Solar Panels Series or Parallel: The Evergreen Solar Dilemma

Solar panel series offer good expansion potential and lower cost, parallel connections are less prone to shading issues, while hybrid options combine the best of both worlds.

Series connected arrays produce higher voltages and low amperage, allowing for growth and low installation costs. In contrast, parallel wiring models produce low voltages and high amperage and are less prone to issues such as array shading. Hybrid, or series/parallel, wired panels combine the characteristics of both types, allowing for excellent installation flexibility.

Another important consideration is how your choice of connection model impacts the rest of your installation equipment choices. For example, series circuits favor MPPT charge controllers, while parallel models work best with PWM types. The same holds for your choice of cabling, connectors, and termination hardware.

Our blog post examines these theories in detail and also gives insight into which model you should choose.

What Are Series And Parallel Circuits?

All direct current (DC) power sources, such as batteries or solar panels, have positive and negative output terminals. The electrical energy they produce flows from the positive terminal through a load (a light bulb or motor) and then back to the negative terminal.

The circuit is straightforward if you are using a single source, i.e., one battery. If, on the other hand, you need to use more than one source, those sources have to be connected somehow. And that’s where series and parallel connections come into play.

Series Circuits

The batteries are connected like a daisy chain in a battery series circuit. One battery’s positive terminal is connected to the adjacent one’s negative terminal. If you can imagine the trucks in a train, that’s what the circuit looks like. This concept is illustrated below.

Parallel Circuits

The same batteries connected in parallel have all the positive terminals connected and all the negative terminals connected. Check out the illustration below for a parallel circuit example.

What Are the Electrical Differences Between the Two Circuits?

To get to grips with those differences, consider the three main parameters in rating DC power sources directly related to solar panel wiring.

1. Voltage: The electrical “pressure” a power source has to push electrical energy through the circuit. Measured in Volts.
2. Amperage: The voltage pressure pushes the volume of electrical energy through the circuit. Measured in Amps
3. Wattage: The strength or capacity of the two previous elements to perform work. Measured in Watts.

Series Connections

In a series circuit, the voltages of each source are added together. The amperage of the combined sources remains the same as the individual ratings, though. Here’s an example. If the two batteries in the series circuit illustration above are rated at 1.5 volts and 500 mA each, the circuit output would be 3 volts (1.5 x 2) and 500 mA.

The following calculation is used to calculate the wattage the circuit can sustain: Amperage x Volts = Watts. In this case, the circuit could deliver 1.5 Watts (3 x 0.5 = 1.5)

Parallel Connections

If power sources are connected in parallel, the series calculation is reversed. In other words, the output voltage remains the same while the amperage doubles. In other words, the output would be 1.5 Volts and 1 (500mA x 2) amp.

So, how does that affect the wattage capacity of the circuit? Let’s take a look using the amperage calculation. 1 Amp x 1,5 Volts = 1.5 watts.

Summary

The voltage increases with every extra battery or solar panel added in series circuits while the amperage remains the same. In contrast, a parallel circuit’s voltage remains unchanged while the amperage increases. However, the wattage remains the same irrespective of which circuit is used.

How Does This All Relate to the Wiring of Solar Panels?

Solar panel wiring methods are important considerations when planning a solar installation. Let’s look at all the benefits, downsides, and different applications of each wiring type.

Connecting multiple solar panels is similar to our battery examples. The math involved is also the same. Here are examples of both ways to wire solar panels and their calculations.

Series/Parallel Solar Panel Wiring

We need to introduce a third option to wire solar panels, hybrid or series/parallel wiring.

A hybrid panel array consists of two or more groups, or strings, of series wired PV panels connected. Although the calculations are slightly more complex, all the theories still hold. Here is an example of a hybrid solar panel setup.

What we have here are two strings of series-wired solar panels. Essentially, each string forms a single solar panel. Those two “panels” are then wired up in parallel; beyond that, the standard parallel theory applies.

Arrays of solar panels wired in a hybrid configuration are popular among solar installers and offer some unique benefits that we’ll examine later.

Here is a video that describes the preceding theories.

What Are the Pros, Cons, and Applications of Wiring Solar Panels in Series or Parallel?

To kick off, let’s look at the four basic elements in a solar system that affect the choice of wiring method. These are:

1. Panel array size
2. Charge controller choice
3. Panel location
4. Environmental factors

Panel Array Size

Small to medium solar panel layouts can be wired in series or parallel, with the deciding factors being any one or a combination of the other 3 elements.

Large solar array layouts are almost always wired using hybrid or series/parallel wiring.

Charge Controller Choice

Series-wired solar panels are ideal for MPPT charge controllers, while PWM controllers are best suited to panels wired in parallel.

Panel Location

Panels located long distances from the charge controller require lengthy cable runs. As parallel-wired panel arrays produce higher amperages, they require heavier gauge wiring. This can increase the installation cost significantly, making series circuits more suitable.

Environmental Factors

It’s not always possible to find a perfect location for your solar array, and the proximity of buildings and trees can cause problems with shading, particularly partial shading. Here’s why.

Try and think of a string of Christmas lights. They are wired in series; if one globe dies, the rest of the string dies. Series wired solar panels are similar in that partial shade falling on one or more panels can play havoc with the array’s performance.

For this reason, wiring solar panels in parallel is often the best choice for locations with partial shading during the day.

Where It’s Best to Wire Solar Panels in Parallel, Series, or Hybrid Configurations

Let’s check out a couple of typical solar installation scenarios and which wiring type would be ideal for each solar panel system.

Small-Scale RV Solar Setup—Scenario 1

Specifications

• 2 x roof-mounted 12 Volt, 3 Amp solar panels
• 24 Volt, 10 Amp PWM charge controller

Series Connection

If you wired the solar panels in series, the output would be 24 Volt (2 x 12) at 3 Amps. Now, while that’s within the maximum input specs of the charge controller, the voltage is maxed out. This will leave you no room to expand the RV solar panel system and probably lower the controller’s lifespan.

Parallel Connection

Wired in parallel, the same panel’s output is 12 Volt at 6 (2 x 3) amps, comfortably within the charge controller’s maximum ratings.

Conclusion

In this scenario, wiring the panels in parallel would be the best choice of wiring solar panels for the following reasons:

1. The solar panel outputs better match the rated maximums of the charge controller.

2. As a roof-mounted installation, the cable run would be short. Any wire gauge increase to deal with the higher amperage would be negligible.

3. RVs are often parked in shaded areas. Parallel-wired solar panels are more efficient and deliver more consistent results in those situations.

Small-Scale RV Solar Setup—Scenario 2

Specifications

• 2 x mobile 12 Volt, 3 Amp solar panels
• 36 Volt, 40 Amp MPPT charge controller

Series Connection

If you wired the solar panels in series, the output would still be 24 Volt (2 x 12) at 3 Amps. The panel output is now well below the controller’s maximum rating.

Parallel Connection

Similarly, wiring the same solar panels in parallel would produce 12 Volts at 6 (2 x 3) amps, which are also comfortably within the charge controllers’ requirements.

Conclusion

In this scenario, wiring the solar panels in parallel or series would perfectly fit the charge controller. However, a series connection would be the better choice. Here’s why:

1. The mobile panel array may be far from the vehicle and charge controller. Having a lower amperage would mean thinner wiring and reduced costs.
2. With mobile solar panels, finding an unshaded location or moving them around as the sun moves across the site is easier.

Small Scale Residential Solar Installation—Scenario 1 – Roof Mount

Specifications

• 4 x roof mount 20 Volt, 5 Amp solar panels
• 48 Volt, 60 Amp PWM charge controller or 100 volt, 30 Amp MPPT charge controller

Series Connection

In this case, wiring solar panels in series would produce 80 Volts (4 x 20) at 5 Amps. This is way above the PWM controller’s maximum rated voltage. The MPPT controller will manage this type of connection method well, though.

Parallel Connection

The same panels wired up in parallel produce 20 Volts at 20 (4 x 5) Amps, both comfortably within either controller’s requirements.

Hybrid or Series/Parallel Connection

A hybrid connection method for this scenario would typically be two strings of 2 series wired panels connected in parallel. The output would look like this.

Both series strings would produce 40 Volts (2 x 20) at 5 Amps. When connected in parallel, the output is 40 Volts and 10 Amps.

