How many solar watches would it take to power an iPhone?
Solar energy is far from a new idea, but Apple (nasdaq: AAPL - news - people ) may be taking the technology to new limits. Many questions have been raised about the possibility–or probability–of Apple using solar energy to power portable devices such as its popular iPhones. It recently became known that employees at the computer, phone and software company have filed a patent to place solar cells on portable devices. (See " Apple’s Solar Strategy")
It’s not a new technology. Rudimentary findings of the potential to harness the sun’s powerful rays for conversion into electricity were first reported in the mid-1800s. The “photovoltaic effect” was discovered by then 19-year-old French physicist Edmund Becquerel in 1839.
Pocket calculators and wristwatches that operate on solar energy have been on the market for many years and are widely used. In 1957, two Pennsylvania engineers marketed a solar powered radio that was smaller than today’s iPod. The technology has come a long way since then and Apple may be the next to capitalize on it.
The biggest difference between those technologies and the patent for which Apple filed is the amount of power consumed by the product, said Michael Filler, a Caltech postdoctoral scholar specializing in photovoltaics.
iPhones are remarkably advanced devices that are small but consume considerable amounts of power. According to Filler’s calculations, it would take 250,000 to 1 million solar-powered wrist watches to generate the energy needed to power one iPhone (and keep the watches ticking). In other words, “the rate of energy consumption of the iPhone is about 250,000 to 1 million times larger than a standard sports wrist watch.” Filler’s calculation is for power consumption rates when both are being used, and take into account that the watch is used 24/7 while the iPhone is used for periods of time and then stored.
Concerns exist over the application of solar energy in portable devices such as cell phones, which are typically stored in pockets or purses and therefore are not constantly exposed to light. Also, while silicon solar cells do not need direct sunlight to work, they will collect a lot less energy indoors or on a cloudy day. Still, Filler said that a solar-powered iPhone “seems reasonable enough.”
The most efficient solar cells on the market convert the sun’s energy into electricity at about 20% efficiency, Filler said. In an optimal use environment, say on a cloudless sunny day in the desert outside Las Vegas, an iPhone equipped with Apple’s potential new technology could generate around 1 watt of energy, Filler explained. “It’s not going to be able to power the entire device but could extend battery life.” Almost anything solar-powered would still need to have a battery to store the captured energy.
Filler also pointed out that there are solar cells that operate at closer to 40% efficiency rates, but they are so expensive that they are mainly used by NASA for spacecraft, satellites and other space-related applications.
According to Apple’s pending patent, devices would integrate the solar cells underneath the liquid crystal display, or LCD, screens. Sandwiching the solar cells inside the device would block some light out and knock down power conversion efficiency even further, Filler cautioned. The light-emitting diode, or LED, of devices like the iPhone are designed to reflect light outwards toward the user. Theoretically, Filler said, if some fraction of the LED were projected backwards into the system, embedded solar cells could capture some of that light as well.
Perhaps the most obvious obstacle Apple may face will be the potential limitation for a gadget meant to be so small to have a large enough surface area on which to embed the solar cells. “Apple has done such a superb job packing so much function into such a small package, that not much area is available to harvest sunlight, even if you were standing in the middle of the desert somewhere in Nevada,” Filler said.
Scott Bourne, executive producer of the Apple iPhone Show on iTunes said he would not expect to see the implementation of a product of this kind for at least five years, but said that it is exciting to consider that it could happen. “Cell phone battery power is always an issue for users who inevitably want longer-lasting power than they have,” he said.
An Apple spokesperson would not comment on anything beyond what was written in the patent.
Apple devotees will just have to wait and wonder. Or buy the company's anti-gravitational stock: Shares of Apple traded up $5.18, or 2.9%, to close at $186.35 in trading Tuesday.
Filler added that those in the photovoltaic field hope to see solar conversional devices in everything we own, including roof shingles, sign posts, clothing, etc. “We want to see solar go beyond major power generation. The iPhone is one example.”