If you’re fitting more than one solar panel to your campervan, there’s an important decision to make: should you wire your solar panels in series or parallel?
Both methods can give you the same overall solar wattage, but they deliver that power differently. Series wiring increases the voltage, while parallel wiring increases the current.
That can affect everything from cable requirements and performance in shade to which MPPT solar charge controller you can use.
So, which setup is better for a campervan? Here’s what you need to know.
Series vs Parallel: The Quick Answer
For two matching solar panels:
| Series | Parallel | |
|---|---|---|
| Voltage | Adds together | Stays roughly the same |
| Current | Stays roughly the same | Adds together |
| Cable losses | Generally lower | Can be higher |
| Partial shading | Can affect the whole string more | Panels can perform more independently |
| Best suited to | Efficient higher-voltage arrays | Roofs where uneven shading is a concern |
Neither option is automatically better. The right choice depends on your panels, roof layout, cable run and the limits of your MPPT solar charge controller.
How Do Solar Panels Work in Series?
When solar panels are wired in series, the voltage of each panel is added together, while the current stays roughly the same as a single panel.
For example, imagine you have two matching 190W solar panels, each operating at approximately:
- 36V maximum-power voltage
- 5.28A maximum-power current
Connected in series, the pair would operate at approximately:
72V and 5.28A = around 380W
You still have a 380W solar array, but you're delivering that power to the MPPT at a higher voltage and lower current than you would with a parallel arrangement.
Advantages of Wiring Solar Panels in Series
One of the biggest benefits of series wiring is the lower current.
Lower current can help reduce voltage drop between your solar panels and MPPT, which can be particularly useful where there is a longer cable run from the campervan roof to the electrical system.
The higher voltage can also help the MPPT reach the voltage it needs to begin charging the leisure battery earlier or continue later in the day.
Series wiring can also make for a relatively simple roof installation because fewer parallel branch connections are required.
Disadvantages of Series Wiring
The biggest thing to watch is voltage.
When panel voltages are added together, you need to make sure the combined open-circuit voltage (Voc) remains safely below the maximum PV voltage of your solar controller.
And you can't simply look at the voltage printed on the panel and multiply it by two.
Solar panel voltage increases as temperatures fall, so the array needs to be calculated using its expected cold-weather Voc. This is particularly important with a controller such as a Victron SmartSolar 100/30, where the maximum PV open-circuit voltage is 100V.
Shading can also be more noticeable in a series string. If one panel is shaded or performing poorly, it can restrict the current flowing through the string.
How Do Solar Panels Work in Parallel?
Parallel wiring does the opposite.
Instead of adding the voltage, the current from the panels is added together, while the voltage stays roughly the same as a single panel.
Using the same two illustrative 190W panels:
36V and 10.56A = around 380W
Again, you have approximately 380W of solar. The difference is how that power reaches the controller.
Advantages of Wiring Solar Panels in Parallel
Parallel wiring can be useful on campervan roofs where the panels are likely to experience different levels of shade.
Because each panel feeds into the common circuit as its own branch, shade affecting one panel may have less impact on the output of the other.
This can be useful on a campervan roof, where Maxxfans, roof bars, aerials and other equipment can all create areas of shade throughout the day.
Parallel wiring also keeps the array voltage lower, which can make it easier to remain within the MPPT's maximum PV voltage.
Disadvantages of Parallel Wiring
The trade-off is higher current.
Higher current can increase voltage drop and may mean you need thicker cabling between the roof and your solar controller.
You also need to pay close attention to the MPPT's maximum PV short-circuit current, as connecting panels in parallel increases the total input current.
Depending on the array, additional branch connectors and overcurrent protection may also be required.
What About Shade?
This is one of the biggest reasons people compare solar panels in series vs parallel.
Parallel wiring is often preferred where panels are likely to experience different shading conditions because a shaded panel is less able to restrict the current of another branch.
But it's not quite as simple as saying:
Shade = always wire in parallel.
Actual performance depends on several factors, including the panel's bypass diodes, where the shadow falls, the orientation of the panels and how the MPPT responds.
For a campervan, one of the best things you can do is consider shading before the panels are fitted.