Conclusion—PWM Controller

In this case, a series connection would be out of the question. On the other hand, a parallel setup would be well suited to the rest of the components. The hybrid wiring option would offer some benefits but would still not be ideal. Here are the facts:

1. The voltage from the series connection is too high for the PWM controller.
2. Both output parameters of the parallel set are ideal. In addition, the rooftop installation would generally place the controller closer to the panels. That would do away with long cable runs and negate the implications of the higher amperage output. The low number of panels would also not create a problem with the larger number of wires involved in parallel connections.
3. The hybrid setup would also work fairly well in this scenario. It would involve less rooftop wiring, not be as susceptible to shading, and produce less amperage. However, the voltage is fairly close to the controller’s maximum, which may require a step up in size with an obvious increase in cost.

Conclusion—MPPT Controller

1. Both series and parallel voltage and amperage outputs are well within the spec for the MPPT controller. However, the lower chance of shading in rooftop mounts, lower amperage, and fewer wires make a series connection the ideal choice. Unfortunately, an MPPT controller is more costly.
2. The hybrid wiring method would also be a good choice for this application, although it delivers better benefits in larger installations.

Small Scale Residential Solar Installation—Scenario 2 – Ground Mount

Specifications

• 4 x ground mount 20 Volt, 5 Amp solar panels
• 48 Volt, 60 Amp PWM charge controller or 100 volt, 30 Amp MPPT charge controller

Series, Parallel, and Hybrid Panel Connections

As we have used the same installation details as the roof-mounted installation, all the output details remain the same as those quotes above.

Conclusion

• Ground mount panel arrays will generally be located further away from the rest of the installation components. And that requires long cable runs. The lowest possible amperage figure is always a priority in planning ground-mount installations to reduce costs and electrical losses.
• Series connected solar panels produce high voltage and low amperage outputs, making them the only really viable solution for this type of installation. The flip side to this reality is that the use of PWM charge controllers is basically ruled out. However, the higher cost of a suitable MPPT controller is usually offset by the associated savings on cabling.

Large Scale Residential Rooftop Solar Installation

We’ll only cover large-scale rooftop solar panel systems because residential ground mount setups are generally small. The charge controller type will also be limited to MPPT, as PWM controllers are generally unsuitable for this type of installation.

Specifications

• 18 x 20 Volt, 5 Amp solar panels
• 250 Volt, 70 Amp MPPT solar charge controller

Series Connection

Connecting all solar panels in series will produce the following output: 360 Volts (18 x 20) at 5 Amps. This would not be viable because the voltage exceeds the charge controller’s maximum rating.

Parallel Connection

In this scenario, wiring the solar panels in parallel would produce 20 volts at a whopping 90 Amps. The amperage this connection method would produce paints it right out of the picture.

Hybrid Connection

Implementing a hybrid connection setup on this installation would produce the following numbers: 180 Volts (9 x 20 for the series strings) at a manageable 10 Amps (5 x 2 for the parallel component).

Conclusion

• Connecting an array of this size in series is not viable due to the excessively high voltage produced.
• The same applies to a parallel connection. The massive amperage produced is way above the controller’s capacity but would require a spaghetti junction of industrial gauge cable to make it work.
• This type of installation is really where hybrid connection methods shine. They allow installers to meet output requirements while manipulating the numbers to stay within reasonable parameters.

What Is the Conclusion in the Great Series vs. Parallel Debate?

One thing that does become abundantly clear here is that planning solar power installations is a balancing act, with each part of the whole affecting all others. Whether to connect solar panels in series or parallel is only one part of that whole, with the rest of the specifics playing a big role in the decision.

Equally apparent is that the choice of connection method can be a great tool in achieving that fine balance. Canny use of each connection method’s characteristics is often invaluable in ending up with efficient and productive solar energy options.

Here are the main takeaways:

• Series wiring solar panels produce high cumulative voltages with low average amperages and are well suited to smaller installations with longer cable runs. They have less connection wiring while being more sensitive to partial shading. Wiring solar panels in series are also more suitable for MPPT charge controllers.
• Parallel wiring solar panels produce averaged voltages and high amperage outputs. They are suited to smaller installations with short cable runs. In addition, parallel solar panels perform well in part, or even fully, shaded locations and are ideally suited to PWM controllers.
• Hybrid or series/parallel wiring of solar panels is the ideal solution for extensive solar power installations. They allow large panels to be set up while keeping voltage and amperage figures within manageable parameters. They are less sensitive to shading and only suitable for use with MPPT controllers.

We hope this article has helped demystify the conundrum of wiring solar panels in series or parallel. If you’d like to comment or have any relevant experiences to share, please use the comments section below.

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