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Wiring Solar Panels in Series vs Parallel | Which is Best?

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This post explains the different ways of wiring multiple solar panels together, providing the information you need to decide how best to configure your camper solar setup.

It starts simply with diagrams for the different wiring configurations and explains how each affects the components needed.

We’ll then delve into the complexities of mixed solar panels (avoid doing this if possible).

We’ve included an interactive series vs parallel calculator so you can decide the best configuration for your solar array.

We’ve made our own mistakes when setting up our campervan solar system.

Hopefully this post will help you avoid these so you can get the best performance from your solar setup from the outset.

Need more advice and support on a specific part of your campervan electrics? Join our new Facebook Group to connect with a growing community of like minded van builders.

wiring solar panels in series vs parallel pin image

This post is part of our series on campervan electrical components.

If you’re new to electrics or van builds, take a look at our starter guide to campervan electrics first.

Build your own camper quick start guide

Ways of wiring multiple solar panels

There’s basically 3 different ways of wiring multiple solar panels on your DIY campervan conversion:

  • In series
  • In parallel
  • A combination of series & parallel

We’ll take a look at each of these in turn before we do a comparison.

Solar panels wired in series

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

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

solar panels wired in series diagram

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 that solar panels wattage is rated under standard test conditions. These 100w panels will provide 100w then but a little more in colder temperatures.

Solar panels wired in parallel

solar panels wired in parallel diagram

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

The connections are made with branch connectors. 

When solar panels are wired in parallel, the voltage of the array 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 and parallel

solar panels wired in a mix of series and parallel diagram

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 2 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 voltage of the 2 strings 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
  • Combined, these 2 strings wired in parallel could produce 35.8 volts and 11.44 amps – a total of 409 watts.

So, when the solar panels in the array are all the same, you can see that while the power output is the same regardless of how the solar panels are wired (at least mathematically), the current and voltage differ.

This is important when it comes to selecting a solar charge controller for your RV or campervan.

But there’s 2 caveats to all of this. 

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

The following sections look at each of these in turn.

Mixing Solar Panels & How Best to Wire Them

In an ideal world, your camper solar setup will consist of a set of identical solar panels.

They’ll all be the same brand, type and wattage, so operating currents and voltages will all be the same.

But we don’t live in an ideal world.

Perhaps you have a few mismatched solar panels to kick off a budget solar setup. 

What if you’re on the road, living in your van full-time and need to replace an existing solar panel or want to add another to your setup but can’t source the exact same panels?

Can you add a different panel? 

Yes you can but determining how best to configure the system isn’t quite as straight forward.

The maths

The calculations explained above for series, parallel and a combination of series and parallel still hold true.

When wired in series, the lowest amp rating of all the panels is used in the calculation.

When wired in parallel, the lowest voltage is used.

So when a solar array uses a mix of panels with different ratings, the power output is no longer the same across all configurations.

Let’s take an example, which happens to be an identical setup to that on Baloo, our Sprinter van conversion:

We have 2 x 95w panels, each rated at 4.5A and 21.1 volts and a 130w panel rated at 7.5A and 17.3 volts.

Wired in series, we add the volts together and use the lowest current rating. So we get 21.1v + 21.1v + 17.3v = 59.5v at 4.5A.

We can get a total of 267.75 watts from our 320 watt panels – a loss of over 16%.

mixed solar panels wired in series diagram

Wired in parallel, we add the amps together and use the lowest voltage rating. So we get 4.5A + 4.5A + 7.5A = 16.5A at 17.3v.

We can get a total of 285.45 watts from our 320 watt panels – a loss of over 11%.

mixed solar panels wired in parallel diagram

Or we can wire them in a combination of series and parallel. We’ll wire the 95 watt panels in one string because they are identical and keep the 130 watt panel in its own string.

  • The 95w panel string could produce 42.2 volts and 4.5 amps
  • The 130w panel string could produce 17.3 volts and 7.5 amps
  • Combined, these 2 strings wired in parallel could produce 17.3 volts and 12 amps – a total of 207 watts a loss of 35%.
mixed solar panels wired in a mix of series and parallel diagram

So which is best? Series, Parallel or a Combination?

Once you’ve run your proposed solar set up through the calculator, you’ll have a good idea of total power output, current and voltage you might expect from each wiring configuration.

But keep reading. The decision isn’t black and white. 

In fact, while the calculated results are interesting and useful for sizing your solar charge controller, we don’t suggest you wire your solar panels based on the minimum power loss.

