As we approach the 9 June 2008 launch announcement for iPhone 2.0, it’s a good opportunity to discuss the iPhone’s power requirements.
I’ve never heard anyone ask if an iPhone can be solar powered, but I have had a professor ask me when someone will “solve the battery problem”. She was annoyed that her mobile phone and computer needed to be recharged daily. Since she works outdoors for a few hours a day, she thought a solar-powered iPhone would be a great invention.
Is that a solar cell in your pocket?
The short answer is that a solar powered iPhone is almost impossible. The iPhone is really a small computer with a very bright LCD screen. It takes a powerful lithium-ion battery to run an iPhone, and that battery needs more power than the sun can provide. Apple’s official page on iPhone batteries has some details and tips, but is light on technical specifications. Even the Apple specs page doesn’t list the battery’s output and charging requirements.
I ended up searching through eBay and Google Checkout listings to find a number that sounded reasonable: 1400 mAh. It takes a few hours to charge that battery from a 2.5 watt USB cable. iPhoneAtlas has a nice article with some tips for extending the iPhone’s battery life
It’s just silly to add a solar panel directly to an iPhone, for three reasons.
- iPhone users like carrying the device in their pockets or purses - and those are places the sun doesn’t shine!
- Many mobile phone users recharge their phones at night, while they are asleep.
- There’s also the problem of heat. Apple recommends keeping the iPhone out of direct sunlight, because heat can damage the battery and the iPhone itself.
Adding a solar cell to the iPhone would probably make the device thicker - according to Wikipedia, the device is 4.5 inches long by 2.4 wide, and is only 0.46 inches thick. A solar cell that is small enough to fit on the device would produce only a few minutes of iPhone power in an entire day of sunshine.
Apple does hold a patent for putting solar panels on portable electronic devices. But the best solar cells can only deliver a 20% efficiency ratio - and that’s when the solar cell is outside on a clear, cloudless day. Solar cells just do not work well indoors or in overcast conditions. This post from TUAW and these two articles from Forbes have some more details.
Solar chargers
It’s easier to design a solar-powered charger than placing the solar panel on the iPhone itself. The solar charger contains a large battery and several solar cells. The user places the charger in the sun for a few hours to charge the built-in battery. Then the user connects their iPhone to the charged solar device, so that the large battery is recharging the iPhone’s smaller battery.
Solio makes a cute hybrid solar charger that can handle an iPhone. It’s shown in the picture, which was provided by benbrown through a Creative Commons license.
Solar Technology sells several models of hybrid chargers, but they only ship to the UK. The Solarmonkey resembles a clamshell phone, but it can charge an iPhone.
Brando of Hong Kong has a more versatile solar device that can charge its battery from an onboard solar panel or through a USB port. It’s designed for charging small devices that require a maximum of 4.5 watts. Brando will ship to the USA. This Gizmodo article has some additional pictures.
Solar furniture
Frankly, it takes a large solar panel to directly charge an electronic device. The designers of the SOLo lounge table have the right idea. they’ve come up with an outdoor glass-topped table that is a very attractive and expensive solar panel. The table costs US$14,000 and is built to order, making the SOLo a good fit for businesses in sunny climates, or homeowners who want an interesting conversation piece.
Related pages and posts on billso.com
- iPhone
- 29 April 2008: New iPhone will be subsidized, faster and thinner
- 7 March 2008: Solar powered Bluetooth headset
