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300 Watt Solar Panel Wiring Diagram & Kit List

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This is a 300 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 electrical systems 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.

Build your own camper quick start guide

What can a 300 watt solar panel power?

How much a 300 watt solar panel 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.

A 300 watt panel will provide about 90-96 amp hours per day. 

That’s about enough to run:

  • an inverter for occasional use,
  • a medium, energy efficient fridge, 
  • recharge a few 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. 

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.

A 300w systems gives you a day or 2 in reserve, depending on your usage and without other sources of recharging.

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.

Who will suit a 300 watt solar panel system?

A 300 watt solar panel set up is a good size for a couple in a medium sized RV.

It can support wild camping or boondocking in your RV for relatively long periods from spring through to autumn with careful use and monitoring of the battery levels.

If your needs are critical, definitely consider the ability to charge your batteries from shore power and the alternator too.

We have 320w on our LWB Sprinter camper and find it perfect from Spring to Autumn. 

We’re confident staying off grid with no shore power or driving for about 5 days. 

We need to be much more careful with our use and monitoring during cold, winter months though. 

If your ideal solar system is larger than 300w, build the system with scaleability in mind.

You can add panels and batteries in the future as your needs grow and budget allows.

You could consider extra juice from a portable solar panel system but that’s for another post.

300 Watt Solar Panel Wiring Diagram

There’s a few points worth clarifying about this wiring diagram before you get into the detail:

  • The wiring diagram shows only the supply side installation of a 300 watt solar panel system. It goes as far as charging the battery. For the load side detail, check out our post on campervan wiring
  • It excludes charging the battery from shore power or the alternator. 
  • For information on how to fit the battery, see our post on campervan batteries.
  • The diagram also excludes wiring an inverter – it sits on the load side of the battery.
  • The 300 watt solar panel wiring diagram assumes 3 x 100w panels are being fitted. If you happen to be fitting 2 x 150w panels instead, see our 200 watt solar panel wiring diagram.
  • We’ve included 2 diagrams below. The first shows a 300w solar panel set up wired in series. In the 2nd diagram, they’re wired in parallel.
  • Read our complete guide to wiring your solar panels in series or parallel if you’re not sure how best to wire your array. It covers mixed panels too and includes an interactive calculator to find the most efficient setup for your panels.

300 Watt Solar Panel Wiring Diagram in Series

300 watt solar panel wiring diagram in series300 watt solar panel wiring diagram in series

300 Watt Solar Panel Wiring Diagram in Parallel

300 watt solar panel wiring diagram in parallel

DIY 300 Watt Solar Panel Parts List

This is a list of every component you need for a 300 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

3 x 100w 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 30A controller is adequate for a 300 watt solar panel set up.

Renogy Wanderer Li 30A PWM Charge Controller

30A PWM (budget option)

Buying from US | UK

Renogy Rover Li 30 Amp MPPT Solar Charge Controller

30A 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.

And 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 300w solar panel set up, you need around 140ah of battery. 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

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

Buying from US | UK

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 3 in panels series, you need 1 single pair of MC4 cable connectors.

For wiring 3 panels in parallel, you need 1 pair of 3 pronged MC4 T-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 MC4Y2 Branch Connectors MMMF+FFFM Pair

T branch MC4 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.

300 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 300 Watt 12 Volt  Solar Premium Kit

300 Watt Solar Panel Kit

Buy here

This is a 300 Watt Solar Panel Kit complete with:

  • 3 x 100W 12V Monocrystalline Solar Panel
  • 40A MPPT Charge Controller (so space to scale up)
  • all cables and connectors
  • mounting brackets
  • fuse holders & fuses.

You need to buy the cable entry housing and battery separately.

How to install 300 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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