This is a 400 Watt Solar Panel Wiring Diagram with a complete list of DIY parts needed and kits available.
Use this as a guide to fitting your RV, campervan, motorhome or caravan solar set up.
We’ve designed the diagram so it’s simple to understand for newbies to campervan electrics.
Campervan electrics can be dangerous so if you’re not sure what you’re doing or don’t feel confident to complete a solar set up yourself, seek the help of an electrician.
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.
What can a 400 watt solar panel power?
How much 400 watts of solar panels can power depends on a number of variables including the time of year, the weather, your location and the type of charge controller you install.
But here’s an idea of what you might expect to get on an average day of 4 peak hours of sun with an MPPT controller.
400 watts of solar panel will provide about 120 – 128 amp hours per day.
That’s about enough to run:
- an inverter for a TV and charging laptops,
- a good sized, energy efficient fridge,
- recharge a plenty of small devices on a USB like phones, tablets and kindles,
- run your roof vent during day and night to stop condensation,
- keep a composting toilet’s fan running 24/7,
- run a diesel heater for a few hours and
- switch on a few LED lights inside the campervan.
Bear in mind this is based on an average sun light day.
A 400w systems gives you a couple of days in reserve, depending on your usage and without other sources of recharging.
You may not be able to replenish the batteries everyday so consider keeping something back as contingency to avoid cycling the batteries more than necessary.
Who will suit a 400 watt solar panel system?
A 400 watt solar panel set up is a good size for a couple or small family with a medium to large sized camper with roof space for the panels.
It can support wild camping or boondocking in your RV for relatively long periods from early spring through to late autumn with careful use and monitoring of the battery levels.
A 400w system is the point where you should be able to run your entire campervan electrical system 100% off solar, year round. No need for shore power or driving.
Even with a 400 watt system, if your aim is to be completely independent of hook up, you’ll need to watch your consumption and battery levels closely.
If your ideal solar system is larger than 400w, build the system with scaleability in mind.
You can add panels and batteries in the future as your needs grow and budget allows, assuming you have space on your roof.
You could consider extra juice from a portable solar panel system but that’s for another post.
400 Watt Solar Panel Wiring Diagrams
There’s a few points worth clarifying about these wiring diagrams before you get into the detail:
- The wiring diagrams shows only the supply side installation of a 400 watt solar panel system. They goes as far as charging the battery. For the load side detail, check out our post on campervan wiring.
- They exclude charging the battery from shore power or the alternator.
- This set up needs a minimum of 150 – 180ah of battery so the diagrams have 2 x 12v batteries wired in parallel.
- For more information on how to fit the batteries or to wire them in series if using 6v batteries, see our post on campervan batteries.
- The diagrams also excludes wiring an inverter – it sits on the load side of the battery.
- The 4 diagrams below show a 400 watt solar panel wiring diagram wired in parallel and series with 2 x 200w and 4 x100w panel configurations.
- For a full breakdown of the detail, comparisons and even an interactive calculator for mixed panels, check out our complete guide to wiring your solar panels in series or parallel.
400 Watt Solar Panel Wiring Diagram in Series with 2 x 200w panels
400 Watt Solar Panel Wiring Diagram in Series with 4 x 100w panels
400 Watt Solar Panel Wiring Diagram in Parallel with 2 x 200w panels
400 Watt Solar Panel Wiring Diagram in Parallel with 4 x 100w panels
DIY 400 Watt Solar Panel Parts List
This is a list of every component you need for a 400 watt solar panel set up on your RV or campervan.
The list includes affiliate links. This mean we may earn a commission from any purchase you make at no additional cost to you.
If you’re buying from Europe or the UK, use the UK link. Otherwise, use the US link.
Solar Charge Controller
Solar charge controllers regulate the current from the panels to a safe level so it can charge the batteries.
A 40A controller is adequate for a 400 watt solar panel set up.
At this size and investment, we recommend installing the MPPT controller.
