John received his “complete solar kit” with a charge controller, solar panels, battery, and connecting wires but no wiring diagram!
It was a 400-watt solar kit.
With his friend Al on the other end of the phone, he carefully wired the kit and got it working.
By his reckoning, it took twice as long as it should, and all through the process, he recalls being tense a fearful, worried that he’d make a mistake!
Sounds familiar? Maybe not.
But perhaps if you ever find yourself in a situation where you’re unsure whether to connect the solar panels in series, parallel, or both, you’d want to have a guide to help you along.
The intended objective of this post is to guide you in deciding how best to wire your string of solar panels – series or parallel!
And, we’ve built a handy calculator tool to help you work out which one to use.
I want to Go Straight to the Solar Panel Series or Parallel Calculator for Solar Panels, Or,
Take me to the Pros and Cons of Connecting in Series vs. Parallel and the Worked examples
The Pros and Cons of Connecting Solar Panels in Series Or Parallel
Overall, you’re probably better off connecting the solar panels in series provide the total voltage and current from the solar panels do not exceed what the charge controller can handle.
You can see the advantages and disadvantages in the table below.
Worked example 1
If I have a 400-watt solar kit with 4 pieces of 12V 100-watt solar panels and a 30A PWM charge controller
Step 1. Confirm the maximum input current and voltage that the charge controller can handle.
From the charge controller user manual, in this case, it might be as follows:
- Maximum input voltage: 25VDC
- Maximum charging current: 30A.
Step 2. Confirm the maximum input current and voltage that the charge controller can handle.
You can get this from the solar panel user manual or the specifications card at the back of each panel.
Assume in our case, it is as follows:
- Optimum Operating Voltage (Vmp): 20.4V
- Optimum Operating Current (Imp): 4.91A
Step 3. Decide on whether to connect them in series or parallel – ensure you do not exceed the voltage and current limits of the charge controller!
Looking at the data in steps 2 and 3, the maximum number of solar panels you can connect in series without exceeding the voltage limit of the charger controller is 1.
(The maximum input voltage of the charge controller is 25V. The solar panel output voltage is 20.4V!).
Therefore, we should probably be looking at connecting all four panels in parallel.
Let’s confirm that with four panels connected in parallel, we’re not exceeding the Maximum charging current: 30A of the controller.
With each solar panel having an Optimum Operating Current (Imp): 4.91A, with four panels this adds up to 19.64V which is below the maximum charging current of 30A.
So, this confirms that with this controller, we should probably be looking at connecting all four panels in parallel. Connecting otherwise will destroy the controller!
Worked example 2
If I have a 400-watt solar kit with 4 pieces of 12V 100-watt solar panels and a 40A MPPT charge controller
Step 1. Confirm the maximum input current and voltage that the charge controller can handle.
From the charge controller user manual, in this case, it might be as follows:
- Maximum input voltage: 100VDC
- Maximum charging current: 40A.
Step 2. Confirm the maximum input current and voltage that the charge controller can handle.
You can get this from the solar panel user manual or the specifications card at the back of each panel.
Assume in our case, it is as follows:
- Optimum Operating Voltage (Vmp): 20.4V
- Optimum Operating Current (Imp): 4.91A
Step 3. Decide on whether to connect them in series or parallel – ensure you do not exceed the voltage and current limits of the charge controller!
Looking at the data in steps 2 and 3, the maximum number of solar panels you can connect in series without exceeding the voltage limit of the charger controller is 4.9.
This is from the Maximum input voltage of the charge controller/ optimum Operating Voltage (Vmp): 20.4V of the solar panels.
Therefore, we should probably be looking at connecting all four panels in series.
Finally, let’s confirm that with four panels connected in series, we’re not exceeding the Maximum charging current: 40A. of the controller.
With each solar panel having Optimum Operating Current (Imp): 4.91A, with four panels in series, this adds up to 4.91V which is below the maximum charging current of 40A.
So, this confirms that with this controller, Therefore, we should probably be looking at connecting all four panels in series safely.
Now, I realize that there’s a lot involved – that’s why I put together this handy tool.
Simply input the charge controller limits and the panels you have in an instant the maximum number of solar panels you can connect in series or parallel.
Note: This is only intended as a guide. Always contact a qualified solar installer.
Closing Thoughts
Aim to connect the solar panels in series to keep the overall charging current to a minimum which means you use thinner, less expensive cables which harvest more solar power from the panels.
You Should NEVER exceed the manufacturer-recommended input voltage and current of the controller or else you’ll destroy the controller.
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