Solar panels come in a variety of guises designed to appeal to consumers looking for greener, plug-free ways to fuel electronics on the go. Prominent among these is Solartab, a portable solar charger and back-up-battery that hit the market in 2015 following a Kickstarter campaign in which it raised more than double its funding goal. We spent some time in the sun to see whether it was up to the task of keeping our devices happy and powered.

Design & connectivity

As the name suggests, using the Solartab is pretty much like handling an 11-in tablet, complete with protective cover. Measuring 9.7 (W) x 7.6 (D) x 0.35 (H) inches (246 x 193 x 9 mm) and weighing in at 2.65 lb (1.2 kg), the unit as a whole has a good heft to it, with the machined aluminum frame, glass top, and embedded electronics providing a density that feels like there's little wasted space at all. Inside the Solartab is a rechargeable lithium-polymer battery with a capacity of 13,000 mAh and on top there's a 5 W mono-crystalline siliconsolar panel. When it comes to porting around extra power, the Solartab's thin profile makes it easy to slip in bags or hold in the hand with other gear.

While the overall utility is fairly straightforward, the blend of function, hardware, and minimalist elegance makes this device stand out as an attractive option for everything from daily use to emergency kits. Solartab is not the first product to combine solar technology with a rechargeable battery and USB output ports, but it's one of very few that understands how solar charging works and does something meaningful about it. In order for solar panels to efficiently capture the most amount of possible power, the surface needs to be perfectly perpendicular to the direction of the sun's rays. Unlike most other portable solar solutions, the Solartab provides four – five if you count flat – easy-set angles with its multi-position cover.

The permanently-attached cover may not be the thickest, stiffest, or most high-quality, but it's sufficient enough to keep the Solartab clean and protected. As long as you're careful with your gear, it'll last over time. The cover itself is slightly larger than the panel's frame, which helps to keep the aluminum edges from scuffing against surfaces. It can also take the brunt of force if you happen to drop the unit. (This was accidentally confirmed, twice, however it's not recommended due to the device being more pretty than rugged by design.) The cover's smooth outside material still offers a bit of grip, and the built-in elastic strap keeps it closed shut when the Solartab is not in use.

Although the cover's inside grooves that angle the Solartab are thin, the device is heavy enough to stay put so long as it's resting on a reasonably flat surface. And if you have a steady hand, you can gradually nudge the it from a minimum (grooved) position of 37 degrees to a maximum of about 81. The cover makes it easier to achieve optimal (or as close as possible) orientation, and it's certainly better than trying to prop up a flat solar panel with whatever – if anything – is available on hand.

The Solartab features a pair of USB output ports that are cleverly located towards the bottom. Devices can connect with short or long cables without dangling or potentially tipping the panel over – an oversight in some portable solar panel designs. The micro USB input port lies on the same edge, but at the opposite end. All three of the USB ports have a companion LED that glows green whilst charging in/out.

Along the top of the Solartab sits a dainty power button next to a series of four LEDs, which provide a rough estimate of remaining power. For reference, the battery will be at about 50 percent capacity as soon as only three of four LEDs are lit. At the other corner is a single, white LED that glows to indicate when the Solartab is charging via sunlight. The unit also comes with a wall adapter, micro USB cable, and microfiber cloth to wipe away dust and fingerprints.

Battery performance

None of Solartab's USB ports are labeled, which is fine because the output ports deliver the same. Whether you have one or two devices connected, the Solartab maxes at 5 W / 2.1 A of total output. That's good enough to charge one tablet or two smartphones at a decent rate. Each of the USB output ports auto-detect and commence charging once you plug something in. When gadgets are full, the Solartab automatically shuts off the individual port(s) and green companion LED(s), which are really only useful indoors since bright sunlight washes them out.

Solartab's 13,000 mAh capacity battery is sufficient to meet most demands, maybe even for power-users. The micro USB input port recharges the battery at a rate of 5 W / 1.5 A through the wall adapter and cable. It takes a little over 10 hours to bring the Solartab from 0 to 100 percent charge this way, which is certainly an overnight process if you need battery power the next day. The 4-LED indicator system next to the power button blinks green while charging via USB, remaining lit when the Solartab is completely full. When charging by sunlight, the solar circuitry deactivates when the internal battery is full. And if placement works out, you can charge the Solartab via USB cable and solar at the same time.

Both input and output currents fluctuate a bit every other second of charging, but only up to about 350 mA below each device's maximum rate. It's worth testing out the Solartab with existing USB cables, since it favors some with better consistency more than others.

Not all batteries are made the same, and your average USB power bank typically delivers around 70 percent of its listed capacity as effective (efficiency). That other 30 percent ends up consumed/lost as the battery charges out to devices. So, for example, a basic battery labeled as 1000 mAh would effectively deliver approximately 700 mAh worth of charge.

After fully charging and discharging the Solartab battery a few times (this helps to level out the charge states of individual cells), we used it on a Lenovo S8-50 tablet housing a 5,700 mAh internal battery. The Solartab was able to consistently provide the Lenovo tablet with a total of 195 percent (give or take two percent) battery power, effectively delivering around 11,115 mAh of charge for each of the dozen cycles. Considering that the Solartab has a 13,000 mAh capacity, this puts the effective output at 85.5 percent. That's a solid number, which certainly reflects upon the quality of Solartab's components.

So with 11,115 mAh worth of battery energy, you can expect (under ideal conditions): 3.4 full charges to a Samsung Galaxy Note 5 (3,220 mAh), or 6.5 full charges to an Apple iPhone 6S (1,715 mAh), or 2.4 full charges to a 7-inch Kindle Fire HDX (4,500mAh) from the Solartab. Pretty good, considering the device's size and portability.

