Some portable electronics already try to take advantage of onboard solar power systems, but size restrictions limit the number of solar cells that can be placed on them, relegating the technology to devices with very low energy needs. In its patent application, Apple proposes layers of solar cells that sit underneath a display; in devices like the iPhone or the much-anticipated Apple tablet, that would mean a large percentage of the device's real estate is capable of generating electricity.
But based on some back-of-the-envelope math, the dream falls short, at least with today's solar technology.
One square meter of the earth's surface receives about 1,000 watts an hour from the sun in ideal conditions, and the iPhone screen is about .003 square meters. Even the most advanced experimental photovoltaic cells boast only around 40% efficiency, so a solar iPhone could generate around 1.2 watts per hour (1,000 watts/hour * 0.003 * 0.4). That's well below the 5 watts per hour that the standard iPhone charger pulls in.
Still, a solar iPhone would have an increased battery life, and the prospect of stepping into the sunlight with your phone on its last sip of juice and watching the power meter creep up a few notches is certainly alluring. And an iPhone studded with solar cells would be a tantalizing piece of eco-bling: What better way to show off your savvy greenness than to whip out one of those babies to glitter in the midday sun?
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