The only catch: compared to a handheld GPS, most smartphones don't pass muster on satellite accuracy or battery life. Otherwise, those apps are pretty impressive. But with today's selection of solar charging options, battery use does not have to be a problem (unless you are short on sunshine). Solar panels now range from elaborate and spendy to ultra-affordable and pocket-sized. Some are the same size or even smaller than your smartphone itself. We're not sure what this means yet for the GPS companies, but this review will give you an idea of how to navigate the rapidly expanding technological world of solar charging devices. Check out our complete Solar Charger Review for a comparison of all the products we reviewed.
Amperage, Voltage, and Watts, Oh My!
Understanding the technical terms associated with your solar device will help you interpret the advertised power and whether or not it will fit your needs. The best way to think about the various units of electricity are in analogy to plumbing. Think of voltage as the water pressure, current (measured in amps) as the flow rate, and resistance (ohms) as the pipe size.
Now for some math: current (amps) is equal to the voltage (think water pressure!) divided by the resistance (or pipe size).
And watts are a measure of electrical power, which is the voltage multiplied by the current (think pressure times flow rate).
Watts and amps are the most common units you will want to be able to use and understand (at least roughly) when deciphering the performance potential of your chosen solar panel. Again, that is the current (amps) and the electrical power (watts).
A 4 or 5 watt panel works great for small handheld devices, such as a simpler cell phone or mp3 player. However, many smart phones like the iPhone (especially the latest models) are extremely power hungry--nearly as much as an iPad or tablet. In general, you need at least a 7 watt panel to be sure you can charge most smart phones.
If you want to start charging more energy-hungry items like an iPad, or you want to charge multiple devices at once, things start to get more complicated (and expensive). In general, you will need a panel with at least 15 watts of power. If you want to start charging laptops, you will almost certainly need a battery and an inverter. And if you want to charge AC devices, you are now in a new category. You will now need a pretty heavy duty panel (25+ watts, a battery, and a DC-to-AC inverter).
Be careful of buying less wattage panels just to save money. Often you can get by with a smaller panel, but you will end up frustrated by the lengthy charging times. We experienced a lot of frustration charging our phones with 4-6 watt chargers. It would sometimes take 3-6 hours to get a full charge when an outlet or higher wattage panel would take 1-2 hours.
Many companies are now circumventing the power issue by integrating panels and batteries or including batteries in solar kits. With the advent of the power-hungry iPhone 5 and the popularity of tablets, most popular solar panels on the market now are either very high wattage panels (10-15 watts) or they have slick proprietary battery packs which can collect the energy from the solar panel at a much lower flow rate (like 1 amp instead of the 2 amps an iPad typically needs to charge at a reasonable rate).
Goal Zero is currently leading the charge on integrated battery systems, and many companies appear to be scrambling to keep pace. Elon Musk would certainly agree with us in saying that high quality batteries will be the key to the energy future.
At best, the output power of your device will have a marked impact on your stress level--at worst, it could mean the difference between charging a device and not. Be sure to match your needs to your amps (a 2.1 amp USB port will charge an iPad more efficiently than the 1.3 amp port), and your use to your watts.
This year, we found an important new challenge in wading through the tech specs of the solar chargers. Some manufacturers report the total amperage output of both ports combined, while others report the max amperage of each port, such that you add them together to get a bigger total amperage output (these companies are under-selling themselves by not making it obvious that their devices have more amps available!). This means that some panels report 2.1A max, so that if you plug in two devices, they will split the power. Others report a 2.1A max, but what they really mean is that one port will give you 2.1 and the other will give you 1A, and they can charge at that amperage at the same time. That is the sign of a powerful device--but read the specs carefully, because it is hard to tell!
An important practical consideration here is how many bright and sunny daylight hours you expect to enjoy--and, realistically, how many of those hours you can have your solar charger out soaking up some rays. Will you be in the Alaska Range in the summer where daylight is abundant but storm cycles are too? Will you be in the rainy Pacific Northwet (not a typo) where the sky is frequently shrouded in rain clouds? In these cases, you may want a fast-charging, powerful panel with high wattage to charge your devices in a hurry, to take full advantage for those special moments when the sunlight peeks out from behind the clouds.
