The YouTube channel Project Farm did some careful comparison testing...
At more than 100 times the diameter and over 300,000 times the mass of the Earth, that enormous ball of plasma at the center of our solar system is the primary energy source for our planet. Without the sun, life on Earth wouldn't be possible, and George Hamilton wouldn't know what to do with himself. According to NASA, the sun produces about 500,000,000,000,000,000,000,000 horsepower worth of energy per second. That's a lot of damn zeroes. It's no surprise that sun deities permeate ancient cultures and mythologies.
With so much energy beaming down from the heavens, free and clear, it's also no surprise that mankind has looked to harness the sun's power by devising various technologies to convert sunlight into electricity. The first photovoltaic cell, which generates electric current when exposed to light, was developed in the 1880s. Photovoltaic technology has continued to improve, with industrial, commercial, and residential installations becoming more common over the past several decades. Solar installations around the globe represented a total capacity of about 177 gigawatts in 2014, according to the renewable energy association REN21.
As with so many kinds of technology, end users benefit as they're productized and miniaturized. From solar-charged watches to sun-powered radios, small and increasingly efficient solar cells have made their way into consumer products. And with so many battery-powered devices proliferating across people's lives, solar chargers are coming of age.
Portable solar charger kits are essentially compact solar cells that output electricity via USB or other jacks. The solar cells might be composed of rigid crystalline panels or flexible thin films; the former tend to be more efficient and rugged while the latter are more compact. The larger the panels, the greater the potential power output. The panels are packaged for convenience (e.g. folded up like a pamphlet) and may also feature electronics to detect the appropriate protocols for charging different types of devices, deal with dips in power output from passing clouds, and so forth. Some have integrated batteries — so the panels charge the battery pack, which then provides power to your devices, rather than routing power directly to your iThingies. More on this later.
The general concept is to place your solar charger in direct sunlight and enjoy the resulting electricity to charge your devices. However, the blunt truth is that if you have consistent access to the power grid, using now-ubiquitous rechargeable battery packs to juice up is generally a better solution than solar chargers. Getting the most from solar chargers can be a fussy and frustrating process.
For example, there's an optimum angle to position solar panels to maximize energy collection from the sun, depending on your geographic location, time of year, and time of day. Our product testing was done in the winter, and based on our location, the proper tilt was approximately 32 degrees from vertical. In our unscientific testing, placing panels completely flat (90 degrees from vertical) versus at the optimal angle resulted in up to a 42-percent decrease in power production. Cloud cover, objects blocking the sun, and precipitation can all significantly reduce power output as well. Trying to ensure proper exposure to the sun for several hours (or all day) in a static position can be challenging enough, much less when you're on the move.
Furthermore, some devices (such as iPhones and iPads) may stop charging if the power input drops temporarily due to shade or a passing cloud. What a waste that would be if you left it unattended to charge or didn't realize it had stopped. Numerous chargers have circuitry to deal with this exact problem so that devices will start charging again once the power level creeps back up.
So why bother with solar chargers? As a prepared individual and/or outdoorsman, you know that you won't always have access to power. The grid may go down for extended periods in an emergency, and there aren't any outlets in the wilderness (much to the chagrin of smartphone-obsessed teenagers everywhere) or often at the range, where we've used solar to charge our cameras, which are more power-hungry than a politician. Solar chargers are perfect for those situations, and if you're a reader of this magazine, no doubt you've said this before: “Better to have and not need …”
One more thing: Given the challenges we've described, we highly recommend using rechargeable battery packs in conjunction with your solar charger rather than connecting your devices directly. This allows you to capture all of the power generated by your panels, and you'll always have the power stored in your battery packs on tap to use no matter the weather conditions. Some products shown in this article have integrated batteries, but you can easily use one or more separate battery packs with stand-alone solar chargers. This will result in having a few more doodads to keep track of, but pay off in a lot more convenience and versatility. Cobbling together your own kit is also a lot cheaper, as pricing on stand-alone rechargeable battery packs has dropped faster than a Forever 21 dress on prom night.
What you should look for in a solar charger kit?
Power Output (rated): The higher the maximum power output of your solar charger, the more you can make use of each minute of sunlight. The larger panels can charge two devices or two battery packs at the same time. Power output is usually expressed in watts, which equals voltage multiplied by current (amps). Tablets and large phones guzzle down 2 amps for optimum charging — at the USB standard of 5 volts that translates to 10 watts of power. More is definitely better here, but there's a trade-off in portability from necessitating larger solar panels. Additionally, while many products tout 2 amps of power output, our measured results often fell short.
Portability: With an intended use for emergencies and while on the go, size and weight matters, especially if you're on foot. None of the chargers in this article are particularly heavy — but some are lighter than others and the larger panels can get a bit bulky. If you carry multiple battery packs, the weight can also start to add up.
Usability: All the products in this guide have some sort of carrying case, often with pockets to store accessories and devices as well as eyelets and carabiners or other methods of attaching the solar panels to backpacks or other objects. Many have multiple rigid panels that fold up for storage. A pocket is useful to hold your device or battery pack, so that they aren't exposed to direct sunlight while charging.
Features: Solar charger kits can be packed with features — smart charging controllers, clever packaging, integrated or included battery packs, accessory cables and adapters, methods to tie them down (we'd suggest packing some paracord with your charger), and more. Some have more weatherproofing than others, which may be important depending on your climate. Also, if you plan to charge devices directly, take note of those that recover from drops in sunlight.
You don't have to drive a Nissan Leaf, wear a man bun, or protest BP to take advantage of solar chargers. Following is a representative selection of solar charger kits, one of which is bound to meet your particular needs.