Think about the position of:
- Roof vents and Maxxfans
- Aerials
- Roof racks and bars
- Awning equipment
- Anything regularly stored on the roof
Choosing a good roof layout in the first place can make a bigger difference than trying to compensate for regular shading afterwards.
Series vs Parallel Example: Two 190W Solar Panels
A common campervan setup is two matching solar panels, so let's look at how the two arrangements compare.
| Two 190W Panels | Series | Parallel |
|---|---|---|
| Total solar power | Approx. 380W | Approx. 380W |
| Operating voltage* | Approx. 72V | Approx. 36V |
| Operating current* | Approx. 5.28A | Approx. 10.56A |
| Main consideration | Maximum MPPT voltage | Maximum MPPT input current |
| Shading | One panel can affect the string | Panels can perform more independently |
*Illustrative figures based on the example panel values. Always use the specifications of your actual panels when designing your system.
For many campervan installations using two higher-voltage matching panels, series can provide a neat and efficient setup.
However, if your roof regularly experiences uneven shading, parallel may be worth considering.
There isn't one arrangement that's right for every van.
Make Sure Your MPPT Can Handle the Solar Array
Whichever arrangement you choose, your panels need to remain within the limits of your MPPT solar charge controller.
There are four important figures to consider.
1. Maximum PV Open-Circuit Voltage (Voc)
This is particularly important with panels wired in series because their voltages add together.
You need to calculate the array's Voc at the lowest expected temperature, rather than relying solely on its 25°C specification.
A 100V MPPT controller must never receive an array Voc of 100V or more.
2. Maximum PV Short-Circuit Current (Isc)
This becomes particularly important when panels are wired in parallel because the current from each branch is added together.
3. Nominal PV Power
Check the combined wattage of your panels against the manufacturer's recommended PV power for the controller and battery voltage you're using.
4. Maximum Charge Current
An MPPT also has a maximum amount of current it can deliver on the battery side.
This is why choosing a solar controller isn't simply a case of looking at the total wattage of your panels.
Can You Run Two 190W Solar Panels on a Victron SmartSolar 100/30?
Two 190W panels give you a total array size of:
190W + 190W = 380W
On a 12V battery system, the Victron SmartSolar MPPT 100/30 has a nominal PV power figure of 440W, meaning a 380W array falls within that figure.
However, that doesn't automatically mean any two 190W panels can simply be connected in whichever arrangement you prefer.
You still need to check the exact:
- Panel Voc
- Cold-temperature voltage
- Panel Isc
- Combined array current
- MPPT input limits
The total wattage is only part of choosing the correct controller.
Can You Mix Different Solar Panels?
Technically, different solar panels can sometimes be combined, but it can make designing an efficient array much more complicated.
With panels wired in series, differences in current can affect performance.
With panels wired in parallel, differences in voltage become more important.
For a straightforward campervan solar system, using matching panels of the same model and electrical characteristics is usually the cleanest approach.
If you need to use significantly different panels — for example, because you're adding solar to an existing setup — using separate MPPT controllers can sometimes be a better solution.
So, Should Campervan Solar Panels Be Wired in Series or Parallel?
For many campervan solar installations, series wiring can be an efficient choice, particularly with matching panels, suitable MPPT voltage headroom and a longer cable run to the controller.
Parallel wiring can make more sense where uneven shading is a major concern or where the combined series voltage would be unsuitable for the chosen MPPT.
The important thing is not to choose based on a blanket rule.
Your solar array should be designed around:
- The exact specifications of your panels
- Your MPPT controller
- Your battery voltage
- Your campervan roof layout
- Expected shading
- Cable lengths and current
- The conditions in which you'll actually use the van
A properly matched system will always be better than simply choosing series or parallel because you've heard one is "best".
Need Help Planning Your Campervan Solar Setup?
At Nomadic Leisure, we stock Victron solar panels, SmartSolar MPPT charge controllers and the components needed to build a reliable campervan electrical system.
If you're unsure which panels, MPPT or wiring arrangement is right for your setup, our bespoke electrical and solar design service can help you plan the system as a whole.
Shop our solar range or get in touch with the Nomadic Leisure team for help choosing the right setup for your campervan.
