Top 7 alternative renewable energy sources

More than solar and wind...

When it comes to renewables, we've all hear of solar, wind and hydro. But what about the teams working away on the slightly more ‘bleeding edge' energy sources? Power & Energy charts the ones to watch.

1. Tornadoes
Their wild cousins may wreak havoc, but man-made tornadoes have potential as an energy source. An atmospheric vortex engine (AVE) produces a controlled vortex whose base remains firmly anchored in the centre of a circular structure. The heat needed to trigger the process can come from solar sources, or simply from naturally occurring warm, moist air.

Power & Energy probability rating: even

2. Algae
It may look like green goo to you, but algae is one of the more advance of the emerging alternative energy sources, with even big players like Exxon Mobil showing an interest. Algae are often considered an ideal renewable energy source because they may grow faster than land plants and can be grown in the sea or on marginal land that is not useful for food crop production.

Power & Energy probability rating: high

3. Kites
Kite energy attempts to exploit the flight of automatically controlled tethered airfoils, which are similar to power kites used in surfing and sailing. The kites operate between 500 and 1000 m above the ground, with electricity generated at ground level by converting the traction forces acting on the tethers into mechanical and electrical power.

Power & Energy probability rating: low

4. Waves
Energy can be captured directly from waves on the surface of the ocean, or from pressure fluctuations below the surface. A number of technologies have been proposed to capture the energy from waves, including terminator devices, an oscillating water column and a point absorber. Some of the more promising of these are currently undergoing commercial testing.

Power & Energy probability rating: high

5. Lightning
Anyone who's been caught in a thunder storm knows the awesome power of lightning. One of the main drawbacks is lightning's unpredictability: a lightning capturing power plant would only be worth building in regions of the world with frequent thunderstorms. Another potential hurdle is the need for infrastructure that could survive the powerful surges created by strikes.

Power & Energy probability rating: low

6. Biogas
Biogas is composed of 40 to 60 percent methane, with the remainder being mostly carbon dioxide. It is produced by anaerobic digestion or fermentation of biodegradable materials such as biomass, manure, sewage, municipal waste, green waste, plant material and energy crops. Methane and carbon monoxide can be combusted or oxidized with oxygen, allowing biogas to be used as a fuel.

Power & Energy probability rating: even

7. Sugar
In 2007, Sony unveiled a fuel cell powered by glucose that could achieve a 50 MW output. The latest version, demonstrated at the International Hydrogen & Fuel Cell Expo last year, can produce 70 MW on 28cc of sugar-filled cola. The battery uses enzymes to breakdown the energy from a glucose solution, and the only bi-product is water. However, its potential for larger scale use is currently unclear.

Power & Energy probability rating: even

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