Solar Charge Controllers

Solar Charge Controllers

How Do I Size a Solar Charge Controller ?

You'll notice that solar charge controllers are specified by both amperage and voltage. You will need a solar controller that can support the voltage of your solar panel array, and then output to the battery bank's voltage (usually 12, 24 or 48VDC).

Next, you'll want to make sure the solar charge controller has enough capacity to handle the current (in amps) from your solar panel array. Take the wattage of your solar panels and divide it by the battery bank's voltage to get a rough estimate of how many amps the controller needs. See more detailed information in our video on how a solar charge controller works in a solar power system:

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More Info on Solar Charge Controllers

The basic formula for sizing a solar panel charge controller is to take the short circuit current (Isc) of the array, and multiply it by 1.56. (What is short circuit current? Glossary of Alternative Energy Terms & Why 1.56? See Sizing PWM Solar Charge Controllers and Sizing MPPT Charge Controllers). Be sure that the solar controller you select can handle at least that many amps.

Please protect this important part of your system with appropriate overcurrent protection before and after the solar controller (see Enclosures, Electrical & Safety for options).

Solar Charge Controller Types

Now that you know what size solar controller to look for, identify which type of solar charge controller is right for your application: MPPT or PWM Charge Controllers. A PWM (Pulse Width Modulated) solar charge controller is the traditional style. They are robust, inexpensive and widely used in solar panel applications. PWM shunt controllers are used less often and mostly in applications where electrical interference is an issue. The MPPT (Maximum Power Point Tracking) solar controller is the shining star of today's solar systems. These controllers actually detect the optimum operating voltage and amperage of the solar panel array and match that with the battery bank. The result is additional 15-30% more power out of your solar array versus a PWM solar controller. Although the MPPT solar charge controller is more expensive than its PWM counterpart, it is generally worth the investment for any solar electric system over 200 watts.

Features and add-ons for Solar Controllers

Once you have decided on a type of solar charge controller, you'll want to identify what features you need. There are many basic-no-frills solar charge controllers that work well. In addition, there are some great features that will make your renewable energy experience even better. An important addition to your system: Battery Temperature Sensors. Battery capacity depends on temperature, therefore proper battery charging can be significantly enhanced with a temperature sensor.

Additionally, some solar controllers offer adjustable control voltage set points, low voltage disconnect, overload protection and displays and metering. If you plan to run a DC load, you can connect it directly to the solar charge controller. If the solar controller is equipped with a low voltage disconnect (LVD), then the solar charge controller can detect when the battery is low and shut off the DC load until the battery is charged. Is all of this still confusing? Give us a call and let us know the short circuit current of your solar panel array (or at least the brand and size of your solar modules) and the system voltage (12, 24, 48 VDC) and we'll be glad to help with a recommendation.

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