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.
Now that you know what size solar controller to look for, identify which type of solar charge controller is right for your application: MPPT, PWM, and PWM shunt 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.
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.
All renewable energy (RE) systems with batteries should include a charge controller. In this article we'll principally be referring to solar charge controllers . Charge controllers prevent battery overcharging and also prevent the batteries from sending their charge back through the system to the charging source (i.e., the solar panels). Think of a solar charge controller as a battery nurse—its job is to monitor the battery bank, feeding it what it needs and checking its vital signs. Since a solar controller does its work in line between the solar panel array and the batteries, it would make sense that its selection and sizing would be influenced by those components. And that’s exactly the case.
Voltage and amperage (or current) are the parameters we use in solar charge controller sizing. The solar controller must be capable of accepting the voltage and current produced by the DC source (usually solar panels) and delivering the proper voltage and current to the batteries. This situation might make you think that the DC source, charge controller and batteries must all share a common voltage. While that is one system design strategy used in many installations, it’s not the only one. More on the alternatives later. For now, it’s one voltage for everyone!
Technically speaking, the DC source must always have a higher operating voltage than the battery bank in order for current to flow from one to the other. A handy way to remember this fact is the statement, “Curent flows downhill.” For the purpose of this discussion, we’ll use nominal voltage which means common battery voltages. Nominal voltage in this sense is synonymous with battery voltage. Since batteries (where they are used) are in many ways the heart of an RE system, we can call the bank’s voltage the system voltage. The system voltage selected for any given installation is usually, though not always, determined by the battery bank required by the application; the inverter, if one is used, will also influence the choice of system voltage.
Sizing comes down to this: there’s the quick method, which will very likely give an acceptable, if perhaps oversized result, but won’t describe the why ; and there’s the more detailed method, which will reveal all the steps for greater understanding and precision. We’ll look at both methods.
Sizing MPPT solar charge controllers by hand can be one of the more difficult takes for a system designer. Unlike PWM or shunt controllers, many MPPT controllers have the ability to down convert higher voltage PV (solar panel) arrays to lower voltage battery banks. In order to do the calculations, a few different NEC (national electric code) factors are required. To explain this process is beyond the scope of this article, but we can give a couple of web links to get you close. If you are unsure of the correct controller for you, contact a solar professional to help, wellsee is the best choice for you!