Portable Solar Panels

This is an addition to our solar setup that I have hummed and hawed over for a long time, as for the most part, when we are off grid, the battery does seem to hold its own.

There are a few parks though, where we would certainly benefit from being able to follow the sun with some panels. Looking for something to help alleviate the Covid boredom over the winter, this mod seemed an ideal candidate.

Way back in 2009 when we purchased our Alto, the only solar panels offered were 68 watts each. In 2015, a little mod to add some battery monitoring morphed into a full on change to the solar components and wiring in the Alto. A Trimetric monitor and solar controller now run the show. At that point in time, lead acid batteries were still the standard, as lithium had yet to fully catch on in the market, and were still very expensive. The goal then was to maximize the charging process, and introduce accurate state of charge monitoring.

The next logical step is the addition of portable panels to increase the amount of overall power available to the controller. An extra 100 watts would in theory get us up to around 236 watts, but more on that number later. This wattage is around what the standard panels now offered by Safari Condo provide. Technology available has evolved a lot. Regardless, any increase would help the charging, even if a site already offers an abundance of sun. 

The first step was to find the appropriate flexible panels. There are literally hundreds of options out there. My research guided me to find panels that were similar in output to those already on the Alto. Physical size was also a factor…do we go with one 100 watt panel, or two 50 watt panels. This impacts not only storage, but how they would sit on a campsite. We ultimately decided on two 50 watt panels, from both an electrical and set up perspective.

I found a Renogy 50 watt panel that was similar in spec to our existing, and were not excessively large. Two panels also gives the option of only setting up one, depending on the conditions. Flexible panels are pretty spartan when they arrive. Simply the panel material and two electrical connections. Next step was to figure out how they would be set up on a site, and this involves tilting them to the sun. Some sort of frame was required. 

I crafted a simple aluminum angle frame, held together at the corners with thumbscrews and wing nuts. The sides also incorporate legs that can be moved to allow the panel to tilt towards the sun. All the pieces come apart quickly, to help minimize the space required for storage while travelling.

Where to store the panels is a bit of a challenge, especially when space is at a premium. These panels can be awkward, as they simply don’t roll or fold. There is really no room inside the Alto, so they must either go into the tow vehicle, or somewhere on the outside of the Alto. 

A solution to the storage issue appeared a while back on the Altoistes FB group. Soon after posting a write up and photos detailing his solar charging and lithium battery retrofit, Vince posted a few photos showing a mock-up of how he thought he might store a couple portable panels. He proposed building a slim storage cabinet that would be fastened to the underside of the Alto. Open a little drop down door and the panels would slide right in. Great idea Vince…so I built one.

nestled up under the Alto

Wanting to keep the overall height of the stacked panels to a minimum, I designed the frames to be removable from the panels. The panels slide into one section, and the frame pieces into another. This allows for a cabinet of only a two inch depth. To ensure the cabinet is not shaken free from its installation spot, in addition to the screws into the underside, I installed four carefully placed bolts through the floor. These are placed under the bench area, out of sight. There was a hell of a lot of measuring going on to make sure an errant bolt did not appear in the middle of the floor, which could happen if not careful!

fabulous when fellow owners share ideas

Now for some electrical mathematics. One could simply assume that adding panels will increase the overall wattage accordingly, but of course that is not the case. Volts and amps come into play in the equation, and can make a big impact. Another factor is whether the panels are wired in series or parallel. Our Trimetric controller is a PMW, and these favour a higher amp input rather than voltage. All the panels will continue to run in parallel.

Each panel on the Alto outputs 16.5 Vmp, with a current of 4.1 Imp. The new panels each output 18.5 Vmp, and a current of 2.71 Imp. A small difference, which will impact the overall usable wattage available. The lowest panel voltage becomes the default output voltage, so this is why it was important to try to best match the panels. 

Based on these manufacturer specs, you can calculate the anticipated wattage output, using the lowest panel voltage, and because they are wired in parallel, the sum of the current  output.

16.5v X 13.62a = 224w

So the calculated wattage being output is 224w, rather than the spec cumulative wattage of 236w. This is the impact of the lowest voltage panels in the equation, a loss of 12 watts. Not bad overall though, as this is a huge gain on the 136 watts of our factory rooftop setup.

I was also curious as to the voltage loss from using 30 feet of 10awg extension wire, so I took a quick measurement. Without any extension, the voltage output was 19.44v. With the 30 foot extension, the voltage was 19.36. A relatively minor 0.07v loss. Of course, all these numbers are based on the solar collection at the time of test, but it was mid afternoon and clear sky, so the panels were probably outputting close to their max.

The portable panels plug into an Anderson connector which is wired to the fused solar combiner. The output of all the panels is then sent directly to the solar controller, which does its magic and sends the resulting output straight to the battery terminals.

Anderson connectors are a solid product

combining the solar juice

In a real test at a campsite, after an evening of battery usage, the ability to set the panels in the sun greatly increased the solar power available. The more input the controller has to work with, the faster the battery recovers to its fully charged state. A simple bubble level helps aim the panel to an optimum angle to the sun.

the shadows of the lines should intersect the little black dot

Being able to follow the sun around a site, or even just gather additional power on an overcast day is a game changer, especially for early Altos with limited solar wattage. It is a bit of a pain moving the panels and wire tether to a couple of different spots on a site, but this minor effort resulted in a battery that regained its full charge consistently. Naturally this may not be the case every day, but any additional juice sure helps. The panels store out of the way nicely in their trunk, and even with assembling the frames, getting the panels up and running only takes a few minutes. 

I can see using these portable panels every time we are off grid, as any increase to the solar input has a very direct benefit. This is a mod that is well worth the effort.