Generating new ideas for meeting future energy needs
Key text
This topic is sponsored by the Australian Government's National Innovation Awareness Strategy.
Concerns about the greenhouse effect, smog and energy security have led to increasing interest in energy sources such as hot dry rocks, wave power and hydrogen.
 |
You will get more from this topic if you have mastered the basics of energy – these links will take you to an annotated list of sites with helpful background information. |
The world has changed dramatically over the last 200 years, thanks largely to fossil fuels – coal, oil and natural gas. These have provided us with cheap and convenient energy, which we use to heat and cool our homes and to run our cars, appliances and industries.
But there has been a cost. No city in the world is immune from the polluting effects of fossil fuels, and they contribute vast quantities of greenhouse gases to the atmosphere, something that many scientists believe causes global warming.
So, in the last few decades, scientists have been looking for ways to produce energy without adverse side-effects. Promising renewable energy sources such as wind, direct solar and biomass are dealt with in other Nova topics (see links at the end of this page). Now we'll have a look at hot dry rocks, waves and hydrogen. It may be some years before these energy sources make a big impact but they illustrate the diversity of options that are available.
Hot dry rocks – a form of geothermal energy
‘Geothermal’ means heat stored in rock. The best evidence of geothermal activity can be seen in regions close to the boundaries of tectonic plates – such as Japan and New Zealand – where hot springs, volcanoes and geysers are plentiful. These resources are already being used in some countries for heating and electricity generation.
The words ‘Australia’ and ‘geothermal’ are not often closely associated. Australia doesn’t have any active volcanoes and relatively few hot springs or geysers. Yet, according to some Australian scientists, we have some of the best reserves of hot dry rocks in the world, offering prospects for a plentiful supply of energy.
Australia’s hot dry rock resources are found in granite rock layers buried up to several kilometres underground, beneath layers of sedimentary rock. They are hot – up to 300ºC – because of what is known as the radiogenic decay of minerals, in which trace elements in the granite slowly break down, releasing heat as they do.
Australian hot dry rock resources are unusually well suited to extraction because of a combination of three factors:
- Heat is being generated in the crust at more than twice the global average.
- The ‘blankets’ of sedimentary rock above the granite provide excellent insulation but are also of an optimal thickness for heat extraction.
- The hot dry rocks are oriented horizontally, providing good (and relatively cheap) drilling access.
The process of extracting the heat is quite simple. Water is pumped down into the hot granite through a bore-hole that may be several kilometres deep. This helps to open up existing tiny cracks in the granite, increasing the permeability of the rock. The water is converted to steam by the heat and is channelled to the surface through another bore-hole, where it can be used to drive a turbine and thereby generate electricity.
Energy from hot dry rocks is often called a renewable resource because of the continuous creation of new heat by radioactive decay. It produces no greenhouse gases or other pollutants and has a very small ‘footprint’ on the landscape (unlike coal mining, hot dry rock energy requires no large-scale excavations). Some scientists say that Australia has enough hot dry rock resources – particularly in the Hunter Valley near Newcastle and the Eromanga Basin near the South Australia/Queensland border – to provide all our energy needs for centuries. A pilot project in the Hunter Valley is now underway.
Wave power
As any surfer knows, there’s plenty of energy in a wave. Waves are a form of solar energy – the uneven heating of the Earth by the sun causes air to move. This wind, in turn, transfers some of its energy to the surface layers of water bodies, particularly the ocean, thereby generating waves.
Putting this energy to use has proved a titanic task for scientists. For example, sea water is highly corrosive, so making generators that are sensitive to small undulations in the sea yet strong enough to withstand the inevitable storms has been a major undertaking. But scientists are now confident that many of these difficulties are close to being solved. They have developed an array of potential machines, although few have been tested commercially (Box 1: Converting wave energy into electricity).