The calculations are all based on the optimal operating conditions for the given solar panels.

In reality, though, those conditions may not be met all the time.

Series v Parallel in shade

The height of the sun in the sky affects the energy produced so this varies throughout the day and indeed throughout the year.

Cloud and shade fall on the solar panels. This may not be much of an issue for solar farms in wide open fields but on an RV or campervan it is.

Parking under a tree or in the shadow of a building varies the power output from the panels depending on how they’re wired.

When shade hits any part of a solar array wired in parallel, the power output from that panel reduces a lot. BUT, any other panels in the configuration are unaffected.

Conversely, when shade hits any part of a solar array wired in series, the power output from that panel reduces a lot. AND every other panel in the configuration is dragged down with it.

Battery charging affect

With a parallel wiring configuration handling mixed panels well and coping with partial shade better, you might think this is the best approach for a campervan solar setup.

But first we need to consider the other components in the solar setup, specifically the batteries.

We have a detailed post on campervan batteries for the full detail but the key point here is a 12v battery needs at least 12.6v to charge (or thereabouts).

So consider all the calculations we’ve used above and your own too. 

The voltage produced by solar panels in a parallel configuration is low – around 17 – 22v, depending on the panels. And this is when environmental conditions meet the optimal operating conditions of the panels.

Anything less and the voltage will fall. 

Let’s take a look at some numbers to prove the point:

4 x 100w panels, each with a rated voltage of 17.9 could produce 17.9 volts when wired in parallel.

The same panels wired in series could produce 71.6 volts.

Both scenarios produce enough volts to charge the battery, when conditions are good. 

But when wired in parallel, the panels must perform at at least 70%. Anything less, the volts will fall below 12.6v needed to charge the battery, rendering them next to useless.

Wired in series, performance would need to fall to around 18% before they stop charging the batteries.

So what’s best?

A campfire with sparks floating up in a forest

We had our mixed panels wired in parallel for a long time.

Why wouldn’t we? Parallel wiring handles the mixed panels far better than in series and we wouldn’t suffer as much loss when we parked in shade.

And then we sat around a campfire with some fellow overlanders and discussed it all at length.

Convinced, we might just have it wrong, we spent 5 minutes the next morning changing the setup from parallel to series.

We’ve not needed hookup since!

The last 6 months we’ve been in Patagonia, throughout the southern hemisphere winter and not driven anywhere – there’s a global issue preventing us from travelling apparently.

We’re not hooked up, our mixed 320w panels are now wired in series with an MPPT controller and with careful management, we’re doing much, much better.

Why? 

Because while we suffer slightly more losses during the optimum operating conditions, we’re producing a high enough voltage to charge the batteries from a little after dawn to almost sunset instead of for just a few hours in the middle of the day. 

So over the course of the day, we charge our batteries for longer.

Result!

Solar Panel Wiring | Series vs Parallel Calculator

calculations for campervan solar setup

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

This calculator allows you to enter upto 3 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 in a dedicated string.

It’s important to only enter each spec on one line.

Aim to choose a configuration that provides a balance between the least loss of total power output and a high enough voltage to charge the batteries all day.

The aim is to get the best combination of watts (power out) and voltage.

If you’d prefer to wire your mix of panels without losses, you’ll need to wire each variant of panel with its own solar charge controller.

So in our set up, we’d need an MPPT controller to handle the string of 95w panels and another for the 130w panel. 

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

For more help sizing your campervan electrics and solar setup check out our other electrical calculators for RVs and campervan conversions too.

Our Recommendations

A hole in the roof of an RV
  • Wire your camper solar setup in series. 
  • Wherever possible, use the same solar panels throughout the entire array.
  • If you must use a mix of panels, try to make them as close to each other’s specs as possible. Avoid putting a 50w 3A 18v panel with a 200w 9A, 21v panel.
  • If you have mixed panels, configure them to maximise the current by wiring appropriate pairs in series.
  • Pay special attention to anything on your roof that could cast shadow on your panels including aerials, satellite dished and vents.
  • Avoid parking in shade to maximise performance.
  • Clean solar panels regularly.
  • Remove any broken or damaged panels for the series so the rest of the panels aren’t affected.
  • Use an MPPT controller when wiring in series so you can handle the higher system voltage.

Don’t forget, this post is just one part of our DIY camper solar setup series. Check out it out for more useful articles.

How to select a solar charge controller for an RV or campervan
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