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Buyer's Guide: The Best Monitors 
powertraveller powermonkey-eXplorer
Florent Alzieu
Test date: July 6, 2010
Test date: July 6, 2010
The battery
If you hook the solar panel up directly to a device with no intermediary battery (be that an in-built device battery or the powermonkey battery supplied), power risks cutting out each time a cloud passes. Your device must also be able to recognise and accept the solar panel as a direct power source, which isn't always the case. We tried hooking up several different portable products and some, in spite of having a compatible voltage, simply refused to charge (probably due to some kind of amperage problem). If this happens, you'll need to use the battery supplied as a kind of go-between i.e the panel charges the battery then the battery charges your device. Plus, the battery provides a greater output than the 0.8 Watts and 5 V of the solar panel alone. In fact, it can provide up to 2.5 Watts at 5 Volts once fully charged. It also won't be subject to output fluctuations caused by changes in the weather!
The powermonkey-eXplorer comes in two parts: a compact, clamshell-style solar panel and a 2200 mAh battery. It's designed to boost to the battery of smaller devices, such as mobile phones, and comes with a decent adapter kit included.
1: solar panel - 2: battery - 3: mains charger - 4: mains and USB adapters - 5: USB and mobile phone connectors.
Let's start with the most important bit, the clamshell solar panel. It's a polycrystalline solar panel with a total surface area of 80 cm² (2 x 8 x 5 cm), and which weighs 82 g (including casing). We tested it in ideal conditions (i.e. bright sunlight) both outdoors and through a window. Here's what we found:
Figure 1: Through glass (brightness approx. 31,000 lux)
Figure 2: Outdoors, using energy directly from the sun.
(Brightness over 40,000 lux)
The best results obtained were around 5 Volts. Through glass, an output of just 0.25 Watts was recorded, whereas outdoors, the maximum recorded output was 0.84 Watts. Don't be fooled by manufacturers' marketing ploys either, as the packaging advertises a 200 mA output for the panels, which is technically possible at 3 Volts, but at 5 Volts, that drops to 165 mA. Compared with the solargorilla, powertraveller's larger and more expensive model, that's not so great. The gorilla can manage 617 mA for its 5 Volt output. That makes the gorilla 3.7 times more powerful, but with a solar panel almost three times larger.
Charging the battery
The battery supplied has a capacity of 2200 mAh. Given that the average amperage when charging is 180 mA, if charging was 100% efficient, it would take 12 hours to fully charge the powermonkey battery. However, as we can assume that around 20% of energy is lost during the process, it'll take something nearer 15 hours to charge. When fully charged, the battery has an output of 2.5 Watts at 5 Volts.
Pluses
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Compact and lightweight
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Mains adapters for all countries
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Charging adapters for a wide range of mobiles
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Three times lighter than the solargorilla
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Supplied with battery
Minuses
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Battery takes around 15 hours to charge
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200 mA max. at 3V
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165 mA max. at 5V
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3.7 times less powerful than the solargorilla at 5V
In the best possible conditions (bright sunlight), the powemonkey-eXplorer will take around 15 hours to fully charge the included battery. You certainly won't want to waste its precious energy, then, and it's only really suitable for occasional use. For more power, pick up the larger (and more expensive) solargorilla.
