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How to Choose the a Solar Charger or Mini Solar Panel

By Jane Jackson ⋅ Senior Review Editor
Thursday May 9, 2019
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There is a myriad of solar panels out there, making it challenging to figure out which direction to go when shopping for a new panel. If you take a look online, chances are you are overwhelmed by the multitude of options that are available at a reasonable price. From battery packs with small 2W panels on them to mega 40W fold-out set-ups, there is no shortage of options from which to choose. Now it is possible to keep all of your electronics (that have become ubiquitous) charged up, even in a backcountry setting.

An assortment of panels from our most recent update.
An assortment of panels from our most recent update.

We've conducted extensive online research, sifting through the hundreds of panels on the market to determine key components that are essential in making a decent portable solar charger. We've selected the top competitors from a few different categories, covering a wide range of styles. From small battery packs that use solar as a back-up to 20W kits explicitly designed to charge laptops off the grid, we've used many different variations on the portable charger theme. This review is a window into the wonderful world of mobile solar technology and will assist you in choosing the best option for your next adventure.

Before we get started, here is a short anecdote about this review.

In our testing a few years ago, there was one that we couldn't get to charge in all of its advertised capacities. It had a vast assortment of laptop plug adapters, but we could never get them to work, and there was no adapter for any Apple product (red flag!). Finally, we gave up and emailed the company. We got a very polite but useless email back and quickly identified that it was a very, very good copycat. The packaging and product looked identical, but it was not the reputable brand it seemed to be.

Keeping a critical eye open to website design and product descriptions has also proven to be a good indicator of overall product quality. Did they take the extra time to dot their I and cross their Ts, metaphorically speaking? One company that has been a leader in previous reviews fell behind this year; when we emailed them, we noticed they had spelled their own employee's name wrong on the website. Solar is a large and growing market, and it pays to notice details and critically examine before you buy.

This discussion is our way of saying, be discerning in your search! Sometimes it is worthwhile to spend a few extra bucks for a reputable brand. This review will help identify several brands that are excellent or falling a bit behind and how to sift through the hype. We've also found, from reading hundreds of customer reviews, that sometimes you get a panel that doesn't work. Be warned! This scenario has never happened to us in our testing, but if it does, try to send the unit back.

Wait, Watt?


As we found in the reviews of previous years, the more advanced our gadgets are, the more power-hungry they become. This trend means those tiny, pocket-sized panels of yesterday have become obsolete when it comes to their ability to charge a phone or tablet efficiently.

When car camping  weight is less of a concern. The bigger the panel  the better  in some situations!
When car camping, weight is less of a concern. The bigger the panel, the better, in some situations!

To accommodate these power-hungry devices, we found that the larger capacity panels are the most effective. In the past few years, we've focused our review on these larger panels, mainly because there are so many options out there. Though these panels are bulkier, they are more effective and thus get the job done faster. We preferred larger panels to the smaller ones because we couldn't stand watching the battery increase by 1% every half-hour (while charging our cell phones). Does anybody have time for that?

We've placed these larger capacity panels side-by-side and tested them against their smaller counterparts. Not only did we take these panels out and about as we traveled around the western US seeking sun, but we also put these panels through rigorous side-by-side testing to make sure we knew which panel was the most effective. We used a standardized external battery and USB cord to eliminate any discrepancies between different batteries' ability to hold a charge. We also set the panels out at the same time, with the same orientation, eliminating as many variables as possible. This way, we got a benchmark time for how long it took each panel to charge the same battery.

Here  we compared the surface area of solar cells on each panel. This is a big factor in its overall efficiency.
Here, we compared the surface area of solar cells on each panel. This is a big factor in its overall efficiency.

In past years, we had trouble getting the small panels to charge off the sun and found the batteries to be cumbersome and bulky. We checked out three new battery pack/panels, all with a 2W panel on a battery (ranging from a 10,000mAh to 25,000mAh). It was time-consuming to charge these batteries from the sun; we did, however, find them to be effective at charging phones and small devices - if the battery pack was full.

The panels race to charge our test battery packs in optimal conditions as we kept track of time.
The panels race to charge our test battery packs in optimal conditions as we kept track of time.

With the addition of these new panels, we still managed to break down the chargers in this review loosely based on wattage. This way, we could see exactly how much wattage mattered in charging small external batteries, phones, and iPads. It turns out, as you might have guessed, the larger the wattage, the faster the devices charged; we think it's worth purchasing a larger panel since they are all (mostly) similar in size anyway. Nobody likes sitting around watching a phone battery indicator all day when they could be out exploring.

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 is 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). 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 electrical power (watts).

Wattage


A 4 or 5-watt panel works great for small handheld devices, such as a simpler cell phone or mp3 player. However, many smartphones, 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 ensure you can charge most smartphones.

If you want to power more energy-hungry items like an iPad, or you have multiple devices, 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 have 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). It used to be challenging to make those three components work well together, but now Goal Zero has kits that make it relatively painless.

Be careful of buying small watt models to save money; they take forever and a day to charge a device. We experienced much frustration in 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 smartphones 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. These batteries can collect the energy from the solar panel at a much lower flow rate (like one amp instead of the two 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 undoubtedly agree with us in saying that high-quality batteries will be the key to the energy future.

Output Power


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.

Note that some manufacturers report the total amperage output of both ports combined, while others say the max amperage of each port, such that you add them together to get a more significant total amperage output (these companies are under-selling themselves by not making it clear that their devices have more amps available!). This fact means that some panels report 2.1A max so that if you plug in two devices, they will split the power. Others say a 2.1A max, but what they mean is that one port will give you 2.1, and the other will provide you 1A, and they can charge at that amperage at the same time. That is the sign of a robust device, but be sure to read the specs carefully.

