Reviews You Can Rely On

How We Tested Solar Chargers

By Jane Jackson ⋅ Senior Review Editor
Friday May 7, 2021

Charge Interruption Recovery

One of the biggest complaints of users is how small, portable models work on days that are less than "bluebird". If you spend a lot of time outside, you know that a perfect blue-sky day is elusive in a lot of places. Because of this, a solar contender that only performs in optimal conditions might not be the best option. To figure out which models did best in sup-prime conditions, we created a test that would compare each one's ability to recover a charge after being shaded. A cloud could pass overhead, a panel could close its self or fall over in the wind, or some other shadow could pass over the panel when left out for a few hours unattended.

Testing charge interruption recovery with the 10W-15W panels using a...
Testing charge interruption recovery with the 10W-15W panels using a human-shaped cloud simulator.
Photo: Jane Jackson

We wanted to make sure our bases were covered, so we had each model charge a battery for 30 minutes in full sun, measuring the output with our multimeter. Then, we shaded each one intermittently for the next 10 minutes and measured its output after being shaded. Some were unable to continue charging the battery after the interruptions, while others continued to deliver charge with portions of the cells covered and even charged the battery pack a few percentage points more after returning to the sun after being shaded. Typically, the smaller watt contenders did worse than the larger wattage models.

Charging Speed

When working with solar power, we learned, through trial and error, the sun, wind, and clouds are constant environmental factors that we had to find ways to work around. This is the beauty of solar power; it is a direct connection from our modern realm of electronic gadgets to the natural world. To get consistent data in our quest to find the best solar model, we had to narrow down our testing time so that we were sure that all the were tested in the same conditions.

Here in our highly advanced outdoor test lab we measure the Outad...
Here in our highly advanced outdoor test lab we measure the Outad 7W's output to the external battery during our "race to charge" test.
Photo: Jane Jackson

To answer the popular question of how long will this model take to charge my iPhone (or Android), we had to narrow down our testing period to see how much charge an iPhone 6 got after plugging into each model. We fully charged phones with the panels as well; to get a side by side comparison, this window proved to be a good limiting factor and gave us a range of numbers as the models worked to charge the phones. We also set up each one side by side and plugged a dead battery into each of them. For the next four hours, we kept track of time while the contenders worked to charge each battery. After three hours, we checked to see which one had produced the most charge in our batteries. This gave good corroborative evidence along with the phone charging test to figure out which were actually the most efficient.

Multiple Device Charging

This category applies to models with a 10W capacity or more. The smaller options just don't have the guns to charge two devices at once, as quite a bit of the output power is lost due to inefficiencies. This means that the BioLite 10+ is out of the running for this category. The Goal Zero Nomad 14 has many extra cords, but is not designed to easily charge more than one device at once.

The miles of extra cord that comes with the Goal Zero Nomad 14.
The miles of extra cord that comes with the Goal Zero Nomad 14.
Photo: Jane Jackson

From this test, we did learn that it drastically decreases the efficiency to have two devices plugged in at once. Because they all have a relatively small wattage, its best to have an external battery or two so, you can charge off of those, rather than relying fully on the panel for all your needs.


Out of the box, all of the competitors appeared to be quite similar. The majority are black, with heavy-duty canvas fabric on the outside, with some kind of pouch to store gadgets and cords. The panels themselves are monocrystalline in composition but have different coatings and additions depending on price. As we scoured the internet and researched each one, we found many complaints among customers about the durability of the model they purchased. Because of this, we paid particular attention to the way each one held up over the testing period.

Here are some of the questions we focused on when assessing the durability of the models. Are they delaminating? Does the Velcro continue to stick? Are they warping or melting? Do they still perform well after a month of use? Two months of use? A year?

The extra canvas panel adds weight and unnecessary excess material...
The extra canvas panel adds weight and unnecessary excess material to the X-Dragon. The flap also tends to flap or blow the panel over in wind.
Photo: Jane Jackson

Weight and Portability

Weight gets high weighting in our scores; pun intended. After all, the whole point of a portable solar panel is to be, well, portable. A model that weighs less than a pound and is very compact is all we take for most outdoor situations: hiking, backpacking, biking, and climbing. If it weighs more than a pound and a half, it needs to do some heavy-duty charging of multiple devices and/or a laptop and is probably not ideal for carrying on a self-supported trip. If you are boating, weight doesn't matter. Take that into account when looking at the scores.

The Anker 21W is almost as compact as its two-panel sibling, the...
The Anker 21W is almost as compact as its two-panel sibling, the Anker 15W. From this angle it is hard to tell which is which, showing how sleek the Anker 21W actually is.
Photo: Jane Jackson

Consider that weight will increase if you need to bring multiple charging cables and/or a case. The weights in our spec sheet indicate the total weight of the setup we reviewed. We like the simplicity of the Renogy 15,000mAh, since it a small battery pack with a solar charger on it. This panel setup weighs only 9.5 ounces, but don't count on the solar panel alone to deliver an effective amount of charge. This panel works best if you charge it up at home and use the sun to keep it topped off on your trips off the grid.