400 Watt Solar Panel Wiring Diagram & Kit List

Graham Bogie

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 setup.

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 unsure about what you’re doing or don’t feel confident completing a solar setup yourself, seek the help of an electrician.

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

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What Can a 400 Watt Solar Panel Power?

How much 400 watts of solar panels can power depends on several variables, including the time of year, the weather, the 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 daily. 

That’s about enough to run:

  • an inverter for a TV and charging laptops,
  • a good-sized, energy-efficient fridge, 
  • recharge plenty of small devices on a USB like phones, tablets, and Kindles,
  • run your roof vent during the 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 sunlight day. 

A 400w system gives you a couple of days in reserve, depending on your usage, and without other sources of recharging.

You may be unable to replenish the batteries daily, so consider keeping something back as a contingency to avoid cycling the batteries more than necessary.

Who Will Suit a 400 Watt Solar Panel System?

A 400 watt solar panel setup 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 RV electrical system 100% off solar, year round. No need for shore power or driving.

Even with a 400 watt system, if you aim 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 scalability in mind.

You can add panels and batteries 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 are a few points worth clarifying about these wiring diagrams before you get into the detail:

  • The wiring diagrams show only the supply side installation of a 400 watt solar panel system. They go 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 setup needs at least 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 exclude 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 2x200 series

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

400 watt solar panel wiring diagram 4x100 series

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

400 watt solar panel wiring diagram 2x200 parallel

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

400 watt solar panel wiring diagram 4x100 parallel

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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 solar kit, check what’s included and what other components you’ll need to buy. 

And make sure it makes economic sense.

400 Watt Solar Panel Kit

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This is a 400 Watt Solar Panel Kit complete with the following:

  • 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.

DIY 400 Watt Solar Panel Parts List

This is a list of every component you need for a 400 watt solar panel setup on your RV or campervan.

Solar Panels

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. 

4 x 100w Rigid Monocrystalline

100w Rigid Monocrystalline

Enter coupon code MowgliAdventures for 10% off at Renogy.com

2 x 200w Rigid Monocrystalline

200w Rigid Monocrystalline

Enter coupon code MowgliAdventures for 10% off at Renogy.com

What Size Charge Controller for 400w Solar Panel Setup?

Solar charge controllers regulate the current from the panels to a safe level so they can charge the batteries.

Selecting an appropriate charge controller is a pivotal choice in your solar panel system setup, with consequences for the system’s efficiency and lifespan.

A charge controller plays the crucial role of managing the current and voltage from your solar panels, safeguarding your batteries by ensuring they receive a safe and optimal charge.

When deciding on a charge controller, it’s essential to consider various factors, such as the combined wattage of your solar panels, your battery bank’s voltage, and your daily energy usage.

These considerations will guide you to make an informed decision that best suits your requirements.

A 40A controller is adequate for a 400 watt solar power setup.

At this size and investment, we recommend installing the MPPT controller.

A PWM controller is a fraction of the cost of an MPPT, but the considerable loss of harvested energy would offset the cost of the larger system.

MPPT Solar Charge Controller

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If you want to scale up your solar capacity, consider a higher rated device, which’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 selecting the right solar charge controller for your setup.

And if you need to know what size to get, use our interactive solar charge controller calculator.

How Many Batteries Do I Need for a 400w Solar Panel?

How large a battery bank you need depends largely on how much power you use and even when you use it.

Use our solar battery bank calculator to work out how much energy you use each day and what size battery bank you need to meet that level.

That said, a battery bank stores the power generated from your solar panels.

If you don’t have a large enough battery bank, you could potentially waste the energy you’ve worked so hard to harvest.

A 400W solar panel setup could generate as much as 33ah of power per peak hour.

However, how many peak hours of sun you can reasonably expect to receive differs by location, time of year, and the weather.

In the US, you’re unlikely to get much more than 5 or 6 hours of peak sun conditions in midsummer.

Therefore, a 400w solar panel system will generate a maximum of 160-200ah daily.

Although you may use some of that energy as you generate it, it’s more simple and prudent to err on the side of caution.

