Bright ideas for powering our homes might be right in front of us.

Credit: Geoff Cook

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If you were to boil down two millennia of wisdom and philosophical enquiry to just one sentence, you might be left with the phrase: 'there's no such thing as a free lunch'. And this holds especially true when it comes to generating energy.

Even 'cheap' energy comes at a cost. Coal and oil are finite resources, and both contribute heavily to the greenhouse effect that is driving climate change. Nuclear is a package deal; you can't get the energy without the risks or the distasteful waste.

Hydroelectric is better, but it disrupts ecosystems and virtually all the choice sites have already been nabbed. Even solar and wind - while having the boon of 'free' fuel - would require vast areas of land to supply whole cities. No free lunches here.

Yet energy abounds all around us: motion is energy; heat is energy; there's energy squirreled away in chemical bonds. Even our bodies generate a surprising amount of power. According to Max Donelan, director of the Locomotion Laboratory at Simon Fraser University in Canada, "an average-sized person stores as much energy in fat as a 1,000 kg battery". Just a walk down the road uses enough energy to power a bright incandescent light bulb.

The question becomes: can we harvest even a fraction of this 'loose' energy into useful power for our homes, businesses and iPods? Could there be such a thing as a free lunch, after all?

Get physical

The human body can be a source of power for energy-hungry devices, such as radios or torches. In fact, this is the principle behind the 'clockwork radio' invented in 1989 by Trevor Baylis (now 'Sir Trevor', thanks to his creation). Cranking the wind-up mechanism stores the energy in a spring, which turns a dynamo to generate a small current as it slowly unwinds.

The device was soon perfected to the point where it could run for an hour with a 25-second crank, and newer models incorporate wee solar cells so they only require cranking at night.

Baylis's clockwork radio led to the founding of the company Freeplay, which now develops and markets a wide range of wind-up devices, from torches and lanterns to low-power LED lights and mobile phone chargers.
An alternative way to extract electricity from muscle motion is with a shake torch, such as the popular Faraday Flashlight.

The principle is simple: a small magnet slides up and down in the cavity that would normally hold the batteries. As it slides, it passes a coil of copper wire, which induces a current. Just 30 seconds of shaking gives you about five minutes of light care of energy efficient LEDs.

On the experimental end of the spectrum is an unusual device developed by Saul Griffith, at the Massachusetts Institute of Technology Media Laboratory, who was inspired by the Aboriginal instrument, the bullroarer. His device "employs a 100 to 200 gram ball tethered via a 0.3 to 0.5 metre string to a handheld generator," says his boss, Joseph Paradiso.

Revolving the ball at one to two spins per second produces three to five watts, ample power for a mobile phone call. However, it's far from ideal for long chats in small rooms.

Walk in the park

Another way of extracting energy from human movement is through tapping the power of your shoes striking the ground. Since the 1920s inventors have been sticking miniature generators in the heel of shoes. The most promising approach comes from a remarkable property of some crystals called piezoelectricity; squeeze the crystal and it will generate a tiny high-voltage electric charge.

The amount of energy generated is typically in the range of milliwatts - enough to power a small biosensor or send a radio pulse a short distance - although multiple piezoelectric units can be strung together to generate more power. These devices are small and discrete enough to slip inside the sole of a shoe and not be noticed during normal walking. Or if you just want to look good, you could try Alberto Villarreal's BrightWalk shoe, which uses piezoelectrics to power funky lights on the side of your shoe.

The vibes

"Portable electricity represents much more than just a convenience to some people," says Max Donelan from Simon Fraser University. "In the developing world, a half-billion children live without easy access to electricity." Devices using piezoelectrics could provide vital power in an affordable and sustainable way anywhere in the world.

Think about how many things around you move or vibrate, even slightly. Simply slap a piezoelectric generator on it, and you have a cheap lunch.

Researchers at Princeton University in the US have gone so far as to stick piezoelectric membranes in devices they are calling 'eels', which flap about in a river current and generate electricity. Each produces only a few milliwatts, but string enough together in a broad stream and they could pump out a considerable amount of power.

How much power can you generate using piezoelectrics? Quite a lot, according to Stef van Dongen, founder of non-profit organisation Enviu. At least, enough to power a fancy dance floor, if not an entire dance club.

Enviu is working with Exendis and the Technical University Eindhoven in the Netherlands, on the Energy-Generating Dance Floor. This will capture the energy of the dancers to light the dance floor dynamically, giving them active feedback on their enthusiasm. It's all part of the sustainable dance club (SDC) project led by van Dongen. The first Energy-Generating Dance Floor should appear in the fully sustainable Club Watt in the Netherlands this year.

The big guns

Generating enough power to fuel your iPod - or illuminate your dancing shoes - is all well and good. But what if you want to power a city? It'll take more than body heat or vibration to do that. Thankfully there's a veritable army of scientists looking at innovative ways of capturing the power of nature in low-impact, sustainable ways. Not just free lunches; free banquets.

Take the oceans. According to Tom Denniss, founder, executive director and chief technology officer of Australian company, Oceanlinx, the energy stored in the ocean's waves contains enough power to satisfy the world's needs 5,000 times over. "Just the waves near to the coast have enough to handle twice the world's power usage," he says.

Denniss was instrumental in the development of a clever new technology that can extract power from waves, all in floating plants far enough off shore that you'd never even know they're there. The trick was to build turbines that could handle the oscillatory nature of waves; most generator turbines only work with a flow in one direction.

There's already a pilot plant off Port Kembla in New South Wales which at its peak pumps out 450 kilowatts - enough to power several hundred homes - and Oceanlinx is hoping to install a 2.7 megawatt plant off the Hawiian island of Maui. Denniss sees a bright future for wave power.

"In 50 years it could supply up to 10 per cent of the world's power needs," he says. "I'm optimistic it can be done. It has to be done."

Waste not…

There are even ways to extract power from waste. It's like giving the half of your sandwich you can't finish to a friend. For them, it's a free lunch.

But for US-based energy company, NanoLogix, it's also big business. NanoLogix has developed a bioreactor that can convert waste - whether it's the runoff from a fruit juice factory or 'activated sludge' from a sewerage plant - into electricity. And it's all thanks to some very clever bacteria.

"The bacteria either metabolise sugar or protein, and they produce hydrogen and carbon dioxide," says Bret Barnhizer, president of NanoLogix. The carbon dioxide is captured leaving the hydrogen, which can be burned to produce electricity. The only by-product? Pure water.

NanoLogix has a pilot bioreactor installed at a Welch Foods fruit juice factory Pennsylvania, US, which generates an impressive 5.5 kilowatts. Barnhizer also sees tremendous prospects for bioreactors in sewerage and wastewater treatment plants around the world. Not only would the bioreactors be able to produce a significant proportion of the power required by the sewerage plant to operate, but it would also contribute to purifying the water in the process.

"There's a vast amount of potential," says Barnhizer. "If our technology was used across the United States in waste treatment plants it could perhaps substitute one per cent of energy from traditional sources. Not vast, but a contribution, and it all adds up."

Lunchtime

So is there such a thing as a free lunch when it comes to energy? Whether it's a watch powered by the heat of your skin, or an inner-sole that drives your iPod as you jog, or even a floating platform that harnesses the waves to power a city, the ingredients are lying all around us. All we have to do is be clever enough to pick them up.