Connecting different solar panels. Series vs Parallel Solar Panels: Which is Best?

Wiring Solar Panels In Series vs Parallel: What’s The Difference Free Calculator

Are you unsure if wiring solar panels in series vs parallel is best? Use our solar panel series and parallel calculator discover the ideal way to wire your solar panels for an optimized camper solar setup. Our comprehensive guide provides practical step-by-step guidance, using clear diagrams and personal experience.

In this post, you’ll learn the various methods for wiring multiple solar panels together to optimize your camper solar setup.

We’ve got you covered with an interactive solar panel calculator to help you determine the ideal configuration for your solar array.

Our guide starts with easy-to-follow diagrams outlining the different wiring configurations and explains how each affects the necessary components.

We’ll even tackle the complexities of mismatched multiple solar panels.

As seasoned, full-time RVers who have experienced hiccups while setting up our RV solar system, we created this post to help you avoid these mistakes.

Consider this post a vital part of our series on RV solar panel systems.

If you’re new to electrics or van builds, start with our beginner’s guide to camper van electrics.

Solar Panel Series and Parallel Calculator

Depending on the number of panels and sizes, your set up could have many different configuration options.

This calculator allows you to enter up to three different panel specs and as many of those panels as you choose.

Enter the details, and we’ll calculate the total power output, voltage and current they could produce when wired:

• in series
• in parallel
• and in a combination, with each panel spec wired in series, then all series groups wired together in parallel,
• and in a combination, with each panel spec wired in parallel, then all parallel groups wired together in series.

It’s important only to enter each spec on one line or your calculations will be skewed.

Aim to choose a configuration that balances the least loss of total power output and a high enough voltage to charge the batteries all day. Calculations are rounded.

We aim to get the best combination of watts (power out) and voltage, so we can spend more time off-grid and make our batteries last longer.

Suppose you’d prefer to wire your mix of panels without losses. In that case, you must wire each panel variant with a dedicated solar charge controller.

We’d need an MPPT controller to handle the string of 95w panels and another for the 130w panel with our setup.

It becomes an expensive pastime, so best to install matching products wherever possible.

Use our other electrical calculators to help size your camper’s electrical system.

Ways of Wiring Multiple Solar Panels

There are three different ways of wiring multiple solar panels on your RV camper:

We’ll look at each of these in turn before comparing.

Solar Panels Wired in Series

Each solar panel has a positive and a negative terminal. A series connection is created when one panel’s positive terminal is connected to the negative terminal of another.

When solar panels are wired in series, the array’s voltage is added together while the current (or amps) stays the same.

In the diagram above, 4 x 100w panels, each with a rated voltage of 17.9 and current of 5.72A, wired in series could produce 71.6 volts and 5.72 amps – a total of 409 watts.

Note, solar panels’ wattage is rated under standard test conditions. So, for example, these 100w panels will provide 100w then but slightly more in colder temperatures.

Solar Panels Wired in Parallel

A parallel connection is created when the positive terminal of one panel is connected to the positive terminal of another, and the negative terminals are connected to each other.

The connections are made with branch connectors.

When solar panels are wired in parallel, the array’s voltage stays the same while the current (or amps) are added together.

In the diagram above, 4 x 100w panels, each with a rated voltage of 17.9 and current of 5.72A, wired in parallel could produce 17.9 volts and 22.8 amps – a total of 409 watts.

Solar Panels Wired in a Combination of Series Parallel

There are no surprises for figuring out what wiring solar panels in a combination of series and parallel means.

Taking the same 4 x 100 watt panels, you’d wire a pair in one string (i.e. in series), the 2nd pair in another string, then wire the two strings in parallel.

When solar panels are wired in a combination of series and parallel, the voltage in each string is added together while the current (or amps) stays the same.

Then, the two strings’ voltage stays the same while the current (or amps) are added together.

In the diagram above, 4 x 100w panels, each with a rated voltage of 17.9 and current of 5.72A:

• The 1st pair of panels wired in series could produce 35.8 volts and 5.72 amps
• The 2nd pair of panels wired in series could produce 35.8 volts and 5.72 amps
• These two strings wired in parallel could produce 35.8 volts and 11.44 amps – a total of 409 watts.

When the solar panels in the array are all the same, the power output is the same regardless of how they are wired (at least mathematically), but the current and voltage differ.

But there are two caveats to all of this.

