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How to Select a Solar Charge Controller: In 2 Simple Steps!

Solar charge controllers are a vital part of any off-grid solar panel system, as they protect the battery from overcharging. To select the right solar charge controller for your system, you only need to worry about two things:

  • Voltage
  • Current capacity (in amps)

In this simple guide, we’ll clarify how to select a solar charge controller in just two steps and help you get the most out of your machine.

Step 1: Select the Right Voltage

Your solar charge controller needs to be compatible with your system’s voltage, so that’s the first thing to take into account when choosing one.

Most systems use one of:

  • 12 volts
  • 24 volts
  • 48 volts

The voltage on your system’s battery and charge controller must match. James P. Dunlop from the Florida Solar Energy Center puts it like this:

While the primary function is to prevent battery overcharge, many other functions may also be used, including low voltage load disconnect, load regulation and control, control of backup energy sources, diversion of energy to and auxiliary load, and system monitoring.

Some solar charge controllers, namely inexpensive PWM controllers, can only be used with one voltage, while pricier MPPT controllers can pair voltages that don’t match.

Step 2: Select the Appropriate Current Capacity

The next thing to consider when learning how to select a solar charge controller is its current capacity. That means your charge controller needs to be large and powerful enough to handle the amount of energy your solar panel array produces.

To calculate the current capacity you need, figure out how many amps your system normally produces and add 25% to account for temporary increases in current levels (2).

When in doubt, it’s always better to go too big than too small when it comes to solar charge controllers.

Using a solar charge controller with too few amps (ie: improper charge controller sizing) can result in inefficient energy conversion and overheating, but using a controller that’s larger than you need will have no ill effects.

An image of Charge Controller Sizing done the right way

Other Things to Look for When Selecting a Solar Charge Controller

As you can see, finding the appropriate solar charge controller for your PV system shouldn’t be too intimidating. If you’re still feeling a bit fuzzy on the process, here’s a great visual to help clarify things:

I won’t spoil it for you, but once you know the basic specs you’re looking for, you’re practically ready to start shopping. However, before you buy a charge controller, there are a few other things that you can take into account in order to find the optimal model for you.

Multi-Voltage Function

Multi-voltage function enabled solar charge controllers let you adjust the charging voltage set point in order to make the device more effective.

Generally speaking, your voltage setpoint should be directly inverse to your battery temperature for it to fully charge without overheating.

In other words, you’ll want to raise the set point during colder weather and lower it during warmer months.

Load Control

Load control refers to the ability to turn off your battery’s output when the charge controller senses the battery bank is too low. Most charge controllers have this function, so it’s mostly a matter of whether you want a controller with automatic load control or if you prefer to do it manually.

Remote Access

If you’re willing to pay a little extra, you can get a solar charge controller that allows you to monitor and control it remotely from anywhere. This is especially useful if you travel frequently and want to keep an eye on your solar panels and charge controllers.

Typical balance-of-system equipment for a stand-alone system includes batteries, charge controller, power conditioning equipment, safety equipment, and meters and instrumentation.

Remote access would fall under the instrumentation category, and this would give you even more control over your energy usage.

Display

It’s important to monitor your system’s charge, current, voltage (including open-circuit voltage), temperature, and more, so make sure the controller you choose has an easy-to-read display. Many newer models feature prominent LCD displays that are easy to read at a glance.

FAQs

The main types of solar charge controllers are PWM (Pulse Width Modulation) and MPPT (Maximum Power Point Tracking). Pulse Width Modulation charge controllers or PWM charge controllers were the original charge controller, built more simply, and are less expensive than MPPT charge controllers.

Maximum power point tracking charge controllers or MPPT charge controllers limit their output to ensure batteries don’t get overcharged, leading to an efficiency rating of 90% or higher. This makes MPPT charge controllers relatively more expensive, but better suited for larger solar panel systems where efficiency matters and colder, cloudier climates (4).

You can get a good deal on a solar charge controller by taking your time and shopping around at places like Your Energy Blog.

Decide whether a Pulse Width Modulation (PWM) charge controller or a Maximum Power Point Tracking (MPPT) charge controller is best for your solar panels and desired connected equipment, then size accordingly to get the most out of your dollars, and machines.

If you’re looking for some recommendations, Click or Tap This for our Buyers’ Guide containing all of our top picks of the year.

You don’t technically need a warranty for your solar charge controller, but having one doesn’t hurt.

Parts do wear out on occasion, so having a warranty is a good idea for solar equipment, especially MPPT and PWM charge controllers as they can get quite expensive. Most charge controller warranties will protect you for three to five years, but you should always check before buying.

  1. Batteries and Charge Control in Stand-Alone Photovoltaic Systems. Retrieved from: http://www.fsec.ucf.edu/en/publications/pdf/FSEC-CR-1292-01.pdf
  2. SOLAR CHARGE CONTROLLERS DEEP CYCLE BATTERY CHARGING. Retrieved from: https://www.bluepacificsolar.com/charge-controllers.html
  3. Balance-of-System Equipment Required for Renewable Energy Systems. Retrieved from: https://www.energy.gov/energysaver/balance-system-equipment-required-renewable-energy-systems
  4. WHAT IS THE DIFFERENCE BETWEEN MPPT AND PWM CHARGE CONTROLLERS? Retrieved from: https://www.renogy.com/blog/what-is-the-difference-between-mppt-and-pwm-charge-controllers/
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