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'll have your solar charger out soaking up 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 the 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 more extended amount of time.

This year, the more significant 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 built-in 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 was either getting a kit with a folding design and included a proprietary battery or buying one of our top-rated options and an external battery separately.

Types of Portable Panels



CIGS


Checking out the Bushnell Bear Grylls SolarWrap Mini on some Big Sur driftwood. It wasn't always easy to orient the flexible panel perfectly to the sun  but there was always an easy way to hang it or drape it over found objects.
Checking out the Bushnell Bear Grylls SolarWrap Mini on some Big Sur driftwood. It wasn't always easy to orient the flexible panel perfectly to the sun, but there was always an easy way to hang it or drape it over found objects.
The flexible panels you will see are made of CIGS thin-film solar cells (which stands for copper, indium, gallium, and selenide). CIGS are cheaper to manufacture and lighter in weight, but not as long-lasting as thicker monocrystalline panels. This tech has obvious applications to outdoor use, with an obvious Achilles heel. Due largely to the integration of a flexible fabric, plastic, or other material, CIGS panels can delaminate or degrade more quickly over time.

Monocrystalline


CIGS panels are lighter and more flexible than the legacy monocrystalline solar panels, which is cool--but they are not quite as rugged and durable as the traditional rigid monocrystalline panels.
Checking out the Instapark Mercury 10 on the rocky shores of Icicle Creek  in sunny eastern Washington. This is a durable yet portable monocrystalline panel.
Checking out the Instapark Mercury 10 on the rocky shores of Icicle Creek, in sunny eastern Washington. This is a durable yet portable monocrystalline panel.
Until folding panels, the rigid form of the monocrystalline panels could be too cumbersome to consider useful for backcountry use. Now, with rigid panels taking all kinds of useful forms, the difference is becoming moot.

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


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 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 when buying solar panels. The monocrystalline panels, being purer, are more efficient than polycrystalline.

"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. More prominent solar manufacturers may use polycrystalline panels to save money on a bulk-scale. The current market reflects this trend, with most backpacking-sized models 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 off with 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 any time 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 are 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 is a logical choice.

The ultimate solution 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



Connections


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 a higher amperage to meet the greedy power needs of the latest model smartphones and tablets.

A close-up of the pocket to store devices  protecting them from blowing sand or snow.
A close-up of the pocket to store devices, protecting them from blowing sand or snow.

While having a USB port meets the needs of most users, since smartphones and tablets charge via USB, you'll want to 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 require a 12-volt cigarette charging port will not work with many of these devices.

Integrated Batteries


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.

A compact panel with an integrated battery pack.
A compact panel with an integrated battery pack.

There are also many solar chargers with integrated batteries. They are typically the size of a smartphone with a small solar panel. This arrangement 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. An excellent integrated solar panel/battery device, for example, might have a battery that is 75-80% efficient; this is not too bad when compared to a typical external model (80-90% efficient), but the solar panel is so small it takes several days of continuous sun exposure to recharge fully (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 only charging AA batteries, you won't need a potent 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.

An essential feature of any good solar charger, according to our reviewers, is what the industry calls "auto-restart technology." Some models 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 characteristic is a deal-breaker for us; we'd recommend you look for products that can be restarted automatically.

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 shade your device from the sun somehow 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!

Weight


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. As many of us know, a little research goes a long way.

This panel has lots of bells and whistles  but also lots of added weight.
This panel has lots of bells and whistles, but also lots of added weight.

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 weight your number one consideration? Or do you like your gear to be robust and durable for years of regular 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.

Portability


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 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 advertise 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 two amp ports; otherwise, it may struggle to charge your power-hungry smartphone or tablet.

The Renogy is about the size of a small journal or book  making it quite portable.
The Renogy is about the size of a small journal or book, making it quite portable.

If we're 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. 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.

Versatility


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), which is great if you are only charging a phone, tablet, camera, or another device with a USB charger.

If you want to power something (like many camera batteries) that only connect to a wall outlet, the only way to charge it is via an inverter or by a Portable Power Station, like the Goal Zero Yeti 150. 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 escapes 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.

Keep in mind that some panels come with features such as grommets to allow hanging on a backpack, tent, or tree, and some come with the capability of daisy-chaining to other units to generate a lot more power. These features add to the usefulness of the products.

Solar Accessories


Many new 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 and which you have to buy separately, or what exactly you can connect to the panel. This situation 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 come with your panel.

Price Per Watt of a Solar Panel


The easiest way to determine value is the price per watt. Take the price and divide it 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 in our eyes. Anything more than $20 a watt is too expensive unless it's also coming with valuable accessories, batteries, or inverters.

Solar Powered Electric Bike: Trek Valencia+ with the Goal Zero Sherpa 120 Kit
Solar Powered Electric Bike: Trek Valencia+ with the Goal Zero Sherpa 120 Kit

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 charge your camping accessories without running your car engine? Portable solar panels are still expensive per watt. However, two factors are essential to consider when deciding if solar is worth it: 1) When you are generating your power, you usually use way less, and 2) Generating your energy is pretty fun.

For example, during this test, we thought it would be fun to use a Goal Zero kit 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, backup 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. Since we got 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 our solar-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 electric grid and transportation system is the grown-up version of building a fort or a treehouse. Manufacturers like Goal Zero have 30-day return policies if it isn't all we've chalked it up to be.

Goal Zero Nomad 7 on a sailing trip in the San Juan Islands.
Goal Zero Nomad 7 on a sailing trip in the San Juan Islands.


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