Are solar panels wired in series or parallel?

Solar panels can be wired in series or parallel and in a few cases, it might be a combination of both. The working current and working DC voltage of the inverter or charge controller choose the greatest number of solar panels that can be connected in series or parallel. Organizing solar panels in series or parallel is called a string plan and this is a necessary part of the design This article deep jumps into the key plan parameters of solar panels and inverters that help to choose if solar panels must be connected in series or parallel.

How does the back of a solar panel look?

If you look at the flip side of a solar panel, you will see a black box and two cables coming out of this box. The dark box is called a junction box (IP 68 rated). There is one positive and one negative cable coming from this box. The junction box is IP 65 rated. The cables are single-center copper with a cross area of 4mm2. You will discover MC4 connectors used at the terminals of the cables. How you connect these cables decides if it’s a series or parallel connection.

What is a series connection?

 A series connection is formed by connecting the positive terminal of one panel to the negative terminal of another panel. You can also create a series connection by connecting the negative terminal of one panel to the positive terminal of the following panel, as shown in the figure below.

What is a parallel connection?

In a parallel connection, you connect all positive terminals together and all negative terminals together.  In the figure below, you can see that all the positive cables connect to a common point, and from there, a single positive cable goes to the charge controller. Similarly, all the negative cables connect to a common point, and from there. A single negative cable goes to the charge controller. This configuration is known as a parallel connection. 

What happens if you increase solar panels in series?

When solar panels are connected in series it is called a string. You can have different strings in a solar installation. When connecting solar panels in series, the voltage increases while the current remains the same. For example, in a 400 Wp (Wp stands for watt top – maximum power the solar panel can produce) solar panel. The maximum power current is 13.15 A and the open circuit voltage is 36.98 VDC. When you connect 400 Wp solar panels in series, the voltage products by the number of solar panels you connect in series while the current remains steady. For example, if you interface 10 solar panels in series, the voltage will be 370 VDC while the current remains at 13.15 A.

What happens if you increase solar panels in parallel?

When solar panels are connected in parallel, the voltage remains steady while the current increases. For example, in a 400 Wp solar panel, the maximum power current is 13.15 A and the open circuit voltage is 36.98 VDC. When the solar panels are connected in parallel, the voltage remains steady while the current multiples by the number of solar panels connected in parallel. For example, if you connect 10 solar panels in parallel, the voltage remains at 36.98 VDC whereas the current increases to 131 A.

What decides the maximum number of panels you can connect in series and parallel?

The short answer is the inverter or charge controller decides the maximum number of solar panels you can connect in series or parallel. Let’s consider two examples to make this better. In example 1 we will consider a 5 kWp solar installation and in example 2 we will consider a 10 kWp solar installation.

Example 1: 

• 5 kW rooftop solar installation. For this case, let us consider a standard 300 Wp solar panel and GoodWe GW5k-DT inverter. A standard 300 Wp board has an open circuit voltage of 44.71 VDC and a short circuit current of 8.94 A.
• GW5k-DT inverter can suit a maximum of 7.5 kW of solar panels and has a max. DC input voltage of 1,000 VDC. The greatest input current is 12.5 A.
• The first step is to get generally how many solar panels you will require for a 5 kW installation. Each solar panel considered is 300 Wp, you will require approx. 16 solar panels for a 5 kW installation.
• There are two ways one can execute this extension. You can have 2 strings comprising 16 panels or 1 string comprising 16 panels. Let’s look at both options.
• Option 1: 8 solar panels are connected in series to shape the to begin with string and another 8 solar panels are connected in series to shape the moment string. In each of the strings, the string voltage is 357 VDC while the string current is 8.94 A. The GoodWe inverter supports 2 MPPTs and 1 string per MPPT.The inverter is connected to one input terminal of each of the strings.
• Option 2:  The 16 panels increase the string voltage to 715 VDC. While keeping the current steady at 8.94 A by connecting them in series, the string directly connects to one MPPT input of the inverter.

Example 2: 

10 kWp roof best solar installation. For this example, let us consider a standard 300 Wp solar panel and GoodWe GW10kT-DT inverter.

• A standard 300 Wp panel has an open circuit voltage of 44.71 VDC and a short circuit current of 8.94 A.
• GW10kT-DT inverter can suit a maximum of 15 kW of solar panels and has a max. DC input voltage of 1,000 VDC. The greatest input current is 12.5 A.
• The first step is to understand generally how many solar panels you will require for a 10 kW installation. Each solar panel considered is 300 Wp, you will require approx. 34 solar panels for a 10 kW installation.
• Unfortunately, if we connect 34 panels in series, the string voltage will be over 1,000 VDCa limiting factor on the inverter. So, in this case, we only have one option. Which is to partition the 34 panels into 2 strings of 17 panels in each string.
• String 1 will have 17 panels, the string voltage for 17 panels connected in series is 760 VDC and the current is 12.5 A. So also string 2 will have 17 panels.

So how do you decide between series and parallel?

The first step is to confirm the solar capacity you need to install. The moment step is to get it how many solar panels you require. The third step is to discover a suitable inverter and get the details on the inverter. The fourth and last step is to plan the string setup based on solar panel and inverter details.

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