With the proliferation of smartphones, tablets, and other portable electronics, many gadget-fiends find themselves low on battery power and away from an outlet. A portable charger - a Li-ion battery pack that can recharge other devices - is a great solution, but it, too, runs out of power eventually. How can a wilderness hiker keep her smartphone charged without packing a bunch of portable chargers? With a single portable charger, such as the HeLi-on, and some sunlight.

HeLi-on, named for its combination of solar cells (Helios was the Greek sun-god) and Li-ion batteries, is a portable charger that contains a 2600 mAh Li-ion battery - sufficient to charge most smartphones at least once, and in many cases with energy to spare. The battery can be recharged via USB or with the included roll-up solar array. At a mere 11.3 cm (4.5”) and 105 grams (3.7 oz), the HeLi-on easily fits in a pocket. To make room for it, a hiker can remove about $90 from the aforementioned pocket - that’s how much the HeLi-on will sell for, assuming its Kickstarter campaign is successful.

Other roll-up solar chargers in the same price range, such as the Bushnell SolarWrap 250, are already on the market. What makes the HeLi-on different? Let’s take a look.

Organic Solar Cells

Unlike the Bushnell SolarWrap 250, which uses thin-film amorphous silicon photovoltaic cells, the HeLi-on charger uses organic solar cells. Although organic PV cells are inherently less efficient than amorphous silicon, they’re much less costly to manufacture, both in terms of money and energy. The energy payback period for amorphous silicon is one year, where it only takes about three months for organic PV cells to generate as much energy as it took to produce them.

HeLi-on’s organic solar cells unroll to a length of 70 cm (28”), giving a surface area of 700 square cm. At full sun in equatorial regions, 70 watts of solar power hits that area. According to HeLi-on maker infinityPV, the HeLi-on’s output is three watts, yielding an efficiency of about 4%. (That’s the price of portability.)

The Bushnell’s amorphous silicon cells unroll to about 43 cm (17”), for a  982 cm² surface area. Bushnell doesn’t specify the PV’s output power, so I can’t estimate its efficiency.

Capacity and Charging Times

infinityPV says that the HeLi-on can charge up to 80% of its full capacity (2600 mAh) in about three hours in full sun or by USB.

According to my calculations, both of those numbers may be optimistic. A USB1 or USB2 port has a 5 V, 500 mA output. In three hours, the USB port can charge the HeLi-on to about 1500 mAh, closer to 60% of full capacity. USB3, on the other hand, can deliver up to 900 mA, so three hours would charge the HeLi-on.

Charging it with sunlight assumes full sun (1000 W/m²), which only occurs around midday in tropical regions. Even under those conditions, it would be difficult to point the solar cells directly at the sun, especially while hiking. Depending on the situation, I think the HeLi-on would take 5-6 hours to charge via sunlight.

Since its discharge rate is the same as its charge rate, the HeLi-on can charge a device in about the same amount of time: 3 hours by USB (with its internal battery) and perhaps 5-6 hours by sunlight.

The Bushnell 250 doesn’t list its capacity, but the company claims that it can charge the average smartphone once, so I’ll assume it’s comparable to the HeLi-on’s 2600 mAh. The 250 has a slightly longer charge time - four hours by USB and six hours by solar.

Portability

At a little over 23 cm (9.1”) and 261 g (9.2 oz), the Bushnell 250 is almost twice as long (rolled up) and three times the weight of a HeLi-on, making it unsuitable for carrying in a pocket but still easy to stow in a backpack. That makes the pocket-friendly HeLi-on (11.3 cm and 105 g) quite a bit more portable.

Durability and Sustainability

Organic PV cells have a reputation for quick degradation, unlike their silicon counterparts. infinityPV has tested its panels against sun, rain, frost, and humidity, and found very little degradation. Since the PV array spends most of its life rolled up in a protective housing, it’s reasonable to assume that it will last at least as long as its battery.

Given that the HeLi-on performs about as well as its closest competitor, a more compact size appears to be its main advantage. But the fact that it’s made from organic PV cells, uses less material, and takes less energy to produce gives it a plus on the sustainability scale. I hope infinityPV also plans to allow users to replace the unit’s battery, or at least return it to infinityPV for proper recycling.

Here’s Dr. Morten V. Madsen, co-founder of InfinityPV, talking about the HeLi-on: