The number of solar panels a charge controller can handle is a critical question when planning solar system installation. This is to make sure that the controller will withstand the power of the panels to avoid permanently damaging the controller. Study this guide well as it will help you ascertain the maximum power of panels a controller can handle.
A solar charge controller comes in different amperage ratings. For a small system, a charge controller can serve but for a large panel and battery bank, two or more controllers are connected to handle the power.
What size of charge controller is best fit for a 500W solar panel?
Solar panels of different watts: Can they work together?
How to calculate how many solar panels per charge controller
The technique used in calculating the number of solar panels for a controller is that the panel’s output voltage shouldn’t be greater than the max input volt or VOC (Open Circuit Voltage) of the controller. What does that mean ? The solar charge controller maximum voltage (VOC) should at all time be greater than the voltage of the panels.
Note: Controller Maximum Voltage is the same as the Open Circuit Voltage (VOC)
For example, If we have a charge controller with a VOC of 100 volts and three panels of VOC 22 each.
If the 3 x 22V of panels are connected in a series, it will sum up to be 66V which is still below the controller VOC (100v). Because of that we can go ahead to add the three numbers of the panel to the controller. But in a situation where it is greater, then we looks for a bigger controller or consider adding another controller to it.
Let give another illustration for clearer understanding.
For the seek of this example we will be considering the MPPT controller most as it is more efficient and reliable than PWM.
The MPPT controller can handle up to 3 solar panels connected in series per string. This is because most of the MPPTs have a high VOC and three panels in a series will still not be up to it.
Some Examples
when you have 3 x 24V solar panels with a VOC of 46V. And 60A MPPT controller with a VOC of 150V. The three panels are in series which sum up the panel voltage together.
26v x 3 = 138V
So the solar array is 138V while the 60A controller VOC is 150V. So the controller can withstand the solar arrays.
Another example. Let’s say we have 3 x 300watts solar panels with VOC of 44V each. And a 50A solar charge controller of 100 VOC.
3 x 44V = 132V.
If we connect two panels in a series and hook them to the controller, it will work fine. But when we combine the three panels in a series the panel volts will exceed the VOC of the controller. So either we go for a higher controller with voc above 132V or we add an additional controller.
Adding safety margin
Our previous way of calculating the number of a Panels solar controller is ok but in other to be on the safer side. You can add for margin to your calculated value in case of emergency and room for adding more panels in future.
Some add about 25% of their calculated value. You can increase and the same time decrease depending on the system you are building.
In a situation where we have three solar panels of VOC 38V each connected in series. Which will sum up to 114 volts. If we calculate the type of controller to use for the system, it will be a 120 VOC controller as it is the nearest to the available match.
And if we choose to add a 25% safety margin to it, then it will sum up to 150 VOC.
114 + 25% = 152
Is not most to choose 25% lesser or higher percentage can be used to finalize your calculation
How many solar arrays can a charge controller handle?
The size of the battery is what determines the size of the solar arrays as the large the battery capacity the more solar panels and vice versa.
But we calculate it by
Charge controller Amps x Battery voltage = solar panel size in watts. So when we have a 30A controller and a 12V battery, then it will be;
30A x 12V = 360watts
And if the battery is a 24V battery then it will be
30A x 24V = 720 watts
The above formulas hold provided the VOC of the controller is not exceeded.
Guide in sizing solar charge controller
Always consider the controller VOC to be always greater than the solar arrays.
The controller size should be of the right size with the battery bank. The is size by dividing solar arrays in watts by system voltage and adding a 25% for a safe margin.
solar array watts/system voltage +25% safe margin = charge controller size.
when 3 solar panels of 41V each are connected in series and we are to size the controller for it. The it will be;
3 x 41V = 123V + 25% = 153.75 watts
The 123V arrays will need a 160 or 170 VOC capacity of a charge controller. 60A MPPT controller will serve the system well.
The charge controller capacity is determined by the max charge current and max input volt
tips to note when using a solar charge controller
- Always include a solar charge controller in your systems as it has many benefits that will contribute to the safe use of the system.
- Go to MPPT instead of PWM especially when it is a large system. This is because there is always a big difference in power loss between the two.
- Study the controller user manual and stick to the instructions. Contact the manufacturer when the information is not clear enough for your understanding.
- Observe the sun hour in your area. The weather conditions of your area like how cold or sunny it always be will help to make a good planning and estimation of solar panels and controllers to use.
- When estimating the size of the charge controller to use, make sure to add a safe margin of 20-25% of the calculated estimate.