Or, perhaps you live in the desert where it is always sunny and dry but you have to carry your weekend's water supply on your back, so weight is at a premium. A smaller panel will likely suffice, if you're able to set it out in full sun for a longer amount of time.
This year, the bigger question has become: do I want a charger with an integrated battery, a kit with a folding panel and a battery, or just a panel? Increasingly, our reviewers feel that getting a small, efficient battery for weekend trips in the backcountry is the way to go, instead of a small panel or an integrated battery/panel device. The integrated chargers are full of false promises and heartbreak. The compromise of the integrated chargers fails to produce a "Jack-of-all-Trades," but certainly makes them "Masters-of-None." Panels, on the other hand, are great for extended expeditions or long road trips. And most panels will charge that little battery for weekend trips. Our favorite answer is either getting a kit with a folding panel and included proprietary battery or buying one of our top rated panels and an external battery separately.
Types of Portable Panels
CIGS is cheaper to manufacture and lighter in weight, but not as long lasting as thicker monocrystalline panels. This has obvious applications to outdoor use, with a very clear Achilles heel. Due largely to the integration of a flexible fabric, plastic, or other material, CIGS panels tend to delaminate or degrade more quickly over time.
CIGS panels are lighter and more flexible than the older monocrystalline solar panels, which is cool--but they are not quite as rugged and durable as the traditional rigid monocrystalline panels.
The CIGS panels are typically a little less efficient than monocrystalline panels, except in low light and cloudy conditions, where the CIGS panels are purported to have a slightly higher low-light performance.
Polycrystalline panels have a bluish hue, whereas monocrystalline panels appear more black. The performance differences, however, are slightly more significant for the discerning consumer. Both types of cells are made of silicon crystals; but as the names suggest, a monocrystalline cell is made up of a single crystal ingot whereas a polycrystalline cell is made up of a growth of multiple crystal ingots. Intuitively, we are drawn to "purity" over "growths" (gross?), and it turns out that inclination holds true when buying solar panels. The monocrystalline panels, being more pure, are more efficient (22%) than polycrystalline (18%).
"By using a single cell, monocrystalline based silicon allows the electron greater freedom to move, so less energy is lost and higher efficiency is created," explains Renogy, an American solar energy company.
For small-scale consumers, monocrystalline is the way to go. It is more expensive, but worth it for the small-time user who is less concerned about the added cost on a (relatively) cheap personal-sized solar panel. Bigger solar manufacturers may use polycrystalline panels to save money on a bulk-scale. This is reflected in the current market, with most backpacking-sized panels now using monocrystalline panels and discarding the less-durable CIGS or less efficient polycrystalline panels.
Solar Chargers vs. External Battery
In many cases you may be better served by an external battery, charged up at home or by a solar panel. An external battery the size of your smartphone will typically provide four to five full smartphone battery charges. They also store power and operate anytime of the day (not just when the sun is shining), and are usually significantly less expensive, bulky, and heavy.
If you use a power-hungry iDevice (especially iPhone 5 and newer), smartphone, or tablet, a high quality battery pack is likely the way to go. You can charge it up, stress-free, at a lower amperage, and then get several smartphone charges or a full tablet charge (or more!) out of the fully charged battery. You can also leave home with it charged up already, giving you a decent buffer against cloudy days and shady campsites.
If you will be without power for four or more days, however, a panel will likely serve you better than a battery, if you had to choose between the two. But for most weekend ventures or mountain escapes, an external battery may be the logical choice.
The ultimate solution, however, may be to pair a panel with an external battery, which is the current trend in the backpacking-sized solar market. It all comes down to what you need to power and how long you'll be without a wall socket.
Important Panel Considerations
All of the solar chargers we tested came equipped with USB ports; several of them, in fact, charged exclusively via USB. And most panels even provided at least one USB port with higher amperage to meet the greedy power needs of the latest model smartphones and tablets.
While having a USB port meets the needs of most users, since smartphones and tablets charge via USB, do recognize that this doesn't mean you can charge any device when off the grid. A camera that plugs into a wall outlet, for example, will need an adapter, and a USB solar panel itself will not work. Also, any devices that need a 12-volt cigarette charging port will not work with many of these devices.
