Difference Between PWM and MPPT Solar Charge Controller and Which Is Better?
If you’ve ever built DIY solar panels of a considerable size, you’ll probably come across this important component — the charge controller. The role of a charge controller is to regulate the charging voltage on the batteries.
When sunlight gets brighter, solar cells produce more voltage. Excessive voltage may cause over-charging which may damage your batteries. You’ll need this component if you want to store excess electricity from your solar energy panels.
Many modern charge controller units have a 3-stage cycle:
1. Bulk Phase – During this phase, the charging voltage gradually rises to approximately 14.4 to 14.6 volts (to charge a 12V battery). It is at this stage when charging current is maximum.
2. Absorption Phase – Voltage is maintained at the bulk level for a specified time. As the battery is charged up, current tapers off gradually.
3. Float Phase – After the absorption phase, voltage is lowered to about 13.4 to 13.7 volts (float voltage) and batteries draw a very small, maintenance current until it goes through the discharge cycle.
There are two main types of solar charge controllers:
MPPT Charge Controller (Maximum Power Point Tracking)
PWM Charge Controller (Pulse Width Modulation)
Here's a quick overview of the differences between PWM and MPPT solar charge controller. I won’t just talk about efficiency and price, because the fact that a device has a certain feature over another does not mean that it is better in all cases. So I’m going to help you understand when you should choose PWM and when you should choose MPPT.
Why Is a Solar Charge Controller Important for Off-grid Systems?
Connecting solar panels directly to a solar battery is not the correct and safest way.
Different types of batteries require different charging methods depending on their chemical and physical properties. The method for charging lithium-ion batteries differs from the method for charging lead-acid batteries.
For example, lead-acid batteries use a three-stage charging system: bulk, absorption, and float. The bulk charge stage uses a constant current to charge the batteries until they reach about 80% capacity. After that, the current starts to decrease during the absorption phase. In the float stage, a low current is applied to keep the battery fully charged.
Charge controllers are designed to charge batteries according to these stages. They sense the internal resistance of the battery and send current to the battery terminals based on the battery resistance.
- If the battery resistance is low, the charge controller will send the maximum current to the batteries.
- If the resistance increases, the charging current will decrease because the battery is almost full.
The charge controller is used in the solar energy system for two basic functions, one during the day and the other at night:
During the day: Prevent the battery from overcharging.
During the night: Prevent the battery from discharging into the solar panels.
Whether you use PWM or MPPT charge controller, both technologies perform these two functions. They differ in the way in which they handle current and voltage, and some secondary functions and features remain on one device above the other.
Solar controller can save the energy produced from solar panels, and convert it with better efficiency to the battery or electric load. Offer system monitoring features such as displaying battery status, battery temperature, solar panels and electrical load, which helps to monitor and improve system performance.
Now that you know that a solar charge controller is an important part of a
solar PV system to ensure longer battery life and improve overall system
efficiency.
Can Solar Panels Charge Battery Without Controller?
Connecting solar panels directly to batteries without a solar charge controller is possible. But as I mentioned earlier, it is not the right way. Here's why.
When the voltage of the panels is greater than the allowable voltage for charging the battery, the battery can be overcharged.
For example, a 12-volt battery is charged with a voltage that can range from 13V to 14.6V depending on the current state of the battery. If the voltage coming from the solar panels is greater than that, the battery is likely to be damaged and shorten its lifespan.
Differences Between PWM and MPPT Solar Charge Controller
1. Differences in Working Principle
MPPT Solar Charge Controller
The MPPT controller contains advanced algorithms to determine the maximum power point at the solar panels. These algorithms are based on analyzing the voltage and current data generated from the solar panels and adjusting the system voltage and current to achieve the maximum efficiency of solar power generation.
After the MPPT charge controller determines the maximum power point (Pmax) of the solar panels, it balances the voltage and current coming from the solar array to obtain the voltage of the battery bank and provide the maximum current for charging it according to the following equation (DC-DC conversion):
Pmax = Vmp * Imp = Vbat * I
PWM Solar Charge Controller
PWM charge controllers can be interpreted as an electrical switch that connects the solar panels to the battery. The switch can open and close at variable intervals depending on the current state of charge of the battery.
When the battery is empty, the pulses (how long the switch will be On and Off) will be as long and as wide. When the battery reaches absorption voltage, the PWM controller reduces the power it sends to the battery by adjusting the width of the charge pulses. After the absorption phase is complete and the battery is almost fully charged, the pulses will be short and rarely transmitted.
2. Differences in Appearance
Both PWM and MPPT solar charge controllers look similar, as they both have electrical connectors to connect solar panels, batteries, and the DC load, and both may have LEDs and an LCD display to check how things are working.
