As a photovoltaic (PV) installer, it's not enough to understand how to wire solar panels or whether to use series vs. parallel configurations for any given system. You must also be able to clearly explain the relative pros and cons of each solar panel wiring configuration to your customers.
And here's why. The average solar panel installation only takes 1 or 2 days to complete. However, given the upfront costs associated with installing panels, it can take months to go from initial consultation to a signed solar proposal.
Clearly outlining the impact that parallel vs. connecting solar panels in series will have on PV system efficiency, solar energy output, and electric bill savings is often critical to making that sale. Which wiring option you choose also influences other aspects of the solar panel installation – like which solar inverter technology to use.
This guide covers the most essential solar panel wiring basics, including the pros and cons of connecting solar panels in series and in parallel.
Solar Panel Wiring Basics
One of the reasons behind solar PV's explosive growth is its modularity:
All you need is one PV cell to start generating solar power
Manufacturers combine many solar cells to produce PV panels
Solar installers connect many panels together to create arrays
With enough solar arrays, you have a utility-scale solar farm
What allows for this scalability is the wiring that connects all these energy production units together. Although there are many different approaches to solar panel wiring, most PV installations feature:
Wiring solar panels in series involves each panel's positive terminal connecting to the next module's negative terminal.
Wiring solar panels in parallel in which all positive terminals are connected to one another – and all negative terminals are connected to each other.
Hybrid solar panel wiring is when the panels are connected using a mix of series and parallel solar panel wiring.
Defining Common Electrical Terms Related to Solar Panel Wiring
From grid connectivity to solar permitting to feasibility studies, you likely deal with technical terms every day. However, the average homeowner usually doesn't understand these concepts. Most barely understand the basics of solar power production. This is why you should always go to solar inspections and consultations armed with a few definitions that are easy to understand.
1. Voltage
Represented with a "V," voltage is the difference in charge between two separate points in an electrical circuit. This difference causes electricity to "flow" – explaining why voltage is often compared to the water pressure in a home's plumbing system.
Temperature affects solar panel voltage through a coefficient called the temperature coefficient of voltage (TCV). These coefficients measure the percentage change in voltage output per degree Celsius temperature variation. A positive temperature coefficient of voltage means that as temperature increases, the voltage output decreases by a certain percentage.
2. Amperage
Amperage represents the rate at which electrons move from areas with high pressure (voltage) to areas of low pressure. This rate is known as electrical current, measured in amps or "A." In plumbing terms, amperage is analogous to the flow of water.
Amperage, or current, is an essential factor in solar panel wiring. It determines the size of the electrical cables needed to handle the current safely and efficiently, ensuring proper operation and minimizing the risk of overheating or electrical hazards.
3. Solar Panel Wattage
Voltage and current are instantly created whenever sunlight hits a PV module. Pushed by voltage, the electrical current courses through the installation until it encounters resistance. This resistance allows the flowing electrons to perform work—like powering lights. Work is measured in watts (W).
Wattage, or power, is a key consideration in solar panel wiring as it determines the maximum amount of electricity the solar panels can generate. Proper wiring sizing and configuration are necessary to accommodate and safely handle the generated wattage.
Watts, volts, and amps can be combined into Watt's Law:
Watts = (Volts x Amps)
Using this formula not only tells you which solar panels and inverters to use for any given PV system, but it also lets you know whether to use series or parallel solar wiring for an installation. The rest of this article explores the benefits of each solar panel wiring configuration – including which solar inverter technology makes the most sense for any given installation.
Solar Panels Wiring in Series
Wiring solar panels in series is the older of the two methods. And it involves literally connecting panels in sequence – just like with traditional Christmas lights. Adding more solar panels increases the total voltage of the entire series. However, the current remains unchanged.
Pros | Cons |
Higher voltage output | Lower overall solar system efficiency |
Simplified solar panel wiring | Affected by shading on a single solar module |
Suitable for long-distance wiring | If one solar panel fails, it affects others |
Advantages of Solar Panels Wiring In Series
The main benefit of this approach is ease. Wiring solar panels in series uses less overall wiring, making this a cheaper and faster option for many solar panel installations. In addition, wiring solar panels in series allows you to connect PV components that might be spaced far apart.