Some solar charging devices include a battery so that you can leave your device unsupervised (save for a few angle adjustments throughout the day) in the sun for hours on end, charge up the battery, and then plug in your devices at night when you're back at camp. These solar kits are leading the charge on efficient and effective personal solar charging.
There are also many solar chargers with integrated batteries. They are typically the size of a smartphone with a tiny solar panel. This would seem like the ideal situation; unfortunately, the reality is a little grim. These combination devices end up being, you guessed it, a Master-of-None. The solar panels are too tiny to charge the battery in a reasonable amount of time, and the batteries are often less efficient at charging your device, or generally of poor quality. A good integrated solar panel/battery device, for example, might have a battery that is 75-80% efficient, not too bad when compared to a typical external battery (80-90% efficient), but the solar panel is so small it takes several days of continuous sun exposure to fully recharge (think 50 hours in ideal conditions). These devices are great, however, as emergency phone chargers. Once depleted, if you have sunlight, you can often eke out a few percentage points for your phone--enough to call mom, your sweetheart, or 911, at least to say "Hi."
If you are just charging AA batteries, you won't need a very powerful panel--but you will need the right adapters. A kit like the Guide 10 Battery Pack will charge four AA batteries in a few hours when connected to a 7 watt panel.
Ease of Use
There is nothing more ironic than venturing out into the woods for some quiet time only to spend hours of your day fiddling with your solar charger because it is glitchy or inconvenient.
A required feature of any good solar charger, according to our reviewers, is what the industry calls "auto-restart technology." Some panels still stop charging when a cloud passes or someone walks in front of your panel, and will not restart without you unplugging and plugging it back in. This is a deal-breaker for our critical reviewers. Look for products that have the ability to restart automatically.
Also watch out for inconvenient set-ups, excessive adapters and cords. Make sure to think through your needs and match them to the device you choose. Will you be using it in sweltering heat where you will need to somehow shade your device from the sun as it sits out to charge? Maybe an integrated stash pocket will keep your device out of the sun while it is charging? Or perhaps you'll be setting it out in cold, windy conditions, and you want a charging cable that is easy to extend so you can keep your device in your tent while charging. It all depends on your use--but make sure this new gadget won't take more away from your experience than it will add!
If you are buying a portable solar panel for travel or backpacking, low weight will be a high priority. If you are looking to power an expedition base camp, however, your needs will be completely different. Unfortunately, it is pretty hard to tell from photos and even the listed specs how much a panel weighs. When comparing weights, make sure you are comparing apples to apples. Sometimes manufacturers list the weight of just the panel. Other times they list the weight of the panel plus all the accessories. A little research goes a long way.
Many CIGS panels will win in the weight competition, but also consider what this means to durability, and how important that is for your uses. Is light weight your number one consideration? Or do you like your gear to be strong and durable for years of reliable use? If you're like any of the reviewers at OGL, you probably lie somewhere awkwardly on the spectrum between the two. That's where choosing gets tough. For many of us, that translates to having a quiver of, say, ten climbing backpacks in the closet, seven of which you hardly use, and two of which are hanging on by mere threads. Turns out fast and light in the mountains does not translate to fast and light apartment-living
Many of the panels we tested have an integrated pocket to stash your device, making it easy to pack up and carry. The integrated solar panel/battery devices do not have a storage system. Instead, they are their own compact, rugged packages that you can put in the brain of your backpack, a stuff sack, or your back pocket--they are that small. These light and portable options are great for short trips and around-town missions when you need to be sure you can stay connected to your smartphone or tablet, but they are advertised as "emergency use only," which means "don't rely on the solar panel"--instead, make sure it's charged up when you leave the house. If these "emergency panels" meet your needs, be sure you get one with 2 amp ports, otherwise it may struggle to charge your power-hungry smartphone or tablet.
If we're really examining the portability of solar chargers, we might seriously consider buying an external battery instead. They are cheaper, smaller, and lighter (though you can get more expensive, bigger, and heavier ones, if you so desire), and for shorter missions, this might be your best bet. To be perfectly honest, many of our reviewers use external batteries on trips of 3-5 days to keep smartphones charged--and that includes using the smartphone's GPS app. So consider your uses, needs, and budget, and that will help guide you to the right product.
