Published by Australian Academy of Science
Harnessing direct solar energy – a progress report Box 5 | Chemical fuels from the sun

Putting the sun’s energy into a light and portable form is the only way to allow all sectors of modern society to run entirely on solar energy.

Solar energy can help to produce energy in a portable form

In Australia, the CSIRO Division of Energy Technology, in collaboration with Pacific Power, has tested the idea of using high temperatures from concentrated solar energy to drive a chemical reaction between carbon dioxide and methane in the presence of a chemical catalyst. The resulting gas (a mixture of hydrogen and carbon monoxide) can then be stored and transported; it releases energy (which can be changed into electricity) when it is allowed to separate back into its two component gases. These can then be recombined with a further energy input from solar power.

Advantages of hydrogen as a fuel

But for many in the field, it’s clear that the ultimate fuel is hydrogen – the lightest substance in the universe. We can produce hydrogen from water, but need energy to do so. Once we have the hydrogen gas, it can be safely stored and transported. Hydrogen is currently only used to power rockets, but with some modifications it could power all our transport and electricity generators. When burnt, hydrogen releases energy and combines with oxygen in the air to form water – a product with no pollution potential! At the same time, the water that was used to produce the hydrogen is regenerated – so the cycle can continue until the sun burns out.

Ways to generate hydrogen

Hydrogen can be generated from water by using an electric current; this is called electrolysis. The electricity can be derived from sunlight. Another possibility would be to simply use very high temperatures from concentrated sunlight, which can literally tear apart the molecules of water into its hydrogen and oxygen atoms. Ideally the gases would then be separated.

But there are much more sophisticated ways of splitting water using sunlight. The secret lies in plants. When exposed to light, green plants continually split water – releasing the oxygen into the air for us to breathe, and combining the hydrogen with carbon dioxide to form sugars. If we could duplicate this process, we would be well on the way to becoming a truly solar society. Research continues.

The future of hydrogen as an energy source

Australia’s Sir Mark Oliphant, the distinguished physicist, is one of several experts who consider that the move to a solar-powered ‘hydrogen’ society will eventually come. If he is right, desert areas could be used for intensive solar collection and the production of liquid fuels would power our world, in much the same way that modern agriculture, with its huge area of wheatfields, continually converts sunlight into solid chemical energy for us to eat. If this comes about, those countries with a large area receiving intense sunlight – such as Australia – could be as rich as today’s oil-exporters.

Related Nova topics:

• Which way ahead for hydrogen cars?

• Fuelling the 21st century

Other boxes

Box 1. Eliminating the zeroes

Box 2. Driving on a sunbeam

Box 3. Light to electricity

Box 4. The Big Dish