How To Size A Solar Charge Controller

Introduction

Information technology is important to have the solar charge controller correctly sized to properly and safely operate your solar power system. How yous size your solar charge controller is dependent on the type of charge controller yous have. (Refer to SunWize's tech note on Solar Accuse Controller Types for more than information.) Due to popularity, we will focus on sizing MPPT Charge Controllers. Let's become started!

MPPT Charge Controllers

MPPT charge controllers currently limit their output, so technically you tin make the solar array as large every bit you desire and the accuse controller will limit the output current to the maximum commanded. There is a practical limit though, if the solar array is too large then the ability is but wasted, since the charge controller is always limiting the output. A typical recommendation is to limit the solar array to 110%-125% of the maximum controller rating.

Example: You accept a 60A MPPT accuse controller and a nominal 24VDC battery. That means we have 1440W of power. We and so go ahead and calculate the 110%-125% of the maximum controller rating to go a range of 1584W to 1800W. The complete calculation looks like this: 60A * 24V = 1440W * 1.1 or ane.25 = 1584W-1800W

Again, a larger solar array volition not damage annihilation; it'south simply a waste of free energy as the controller volition always exist restricting the maximum output to the current limit. Overcurrent protection can be rated to the maximum current if the overcurrent device is designed to operate at 100% of rating. As an example, you can apply a 60A circuit billow with a 60A MPPT charge controller if the excursion breaker is rated to operate at 60A continuously. This is per an exception to the NEC. Commodity 690.8 (B)(i)(a) states "Circuits containing an assembly, together with its overcurrent device(s), that is listed for continuous operation at 100 per centum of its rating shall exist permitted to be used at 100 percent of its rating."

All Other Charge Controllers

Shunt, series, and PWM charge controllers are unable to limit their electric current output. They simply pass through the array electric current. If the solar array can produce 40A of current and the controller is only rated to 30A, then the controller or arrangement could be damaged. For this reason, the charge controller should exist rated for the maximum array output plus a safety margin. Further NEC states that the assortment brusque circuit current (Isc) should be used, plus a 125% rubber factor for cloud enhancement, plus an additional 125% safety cistron for design margin.

Example: You have an array with an Isc of 8A. Using the 125% safety factor, the charge controller should be rated for a minimum of 8A * i.25 * one.25 = 12.5A.

Overcurrent protection should be sized the same way, and the next nearest size device used. In this example, a 15A circuit breaker would exist used. Note: this should be paired with the maximum series cord fuse rating of the solar module and a combiner box or boosted overcurrent devices may exist needed, refer to SunWize's tech note on Combiner Box Requirements.

Some solid-country charge controllers may have inherent design margins or overload protections that allow yous to use lower safety margins in your sizing. If strict NEC adherence is not required, consult with the charge controller manufacture for their sizing recommendation. Typically, information technology's the assortment Isc * 110%-125%. For safe purposes the overcurrent protection should still be sized per the NEC.

Determination

Agreement how to size a solar charge controller is disquisitional to the operation of your overall system. As we have seen, understanding the different charge controller types and appropriately sizing them can result in a properly running power organization. Accept more questions? Feel complimentary to sentry our more than in-depth webinar on the Charge Controller Types and How to Size Them. Chat with us through our conversation box or telephone call us at (866) 827-6527.