Disadvantages of Wiring Solar Panels in Series
Unfortunately, shading on one solar panel can reduce the current of the entire string. This is because the panel with the lowest amperage sets an upper limit for all the other connected panels in the string. This problem isn't just limited to solar modules. It also impacts the wires used in between. If one wire goes out, the whole series of solar panels stops working (much like traditional Christmas lights).
While microinverters and Maximum Power Point Tracking (MPPT) technology can overcome these limitations, both workarounds can increase the total cost of solar panel installation.
Solar Panels Wiring in Parallel
As mentioned before, parallel solar panel wiring involves connecting all the panels' positive terminals to one another – and all negative terminals together. Adding more panels increases the total current of the circuit. However, the voltage remains unchanged.
Pros | Cons |
Higher overall solar system efficiency | More complex solar panel wiring |
Better performance when the array is shaded | Requires larger wire size and possibly more components |
If one solar panel fails, others continue producing | Less suitable for long-distance wiring |
Advantages of Wiring Solar Panels in Parallel
The main benefit of parallel solar panel wiring is that every panel acts independently, which allows the entire system to continue generating power even if one panel stops working due to shading or a malfunction. In effect, every solar module becomes an autonomous circuit, making MPPT less necessary.
Disadvantages of Solar Panels Wiring in Parallel
Again, each solar wiring configuration has disadvantages. Parallel solar panel wiring is more complex to set up due to the extra materials involved, such as junction boxes and fuses, which can drive up solar system costs. Also, increasing voltage after the fact is challenging, which makes optimizing existing PV systems much harder.
Tips for Solar Panel Wiring
Based on the above, it's reasonable for your solar energy clients to conclude that series wiring is best for installations that receive some shade – and parallel wiring is better suited when shading isn't an issue.
They wouldn't be entirely wrong. Unfortunately, it's not that simple. There are some additional factors worth considering.
Make Sure Your Voltage Is Within the Solar Inverter's Range
Every solar inverter comes with a voltage range. For maximum power generation, it's critical that the PV panels (and wiring) lie within each inverter's recommended spectrum:
The installation won't generate any usable power if the array's voltage falls below this range. The inverter doesn't become operational until it achieves its "start" voltage. Your panels may be producing energy, but none of that energy is saving you money or helping the environment.
If the solar array's voltage is above this range, your panels will generate more power than the inverter can accommodate. This indirectly reduces your client's electricity bill savings and may also shorten the inverter's lifespan.
Know Your MPPTs
Maximum Power Point Tracking is an inverter technology that can optimize solar energy output even as conditions change. It accomplishes this by monitoring the system to help the inverter find the optimal balance of voltage and current for "maximum" power generation.
Tracking this sweet spot in real-time allows inverters with MPPT technology installed to generate more clean energy per square inch than legacy inverters can.
Use Good Solar Design Software
Which solar panel wiring configuration to use ultimately depends on the PV system in question. This involves crunching the numbers as you review multiple photovoltaic system designs for each potential project.
Fortunately, solar design software is helping to automate this process – complete with solar panel wiring recommendations, AC and DC disconnects, energy production calculations, manufacturer specifications, monthly power bill savings, and 3D renderings -- all generated with a few mouse clicks. Solar design software helps save time and can move you closer to making that sale.
Solar Panel Wiring in Series Vs. Parallel: Which Is Better?
Every installation is unique. The best way to determine which solar panel wiring approach to use requires examining different design arrangements and determining which solar panel wiring configuration delivers the best returns for the client.
As a rule, you'll usually be OK using series wiring or solar panels in situations where:
Shading from trees or buildings isn't a problem
You need higher voltage – like if your array falls below the inverter's recommended minimum
Installing microinverters and MPPT technology is cost-effective
Parallel solar panel wiring is typically the better option in situations where:
Partial shading could impact total solar panel system performance
You want to add more panels without exceeding the inverter's voltage limits
When panels, inverters, and solar battery banks are spaced close together – reducing potential transmission losses
In addition, many larger PV systems use hybrid solar panel wiring to achieve the optimal balance between voltage and amperage for more complex applications.