The solar charging market has fully embraced the modern obsession with smartphones and tablets. Many of the panels and chargers you will find will have one or two USB ports, sometimes with different amperage ratings (2.1 amps for a tablet, 1 amp for your phone). This is great if you are only charging a phone, tablet, camera, or other device with a USB charger.
However, if you want to charge something (like many camera batteries) that only connects to a wall outlet, really the only way to charge it would be with an inverter. Cigarette lighter adapters (like the one that you would plug into your car to turn the 12 volt DC into 110 volt AC) can be relatively cheap. Keep in mind, however, that much of the power is lost in this conversion. Some of our testers have even seen these inverters go up in smoke in a standard car-charging setup. USB is the simplest way to charge your devices with a solar panel.
Also keep in mind that some panels come with features such as grommets to allow them to be hung to a backpack, tent, or tree, and some come with the capability of daisy-chaining to other panels in order to generate a lot more power. These features add to the usefulness of the products.
Many modern solar panels only come with a USB connector, since many of our favorite handheld devices charge swiftly off this simple connection. Others come loaded with adapters, alligator clips, extension cables, charging indicators, or carabiners.
It can be hard to tell what accessories are included with a panel and which you have to buy separately--or what exactly you can connect to the panel anyway. This can be particularly troublesome when trying to charge some older cameras, for example, that do not charge via USB. Make sure you know what accessories you need and which ones actually come with your panel.
Price Per Watt of a Solar Panel
The easiest way to determine value in a solar panel is the price per watt. Take the price of the panel and divide by the number of watts. For example, if your panel costs $70 and is 7 watts, that is $10 per watt. $10-15 per watt is a good value. Anything more than $20 a watt is too expensive unless the panel is also coming with valuable accessories, batteries, or inverters.
Is Buying a Solar Panel Worth It?
Solar power from a portable panel is still generally more expensive than electricity from the grid. But if you don't have access to the grid and you need to power something, a portable solar panel is often the only option.
What if you want to power your home office? Or power your camping accessories without running your car engine? Portable solar panels are still expensive per watt. However, two factors are often missed when deciding if solar is worth it: 1) When you are generating your own power, you usually use way less, and 2) Generating your own power is pretty fun.
For example, during this test we thought it would be fun to use the Goal Zero Sherpa 120 Kit (now discontinued) to power a small home office (laptop, 24" LCD monitor, USB hub and external hard drive). We found it was possible as long as we turned off any accessories we were not using (lamps, printers, extra hard drives, scanners). So while the price per watt may still have been high with our solar panels, we were more aware of our power usage and overall used much less electricity. We did the same thing with our Trek Valencia+ pedal-assist electric bike. We found we could extend the range of the bike by taking the Sherpa 120 kit with us. Suddenly we needed the car much less. In fact, since we got the the pedal-assist electric bike, driving mileage has gone from 1,000-2,000 miles a month to 250-750. With a car that gets 28 mpg, that is a savings of $75-175 a month.
Read more about oursolar-powered electric bike project and dream up ways you can use solar power to your advantage.
Plus, it can be just plain fun to create little systems like this. Building your own electric grid and transportation system is the grown-up version of building a fort or a tree house. Manufacturers like Goal Zero have 30-day return policies if it isn't all we've chalked it up to be.
A Word for the Wise
During our testing, we received a solar panel that was designed to look exactly like a very popular model. It took some hunting to find the company's email address, and when we sent them an email, asking why it didn't work as advertised, we got a very polite response from a company in China that did not solve the problem at all. The panel was either a very old model or just didn't work. We had received a very good copycat--except, of course, for the fact that the panel didn't work as it was supposed to.
Keep an eye out for imposters in the realm of solar chargers, and be sure to do a little of your own research before purchasing any solar panels online.
Keeping a critical eye open to website design and product descriptions has also proven to be a good indicator of overall product quality. So much solar technology is coming from China that it was possible for us to ascertain a company's attention to detail in the quality of their English on their website: Was the website slapped together, or did they take the extra time to dot their I's and cross their T's, metaphorically speaking? One company that has been a leader in previous reviews fell behind this year--and when we emailed them, we noticed they had spelled their own employee's name wrong on the website. Solar is a vast and growing market--it pays to notice details and look critically before you buy.