers: MPPTs almost always have higher PV voltage limits than PWMs, letting you wire more panels in series. For example, a common PV voltage limit for MPPTs is 100 volts. Many popular 12V 100W solar panels have an open circuit voltage (Voc) of around 22V, so you could connect up to 4 of them in series without exceeding this limit. Series wiring keeps current low, saving you money on wiring and equipment costs.
Note: Series wiring isn’t always the best option, though. For instance, parallel wiring is advantageous when the panels spend a lot of time in mixed light conditions. For a full tutorial and breakdown of series vs parallel wiring, check out my guide on how to wire solar panels in series and parallel.
Mounting Space
PWM charge controllers are better suited for when you have lots of roof or mounting space.
MPPT charge controllers are best when roof or mounting space is limited. Because they’re more efficient, they’ll extract the maximum amount of solar energy from a limited space.
Battery Type
PWM charge controllers: Many PWMs are only compatible with lead acid batteries (sealed, gel, flooded, AGM).
If a PWM is compatible with lithium (LiFePO4) batteries, it tends not to treat them as well as an MPPT would. Why? Because it may not offer the option to connect a temperature sensor or battery voltage monitor (BVM) for improved temperature compensation and voltage readings. Others don’t have custom charging profiles, in case you want to customize the boost, float, and absorption voltages of your battery. And I’ve found in my testing that PWMs often have less accurate battery voltage readings, meaning they can chronically over charge or over discharge your battery, shortening its lifespan.
MPPT charge controllers: Most of the MPPTs I’ve used work with lead acid and lithium (LiFePO4) batteries, or at least offer the ability to create custom charging profiles.
MPPTs usually have the option to connect a temperature sensor and battery voltage monitor. I’ve also found their battery voltage readings to be more accurate. If you’re using expensive batteries that you want to last as long as possible, I’d recommend an MPPT.
Distance from Charge Controller to Battery
PWM charge controllers: If your PWM is forcing you to wire solar panels in parallel and increase wire gauge as a result, longer wire runs can increase wiring costs substantially.
MPPT charge controllers: MPPTs let your wire more solar panels in series which keeps PV current low and allows you to use smaller wire gauge.
PWM vs MPPT Test Results
The rule of thumb conversion efficiencies for PWM and MPPT charge controllers are averages. They try to capture the average conversion efficiencies across temperature ranges, weather conditions, solar array voltages and other conditions.
Simply put, it’s rare that the 75% and 95% efficiency numbers will hold true for your particular situation.
To illustrate this, I connected a PWM and MPPT charge controller each to a 100W 12V solar panel and 12V 100Ah LiFePO4 battery. Then I placed the solar panels outside and monitored each charge controller’s output over the course of a day with a watt meter.
| 9AM output – full shade | 2.1 W | 1.4 W |
| 11AM output – full sun | 65.8 W | 73.4 W |
| 12PM output – full sun | 70.8 W | 75.9 W |
| 1PM output – full sun | 72.0 W | 73.9 W |
| 2PM output – full sun | 67.7 W | 69.1 W |
| 3PM output – half shade | 4.3 W | 4.6 W |
| 4PM output – full shade | 3.4 W | 2.9 W |
| Peak current | 5.41 A | 5.85 A |
| Peak output | 72.3 W | 76.2 W |
| Total power output | 284.4 Wh | 292.2 Wh |
Note: This test was conducted on a sunny day in mid April in Alabama.
Findings
- The PWM charge controller output a total of 284.4 watt hours, while the MPPT charge controller output at total of 292.2 watt hours. That’s a difference of only 7.8 watt hours. If we assume the MPPT operated at a 95% conversion efficiency, then each solar panel generated around 307.5 watt hours (292.2 ÷ 95% = 307.5). This would mean the PWM operated at 92.5% conversion efficiency (284.4 ÷ 307.5 = 92.5%).
- In full shade, the PWM actually slightly outperformed the MPPT.
- The MPPT’s output seemed to be affected by heat more than the PWM’s. This isn’t really captured in the numbers, but as I watched each charge controller’s output over the course of the day, the MPPT’s seemed to slowly drop as the day (and panels) heated up. This is in line with the finding that, in hotter climates, MPPTs perform similarly to PWMs.
What Is a PWM Charge Controller?
PWM solar charge controllers use a method called pulse width modulation (PWM) to reduce solar panel voltage to the right level for safely charging the battery.
Pulse width modulation is like turning a switch on and off at an extremely fast rate. By adjusting (or ‘modulating’) how long the switch stays on and off, you can in essence adjust the output of the solar panel.