Solar Wiring FAQs
Read on to gain answers to some of the most common questions from solar contractors.
Can I combine series and parallel solar panel wiring?
Series-parallel solar panel wiring is a configuration where solar panels are connected both in series and in parallel. Combining series and parallel wiring in a solar panel system is a common practice. Series-parallel solar wiring allows for achieving higher voltage and current outputs, which can be beneficial in certain solar power system designs.
This hybrid solar panel wiring configuration provides flexibility to optimize voltage and current, enhancing system performance. It allows for customization based on specific project requirements, ensuring efficient energy production.
Which solar panel wiring configuration is most efficient?
The efficiency of solar panel wiring depends on factors like shading and system size. Series solar panel wiring is more efficient in ideal conditions, optimizing voltage. Parallel wiring performs better for shaded applications, allowing independent panel operation. Combining series and parallel wiring configurations offers flexibility to tailor the system based on specific project requirements and environmental conditions, providing an efficient and adaptable solution.
Do I need special equipment for series or parallel solar panel wiring?
Both series and parallel solar panel wiring require standard equipment. Additional components may be necessary for shading mitigation in series solar panel wiring configurations, while parallel setups may demand larger wire sizes and extra junction boxes.
Is series solar panel wiring less expensive?
Series solar panel wiring is often less expensive for smaller installations due to its simpler design and reduced need for additional components. However, costs depend on various factors, including system size and specific project requirements. Parallel wiring may offer advantages for larger installations or those with shading concerns. Still, it can be more complex and potentially costlier due to the need for larger wire sizes and components.
Can solar panel wiring cause underperformance?
Poor solar panel wiring practices, such as loose connections and faulty wiring, can lead to underperforming solar panel systems. Electrical problems caused by improper wiring can disrupt the flow of electricity and reduce power output, leading to underperformance. Additionally, using thin wires can lead to voltage drops, further reducing system performance. It is crucial to ensure proper installation, including correct wiring, secure connections, appropriate wire gauge size, and appropriate materials, to prevent these issues and maximize system performance.
Are there safety standards for solar panel wiring?
The safety standards for solar panel wiring include compliance with the National Electrical Code (NEC) and obtaining necessary solar permits required by the authority having jurisdiction. The NEC provides provisions specifically related to solar energy systems and covers electrical components and systems involved in PV installations.
Solar permitting ensures that projects meet local safety regulations and code requirements for grid-connected solar systems. Adhering to these standards for solar panel wiring is essential to ensure safe and reliable operation.
How do I select the proper wire gauge for solar panel wiring?
Several factors must be considered when selecting the proper wire gauge for solar panels, including the maximum current output, voltage drop limitations, and PV system configuration. It's crucial to perform the necessary calculations or consult with solar professionals to ensure the wire size can handle the anticipated current. Referencing American Wire Gauge (AWG) charts can help determine the appropriate wire gauge based on the maximum current the setup can handle.
Remember that the GreenLancer network is available for help with solar plan sets, engineering reviews, and solar permit applications. Complete an account to begin shopping for solar design, engineering, and permit design services.
How do I wire solar charge controllers?
To wire a solar charge controller, you will typically need to follow a wiring diagram that includes the solar panels, the charge controller, the battery, and the load. This solar wiring diagram will outline the specific points of connection between these components. It is essential to familiarize yourself with the wiring diagram provided by the manufacturer, as specifications may vary depending on your charge controller's specific make and model.
The Quest for Optimum Solar Panel Wiring
Electrical wiring isn't the most exciting topic, but conveying the benefits of connecting solar panels in series vs. parallel will help your customers make better-informed decisions about their clean energy investments. In fact, communicating ideas clearly (and visually) is essential to the solar sales process. For more solar installation tips, check out the GreenLancer blog, considered a leading renewable energy blog.
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