Future Alternatives

It's quite feasible that new forms of renewable energy will be developed that don't suffer from the same drawbacks as the current options. Failing that, there may be new ways to reduce the impact of fossil fuels on global warming.

One unusual form of renewable energy in development is the solar chimney – a cross between solar power and wind energy. A vast glass canopy sits at the foot of a huge chimney. This is ideally located in desert-like conditions, as the canopy uses sunlight to heat the air beneath it.

Provided the chimney is sufficiently high, a kilometre or more, warm air is drawn up at a considerable rate due to the temperature difference between the top and bottom of the stack. Placing turbines near the base of the chimney allows the airflow to be used to generate electricity.

Although still relatively obscure, the concept of solar chimneys has been around for more than 100 years. An operational prototype was built near Madrid in 1982, producing 50 kilowatts of power before being decommissioned in 1989. This is just one hundredth of the power produced by the first nuclear reactors that were built more than 50 years ago. The largest nuclear power station, under construction in Finland, will be capable of producing 32,000 times more power than the prototype solar chimney.

But at only 195 metres high the Madrid stack by no means demonstrated the full potential of solar chimneys. And now a project in New South Wales, Australia, is set to build a one-kilometre-high chimney with a canopy diameter of 3.5 kilometres. According to its developers, Solar Tower, it would be capable of producing 200 megawatts of power, enough to supply electricity for a city the size of Brighton.

If solar chimneys sound out of this world then solar power satellites (SPS) will seem even more outlandish. SPS involves placing a huge arrays of solar cells, covering more than one square kilometre, into space to harvest vast quantities of electricity from the almost constant sunlight. The energy collected would then be sent back down to Earth in beams of focused microwaves and collected by huge antenna-like devices called rectennas.

As bizarre and unfeasible as this might appear, Nasa has showed an unfaltering interest in SPS for decades, despite the prohibitive costs of getting the solar cells into orbit. Given that it currently costs $10,000 to launch one kilogramme into space it's safe to assume that SPS is still little more than a pipe dream.

So in the meantime how about trying to clean up fossil fuel? While oil and gas reserves are in danger of drying up, there is still enough coal to last hundreds of years. There are now projects underway to create zero emissions coal-fired power plants, such as the US FutureGen project. This involves using relatively untested carbon capture and storage methods, where carbon dioxide emissions are literally collected from flue gases and then buried in the ground at suitable sites, such as empty oil fields.

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