IEEE Spectrum November, 2016 - 25

RESOURCES_REVIEw

of course; you wouldn't use it to run a refrigerator). But it adds bulk-159 grams-and you
lose some energy in converting DC to AC.
Rather than an inverter, Voltaic's system
relies on an impressive array of DC adapters and USB chargers. I got USB battery
chargers for our Sony and Canon cameras
($7.50 to $10 each) and a Magsafe 2 adapter
($20) for our Apple MacBook Pros.
The solar panels are light and flexible
enough to be draped from backpacks, so in
theory I could have charged as
I hiked. I didn't actually do that.
Instead, once we reached our
destination, I located a flat, unshaded spot. When the morning sun emerged, I laid out the
panels, angled them toward the
light, and connected the batteries. Goal Zero's instructions
caution against letting the battery get too hot, but I didn't find
that to be a problem. What was
an issue was the ever-present
dust, which had me wiping off
the panels several times a day.
My photographer and I
never wanted for power. Every night she
FolDABle solAr poWer: Goal Zero [left] and
Voltaic Systems [right] offer portable solar panels
downloaded photos and video from her camthat can fit into a backpack and charge battery
eras
and her iPhone to her laptop, backed
packs with enough capacity for smartphones,
them up to an external drive, and recharged
digital cameras, and laptops.
the occasional camera battery. I used my
computer and camera more sparingly, but I
obliged several requests from others to recharge phones, cameras, and a GoPro.
The panels got about 10 hours of sun daily.
21 by 2.5 centimeters. The battery has two
USB ports, a laptop port, and a 12-volt port. The Goal Zero battery is supposed to take
I never found a use for the latter, but it's des- 10 to 20 hours to fully charge, but even when
ignated for lighting. Also included are an AC the battery started from a partial charge, it
wall-outlet adapter and car-lighter adapter. never reached 100 percent. Several times
scattered clouds caused the unit to stop
The entire kit weighs 2 kilograms.
Voltaic Systems is an up-and-coming charging. Those same clouds did not pose a
player. Its $278 kit comes with a 2,200-mAh problem for the Voltaic system. Voltaic's batlithium-polymer battery, a 20‑W solar panel tery, which the company says takes 7 to 10
that folds to 19 by 25.5 by 2 cm, plus an AC hours to charge in full sun, did indeed fully
adapter and lighter adapter. The battery has charge every day.
So which system did I prefer? Both seem
one 5‑V USB port and a DC port for laptop
well made and engineered, but the Voltaic
charging. The kit weighs 1.5 kg.
One key difference between the kits is the in- system had the edge in solar charging. And
verter-Goal Zero's has one, Voltaic's does not. factoring in the significant difference in price
The inverter screws into the battery and lets you and weight, I'll opt for Voltaic for my next offpretend you have a wall outlet (within reason, grid adventure. -JeAn KumAGAi

soLAr ChArgIng
KIt showDown,
hImALAYAs eDItIon
voltAic systems' Arc 20w
outshines goAl Zero's
sherpA 100

'm not an outdoorsy person.
But when a reporting assignment
came up recently that required
trekking in the Himalayas, there was really
only one response: Yes!
The assignment would take me to a village
that had no grid power and was a day's hike
from the nearest road. My photographer and
I would be carrying two laptops, three digital cameras, and a smartphone between us.
So finding a reliable and portable source of
power was essential.
We were heading to the Ladakh region, a
high-altitude desert blessed with a spectacular amount of solar radiation. Looking around
for lightweight solar panels and batteries, I
found plenty of options. I ended up trying out
two units, loaned to us by the manufacturers:
Goal Zero's Sherpa 100 Solar Kit and Voltaic
Systems' Arc 20W Solar Charger Kit.
Goal Zero is a well-established company,
and its US $550 Sherpa 100 kit comes with
an 8,800-milliampere-hour lithium-ion battery, a detachable 110-volt AC inverter, and a
20-watt solar panel that folds down to 33 by

left: goAl Zero; right voltAic systems

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Table of Contents for the Digital Edition of IEEE Spectrum November, 2016