Solar experience

The company markets Solartab as having three positions for solar charging, but there's actually five if you flip and fold the cover. You can lie the Solartab flat, which can be great for when the sun is shining directly overhead, depending on geographic latitude. The cover's first position puts the Solartab at about 37 degrees, and you can gradually nudge it to the second groove, which angles at about 54 degrees. You can continue nudging the Solartab to about 81 degrees (ideal for when the sun is low on the horizon) before it's ready to tip. And if you tuck the cover under and make a triangle (see photos), you can also set the Solartab at 25 and 17 degrees.

It's possible that all of these angles aren't necessarily important (like the last two, although they're stable), but it depends on how much power over time you want from the sun. Orientation and angle of incidence are (arguably) the most important factors when it comes to solar power generation. Optimal positioning for the Solartab (any solar panel, really) would want it perfectly perpendicular to the sun's rays, as if you're reflecting the beam of light right back at the source. Check the math; it's all there. With that being said, geographic location and the day of the year, respective to the time of day, also play crucial parts for individual results.

In order to get the most out of the Solartab, you'll want full, unobstructed sun. The solar charging indicator LED glows a hot white with best positioning. But as soon as the orientation/angle is off too much, or if the slightest bit of shade covers part of the solar circuitry, that LED darkens halfway. More shade (depending on which parts are obscured) or skewed angling leads to the indicator LED turning off completely.

You can have the entire top (or bottom) 60 percent of the Solartab cloaked, and the LED will still glow to indicate solar charging. However, when you take a stick (more than 1 cm in diameter) and cast a full-length vertical shadow, the charging abruptly ceases. But as soon as you raise/lower that stick so it's covering less than 60 percent (vertically), the Solartab is back in business with a dimly-lit indicator LED. This may seem strange and fickle for sure, but there it is.

What's nice about the Solartab is that the circuitry resumes solar charging without human intervention. So, unlike some other solar charging devices out on the market, if a cloud lumbers overhead to cause temporary shade, you won't need to reset or press anything after it passes. The solar charging indicator LED responds immediately and the variation in its brightness helps set ideal positioning. Throw the Solartab down flat in full sun and the LED glows dim. But as soon as you start angling it to the point where it's collecting more sun energy, the LED flickers brighter. It steadily, albeit subtly, increases intensity until it hits max. The only drawback to this is that you tend to spend a lot of time staring at the bright LED.

When left out in the sun for hours, the Solartab unsurprisingly gets warm/hot to the touch. Thankfully, the cover makes it easy and painless to scoop it up and put away. And if you choose to charge devices while Solartab collects energy from sunlight, smaller ones can tuck under/behind the cover to stay shaded (recommended). The Solartab works effectively indoors too, so long as the sun can provide a full beam through a clean window pane. Any type of window tinting or mesh screen that filters/blocks sunlight will, at best, provide only a dimly-lit indicator LED. Wispy-thin traces of clouds can also cause the LED to flicker on/dim/off.

We put the Solartab through a variety of solar charging scenarios, both indoors and out. The best results came from clear skies while checking the angle, orientation, and indicator LED every 15 or so minutes. With unfettered sunlight, the Solartab was (repeatedly) able to draw enough energy to deliver 20 percent charge (1,140 mAh) per hour to a Lenovo S8-50 tablet (5,700 mAh battery capacity). Considering that a few hours in this kind of sun could provide two full charges to an iPhone 6S, it's not too bad at all – especially when you think of the time one can spend by a pool, park, beach, or office window.

Not all solar charging situations are ideal. But as long as the Solartab is receiving sunlight, it can collect a amount of usable energy. With patchy clouds passing overhead it can draw enough energy to deliver 10 to 16 percent charge per hour to a 5,700 mAh battery.

If the Solartab's indicator LED is dim the entire time, you can expect only about 6 percent per hour. While the Solartab can charge out to devices while charging up from the sun, it needs to have a significant amount of energy in its battery to do so. Otherwise, you'll be waiting at least 90 minutes (broad daylight) for the Solartab to collect before it starts to discharge out to an attached smartphone or tablet.

The verdict

If you're looking for a solar charging solution that is smart and looks elegant while doing its job, the Solartab checks off those boxes and more. The slim design with integrated battery offers travel-friendly portability that tends to be more convenient to carry than some of its brick-/box-shaped counterparts. And the Solartab's battery output is appreciably efficient. Now, for Solartab's US$139 retail price, one could spend a third less on an external power bank and separate multi-folding, polymer-covered, canvas-sewn, eye hole-equipped solar panel. However, such an option can tend to be more of a hassle than the savings are worth.

What makes the Solartab so easy effective is the built-in battery, integrated cover, and solar charging indicator LED. Flip it open, adjust for angle/orientation, check that the LED is active, and enjoy harvesting free energy from the sun. With a stable surface, the Solartab takes the guesswork out of trying to achieve optimal positioning. There's no awkward unfurling, hanging, balancing, propping up, and/or convoluted cable connecting to deal with, as tends to occur with solar panels that handle like thick file folders. And since Solartab closely resembles a tablet, you can use it outside at a coffee shop or pub without feeling at all ridiculous.

Despite its strong points, the Solartab may not be a fit for everyone's needs. Although well-built, it does lack rugged, water-resistant, and dirt-proof features. And if you really wanted to march around outdoors with a solar panel attached to your backpack, the Solartab couldn't help there either. Those looking to be able to charge two tablets/phablets simultaneously may also prefer something larger that's capable of more than 2.1 A total output. However, if you have an eye for premium design and favor simple yet powerful devices that just work, the Solartab hits the sweet spot for price, size, and function.

Product page: Solartab