So the minimum size battery bank you need for a 400w setup is 200ah – more if you don’t install Lithium batteries.

You may have more than one charging source or want some contingency, so you can increase that size as much as you like.

There are 3 types of campervan batteries. We recommend choosing Gel, AGM, or Lithium batteries.

Lithium Ion Battery

Enter coupon code MowgliAdventures for 10% off at Renogy.com

If space isn’t a significant issue, you’ll never be unhappy with 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:


Solar Panel Mounting Brackets

Solar Panel Mounting Brackets

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These allow you to mount the solar panel to your van without drilling holes in the roof. You need one pack for every panel.

Always resist any urge to breach your roof.

MC4 Connectors

MC4 Connectors

Solar panels come with about a meter of cable, which is not normally long enough to reach your battery bank. 

MC4 connectors are rated to cope with the current and are weatherproof, 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 T-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

Solar Panel Cable

The point of using different colors 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. 

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 for both the positive and negative sides.

What Size Cable for 400w Solar Panel Setup?

The selection of the appropriate wire size, as dictated by the American Wire Gauge (AWG) system, is a vital step in the solar panel installation process.

This choice directly influences both the efficiency and safety of your solar power setup.

Several factors come into play when deciding on the correct wire size. These include the total power output of your system, the operational voltage, the system’s layout, and the distance between your solar panels and the charge controller.

For example, a 400W solar arrangement wired in series would need a different wire size than the same setup configured in parallel.

Choosing a wire size that isn’t suited for your system can result in energy wastage and potential safety risks, making it imperative to consider this decision carefully.

Solar Panel Gland Seal

Solar Panel Gland Seal

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

Fuse Holder

Fuse Holder

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

ANL fuse holders are easier to mount than inline holders. However, the fuses needed for these are more difficult to find than the standard blade fuses

Bear this in mind if you’re traveling 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 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 Optimum Operating Currents of all the panels in the array (see the back of the panel for their specification).

2 x 1250 Amp Battery Cut Off Switches

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.

Battery Terminal Eyes / Wire Lugs

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.

1/4” Red & 1/4” Black Heat Shrink

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.

Sikaflex 221 (Panel Adhesive)

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.

For a robust bond, you need about 4 or 5mm of sealant between the bracket and the panel. 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.

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 refers to how to install multiple panels.

It may come in useful when considering upscaling your setup

There’s also a section about the tools you need to install your campervan solar panels. 

Some of these tools can be expensive, so unless you expect to get a lot of use out of them in the future, try to borrow them where possible.

We encourage you to invest in a multimeter, and keep it in your RV toolkit while traveling and living in your van.

Check out our complete guide for using a digital multimeter in your camper.

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

Graham Bogie

Graham Bogie - Expert in RV & Campervan Electrics - Mowgli Adventures

Graham is a seasoned marine electrical engineer with two decades of experience designing customized electrical systems for plant machinery and converting campers and overland vehicles. His expertise has led him to author the reputable Campervan Electrics Handbook and become the chief designer of our Campervan Electrical Design Service. As a knowledgeable figure in the field, his YouTube channel, blog, Facebook group, and newsletter, offering electrical advice and product reviews, reach more than a million users each year.

5 thoughts on “400 Watt Solar Panel Wiring Diagram & Kit List”

  1. I have 4 100 watt panels. Making a campervan. Why would I choose to wire the panels one panel to the next and then into the van rather than all 4 running to a connector then into the van. What is the difference and why is one way better than the other way?

  2. Great article. I’m trying to figure out fuse size between the panels and the charger controller. You explain how to calculate it when in parallel and when in series. If I do 2P2S, should I double the optimal operating current? Specifically, my panel says the Optimum Operating Current (Imp): 5.38A. If i do 2P2S, should the fuse be 10.76? Thank you!!!

    • Yep – that’s exactly right. Each series uses the lowest Optimum Operating Current (so each has 5.28a in your case) and then you total them for the parallel set up into the controller. As you only have 2, you double it. Hope that helps. G


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