Understanding Solar Charge Controllers

What is the difference between MPPT and PWM charge controllers?

Charge controllers are an essential part of every solar installation. They ensure your system runs efficiently and safely by supplying batteries with a steady and optimum level of power, in addition to preventing battery drainage. Because of the different technologies available, there’s some important things to consider when shopping for a solar charge controller.

What do solar charge controllers do?

Solar charge controllers sit between the energy source (solar panels) and storage (solar batteries) and prevent the overcharging of batteries by limiting the amount and rate of charge to your batteries. There are many changing variables that influence how much power is being generated by your panels, such as the level of sunlight, temperature, and your battery’s state of charge. Charge controllers monitor this to ensure the optimal amount gets fed into your battery bank. They also prevent battery drainage by shutting down the system if stored power falls below 50 percent capacity and charge the batteries at the correct voltage level.

Charge controllers also offer some other important functions:

  • Overload protection: If the current flowing into your batteries is much higher than what the circuit can deal with, your system may overload. This can lead to overheating and cause fires. Charge controllers prevent this from happening by providing overload protection. In larger systems, we also recommend a double safety protection from circuit breakers or fuses.
  • Low voltage disconnects: Charge controllers will automatically disconnect non-critical loads from the battery when the voltage falls below a defined threshold. This will protect equipment from operating at dangerously low voltages.
  • Block Reverse Currents: Solar panels pump current through your battery in one direction. Without a charge controller, solar panels may pass some of that current in the reverse direction. This can cause a slight discharge from the battery. Charge controllers prevent this from happening by acting as a valve.

Do I always need a charge controller?

You don’t need a charge controller with smaller 1 to 5 watt panels. If a panel puts out 2 watts or less for each 50 battery amp hours, you probably don’t need a charge controller. Anything beyond that and you do.

What are the different types of charge controllers?

There are two types of charge controllers to consider: Pulse Width Modulation (PWM) controllers and Maximum Power Point Tracking (MPPT) controllers. PWM charge controllers are cheaper, but they are also less efficient than MPPT charge controllers. Both pulse width modulation and maximum power point tracking charge controllers have a lifespan of about 15 years, although that will vary based on the specific controller.

Pulse Width Modulation Charge Controllers: The pulse width modulation controller is simpler and less expensive than MPPT controllers. PWM controllers regulate the flow of energy to the battery by reducing the current gradually, called "pulse width modulation". When batteries are full, PWM charge controllers continue to supply a tiny amount of power to keep batteries full. PWM controllers are best for small scale applications because the solar panel system and batteries have to have matching voltages.

Cost: $20-$60

Pros:

  • Cheapest charge controller option
  • Best for smaller systems where the efficiency is not as critical
  • Typically longer lifespan due to less components that may break
  • Best for warm sunny weather
  • Performs best when the battery is near the full state of charge

Cons:

  • Less efficient than MPPT controllers
  • Because solar panels and batteries have to have matching voltages with these controllers, they are not ideal for larger, complex systems

Best for: Those with smaller systems (vans, RVs, tiny homes), those living in warmer climates

Maximum Power Point Tracking Charge Controller: Maximum Power Point Tracking controllers are efficient at using the full power of your solar panels to charge your batteries. MPPT controllers will monitor and adjust their input to regulate a solar system’s current, and they will step down the voltage and boost the current. For example, if it becomes cloudy, your MPPT charge controller will decrease the amount of current drawn in order to maintain a desirable voltage at the output of the panel. When it becomes sunny again, the MPPT controller will allow more current from the solar panel once again.The overall output will increase as a result and you can expect efficiency ratings of 90% or higher.

Cost: $100-$729

Pros:

  • Highly efficient
  • Best for larger systems where the additional energy production is valuable
  • Ideal for situations where the solar array voltage is higher than the battery voltage
  • Best in colder, cloudier environments
  • Performs best when the battery is in a low state of charge

Cons:

  • More expensive than PWM controllers
  • Typically have a shorter lifespan due to more components

Best for: Those with larger systems (cabins, homes, cottages), those living in colder climates

What size charge controller do I need?

In order to size your solar system and evaluate your energy needs, we first recommend using our solar sizing calculator. Charge controllers are rated and sized depending on your solar array's current and the solar system’s voltage. You typically want to make sure you have a charge controller that is large enough to handle the amount of power and current produced by your panels. If your solar system's volts were 12 and your amps were 14, you would need a solar charge controller that had at least 14 amps. However, due to factors such as light reflection, sporadic increased current levels can occur, you need to factor in an additional 25% bringing the minimum amps that our solar charger controller must have to 17.5 amps. We’ll round up in this case, so in the end, you would need a 12 volt, 20 amp solar charge controller.

Can I use more than one charge controller?

You can use multiple charge controllers with one battery bank in situations where a single charge controller is not large enough to handle the output of your solar panel array. However, we do recommend using the same type of charge controllers if you are using more than one. So if you have one MPPT charge controller, all of your charge controllers should be MPPT.

Conclusion

Whether you’re living a mobile lifestyle on the open road or off-grid on a plot of land, charge controllers play an essential part of your solar installation. Charge controllers prevent the overcharging of batteries by limiting the amount and rate of charge to your batteries, provide overload protection, disconnect at low voltages, and block reverse current. Depending on your specific needs, there’s a PWM and MPPT charge controller to suit your solar installation’s needs.