• Firstly, the calculations only hold when all the solar panels in the array are the same.
• Secondly, the power output calculations are based on optimal operating conditions.

The following sections look at each of these in turn.

How to Wire Solar Panels in Series

Video Tutorial

Here’s a short video I made showing how to wire solar panels in series. Check it out and consider subscribing to my YouTube channel if you like DIY solar videos like this!

• 2 identical solar panels

Tools

• Multimeter (optional)

Notes

• It is recommended that you use identical solar panels
• If the solar panels are not identical, they should have the same current rating

Step 1: Identify the Positive and Negative Cables on the Solar Panels

There are two ways to identify the positive and negative cables on your solar panels.

The easiest way is to look at the cables themselves and see if they’re already marked. For instance, my solar panels both had plus and minus tags attached to the positive and negative cables.

If yours don’t, there may also be small plus and minus signs on the MC4 connectors or the junction box.

If your panels give no indication which cables are which, use a multimeter to measure each panel’s open circuit voltage (Voc). If the voltage is positive, the positive multimeter probe is touching the positive cable. If the voltage is negative, the positive probe is touching the negative cable.

Tip: If you’re worried about forgetting which cables are which, mark the positive cable on each panel with some tape.

Step 2: Place the Solar Panels Face Down

Place them face down on the ground, on top of a blanket or towel to protect the panel glass.

• Gives us easy access to the cables
• Stops the solar panels from generating power while we’re working with them

Step 3: Connect the Positive Cable of the First Solar Panel to the Negative Cable of the Second

This step takes all of 10 seconds. Here’s a video showing you how to do it:

Your two solar panels are now wired in series.

If you want, you can confirm they’re correctly wired in series by taking the panels outside and using a multimeter to measure the string’s open circuit voltage. It should be close to the sum of the 2 panels’ open circuit voltages.

For instance, each of my panels has an open circuit voltage of 22.6 V. The sum of these is 45.2 V (22.6 22.6). So I expect the open circuit voltage of the 2-panel string to be close to this.

Indeed, when I took it outside and measured its open circuit voltage, I got a reading of 38.7 V (a little low because the panels were in full shade for photo-taking reasons). That’s in the ballpark of 45.2 V, so I know my 2 panels are properly connected in series.

Want to wire 3 or more solar panels in series?

Easy. Just connect the positive cable of the third solar panel to the negative cable of your 2-panel string. You can string together as many panels as you want like this.

Step 4: Connect the Solar Panels to the Solar Charge Controller

Note: Before you do, make sure your charge controller’s max PV voltage is greater than the max open circuit voltage of your solar panel string.

Place the solar panels outside in direct sunlight and they’ll start generating solar energy.

If your charge controller displays system specs, you can locate the PV voltage and confirm that it’s as expected. Because the panels are now connected to the charge controller, you aren’t looking at the open circuit voltage anymore, rather the max power voltage (Vmp or Vmpp).

How to Wire Solar Panels in Parallel

Parts

• 2 identical solar panels
• 1 pair of Y branch connectors
• MC4 inline fuses (if necessary)

Tools

• Multimeter (optional)

Notes

• You may have to connect MC4 inline fuses between the positive solar panel cables and branch connector. Here’s a good video showing you when you need to fuse your solar array.
• It is recommended that you use identical solar panels
• If the solar panels are not identical, they should have the same voltage rating

Step 1: Identify the Positive and Negative Cables on the Solar Panels

Once again, the easiest way to do this is to looks for plus and minus signs on the cables, MC4 connectors, or junction box. If that doesn’t work, use a multimeter as described above.

Step 2: Place the Solar Panels Face Down

Place them face down on the ground, on top of a blanket or towel to protect the panel glass.

Step 3: Connect the Cables to the Y Branch Connectors

They’re used for wiring 2 solar panels in parallel. You’ll need to get a pair to complete these steps.

Connect the 2 positive solar panel cables to the compatible Y connector. This will likely be the FFM connector. (FFM stands for “female, female, male,” meaning the Y connector with 2 female MC4 connectors and 1 male MC4 connector.)

Then connect the 2 negative solar panel cables to the other Y connector. This will likely be the MMF connector.

Note: If using MC4 inline fuses, connect them between the each positive cable and the Y connector.

Done! The 2 solar panels are now wired in parallel.

Need to wire more than 2 solar panels in parallel? Simple — just get the right size branch connector.

For example, if wiring 3 solar panels in parallel, use a pair of 3 to 1 branch connectors.

