Adding a Portable Solar Panel to an Existing System

Already have fixed solar but need a bit extra for longer trips or shady campsites? Can portable solar panels be added to an existing system? Adding a portable solar panel to an existing system is a great option to help top up your batteries, but there’s a few things to keep in mind.

 

Adding a portable panel is not as simple as plugging it in to an existing solar controller that is connected to existing roof solar, even if the controller is sized such that there is sufficient current available. Connecting a portable panel into the same controller as fixed solar can result in (at best) significantly reduced or (at worse) zero additional energy production – which is money down the drain.

 

In this guide, we’ll walk you through how to safely and efficiently expand your solar system with portable panels, what mistakes to avoid, and which products make the process easier.

 

KEY TAKEAWAYS

  • Use Seperate Solar Controllers: Never connect portable and fixed panels to the same solar controller. It kills performance.
  • Know your Setup: Check if any solar input plug on your caravan/camper feeds into an existing controller.
  • Check Cable and Circuit Protection Sizes: Ensure correct cabling and circuit protection for increased current added.

 

 

WHY ADD A PORTABLE PANEL?

Extend Your Charge in Shade or Winter

Roof panels are great, but they’re stuck in place, and point in one direction - up. Park under trees, or camp in winter when the angle of the sun is greatest, and your charge rate can drop off a cliff. A portable panel lets you chase the sun, which can result in up to 40% more energy capture throughout the day.

Stay Out Longer

Running a fridge, lights, cooktops and charging devices can add up fast. A portable panel gives you that bit extra when conditions are less than perfect, or during high-use periods.

 

WHY YOU SHOULDN'T USE THE SAME CONTROLLER

Panels Must Match Closely in Voltage

When connecting panels to the same controller, their voltages need to be within 1 volt. If not, the controller drags all voltages down to the lowest panel. That means even in the best conditions, with your panel angled perfectly, you’re energy harvest will be diminished.

Mixing Portable and Fixed Panels Hurts Output

Even if the voltages match, never mix portable and fixed panels. Your controller sees them as a single array. If one (like your roof panel) is shaded or off-angle (which it always is), it limits the whole array, even if your portable panel is in full sun.

Real world: We’ve seen full-shade roof panels drag portable panels in full sun down to zero output when connected to the same controller.

 

HOW TO ADD A PORTABLE PANEL CORRECTLY

Step 1: Check Your Existing Setup

Find out if any external solar input plug is wired into your current controller. Unfortunately, this is the usual (and incorrect) practice taken by caravan and camper trailer manufacturers. If it is attached to the same controller that is connected to your roof solar, plugging a new portable panel into that input won't work efficiently.

Step 2: Run a Second Input Direct to the Battery

You’ll need a new cable run direct to your battery, bypassing the existing controller, or you can remove the cable connection to the existing controller and re-direct the cable directly to the battery. Make sure that the cable (new or existing) is sized correctly for your new portable panel, and protected with the appropriate circuit breaker or fuse.

Step 3: Use a Separate MPPT Controller

Each panel or array needs its own solar controller. To work out the correct size, take the wattage of the panel and divide it by the battery voltage, then round to the nearest controller size.

For example, with a 400W panel, in a 12V system, 400/12 = 33.3, so 30A is sufficient.

For higher voltage panels (or panels wired in series), ensure also that the solar controller can handle the Open Circuit Voltage. So for the 400W High Voltage Quad Panel, you need an MPPT with a minimum 45V, or two 200W Glass Panels wired in series would need a minimum 50V (as voltages are added together when panels are installed in series). For the 400W Low Voltage Quad Panel you only need a solar input of 30A (meaning it is suitable for DCDC's such as RedArc). 

Step 4: Combine Inputs (Safely)

If you are using more than one portable panel, you can use a double adapter to feed both controller outputs into your solar input*. Again, cable sizing and fuse/breaker ratings must be sized correctly for the current.

 

REAL-WORLD EXAMPLES

Scenario 1: Adding to a RedArc Manager30 Setup

  • Existing rooftop panel is connected to the RedArc solar input
  • Add an AllSpark 250W Solar Blanket with its own 20A Tracer MPPT controller
  • Ensure solar input runs directly to the battery with 8B&S cable and a 50A fuse/circuit breaker

Scenario 2: Two Portable Panels

 

STEP BY STEP - HOW TO ADD A PORTABLE PANEL

  • 1. Identify your current controller: Is it a DCDC or a Solar Controller? What size is it?
  • 2. Check where your solar input feeds to: Does the input go directly to the battery, or does it connect to the existing controller?
  • 3. Plan a second cable run: If the solar input goes to an existing (used) solar controller, run a cable directly to your battery.
  • 4. Purchase a separate solar controller: If your existing solar controller is being used, you will need to purchase a stand-alone solar controller for your portable panel.

 

Adding a portable solar panel is a great way to ensure your batteries can keep up with your power consumption,  but only when set up correctly. The biggest mistake is trying to feed multiple panel arrays (which experience different conditions and/or have different specifications) through the same controller. Avoid that, and your portable panel can work efficiently when you need it most.

AllSpark's range of Quad Fold Panels and Solar Blankets make it easy to expand your system with safe, efficient gear backed by real warranties. Not sure if your system setup is correct? Contact Offroad Living for expert help.

 

FAQs

Q: Can I connect a portable panel to my existing solar input?
A: Only if that solar input runs directly to your battery (in which case a solar controller is needed for your portable panel), or it connects to an existing solar controller that is sized appropriately AND not connected to any existing solar array.

Q: Why can’t I use the same controller for both fixed and portable panels?
A: Panels on the roof are mounted horizontally, and will experience different conditions (eg. Shade, angle to sun) than a portable panel. The controller will drag both solar arrays down to match the weakest voltage, resulting in significantly reduced (or even zero) solar harvest.

Q: How do I work out what size controller I need?
A: To determine the size controller you need interms of amps, divide the wattage of the panel by the battery system voltage (eg. 12 or 24V). To determine the voltage input required for the controller, check the Open Circuit Voltage of the panels.  

Q: Can I combine two portable panels?
A: Yes, but it is best practice for each to have their own controller. Then you can combine outputs, as long as cables and breakers suit total current.

 

*Keep in mind that a 50A connector can actually handle up to 120A, so long as the current is not live immediately. As solar is not “live” until the controller detects a battery connection, even if your portable solar panels produce over 50A combined, the 50A connector is able to handle the current safely and efficiently.