However, they differ in weight and size. Since MPPT charge controllers contain DC-DC converter coils, they are larger and lighter than PWM controllers.
3. Efficiency
The actual efficiency of the PWM solar controller is very much related to the voltage of the panels used, and the state of charge of the battery.
The voltage of the panels used: The smaller the voltage difference between the solar panel and the batteries, the higher the PWM efficiency.
Battery state of charge: The higher the state of charge of the battery, the greater the efficiency of the PWM controller.
While the efficiency of the MPPT charge controller remains constant between 95% and 98%. If the power produced from the panel is less than the power expected to be produced (e.g., 67 watts from a 100-watt panel), this is not related to the efficiency of the MPPT, but rather to the amount of solar radiation falling on the solar panel.
Many professionals assert that over the course of a day, PWM charge controller may harvest between 60-85% of the PV power actually produced by the solar arrays, while an MPTP will harvest 98%.
How Much More Efficient is MPPT vs PWM?
To illustrate the efficiency difference between the two technologies, this video shows MPPT vs PWM test in the same conditions.
100-watt panel, Vmp = 36V, Imp = 2.78A.
Using PWM controller, the power drawn from the panel is 2.83A * 13.2V = 37W, the panel's amperage is slightly higher than the Imp (Check out the shape of the I-V curve).
Using MPPT controller, the power drawn from it is 4.75A * 14.1V = 67W, which is about 40% more power than the PWM controller.
The large difference in efficiency between PWM and MPPT is explained by the large difference between the voltage of the solar panel used (Vmp = 36V) and the battery voltage (12V).
4. Price
The price of MPPT controller can range from $75 to $500, depending on the electrical rating (amps) and voltage that can be controlled, as well as the brand.
As for the PWM controller, the price ranges from $12 to $100, which also depends on the brand, and capacity required.
Thus, PWM charge controllers are cheaper than MPPT controllers. Depending on your budget and needs, the cost will play an important role in your choice.
5. Series vs Parallel Connections
The MPPT has a large PV voltage limiter. Up to four 12V panels can be connected in series for a 12V battery system.
By contrast, a PWM controller can only support one 12V solar panel in series for a 12V battery system.
So, when you use the PWM controller to charge a 12V battery system you have to connect your 12V solar panels in parallel in order to get the maximum power from your solar array.
Do I Need a PWM or MPPT Solar Charge Controller?
1. Where Do You Live (Whether it's Sold or Very Hot)
PWM charge controllers perform as well as MPPT in warm climates (when the solar panel gets too hot), PWM is probably all you need.
In cooler temperatures and cloudy/rainy weather, MPPT charge controllers will work better. So if you need flexibility within your system, MPPT is the best choice.
2. Size of Your System
In large systems of 400 watts or more, where efficiency becomes a top priority to avoid wasting energy, the use of MPPT may be sufficient to justify its additional cost.
But for simple systems whit 300-400 watts or less, the efficiency difference between PWM and MPPT may not be enough to justify the price difference. Thus, in this case, a PWM controller is often sufficient.
3. Mounting Space (Large Area or Limited)
When you have a large area to install solar panels, PWM controllers will be suitable for you in order to reduce system costs.
But if the installation space is limited, you will often use solar panels that have a high power output. In order to extract the maximum amount of power from these panels, MPPT solar charge controllers will be suitable for you.
4. The Voltage of The System Array
| I need a solar charge controller | PMW | MPPT | |||||
|---|---|---|---|---|---|---|---|
|
Battery voltage
|
12V | 24V | 48V | 12V | 24V | 48V | |
|
The voltage of the system array
is within
|
17-19V | ✔ | - | - | - | - | - |
| 19-30V | - | - | - | ✔ | - | - | |
| 30-34V | - | ✔ | - | ✔ | - | - | |
| 34-56V | - | - | - | ✔ | ✔ | - | |
| 56-64V | - | - | ✔ | ✔ | ✔ | - | |
| >64V | - | - | - | ✔ | ✔ | ✔ | |
Conclution
There are several different brand of charge controller to choose from — some with fanciful LCD displays and others with battery temperature monitor. If you are building your first solar power generator, it may be more practical to buy basic ones to begin with. After you’re more acquainted with these components, you’ll have more knowledge to get the most out of more advanced charge controllers. Most multi-stage, Pulse Width Modulation (PWM) types of charge controllers will do great, really.
Mohamed Bellamine
I'm the blogger behind Goo SolarPower. As a solar engineer, and a strong supporter of renewable energy. I've always been interested in Solar devices. I loves to write articles, guides, and tutorials about solar PV technology. Through goosolarpower.com I want to help people build and understand how solar power systems work.