And if wiring 4 solar panels in parallel, use 4 to 1 branch connectors.

Note: When wiring solar panels in series, I showed you how to confirm that they were correctly wired by checking the open circuit voltage of the 2-panel string with a multimeter. Technically, you could check that your panels are properly connected in parallel by measuring the string’s short circuit current (Isc). BUT, many multimeters have a 10 amp current limit, and, in many cases, two solar panels wired in parallel have a combined short circuit current that is greater than 10 amps.

Step 4: Connect the Solar Panels to the Solar Charge Controller

Connect the charge controller to the battery, if you haven’t already.

Connect the solar panels to the charge controller like normal.

Note: Before you do so, make sure that the maximum expected charging current from your controller to your battery doesn’t exceed the current ratings of your wiring, fuses, and charge controller. Also, make sure this number doesn’t exceed your battery’s recommended maximum charge current.

If you want to make sure everything’s wired and working properly:

Wait until the panels are in direct sunlight, then locate the PV current on your charge controller (if it displays it) and confirm that it’s as expected. Because the panels are connected to the charge controller, we’re now looking at max power current (Imp or Impp) instead of short circuit current.

Wiring Solar Panels in Series vs Parallel: What’s the Difference?

Wiring solar panels in series sums the voltages, but the current remains the same.

Wiring solar panels in parallel sums the currents, but the voltage remains the same.

Note: You can calculate the power output of your series and parallel wiring configurations with our solar panel series and parallel calculator.

Example

For example, let’s say you have two 12 volt 100 watt solar panels that each output 8 amps. If wired in series, the 2-panel string would have a voltage of 24 volts and a current of 8 amps. If wired in parallel, the 2-panel string would have a voltage of 12 volts and a current of 16 amps.

Regardless of whether you wire the 100 watt panels in series or parallel, the 2-panel string will produce a max output of 200 watts.

When Should I Wire Solar Panels in Series and Parallel?

Pros

• No extra parts or equipment required
• Keeps current (amperage) low — you can use smaller gauge wire and save money
• Series strings work better at the beginning and end of the day

Cons

• Doesn’t work well in shade — when a single panel in a series configuration gets shaded, the power output of the entire array drops

When to Use

• Your solar panels will spend most of their time unshaded
• You want to save on wire and equipment costs — equipment with lower currents ratings is less expensive
• You’re using an MPPT charge controller — PWM charge controllers are much less efficient than MPPTs when the voltage of the solar array is much higher than the voltage of the battery bank

Most of the time, I prefer wiring solar panels in series. It’s easy to do, doesn’t require extra equipment, and saves you money on wiring costs. The main thing you have to take into account is the max PV voltage of your charge controller. Make sure the expected max voltage of the series string doesn’t exceed this number.

Pros

• Works well in shade — when a panel in a parallel configuration gets shaded, the remaining panels will continue to output power as expected

Cons

• Requires branch connectors
• May need to fuse the solar panels
• Increases current — you need to buy thicker, more expensive wire, and equipment with higher current ratings
• Doesn’t work as well at the beginning or end of the day

When to Use

• Your solar panels spend most of the time in the mixed-light conditions
• You’re using a cheaper PWM charge controller — PWM controllers reduce the PV voltage to match the battery voltage, so are best used when these two voltages are similar

Wiring panels in parallel requires a bit more care. When I do it, I calculate the expected max charging current I expect my charge controller to output and make sure all my wiring and equipment are rated for that level of current. I also make sure I’m not exceeding the recommended max charge current of my battery. Doing so can reduce its lifespan.

Nowadays, I only really use parallel connections is when I’m connecting a couple 100 watt or smaller solar panels to a PWM charge controller such as the Renogy Wanderer 30A. With that size solar array, the max amperage is still relatively small, so I probably won’t have to buy any new equipment for the increased current.

Minimising voltage drop

You’ll need different wires to connect:

• Solar panels to the main inverter
• Inverter to the batteries
• The batteries to the battery bank and/or the inverter directly to the electric grid

When current flows through an electrical circuit, some voltage loss, called voltage drop, will occur due to resistance in the wires. This voltage drop reduces the solar array’s production and the longer the wire run, the more resistance. If you’re designing a PV system, give consideration to solar power wiring. Keep voltage drop to a minimum so that your array performs as close as possible to its peak rated output. Industry best practice considers voltage drop at 3% or less as acceptable, though you should aim for below 2% if it’s not too impractical.