You can actually see pulse width modulation in action using lights. To illustrate it, I set up two LEDs and programmed them to turn on and off very quickly. The LED on the left was programmed to be on for 5 milliseconds and off for 10 milliseconds. The LED on the right was programmed to be on for 15 milliseconds and off for 5 milliseconds.
To the human eye, both lights appear to be constantly on. However, as you can see in the photo, the light on the left is much dimmer than the light on the right.
This is pulse width modulation in action. By adjusting how long a switch stays on and off, you can affect the average output. In this case, the more time the light spent turned off, the dimmer it appeared.
Now consider PWM in the context of solar panels. A solar panel’s output is constantly changing depending on how sunny it is. So the voltage and current need to be regulated to safely charge the battery. Because, for example, if the solar panel’s voltage gets too high, it could damage the battery.
So, PWM charge controllers are essentially turning the solar panels on and off very quickly to regulate their output.
This helps us understand why it’s important for your battery and solar panel to have similar voltages when using a PWM charge controller. If the solar panel voltage is much greater than the battery voltage, the solar panels will spend much more time ‘turned off,’ greatly reducing how much power they can generate.
Best PWM Charge Controllers
After testing some of the best PWM charge controllers on the market, here are my recommendations:
What Is an MPPT Charge Controller?
MPPT solar charge controllers use a method called maximum power point tracking (MPPT) to harvest the maximum power from the solar array. They use more sophisticated technology, and are thus more expensive.
Essentially, they are always ‘tracking’ at what point along the IV curve the solar panel output is greatest. This point of max power is, unsurprisingly, called the maximum power point.
Once an MPPT has found the maximum power point, it collects all that solar energy and then steps the voltage down to match the voltage of your battery bank while boosting the current to make up for the lower voltage. The result is minimal conversion losses.
Best MPPT Charge Controllers
After testing some of the best MPPT charge controllers on the market, here are my recommendations:
- Top Pick:Victron SmartSolar MPPT 100/30
- Budget Pick:Renogy Rover 40A
- Honorable Mention:EPEver Tracer 4215BN
The Bottom Line
The main differences between PWM and MPPT charge controllers are cost and conversion efficiency. PWM charge controllers are cheap and inefficient, while MPPT charge controllers are efficient but pricey. The rule of thumb conversion efficiencies are 75% for PWM and 95% for MPPT.
In reality, though, these conversion efficiencies will likely not hold true for your specific situation. As happened during my real world test, a PWM may actually perform better than expected.
And I think the general claim of “PWM is cheap and MPPT is expensive” is also a bit misleading. PWM charge controllers are often only compatible with 12V and 24V solar arrays and battery banks. To connect multiple solar panels to a PWM, you’ll usually have to wire them in parallel, which requires buying branch connectors and can also result in higher wire and equipment costs, especially in systems with long wire runs.
Personally, here’s how I’d decide which controller to get for my next solar project:
I’d use PWM charge controllers when building a solar power system of 300-400 watts or less, where I don’t need to squeeze out every watt from my panels.
In any other situation, I’d use an MPPT charge controller. I’d even consider an MPPT from the start if I knew I’d probably expand my solar array later on. They’re so much more versatile and feature-rich that you can add many more panels before having to upgrade.
Solar Charge Controllers: A Complete Guide
Solar charge controllers, also known as solar regulators, convert the raw power delivered from a PV solar panel into a usable charge for the battery. Charge controllers sit between the panels and the batteries, acting as a converter for the mismatched voltages of the two components.
The voltage in a PV array varies with temperature, light intensity, and other factors. Batteries expect a specific voltage and cannot handle fluctuations in power on their own. To regulate these changes in voltage, you need to install a solar charge controller between your PV array and solar battery bank.
There is more than one type of solar charge controller—which one is suitable for your array?
The Two Types of Solar Charge Controllers
There are two main types of solar charge controllers: Maximum Power Point Tracking (MPPT) and Pulse Width Modulation (PWM). The two perform similar functions, but MPPT is typically the better choice for residential solar systems. Let’s take a look at the differences.
MPPT (Maximum Power Point Tracking) Solar Charge Controllers
MPPT (Maximum Power Point Tracking) charge controllers employ newer, more advanced technology than PWM controllers. MPPT controllers allow the solar array to perform at its “maximum power point,” which is the ideal current and voltage. Other charge controllers will waste excess energy generated by the solar panels, while MPPT controllers can convert this into more power for the batteries.