A PWM controller is a fraction of the cost of a MPPT but the considerable loss of harvested energy would offset the cost of the larger system.
If you think you may want to scale up your solar capacity in the future, consider a higher rated device and it’ll be more cost effective in the long term.
- 600 watt solar system | 60a (50a will be fine if you can find one)
- 800 watt solar system | 100a (70a will be fine if you can find one)
Check out our complete guide on how to select the right solar charge controller for your setup.
If you need to know what size to get, use our interactive solar charge controller calculator.
There’s 3 types of campervan batteries. We recommend choosing Gel or Lithium-ion.
For a 400w solar panel set up, you need around 180ah of gel battery or 150ah of lithium. These are next closest sizes we could find.
If space isn’t a major issue, you’ll never be unhappy of a bigger battery so always go up a size rather than down.
Solar panels come with about a metre of cable so not normally long enough to reach your battery bank.
MC4 connectors are rated to cope with the current and are weather proof so you can extend the cable.
For wiring 2 panels in parallel, you need 1 single pair of MC4 cable connectors and a pair of Y branch MC4 connectors.
For wiring 2 or 4 panels in series, you need 1 single pair of MC4 cable connectors.
For wiring 4 panels in parallel, you need 1 pair of 4 to 1 solar branch connectors and 1 single pair of MC4 cable connectors.
Solar Panel Cable
The point of using different colours is to easily identify the negative and positive wires.
If you can’t get red, use the black cable and mark it with red electrical tape or heat shrink.
Measure how much extension cable you need before you buy.
For both the positive and negative sides, you need enough to run from the end of the existing solar panel cables to the battery, via the solar charge controller and kill switch.
This sits between the solar charge controller and the battery cut off switch.
Bear this in mind if you’re travelling to areas where online shopping may not be an option.
When wiring in series, the fuse between the solar panel and the solar charge controller should be 1.3 times the size of the lowest Optimum Operating Current of the panels in the array (see the back of the panel for their specification).
When wiring in parallel, the fuse between the solar panel and the solar charge controller should be 1.3 times the total of the Optimum Operating Currents of all the panels in the array (see the back of the panel for their specification).
The fuse between the solar charge controller and the battery, should be the same rating as the solar charge controller.
2 x 1250 Amp Battery Cut Off Switches
Cut off switches on the battery supply line and the circuit supply lines allow the battery to be isolated.
The battery cut off switch must be greater than the total capacity of the battery bank.
If you want to upscale in the future, it’s worth fitting a larger one now to save changing it later.
Sikaflex 221 (Panel Adhesive)
Use this adhesive to secure the solar panel mounts to the van roof.
It’s a bit messy, so wear latex gloves when applying it.
You need about 4 or 5mm of sealant between the bracket and the panel for a robust bond. It takes about 24 hours on a dry day to cure.
Fuses and wires must be rated for the system’s load and cable run length. We’ve covered everything you need to know in our campervan wiring post.
400 Watt Solar Panel Kit
If you’d prefer to avoid shopping around, you can buy pre-configured solar panel kits.
They usually include the solar panel, solar charge controller and mounting brackets. Some include extension wires.
If you opt to buy a kit, check what’s included and what additional things you’ll need to buy.
And make sure it makes economical sense.
400 Watt Solar Panel Kit
This is a 400 Watt Solar Panel Kit complete with:
- 4 x 100W 12V Monocrystalline Solar Panel
- 40A MPPT Charge Controller
- all cables and connectors
- mounting brackets
- fuse holders & fuses.
You need to buy the cable entry housing and battery separately.
How to install 400 Watt Solar Panel System
Our guide details everything you need to install a campervan solar panel system.
It’s written to suit any size of system so it makes reference to how to install multiple panels.
It may come in useful when considering upscaling your set up though.
There’s also a section about the tools you need to install your campervan solar panels.
Some of these tools can be quite expensive so unless you expect to get a lot of use out of them in the future, try to borrow them where possible.
It’s on our van life essentials list for good reason!