Wiring Solar Panels

A very important consideration when setting up a solar power system, especially a DIY or off-grid one, is how to wire solar panels together. There are two primary concepts to learn, series and parallel.

The basics

A solar panel has two wires coming out from it, a + and -. The + and - refer to each wire's "polarity"
Each wire usually has a special connector on the end, usually an "MC4"
To be used, a solar panel must get hooked up to a charge controller. "Inverters" or "power stations" often have one or more charge controllers for solar.

If you just use a single panel, there aren't any wiring options other than to hook up the + and - wires to the two terminals of the charge controller. But a single panel rarely provides sufficient power, so you have choices to make when using two or more panels.

You can see the concepts of series and parallel at work on our Solar Panel Finder. We tell you which wiring options produce the most power per dollar for a DIY system.

Why do solar panel wiring options matter?

How you wire together your solar panels will determine:

Compatibility: Charge controllers have certain limits that must be followed for safety and to prevent damage.
Power production: Wiring also determines how much power you can get from a set number of panels

So what is "series" and "parallel"?

These two concepts can be used together in systems, but for now let's talk about them separately. We'll use the analogy of people holding hands to help explain. It's a little weird, but to start it's more intuitive than talking about electricity.

The physical connections

People holding hands in series side by side - Image by gstudioimagen on Freepik

Series hand-holding

People holding hands into center of a circle - Image by Freepik

Parallel hand-holding

Series hands

Let's pretend the people in these pictures represent solar panels. And just like a solar panel has two wires, one + and one -, each person has two arms. Let's say left arm is - and right arm is +. You can see in the series picture that the people are standing side-by-side in a line. Each person's - arm holding the next person's + arm. And the first and last person in line has a free arm, one - and one +.

This is a great analogy to the physical connections made in a series solar panel string. By the way, "string" means line of panels connected in series. Panels are connected together like a chain, with a free wire on each end of the string.

Parallel hands

Now let's look at the parallel picture. The people are all holding their right arms into the center of a circle. Every person is touching the same spot with their right hand, so all their right hands are basically connected. This is what happens in a parallel wiring. All the + wires are connected together in one spot, and all the - wires are connected in one spot.

The electrical connections

Each type of physical connection listed above has a corresponding electrical behavior.

Series

Voltage (Volts) of each panel adds up, current(Amps) settles on the lowest value of all the panels

Wiring diagram - 3S2P

Voltage and Current - 3S2P

3 Series 2 Parallel

← Parallel junctions →

Charge controller

wattbuild.com

Parallel

Current (Amps) of each panel adds up, voltage settles on the lowest value of any panel You pick one connection type over another in a given scenario based on what electrical behavior you want.

How do I pick between making voltage or current add up?

Anything you connect solar panels to will have a maximum safe voltage and a current limit. The goal is to allow as many solar panels to be connected to a device as possible while making sure the voltage and current are within limits. Let's look at some examples.

Example 1: A charge controller limited to 98V and 10A

A charge controller is a device that sits between solar panels and a battery. Let's say our charge controller has a maximum voltage of 98V and a maximum current of 10A. If you have a single panel that has a V_oc of 50V and a max current of 5A, you can connect it directly to the charge controller. But you have two panels, and you want to get as much free sunshine electricity as possible!

You can't connect them in series, because the voltage would be 100V (50V + 50V), which is over the limit. You could connect them in parallel, because the current would be 10A, which is just at the limit. So, you would connect them in parallel.

Example 2: A charge controller limited to 102V and 9A

In this scenario, let's say our charge controller is limited to 102V and 9A, and we still have those two panels with V_oc of 50V and a max current of 5A.

In this case, we can't connect them in parallel, because the current would be 10A (5A + 5A), which is over the limit (it's actually safe to break this rule, it's called overpaneling, but let's ignore that for now). We could connect them in series, because the voltage would be 100V, which is under the limit. So, we would connect them in series.

Hopefully this was helpful! Stay tuned for more updates on combining series and parallel connections into one system!