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.
Let’s get started.
PWM vs MPPT Comparison Table
| PWM | MPPT | |
|---|---|---|
| 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 – More 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.
Warning: Some shady online sellers will intentionally mislabel their PWM charge controllers as MPPT charge controllers. If you find an MPPT charge controller for a price that is too good to be true, then it probably is.
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.
Here are my results:
| PWM | MPPT | |
|---|---|---|
| 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:
- Top Pick: Renogy Wanderer 30A
- Budget Pick: Renogy Wanderer 10A
- Honorable Mention: Morningstar SunSaver
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.
