5 future mobile battery charging technologies

As we search for greener means to fuel our energy-sapping habits, boffins are constantly hunting for ways to generate power without relying on fossil fuels and icky emissions.

That hunt extends to your mobile, and scores of researchers are trying to find a way to recharge your Android without depleting the world's oil supply and killing several species.

That means the humble three-pronged charger is out, and renewable supplies are in, peeps.

We've combed through scientific journals and university research papers to find some futuristic ways you might charge your iPhone 7. Or iPhone 6S - whatever it's called.

Getting all riled up and bellowing at a pixelated pig might send your blood pressure through the roof, but it could send your phone's battery level rocketing, too.

Researchers from South Korea are currently conducting the first experiments into turning noise into electrical current. That means having a conversation, listening to music, or just having your phone in a noisy cafe or nightclub would replenish the battery life.

At the nanotechnology division of Sungkyunkwan University, scientists placed strands of zinc oxide between a pair of electrodes. A sound-absorbing pad up top vibrates when sound waves crash against it, causing the nanoscopic zinc oxide wires to compress and release.

This minuscule amount of kinetic energy results in a charge. Unfortunately, it's a very tiny charge in exchange for a very huge noise: 100 decibels can pump out just 40 millivolts of electricity. That means the sound of a freight train hurtling past you doesn't generate enough current (yet) to get the iPhone charging.

It's early days, though. The university's Sang-Woo Kim reckons he can squeeze more juice out of noises by further tweaking the materials and structure of his prototype. Get your vocal chords limbered up now.

If you boost the size of the charger, you can get more energy from less noise. Mobile firm Orange dabbled with this idea in their Orange Sound Charge T-shirts earlier this year, which could juice up a blower by harnessing the cacophonous din of 2011 mudfest Glastonbury.

You have to work with what you've got around you. So in Sub-Saharan Africa, where charging stations are often a multi-hour trek away, researchers have had to look a little closer to home.

A new device uses something that Africans have in a rather large supply: dirt. It's not actually the silty desert matter that's making a charge, mind. It's the pesky bacteria that inhabits all sorts of mundane, everyday materials.

Harvard University researchers are plugging away at a microbial fuel cell (MFC) that nicks free electrons, produced by the metabolic processes of these bacteria, for power.

The small device's conductive surface sends those harvested electrons through an anode-cathode-resistor circuit to generate electricity. The first steps have been promising, with Harvard researchers making enough energy to power LED lights in Tanzania and Namibia.

The next step is to charge a mobile. "Our goal is to make a charger that would cost a dollar and could completely charge a phone in 24 hours," Harvard's Aviva Presser Aiden said. Microsoft's co-founder is even helping out, as The Bill and Melinda Gates Foundation recently granted the project $100,000.

The human heart is a pretty effective machine. The average ticker manages a steady 72 beats per minute, and it never lets up. Or you'd die. Obviously.

If only there was a way to harness the organ's reliable beat and turn it into a steady flow of kinetic energy...? Well, that's the goal for researchers at Georgia Institute of Technology.

Like South Korea's yelling mobile, Georgia scientists are looking into the piezoelectric power of zinc oxide nanowires, which can generate a tiny electric current when strained or flexed.

For a long time, these tiny wires (so small that 500 of them could fit inside a human hair) have only pumped out tiny, insignificant charges. But by sticking a bunch of them together and combining their shared power generation, Zhong Lin Wang and colleagues have boosted energy output by 150 times.

Five nanogenerators stacked in a row can produce about three volts, which is around the same voltage generated by two regular AA batteries. Not enough for a phone, but maybe for a Game Boy Advance.

The next step is to decide how to strain and flex the wires, and that's where our faithful cardiovascular friend comes in. While nanogenerators could be slipped into your shoe to charge while walking, the best bet is to shove it in your chest and borrow those handy 72 beats a minute.

In one second, our sun produces enough energy to meet the current needs of the entire earth for 500,000 years. We're just, despite our best efforts, a bit rubbish at harnessing it.

For one, a typical solar panel produces a pitiful amount of energy. A solar-powered watch works well, but it requires about 1 microwatt (µW) of power to tell you the time. That's 1/10,000th of the energy a bog standard mobile needs to survive, even with the display set on the lowest brightness.

Solar panels are also crazy expensive, and in the places they'd be most handy - in sun-kissed developing countries where they're still using ancient Nokias - the prices are astronomical. We'll stick with dirt, thanks.

Despite these hurdles, researchers aren't giving up on that big blazing ball of energy just yet. That includes Nokia, who is currently faffing about on the Baltic Sea, in a Swedish forest, above the Arctic Circle, and in Kenya to see if it can attract enough sunlight to power the ultra-basic Nokia C1-02.

To the gadget industry's credit, there are already a few solar-powered devices. Samsung's Blue Earth powers its touchscreen and calling functions with a solar panel around back. Puma and Sagem teamed up to make a basic mobile that can be recharged from the sun.

But the days of maxing out your iPad's battery by pointing it in the general direction of our nearest star are still a way off.

Yes, that's right. A phone that runs on the brown sugary slurry that is cola. What's important though, above brand names and taste, is the drink's bountiful supply of carbohydrates.

Chinese designer Daizi Zheng reckons that a basic phone could run on a biological battery that grabs energy from the drink's sugar. Enzymes would act as a catalyst to quickly convert it from cola to power.

That would mean all you need is a six-pack of your favourite soda. Chug a few cans for yourself, and tip the rest into this test tube-shaped mobile to juice up your battery and make a call.

To your dentist, probably.