To reduce the voltage drop in grid systems:

• Minimise the length of the solar system wiring run.
• Be strategic in the inverter placement. AC wiring from the inverter to service panel is often more vulnerable to voltage drop than high voltage DC wiring that run from the panels to the inverter or controller. Battery storage systems should be within 20-30 feet, and the charge controller should be mounted within a yard or metre of the batteries. If the DC voltage from the solar array is:

• Higher than the utility service panel: install the inverter closer to the utility service panel.
• Lower than the utility service panel: install the inverter closer to the solar array.

Solar panel wiring: series vs parallel

Are solar panels wired in series or parallel? That depends on what you’re trying to achieve. Wiring solar panels in series increases the array’s voltage while keeping the amperage the same. Wiring solar panels in parallel increases the amperage but keeps the voltage the same.

Series wiring is typically done for a grid-connected inverter or charge controller that requires 24 volts or more.

Solar panels are similar to batteries in that they have two terminals: positive and negative. A series connection is made by connecting the positive terminal of one panel to the negative terminal of another. Connecting at least two solar panels in this manner becomes a PV source circuit.

Which wire is positive on solar panels?

Solar panel wires and connectors work together to make the job easier. Use MC4 connectors, which have a locking mechanism, making them ideal for outdoor environments. If you’re an installer, the modules you’re working with will most likely have been manufactured with this connector attached to the junction box on the back of the panel. The junction box will contain two wires:

• One wire is the DC positive : this solar DC wiring is typically for the female MC4 connector
• The other is the DC negative (-): this is for the male connector

By series wiring the panels together, you’re left with a single positive and negative connection. The voltages of each individual solar panel add up together to give the array’s total output voltage:

• Let’s say a 60-cell panel as shown above produces 30 volts at 7.25 amps
• In series wiring, we’re looking at a total output of 150 volts (30 volts x 5 panels), at 7.25 amps

Although our example is about identical panels, panels with different power ratings can also be series wired. With different power ratings, the amperage will vary panel to panel as well. Let’s say the highest panel is 4 ampere and the lowest is 1. In this scenario, the overall amperage will be restricted to the lowest value, which is 1 ampere, which is incredibly inefficient.

The advantage of series wiring is that electricity transfers easily over long distances. The disadvantage: if just one panel becomes shaded or covered with leaves or other debris, it impacts the entire string – you won’t see much production.

Tips for Stringing Solar Panels

Now that we have the types of solar panel connections down, we can take a look at some additional tips to ensure that your system will work all day optimally.

Consider your Inverter’s Voltage Range and Specifications

As we mentioned earlier, it’s imperative that you are well-versed in the specifications of your chosen inverter before you begin your installation or planning. Inverters must be able to handle the energy capacity that your array is producing, but they also must receive a minimum voltage, or else they might not work at all.

To size an inverter to a system, you can use the array-to-inverter ratio by dividing the DC rating of your solar array by the maximum AC output of your inverter. You should aim for a ratio of around 1.15 – 1.55. Surpassing a ratio of 1.55 could cause issues and isn’t recommended.

At the same time, consider your location when choosing an inverter. For example, hot, sunny areas such as Nevada and Arizona receive more sun than, say, Washington State, but they are also warmer, which could decrease the panels’ output. The inverter you select should account for how much possible power can be generated in a given day, depending on what state and conditions you’re operating in/under.

Avoid Inverter Clipping

Inverter clipping happens when the inverter you selected can’t handle all the power being fed through it, causing the additional electricity generated to go to waste. To avoid this, choose an inverter with a power rating above what you expect the system to generate on an average day, or take this into account when sizing your system.

Separate Strings by Condition

Inverters have Maximum Power Point Trackers (MPPTs) in their builds, which are circuits that convert DC to DC current to maximize the system’s energy output. Suppose an inverter with a single MPPT is connected to a series of strings with wildly different conditions (different tilts, orientations, azimuths, solar irradiance levels, etc.). In that case, your system won’t perform optimally.

One way to account for this is to build your strings based on similar conditions. For example, suppose you’re installing panels on more than one facet of a roof. In that case, you’ll want to separate these strings and connect them to separate MPPT ports in the inverter so that the inverter can maximize the power from each string on an individual basis based on the different amount of sun exposure each group of modules will see.

