The impossible solar iPhone

by billso on Saturday, 7 June 2008

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.

  1. iPhone users like car­ry­ing the device in their pock­ets or purses — and those are places the sun doesn’t shine!
  2. Many mobile phone users recharge their phones at night, while they are asleep.
  3. 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

Solio charger in a Prius by benbrownIt’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

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Tagged as: Apple, battery, electricity, iPhone, mobile, power

  • Aimee Blom

    Hey,

    I have a ques­tion: Would it be the impos­si­ble to make a solor bat­tery small enough. I mean look at how far tech­nol­ogy has come. Obvi­ously I dont know any­thing about bat­ter­ies and solor bat­ter­ies, Is is that far out to think it can de designed and made.

    Also which phone do you think is more efficent/effextive… the new black berry, or the the new iPhone?

    Thanks,

  • http://billso.com billso

    Good ques­tion, Aimee. It’s not so much the bat­tery size as the solar cells… they’d need to be huge to directly power an iPhone. That last link in my entry to the patio table will give you a good indi­ca­tion of the size required.

    Bat­tery tech­nol­ogy is improv­ing incre­men­tally. There have been some inter­est­ing advances, but these mod­els are still in the labs.

    The most promis­ing alter­na­tive to bat­ter­ies is liq­uid fuel cells, pow­ered by methyl alco­hol or butane. It’s easy to recharge these cells — peo­ple have pro­posed lit­tle vend­ing machines that just squirt new fuel into the device.

    In devel­op­ing coun­tries, peo­ple could just dis­till their own fuel.

    The amount of fuel inside one device’s fuel cells is not enough to cause a seri­ous explo­sion or fire.

    I’d have to guess that most Black­Ber­rys have bet­ter bat­tery life than the iPhone, sim­ply because the iPhone has a huge screen and WiFi. Turn­ing on WiFi will really ham­mer the device’s bat­tery life.

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