Australia has 600 years of cheap coal supplies. Burning it might just make the planet uninhabitable. This topic guide surveys alternative, cleaner sources of electricity.

About 80 per cent of Australia’s energy comes from coal, 12 per cent from natural gas and 7 per cent from hydro-electricity schemes such as the Snowy River. Only about one per cent comes from renewables such as wind, solar and biomass. 

Australia has an estimated 600 years of coal reserves. Coal accounts for about 40 per cent of our total greenhouse emissions. Australia is the world's largest coal exporter, earning $22 billion a year, and coal gives us some of the cheapest electricity in the world (about $35 per megawatt hour).

Natural gas 

Produces a third of the CO2 of coal. But it’s still a fossil fuel and unsustainable in the long run. Also, leaks from natural gas pipes can emit a lot of C02. Although rarely included in comparative figures, these leaks cancel out much of the benefit of gas. 

Hydro-electricity

Given Australia's water shortage, there's little prospect of expanding hydro-electricity, which would require many new dams. In fact, poor snowfall in 2006 left the Snowy River Hydro dam less than a tenth full. 

"Clean coal"

Involves a process known as carbon capture, or "geosequestration". That means turning the CO2 emissions from coal-fired power stations into liquid, then injecting it deep underground into natural rock cavities, where it would remain for thousands or millions of years.

That's the theory. In reality, the technology is still on the drawing board and unlikely to be commercially ready before 2020 - if at all. And carbon capture will be expensive, increasing the price of coal to a point where other options may be cheaper.

Nuclear power

The Howard Governent's Switkowski report found Australia could have 25 nuclear power stations by 2050, providing a third of the country's energy. Australia has a lot of uranium - around 40 per cent of the world's known reserves - and will benefit economically by an expansion of the global nuclear industry. 

It's unlikely nuclear power stations could be operational in Australia before about 2020, as Australia would be building a nuclear industry from scratch. There would be fierce local opposition to any proposed nuclear power station site. Disposing of radioactive waste is an unsolved problem, as is the risk of a Chernobyl-type accident or of processed uranium ending up as fuel for nuclear weapons in the hands of terrorists or rogue governments. 

Nuclear energy also requires a huge initial investment, making it a commercial risk. In fact no nuclear power station has ever been build without government subsidies. By the time nuclear power stations are up and running, renewable energy might be cheaper anyway.

Wind power 

The CSIRO estimates wind could provide 85 per cent of Australia's energy. In the past 15 years, the cost of wind power has halved to around $70 per MW/hour (megawatt hour) and this figure should keep falling with technological advances and larger volumes of production of wind turbines. 
  
Critics say huge areas of land must be covered in turbines to supply enough power to replace coal-fired power stations. But most of these turbines would be built on existing farmland, providing farmers with additional income without disturbing crops or livestock. And while wind power is unreliable in any single spot, if you have thousands of turbines spread across a wide area the overall output is fairly constant. The wind will always be blowing somewhere.

Solar

It's estimated an area of 50 sq km of solar power could supply all of Australia's energy. Intuitively, solar would seem the obvious source of free, clean energy. But large-scale solar power is still in its infancy, and there are different approaches to harnessing it. It's not clear which technology will prove the best. 

For instance, one Australian company, Enviromission, wants to capture heat in a giant greenhouse, from where it will rise up into a chimney hundreds of metres tall to drive turbines by convection (that is; movement created by rising hot air). This process is known as solar thermal power. Others, such as Solar Systems or Ausra (a California-based company run by Australian David Mills), use arrays of parabolic mirrors to focus sunlight onto PV cells, or to boil water to create steam.

The sun doesn't shine at night, and some days are cloudy, so solar energy needs to be stored if it is to be used around the clock. But storing energy on a large scale is expensive. That is precisely what makes fossil fuels so attractive – they provide cheap and convenient energy storage. For solar to become a major part in the energy mix, we need lower-cost ways to store large amounts of energy.

This might be done by pumping heated air from a solar thermal power station underground to heat up rocks. Solar energy could also be used to pump water up into a hydro-electric dam (a process called “reverse hydro"). The energy can then be used on demand in the form of hydro-electricity.

Geothermal power

An emerging green energy source is geothermal power. It harnesses heat trapped deep beneath the earth's surface. In some countries, this heat naturally emerges as volcanoes and hot springs, but in Australia the big hope for geothermal energy is a huge area of rocks, heated to about 300C, that lie 3-4km underground in central Australia. Companies such as Geodynamics and Petratherm are working to harness this energy by pumping water in pipes through the rocks. The water is heated and turns to steam.

The CSIRO estimates these hot rocks could supply Australia's energy needs for the next 800 years – and they could be providing 10-20 per cent of Australia's power within 30 years.

Biomass

Burning biomass (organic matter) produces the same amount of CO2 as the plants absorbed as they grew. It is thus regarded as carbon-neutral. But critics claim increased production of biofuel is competing with food production, driving up the price of food stables and leading to food shortages poor nations.

This claim is contentious. Other factors may be driving up food prices, such as rising oil costs, increasing meat consumption in countries such as China (because animals eat a lot more food than they produce) and crop diseases.

So-called second generation biofuel does not compete with food crops. Instead, it comes from municipal waste (that is, rubbish) or agricultural waste (inedible parts of plants, which are normally discarded. It’s estimated this could provide 17 per cent of Australia's energy within 15 years. Instead of dumping organic waste in landfill, the idea is to burn it to generate energy.

This also removes the problem of decomposing organic matter in landfill, which releases methane, a potent greenhouse gas.

Wave and tidal power

A dark horse of green power, the potential of wave and tidal power is hard to judge. The world's first commercial wave farm, off the coast of Portugal, was only launched in 2006.

The most common approach to wave and tidal power involves floating buoy-like devices fixed to hydraulic pumps on the ocean floor. As the buoys rise and fall on the waves, their movement drives pumps below. However, making equipment that can survive for years in stormy seas is a significant challenge.

Energy costs

A MW/hr of solar costs around $100 MW/hr, wind $70 and biomass $80. By 2020, increased scale of production and improved technology should cut the cost of each of these renewables to $45-50 per MW/hr. Geothermal is tipped to be in the same range. That is comparable to natural gas and likely to be cheaper than both “clean coal” and nuclear power.

None of these energy sources can compete with the current price of coal, which costs about $30-$35 per megawatt hour (MW/hr). So a key factor to switching away from coal is to introduce a price on CO2 emissions, in the form of emissions trading or a carbon tax.

However, the rising cost of water is also pushig up the price of coal. For example, three coal-fired power stations in Victoria use the equivalent of 20 per cent of Melbourne's water supply. In the first half of 2007, this forced the price of coal-fired electricity up from around $35 per megawatt to more than $70. This increase hasn't been passed on to domestic consumers yet because energy suppliers have long-term contracts with the power stations.

Can renewable provide baseload power?

Electricity grids depend on two sorts of power inputs. One is a core of constant baseload power. Baseload power is a constant, cheap, supply that is always available. The other is power inputs that can be turned on and off quickly as demand rises and falls during the day. Both are important. Coal-fired power stations provide reliable constant, cheap, baseload power but can’t easily be turned on and off.

Critics say wind and solar cannot provide baseload power because the wind doesn’t blow and the sun does not shine for 24 hours a day.

But other renewables, such as geothermal and biomass, can provide baseload power. And in fact, if you build thousands of wind turbines spread over a huge area, they will provide a fairly constant amount of energy to the grid. There may also be ways of storing solar for baseload power (See Solar Power, above).

Reducing energy demand: Energy efficiency

The International Panel on Climate Change estimates that a third of the world's energy is wasted through energy inefficiency. They identified improving energy efficiency – such as better insulation – as the most cost-effective way to reduce greenhouse gas emissions.

Microgeneration

Transmitting energy long-distances along an electricity grid is expensive, and a percentage of energy is lost during transmission (typically about 10 per cent). Some renewable energy can be generated locally in homes or business premises. This is known as microgeneration. Solar panels and solar hot water are the most common forms of microgeneration.