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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 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.
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.
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 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 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.
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.
- 400 watt solar system | 40a
- 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.
And 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 300w solar panel set up, you need around 140ah of battery. 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.
Use our battery sizing calculators to get the right size and type for your needs:
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.
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.
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.
300 Watt Solar Panel Kit
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.
It’s on our van life essentials list for good reason!
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