Why your solar panels are doing less than you think

We've been promoting solar panels as an must-have accessory for Airstreamers for several years. I've personally had solar on my Airstreams since 2006, and I wouldn't be without it.

But even though I'm a big fan, I feel obliged to reveal a slightly unpleasant truth: most solar panels don't do quite as much as you think.

We all know that solar power generation is compromised when the skies are cloudy. And most people know that the angle of the panels is important (which is one of the reasons I prefer portable solar that can be re-adjusted to face the sun, over fixed rooftop solar).

But there are other factors in play, too.

For example, I recently bought an inexpensive set of folding solar panels at an RV show, just to try them out. They were rated for 200 watts, just like the panels we currently sell at AIR GEAR—but at half the cost. I wondered, how did they really perform?

So I did some side-by-side testing. Twice, under identical conditions, at the same time, I tested different sets of portable solar panels—and I was shocked at the different in performance. Here's what I discovered.

The Panels

I had four sets of panels to test:

• AIR GEAR 170 watt Portable Solar Panel Kit (previous generation), $999
• Newpowa 200 watt folding solar panel, $299
• JCN Solar 200 watt folding solar panel, $399
• AIR GEAR 200 watt Portable Solar Panel Kit (current generation), $599

All of the panel kits weighed between 18 and 24 pounds, with accessories such as the charge controller and extension cable. All of them folded down to a portable size. The AIR GEAR kits have carry bags, and the others just fold into themselves.

Ratings vs. the Reality

It's important to note that three of the kits were rated for about the same output (200 watts). But in real life use, there were big differences in how they performed, and that's what you care about when you need to charge up.

I didn't measure the panels' output based on the displays that came with some of solar kits. They can be inaccurate, especially the cheap ones. Instead, I tracked the performance of each kit with a highly-accurate Victron amp-hour meter attached to the Airstream's batteries.

To simulate a discharged battery, I turned on enough 12 volt appliances in the Airstream to draw about 170 watts, then measured how much power each solar kit could supply.

In Arizona, in March, with full sun at about 2:00 pm (which means pretty close to the best conditions you'll ever encounter), the output of the panels varied from 90 watts from the worst panels, up to 150 watts from the best.

Features and Quality Matter

Of course, you're wondering why there was such a big difference—and why none of the panels achieved the 200 watt rating they claim. There are a lot of contributing factors, and here's a few of the major ones:

1. Not all solar panels are created equal. Generally speaking, flexible panels will be less efficient than rigid panels mounted in glass or EFTE (a kind of plastic). But even so, the 170-watt flexible panel that AIR GEAR previously sold easily outpaced the "200-watt" flexible panels by JCN Solar and Newpowa. That's the result of better design and construction.
2. The cheaper solar panels kits use thin wires, which aren't as efficient over long distances. This is the case with the two el-cheapo kits by JCN Solar and Newpowa.
3. Cheap charge controllers are a definite drag, too. The JCN and Newpowa kits use Pulse Wave Modulation (PWM) controllers, which aren't as efficient as the Multi-Point Power Tracking (MPPT) controllers used on the AIR GEAR kits.

Even the best-performing panel, which was (not surprisingly) the new AIR GEAR 200-watt Portable Solar Kit, didn't produce 200 watts in full sun. That's simply because the ratings manufacturers put on their solar panels are for comparison only. Nobody gets the actual full rated output. Getting 150 watts is pretty darned good, though.

Two Big Takeaways if You're Shopping for Portable Solar Systems

One of our biggest learnings after researching and testing solar panel systems since the beginning of this year is: Don't be seduced by a high wattage rating and a low price. These two things aren't compatible.

To get the super-low prices, manufacturers cut corners. Check out the comparison chart above for a few examples. Manufacturers know most people won't notice the differences, so they design for lowest cost instead of highest efficiency.

The second is the importance of assessing the quality of the charge controller. Throughout our research, we were dismayed at the very low-quality charge controllers that come on many solar panel kits. For instance, the controllers supplied with the JCN and Newpowa kits are flimsy plastic, with absolutely no protection against dust or water. That's a terrible idea for an electrical product that is intended to be used outdoors.

Our portable solar kit uses a controller with a metal case and a high Ingress Protection rating of IP54, which means it's "dust tight" and protected against water drips and splashes. Don't submerge it—but the charge controller in our kit will be fine in a light rain.

Bottom line: With portable solar panel kits, a wattage rating isn't the full story. Generally, you get what you pay for.