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  • Austin Brentley

Solar Panel Wiring: How To Connect Solar Panels



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 configuration to your customers.


And here’s why.


The average solar installation only takes 1 or 2 days to complete. But given the upfront costs associated with installing panels, it can take months to go from initial consultation to a signed solar proposal.


Being able to clearly outline the impact that parallel vs. series wiring will have on PV system efficiency, output and savings is often critical to making that sale. Which wiring option you choose also influences other aspects of the installation – like which inverter technology to use.


This guide covers the most essential elements of solar panel wiring, including the pros, the cons, and a few best practices.


How to Connect Solar Panels

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 cells to produce panels

  • Installers connect many panels together to create solar arrays

  • With enough solar arrays, you have a utility-scale PV 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:


  • Series wiring in which each solar panel’s positive terminal connects to the next module’s negative terminal.

  • Parallel wiring in which all positive terminals are connected to one another – and all negative terminals are connected to each other.

  • Hybrid wiring in which the panels are connected using a mix of series and parallel arrangements.


Defining Common Electrical Terms

From grid connectivity to solar permitting to feasibility studies, you likely deal with technical terms every day. But the average homeowner normally doesn’t understand these concepts. Most barely understand the basics of solar power production.


This is why you should always go to 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 is what causes electricity to “flow” – explaining why voltage is often compared to the water pressure in a home’s plumbing system.


2. Amperage

Amperage represents the rate at which electrons move from areas with high pressure (voltage) to areas of low pressure. Known as electrical current, this rate is measured in amps or “A.” And in plumbing terms, amperage is analogous to the flow of water.


3. 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. It’s this resistance that allows the flowing electrons to perform work – like powering lights. Work is measured in watts (W).


These three values can be combined into Watt’s Law:


Watts = (Volts x Amps)


Using this formula not only tells you which panels and inverters to use for any given system, it also lets you know whether to use series or parallel wiring in that installation. The rest of this article explores the benefits of each configuration – including which inverter technology makes the most sense for any given installation.


How to Wire Solar Panels in Series

Combining 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 panels increases the total voltage of the entire series. However, the current remains unchanged.


The main benefit of this approach is ease. Panels connected in series use less overall wiring, making this a cheaper and faster option for many installations. In addition, wiring solar panels in series allows you to connect PV components that might be spaced far apart.


However, series connections do have certain drawbacks:


  • Shading on one panel can reduce the entire series’ current. This is because the panel with the lowest amperage sets an upper limit for all the other connected panels in the string.

  • The above problem isn’t just limited to the panels. It also impacts the wires used in between. If one wire goes out, the whole series of panels stop working (much like traditional Christmas lights).


While it’s possible to overcome these limitations with microinverter and Maximum Power Point Tracker (MPPT) technology, both workarounds can increase the total installation cost.


How to Wire Solar Panels in Parallel

As mentioned before, parallel 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.


The main benefit of parallel connections 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 control less necessary.


But again, every wiring configuration has disadvantages:


  • Parallel wiring is more complex to set up due to the extra materials involved

  • It’s very difficult to increase voltage after the fact. And this makes optimizing existing PV systems much harder


Tips for Wiring Solar Panels

Based on the above, it’s reasonable for your solar energy clients to conclude that series wiring is best for installations that receives some shade – and parallel wiring is better suited when shading isn’t a problem.


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 Inverter’s Range

Every 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:


  • If the array’s voltage falls below this range, the installation won’t generate any usable power. This is because 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.

  • If the array’s voltage lies above this range, your panels will generate more power than what the inverter can accommodate. This indirectly reduces your potential savings. And it may also shorten the inverter’s lifetime.


Know Your MPPTs

Maximum Power Point Tracking is a relatively modern type of inverter technology that can optimize PV 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 the Right Design Software to Plan Systems

Which wiring configuration to use ultimately depends on the PV system in question. And this involves crunching the numbers as you run through multiple solar power system designs for each potential project.


Fortunately, an emerging generation of solar design software is helping to automate this process – complete with wiring recommendations, energy production calculations, monthly savings, and 3D renderings all generated with a few mouse clicks. This software not only helps save time, but it can also move you closer to making that sale.


Connecting Solar Panels in Series Vs. Parallel: Which Is Better?

Every installation is unique. And the best way to determine which wiring approach to use requires looking at different design arrangements and seeing which configuration delivers the best returns for the client.


As a rule, you’ll usually be OK using series wiring 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


And parallel 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 battery banks are spaced close together – reducing potential transmission losses


In addition, many larger PV systems use a hybrid wiring approach to achieve the optimal balance between voltage and amperage when powering more complex applications.


Conclusion

Electrical wiring isn’t the most exciting topic, but being able to convey the benefits of connecting solar panels in series vs. parallel will help your own customers make better informed decisions about their clean energy investments. In fact, being able to communicate ideas clearly (and visually) is essential to the solar sales process.


Work with our network of talented designers and engineers to build the best possible systems for your clients. Connect with a rep today.