DC Solar Panel Basics – An Example 12-Volt Solar System For Your Rig

Rigid mounded 100 Watt Solar Panel

Getting Started With Solar Panels For Your Rig & How They Work In 12-Volt Systems

If you’re having trouble finding information about vehicle-based solar power, you’re not alone. Most of the information available is for commercial or residential structure applications. In this post, we will go over some solar panel and 12-volt system basics. Hopefully, this will help make you informed and confident in building out your dream solar system on your rig.

Best of all, you can rest easy knowing that it will work right and not catch on fire!

Note: If you’re uncomfortable with this type of work, it’s always a great idea to have an electrician either check your work or do it for you!

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The basic components you will need to start your own solar panel system are:

  • Solar panel, preferably with bypass diodes
  • Correctly sized wiring & fuses
  • Solar charge controller
  • A way to mount your panel if using a rigid panel
  • The sun

DC Power Basics

Anderson Plug for Aux folding panel

“DC Power” stands for direct current. It is the power that runs vehicles, boats, computers, etc. What comes from a standard power pole is AC (alternating current) power. AC power won’t be relevant in this post unless we are talking about power inverters. All you need to know is that AC is very good at sending power long distances, which is why they use it on the power poles.

I won’t bore you with all the math details, but DC power is governed by one basic equation:

  • Ohm’s Law Resistance = Voltage/Current

It basically means that as you increase the power draw on a given system, the voltage and the current (amps) increase at the same rate. In a 12-volt system, the voltage always has to remain around 12 volts within a 1-2 volt variance. This means that for more power-demanding equipment, the amps have to increase since voltage can’t.

Amps are what can cause wires to melt or worse, cause fires. It’s important to always use a DC wire size calculator so you can make sure you don’t cause damage to your vehicle or the loved ones inside it! Here is a handy calculator to determine how many amps your accessories will draw.

How Solar Panels Work

Flexible Soft Folding Solar Panel

Unless you’ve been living under a rock for the past decade, you know that solar panels essentially convert sunlight into electricity. Pretty neat, huh?

In more technical terms, they are actually small semiconductors sandwiched between different types of protective layers and are called photovoltaic cells. One cell only produces about 1-2 Watts of electricity. Solar panel manufacturers string many of these cells together and sell you an entire panel rated for a certain amount of watt generation. A common rating such as the one I installed on my roof rack is for 100 Watts.

When the sun hits the solar panels, the amount of power generated is based on how intense and direct the sun is shining. If the sun isn’t shining directly 90 degrees onto the panel, the amount of power that is produced drops off fairly quickly. This is why when you see pictures of big solar farms, they are all positioned at an angle.

In a mounting application such as a roof rack, you will generate a fraction of the panel’s rating unless it’s high-noon.

The last thing that can lower the actual output of your solar panel is the ambient temperature. Most panels assume 60-80 degree weather for their ratings. How many times have you touched your roof in the summer when the sun is shining and thought, “Wow, this piece of metal is cool-to-the-touch.” Yeah, me neither.

Bypass Diodes

While we are on the subject of the panels themselves, something to look out for is solar panels that don’t have bypass diodes. This is less common now, but if you go with an ultra-budget priced solar panel, they might not have them.

Without bypass diodes, if just one cell is shaded by debris sitting on the panel, the whole panel will stop producing electricity. That’s not great if you are out on the trail during the fall.

For additional solar panel information, click here.

Solar Controllers

Redarc BCDC12250

Solar panels in the sun produce voltage and amps, but depending on the conditions, the amount can vary. In direct sun, it may produce up to 50 volts. If you were to connect this directly to your 12-volt battery, it could damage it quite a bit. This is why you have to get a solar controller to actually harness the power of your panels. With it, you can use it to do something useful like charging your auxiliary battery.

Fuses & Solar Controller

A 12-volt solar controller modifies the voltage down to a safe charging voltage of around 14.6 volts.

If you remember from earlier in this article, that means the amps have to go up to compensate and balance the equation. There are two types of solar controllers, MPPT and PWM. Comparing the two could probably be an entire article by themselves, but here’s quick and dirty:

  • MPPT Controllers: Boost the amps so you always get the most power for the current light level on your panel.
  • PWM Controllers: Cut any excess amps produced when voltage is above what a 12-volt system can handle.

MPPT controllers are typically more expensive and can have extra features such as optimizing charging times and switching over to a trickle charge state when the battery is full. PWM controllers, on the other hand, are usually the cheaper option and will work fine if you don’t need to get the maximum charge out of low-light conditions.

My Set-Up

4Runner Solar Panels

My setup is one rigid-mounted 100-watt solar panel on my roof rack. It’s connected to a Redarc battery management controller attached to both my start battery and my auxiliary battery that runs my DC fridge. The Redarc controller has a built-in MPPT controller. It also has tons of other functions such as choosing between solar power or my alternator to charge both batteries. I also have a folding 90-watt solar panel I connect in parallel with my rigid panel.

Below are some links to the main components I used for my setup:

Here is a basic wiring diagram of the way it is currently running in my 4Runner.

Solar Wiring Diagram

    I really like this setup as it allows me to have some solar power all the time to keep my batteries topped off. If I’m parked for a camping trip, I can whip out the foldable panel and move it into the direct sun with the proper angle, keep my fridge going for much longer, and charge all my devices.

    Final Thoughts

    Using Solar Panels On 5th Gen 4Runner

    I hope all this gives you some basic knowledge of how a solar system can really up your overlanding game. A proper system will allow you to keep all your accessories running as long as the sun is shining! I also hope this gives you the confidence to start planning your own system!

    I learned most of this by just trying it out myself, along with a healthy amount of research. If there is something I missed or you would like to get more detail on it in a future post, let me know! I’m always up for learning or sharing something new.

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    4 months ago

    Great article. I have the Redarc charger and this helped with some brainstorming. I was curious where you got that mount for your weBoost? Thanks.

    9 months ago

    Pretty damn good 15-minute read for all of mobile solar.

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