When we covered the Solar Paper Kickstarter campaign last year, the team shot for the moon but ended up reaching the sun. At the close of funding, the solar charger project had raised an impressive one million dollars in pledges from an almost 6,300 backers. Does Solar Paper live up to all the hype and energy? The team sent us a unit, to find out.

Design & connectivity

Yolk's Solar Paper can have huge appeal to those who appreciate significant functionality in a compact form – not unlike how modern smartphone size belies its overall capability. As thin as a slim-cased "phablet" and a mere two fingers taller and half a finger wider, Solar Paper is about as portable as you can get without much sacrifice. Many similarly-powered solar panels fold up to the size of a sheet of paper, but tend to be twice as thick as a standard tablet. Yolk's version measures 19 x 9 x 1.1 cm (7.5 x 3.5 x 0.4 in) at a scant 170 g (6 oz). So if you prefer gadgets that are lightweight and pocket-friendly, Solar Paper certainly makes an excellent choice.

The base unit features an LCD screen and dual USB ports mounted at the top of the printed circuit board. The matte black solar cells are gridded by gold accents, all of it left uncovered from any glass, plastic, or laminate. For those into subdued, classy appearances, Solar Paper does it quite nicely.

By itself, the base unit is capable of delivering up to 5 V / 500 mA, or 2.5 W of output. Each additional Solar Paper panel adds the same amount, magnetically attaching at the sides to hold together while passing current through the terminals (polarities prevent connecting them incorrectly). The device's total power can be expanded up to a maximum of 15 W (5 V / 3 A) and when done, the panels neatly stack atop each other. The magnets are just powerful enough to stick to a refrigerator and sustain grip without letting the panels slide down.

Using the Solar Paper is simple; align under full sun and plug in USB device(s). There are no buttons to press or switches to flip, as the circuitry handles everything itself. Cloud/shade passing overhead? No problem. The device auto-resumes charging without human intervention. Any kind of tinkering that may need be done would be related to orientation and angle of incidence with respect to the sun – arguably the most important factors when it comes to solar power generation. Holes in each corner of the panels offer a creative means to hang/attach Solar Paper almost anywhere.

Getting the most out of Solar Paper will require proper angling, and the LCD screen with built-in meter helps to eliminate much of the guesswork. When exposed to a sufficient amount of sun, the screen lights up and displays a numerical voltage. As soon as you plug in any USB device, the screen automatically switches to show the real-time current output. Using this, it becomes easier to find the optimal position for maximum possible charge.

Included with the Solar Paper is a silicone seal (pre-installed, covering the USB ports), a protective sleeve for scratch-less storage, and an assortment of teeny plastic nuts, bolts, and silicone "hinges" to help safely hang the panels (less chance of damaging the corners).

Solar experience

Outside with clear skies, using Solar Paper does indeed make the sun feel like a convenient socket for plugging in and powering devices. One needs only to prop the panels up so that the rays of light strike as close to perpendicular as possible. Results can vary, depending on geographic location, day of the year, and the time of day. But even through wispy-thin veils of clouds, you can expect to draw at least 5 W (5 V / 1 A) of power using only three panels. With nothing but unfiltered sun, the amps quickly push past that value and – depending on the preferred draw of connected device(s) – almost maintain the maximum load.

The built-in LCD screen is absolutely brilliant, updating quickly so one can see how effectively Solar Paper has been positioned. Not only is the display visible in broad daylight, but it has a great viewing angle so you can read the numbers while sitting off to the side.

Of course, there are USB power meters that serve the same purpose when paired with solar panels, but why carry another gadget when Solar Paper has the functionality baked-in? Using both a PLX Devices Legion Meter and a battery monitor app (run on a Samsung Galaxy Note 4) for testing purposes, we were pleased to find Solar Paper's flow of energy to be steady and accurate, with the screen consuming very little in the process.

A hand-sized shadow placed anywhere can effectively halve the output power, while a slim horizontal bar (think ruler) reaching end-to-end leaves a mere trickle of energy flowing. Thanks to the auto-resume feature, passing shade affects the charging process for only as long as it covers any portion of Solar Paper's panels. Although the two USB ports are identified as being meant for Apple and non-Apple devices, we had no problem (couldn't tell the difference – probably optimized for Apple) plugging an Android smartphone or other USB-powered products into either side.

Solar Paper can work indoors through clear windows free from tinting, mesh screens/filters, and/or a buildup of dirt/dust. Under ideal conditions with full beams of sunlight, the panels operate as effectively as if they were placed outside. And since Solar Paper (in its carrying sleeve) handles like a small tablet, there's little reason to not keep it as a part of everyday mobile gear. Opportunities for free energy can happen each time you find yourself sitting outside to enjoy a morning coffee, afternoon beer, or some natural vitamin D.

Things can get a touch tricky when it comes to deploying and adjusting Solar Paper's panels. Unless the sun is directly overhead, laying it down flat won't generate much power. Unlike the Solartab solar charger, which features a built-in stand, Solar Paper requires some positioning creativity for ideal results – the lip on the rear side of the main panel is a good place to start.

While Solar Paper's magnets are strong enough to hold/hang together, a small bump (often when attempting to plug in a USB cable) can be all it takes to send the pieces clattering apart. Although they quickly snap back together, other folding solar panels with single, continuous construction don't have this issue, especially over uneven surfaces.

Solar Paper lacks the extreme ruggedness found in many outdoor solar panels. While it is water-resistant (thanks in part to the covered USB ports) and can be wiped clean of dirt, it has a tendency to create an awful scraping noise when rubbed against rock or concrete. This occurs when the panels are dragged/pushed in order to re-orient towards the sun. It's certainly a case of the "bark" being worse than the "bite," as residual wear along the bottom likely won't affect long-term use. But considering how Solar Paper's attractive looks are without a protective layer, one might do well to keep abrasive surface textures in mind.

If you're prone to clever fits of engineering, the Solar Paper doesn't ever have to touch the ground. With the grommet-like holes in each panel, included attachment accessories, and a length of 550 paracord – and possibly some basic knowledge of tying knots – you can strap and hang the panels any which way you like.

Those with bigger hands are likely to find the miniscule bolts, nuts, and silicone hinges quite fiddly, but they serve the intended purpose of alleviating the corners from direct stress. You can thread paracord through the holes, but run the risk of accidental force-related damage. And if you're smart about which way to face the nuts and bolts, you'll still be able to magnetically stack the panels atop each other without any problem.

The verdict

While Yolk's Solar Paper may not be as thin as the those recently created by researchers at MIT, it's likely one of the most compact folding solar chargers available to consumers today. Those who prefer streamlined gear that maximizes functionality versus mass and volume would do well to check this one out. Properly angled under full, unobstructed sun, the three-panel version of Solar Paper consistently delivers very close to the advertized 5 V / 1.5 A (7.5 W) output. It's enough to supply a pair of small gadgets or one power-hungry mobile device.

In order to charge both a smartphone and a tablet simultaneously, one can expand Solar Paper's panels up to six for a total of 15 W. Although handling multiple, magnetically-attaching panels can be somewhat involving, it's not too bad with a level surface and something to prop them up against.

If you're looking for a solar charger to strap to your backpack while biking through wilderness trails, Solar Paper probably won't be able to rough it out. But if a portable solar solution the size of a grade-school chapter book is more your thing, then expect to be quite pleased with the overall quality and performance. Just be prepared to handle the sticker shock. Prices start at US$135 for the 5 W (two panel) Solar Paper, with additional sub-panels available for $50 each.

Product page: Yolk Solar Paper

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