The advocates of wave power foresee few environmental side-effects from a large-scale adoption of the technology. There is little potential for pollution – either chemical, visual or noise – and no greenhouse gas emissions. Floating devices are not expected to have any significant impact on the coastal environment, but they could present a hazard to shipping.
Australia has a huge coastline and significant wave energy resources – particularly along the southern coast of the mainland and the west coast of Tasmania. But the potential for wave power to provide a significant amount of our energy needs remains untested
Hydrogen
You don’t have to be a rocket scientist to see the potential benefits of hydrogen as a fuel. But, actually, it helps – today’s rockets and space-shuttles are all powered by hydrogen. Many experts are predicting that this, the most simple and most common of all the elements, will revolutionise the energy sector.
Hydrogen is not so much an energy source as an energy carrier. It exists on Earth in its free form (H 2 ) in only minute quantities, so we need to manufacture it from materials such as water and hydrocarbons. This requires energy – and you don’t get out more than you put in. So what’s so great about it?
Hydrogen’s usefulness lies in its ability to store energy at high densities and to produce it on demand – much like petrol and natural gas do today. It can be used to generate electricity at times when primary energy sources (like wind, wave or solar) are producing insufficient power to meet demand. Conversely, such energy sources can be used to produce hydrogen when they are generating more electricity than is required by the grid. It can be used in much the same way as petrol, providing fuel for cars and aeroplanes. And it can provide power for fuel cells that can be used much like batteries and recharged at will.
Significant quantities of hydrogen are produced and consumed each year, mostly by the chemical and petroleum industries (eg, in the production of methanol from natural gas and in the manufacture of ammonia), but hardly any is used as fuel. The most common way of producing it at the moment is from natural gas (mostly methane, CH4 ) using a process called steam reforming.
It can also be produced by splitting water (H2 O) into its constituent parts – hydrogen and oxygen. A common way of doing this is by the process of electrolysis. If the electricity is generated by a renewable energy source, this process causes almost no pollution.
But there are some other rather interesting ways to produce hydrogen. For example, it can be derived from biomass by processes called gasification and pyrolysis.
Another intriguing technique involves the use of certain strains of algae and bacteria, which can produce hydrogen from water as a by-product of photosynthesis, using solar energy. The current efficiency of this process is quite low but, with the aid of genetic engineering, scientists hope to achieve significant advances in the next decade or so.
A novel way of producing hydrogen using water and solar energy is called photoelectrochemical (PEC) technology. This combines a photovoltaic cell, which produces electricity when exposed to sunlight, and an electrolyser to convert water directly to hydrogen and oxygen. Again, the technology is not yet perfected. One of the problems is to find a photovoltaic cell that isn’t corroded by the electrolytes in solution but is still cheap enough to be competitive with alternative techniques and fuels.
The widespread adoption of hydrogen as a transport and industrial fuel would clean up our cities in dramatic fashion. The extraction of energy from hydrogen is simply a reversal of the electrolysis process, so the only chemical output would be water. In fact, the waste product from the hydrogen fuel cells used on board space flights also serves as drinking water for the crew. If you can imagine a traffic jam in which the only fumes are a little water vapour then you might start to appreciate what a hydrogen fuel economy could mean for our quality of life.
Change will take time
In Australia, about 9 per cent of Australia’s electricity is generated using renewable resources (mostly hydroelectricity), and the federal government wants this to increase to 11 per cent by 2010.
Effecting a change will take time – time for alternative fuel technologies to develop so that they are competitively priced and capable of providing substantial amounts of energy. We must also develop the necessary infrastructure, so that when consumers buy a hydrogen-powered car they can refuel it in Cloncurry, Oodnadatta or downtown Sydney, just as they can now with a petrol-powered car.
Box
1. Converting wave energy into electricity
Related Nova topics
Harnessing direct solar energy – a progress report
Wind power gathers speed
Biomass – the growing energy resource
Fuelling the 21st century
Which way ahead for hydrogen cars?
Posted July 1999.