This concept works for shaded panels as well. If there’s a large tree shading a portion of the roof for an hour or so every day, string all the affected panels together to output a similar amount of power while the rest of the system isn’t affected.

Pitch Microinverters Where Possible

Microinverters have been taking off in the solar industry lately, and for a good reason. Microinverters are tiny inverters attached to each solar panel that are capable of converting and maximizing electricity on a panel-by-panel basis.

Using a microinverter instead of your traditional string inverter will ensure that each panel is outputting an optimal amount of power and will account for the issues we mentioned above when panels or strings experience different conditions, affecting the performance of the whole array.

If you don’t sell or pitch microinverters yet, now is the time to start. Not only do they eliminate a lot of common issues associated with string inverters, but they also allow for better system monitoring and make it very easy to add to solar systems in the future since all you need to do is install an additional panel/microinverter to the array without having to rewire the whole system.

Use Identical Panels from the Same Manufacturer to Avoid Issues

No matter how much of a solar professional you are, it’s considered a best practice to use only one type/size of solar panel from a single manufacturer per system. Using panels with different ratings could lead to unexpected results or be dangerous.

Plan your Wiring and the Route to the Home in Advance

If you want to install the cleanest, most visually appealing system possible, plan out where each component will attach and lead before getting up on the roof and starting the installation process.

If the home has an attic, consider running the wiring through it to hide all the cables from view and use cable clips where necessary to group wires together into bundles. Make sure any holes made in the roof are sealed and protected from the elements. Mapping out your route in this way will also make your installation a breeze.

Using Software to String Solar Panels and Design Systems

Manual calculations used to be the most time-consuming part of the solar design and installation process. Handling many different formulas and values created tons of opportunities for human error, but they also left much to be desired in terms of working with the client and finding good solutions to their problems quickly.

Today, Solargraf is here to help you design the most accurate systems possible and fast by doing all the heavy lifting. Here’s how.

Automatically Determine the Optimal Amount of Panels

Outline the roof facet you’d like to place the panels on, and let Solargraf fit the system for you. With an extensive library of solar panel makes and manufacturers pre-loaded into the software, you can choose your panel of choice from a drop-down menu or import your own if you have a datasheet on hand.

Solargraf will take the specifications/dimensions of your panels into consideration and fill the surface with the optimal number of modules for the job.

Size Inverters in Seconds

Like the panel tool, Solargraf will also determine the number of inverters required for the number of solar panels based on the type and model of inverter you select from a drop-down list or import into your account via its datasheet.

Instead of calculating all of this information by hand, you can now have it automatically determined by software and complex algorithms in a few clicks, leaving you with more time on hand to FOCUS on sending out more quotes and growing your business.

Offer Multiple System Configurations and Make Changes on the Fly

On top of enabling solar professionals to design their systems from anywhere in seconds, Solargraf also offers users the ability to display up to three separate solar designs on one single proposal with its good, better, best feature.

You can now prepare three options for homeowners using different panel configurations, models, pricing, financing options, etc. You’ll only need to determine your panel strings after the client selects the design and price they would prefer, opening up the opportunity to create as many new proposals for them as you’d like beforehand without all the extra work usually associated with revising quotes.

Have your Strings Determined by a Design Team

When you complete your solar design and the software has determined the ideal number of panels, orientation, and best configuration possible, you can order your permits through the tool with a 24 – 48 hour turnaround time where our design team will do all the heavy lifting for you and define the panel strings.

Instead of all the extra planning, math, and busywork, all you need to do is define your offset, select the roof surfaces you’d like the system to be installed on, and pass it on to Solargraf to get the rest of the job done.

This makes for a more streamlined design and sales process. Fewer revisions are required when the client signs on the dotted line and you need to begin the permitting process to get the installation started. This makes each individual job easier and also opens up more time in the workday for booking more meetings, generating more proposals, and spending time on the roof installing other systems.

In Closing

Correctly wiring solar panels might seem challenging, but it is quite simple with the right knowledge, tools, and software in your back From determining whether your system is best wired in series or parallel, calculating the number of panels in a string manually, and using our tips and best practices, solar panel wiring doesn’t have to be as complicated as it appears on the surface.

Take your PV designs and proposals to the next level with Solargraf’s solar software designed to help you get more done faster, and more accurately. With team and project management capabilities, accurate and easy solar designs, fully customizable proposals, speedy permits, financing integrations, and more. Book your free demo today to learn more about how Solargraf can help busy solar professionals close more deals than ever.