MPPT technology has been around for a few decades, but it has only recently become affordable enough for the average homeowner. Most advanced residential solar power systems utilize MPPT charge controllers. Some estimates claim that using an MPPT controller can increase the efficiency of a solar system by around 30%. MPPTs achieve higher efficiency by boosting the amperage provided to the battery by converting excess voltage.
MPPT controllers are always the better choice for residential solar setups. Any system that uses multiple panels will benefit significantly from the higher efficiency of an MPPT controller. This is true for all systems where the PV array operates at a higher voltage than the battery bank. Other types of controllers would waste this excess power.
MPPT charge controllers will generally cost more than PWM controllers. However, the higher initial purchase cost provides savings over time due to the controller’s ability to harvest more power from the same amount of solar panels.
When batteries are nearly depleted, they operate at a lower voltage and usually receive a charge at a lower rate. An MPPT is helpful in this situation, as it can convert the extra voltage into more amps for the depleted battery.
If crafting your own solar system piece by piece seems overwhelming, there are also all-in-one bundles that simplify the installation process. For example, EcoFlow Power Kits have everything you need to set up a high-quality off-grid solar system. It includes the battery, cables, distribution panels, and a power hub with a built-in MPPT solar charge controller. Just purchase your required solar panels, and you’re ready to start harvesting renewable electricity from the sun!
Let’s recap the pros and cons of MPPT charge controllers.
- Efficiency — MPPT Controllers can convert excess voltage into more usable current.
- Ideal for large systems that have varying voltages, such as a PV array with a higher voltage than the battery bank
- Performs well in both warm and cold climates
- Useful for both small and large applications, including RVs, cabins, and traditional homes
PWM (Pulse Width Modulation) Solar Charge Controllers
Pulse width modulation controllers are an older, cheaper technology. They are less efficient than MPPT charge controllers. If all other factors are the same, a solar array will take longer to charge a battery bank when running through a PWM controller.
PWM controllers perform a similar function to MPPT controllers, as they still regulate the energy that flows to your battery bank. However, they accomplish this action in a different manner.
The “pulse width modulation” refers to how a PWM controller slowly reduces the current while charging the batteries. When the batteries reach maximum charge, PWM controllers will trickle charge the batteries — this means that they will continuously provide a small amount of power to keep the batteries topped up.
To use a PWM controller, your batteries and solar panels must operate on the same voltage. Large residential solar systems will not be well-served by this type of controller.
PWM controllers can only use the power you generate up to the voltage of your battery bank, which is usually around 12V. The extra power goes to waste if the solar panels provide more energy. The loss of solar energy from using a PWM is in contrast to the ability of MPPT controllers to step down the voltage and boost the current.
PWM controllers are best for warmer climates where the MPPT “boost” does not benefit a system as much. And since the controllers are cheaper, PWM may be suitable for small systems where investing in an MPPT controller isn’t cost-effective.
Let’s recap the pros and cons of PWM charge controllers.
- Great for warm, sunny weather
- Affordable
- Works well for small, single-panel systems
- Not designed for complex solar arrays that contain varying voltages
- Inefficient—excess power produced by your solar panels goes to waste
How to Determine Which Solar Charge Controller Is Right For You
For modern residential or large recreational solar systems, the only real choice is between MPPT and PWM charge controllers. You may see some mention of shunt or series controllers, but these are no longer used for residential applications.
MPPT charge controllers are always the right choice for a DIY home solar system. Their superiority extends to RVs, cabins, and other off-grid applications. Unless you are only using one or two panels — such as on a camping trip — the additional benefits of an MPPT charge controller are worth the slightly-higher investment.
In some cases, you won’t need to purchase a separate solar charge controller. EcoFlow Power Kits are a popular way to get started with solar quickly, and the MPPT charge controller comes built-in! It also makes for a safer solar system for inexperienced homeowners, as there is no chance of improper installation, compatibility issues, or choosing the wrong controller.
Conclusion
Now that you know the differences between the two types of charge controllers, you can go out and purchase your own. The only thing left to determine is what the amp rating of your controller needs to be. You can make this decision easy by buying a controller with a higher power rating than what your solar array will provide.
If creating your own DIY solar power system isn’t your style, look at all-in-one options. EcoFlow Solar Generators make solar power accessible for anyone — all you need is the generator and a solar panel to get started on your journey towards renewable energy independence.
EcoFlow is a portable power and renewable energy solutions company. Since its founding in 2017, EcoFlow has provided peace-of-mind power to customers in over 85 markets through its DELTA and RIVER product lines of portable power stations and eco-friendly accessories.
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.