400 Watt Solar Panel Wiring Diagram & Kit List

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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.

This post is one part in our DIY campervan solar system series which includes 12v solar panel wiring diagrams for other sizes too.

400w RV solar panel wiring diagram image for pinterest


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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 2 x 200w in series

400 Watt Solar Panel Wiring Diagram in Series with 4 x 100w panels

400 watt solar panel wiring diagram 4 x 100w in series

400 Watt Solar Panel Wiring Diagram in Parallel with 2 x 200w panels

400 watt solar panel wiring diagram 2 x 200w in parallel

400 Watt Solar Panel Wiring Diagram in Parallel with 4 x 100w panels

400 watt solar panel wiring diagram 4 x 100w in parallel

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 Panel

Solar panels harvest sunlight, converting it to electricity.

There are different types of solar panels but we recommend using monocrystalline as they’re the most efficient. 

1 x 100w Rigid Monocrystalline

4 x 100w Rigid Monocrystalline

Buying from US | UK

or

200 Watt 12 Volt Monocrystalline Solar Panel

2 x 200w Rigid Monocrystalline

Buying from US | UK


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.

Renogy Rover Li 40 Amp MPPT Solar Charge Controller

40A MPPT

Buying from US | UK

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. 

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.


Batteries

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.

Renogy Deep Cycle Hybrid GEL Battery 12 Volt 200Ah

200ah Gel

Buying from US | UK

Renogy Lithium-Iron Phosphate Battery 12 Volt 170Ah

170ah Lithium

Buying from US | UK

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.

Use our battery sizing calculators to get the right size and type for your needs:


Fittings

Solar panel mounting brackets

These allow you to mount the solar panel to your van without needing to drill holes in the roof. 

Always resist any urge to breach your roof.

Renogy Solar Panel Mounting Z Bracket -- Set of 4

4 x Renogy Solar Panel Mounting Z Bracket – set of 4

Buying from US | UK

Only 2 pairs needed if mounting 2 x 200w panels


MC4 Connectors

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.

Pair of MC4 cable connectors

Single MC4 cable connectors

Buying from US | UK

Renogy Solar MC4 Branch Connectors MMF+FFM Pair

Y branch (1 to 2) MC4 cable connectors

Buying from US | UK

4 to 1 mc4 solar connectors

4 to 1 solar branch connectors

Buying from US | UK


Solar Panel Cable

10 Gauge Wire 100ft Red & 100 ft Black

Red & Black Solar Panel Wire 10 AWG / 6mm

Buying from US | UK

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.


Solar panel gland seal

Sadly, the only way to run the solar cable into the van is by drilling a hole. Plug it up and make it water tight with a gland seal.

Renogy cable entry housing (gland seal)

Solar panel gland seal

Buying from US | UK


Fuse Holder

This sits between the solar charge controller and the battery cut off switch.

ANL fuse holders are easier to mount than in-line holders. However, the fuses needed for these are more difficult to find than the standard ones

Bear this in mind if you’re travelling to areas where online shopping may not be an option.

ANL Fuse Holder with 30Amp ANL fuse

ANL Fuse Holder

Buying from US | UK

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.

Battery isolator switch

2 x Battery isolator cut of switches

Buying from US | UK

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.


Battery Terminal Eyes / Wire Lugs

These allow you to connect the cable to the battery. 

Choose a lug size rated greater than your wire gauge and with an eye large enough to fit on the battery terminal.

Heavy Duty Wire Lugs

Heavy Duty Wire Lugs

Buying from US | UK


1/4” Red & 1/4” Black heat shrink

Heat shrink seal electrical joints to cover the bare wires.

On this solar install, you’ll need it to connect the inline or ANL fuse and the battery terminal connectors.

Heat shrink

1/4″ red & black heat shrink

Buying from US | UK


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.

Sikaflex 221

Buying from US | UK


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.

Renogy New 400 Watt 12 Volt Solar Premium Kit

400 Watt Solar Panel Kit

Buy here

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.

We do encourage you to invest in a multimeter though and keep it in your toolkit while travelling and living in your van.

It’s on our van life essentials list for good reason!


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400w RV solar panel wiring diagram image for pinterest

We're handy DIY camper van convertors, not professional coach builders, technicians or electricians.

While we're happy with the techniques and products we use, be sure to check all methods and materials you use are compatible with your equipment and abilities.

Regardless of what we recommend, consult a professional if you're unsure about working on your RV, campervan or motorhome.

Any task you perform or product you purchase based on any information we provide is strictly at your own risk.