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Renewable energy: The role of hydrogen

Jan Smit explains the way that hydrogen could be used to help to resolve the world’s energy crisis.

The world is facing an energy crisis. A crisis that will escalate unless serious efforts are made to relieve it. Let us start by first focusing on energy and the increasing need for energy in modern society.

The primary source of energy on Earth is the Sun. All energy we use today comes from the Sun. Energy from the Sun makes waves in the sea, causes winds and rain, and makes plants grow, and plants produce food for animals and humans. Coal, oil and gas are fossil fuels that were deposited millions of years ago as a result of plant activity using the Sun’s energy. We have become dependent on fossil fuels such as coal and gas to produce electricity on a large scale, on petroleum products for transport and for the cultivation of land for grain and other food for humans and animals. An unwanted by product of electricity generation is pollution. Carbon dioxide, acid rain, soot and fine dust are pollutants that cause serious threats to the Earth’s ecology and to our future existence. There is thus a serious need for large scale production of renewable energy – energy that does not pollute in its generation.

Let us look briefly at modern society. Humans became adapted to the old world (roughly before 1750 when the Industrial Revolution started) over many centuries. People worked and slept according to the day-night cycles determined by the Sun. People used their own muscles to work. Wood, animal oil and plant products provided heat to cook food and to provide warmth in winter. Transport was slow, with ox wagons, horse and donkey carts and wind driven ships. Communication was limited to messengers on foot, smoke and light signals and letters.

Since the Industrial Revolution started in about 1750 the basic sciences, mathematics, physics and chemistry developed rapidly. Technological developments that were based on the principles, laws and methods of the basic sciences influenced nearly all parts of modern society. In the previous century and the first two decades of this century, technological developments accelerated and influenced all parts of modern society. Our world has changed enourmously. Consider communication by cellular telephones, the Internet, TV and the role of satellites in global communication. Food preservation by freezing, tinning or addition of preservatives has made us largely independent of seasons and distance. Travel by aeroplanes and motor vehicles brings far away destinations within easy reach in relatively short times. All the electric appliances in our households such as stoves, electric lights, and water heating were unknown a century ago. Fridges, hair dryers and many more appliances can be added to the list. And don’t ignore developments in medicine and health care and their consequences.

Focus for a moment on one aspect of these developments. Consider the question: How would life be if all of a sudden electricity should disappear?

It is apparent that human dependence on energy increased tremendously during the recent past. There are two alarm signals that cannot be ignored or the consequences for humankind and the environment could be disastrous. First, fossil fuels are limited and will certainly become depleted or unaffordable in the near future at the present rate of utilisation. These sources are not renewable. Second, the growing human population consumes more and more energy. An obvious solution is to find alternative sources of clean renewable energy. One such a source is hydrogen.  It is the simplest element, the first one on the Periodic Table.

Hydrogen

Hydrogen is abundant on Earth: all water contains hydrogen. At standard temperature and pressure, hydrogen is colourless, odorless, tasteless, non-toxic, nonmetallic and a highly compustible gas, with the molecular formula H₂.

Hydrogen gas is highly flammable and will burn in air. Pure hydrogen-oxygen flames emit ultraviolet light and are nearly invisible to the naked eye, see here in the faint plume of the Space Shuttle main engine.

When hydrogen gas combines with oxygen gas, energy is released. If the released energy is in the form of electricity, it can be utilised for many purposes. How can the hydrogen in water be utilised in such a way? Modern technology makes this possible. How?

Using hydrogen and sunlight

A solar panel converts the Sun’s energy to electricity. The electricity dissociates water in its two elements, hydrogen and oxygen in a fuel cell that operates in a reverse mode.

This process is called electrolysis and it takes place in an electrolyser. The fuel cell is a new technological device, which is currently being optimised. The oxygen produced during electrolysis is allowed to escape into the air. The hydrogen is captured and stored in a container until it is needed to produce electricity. This type of cell has an advantage over solar cells, which can generate electricity only when the Sun shines. This solar generated electricity can be stored in batteries, but batteries are bulky, heavy and the storage capacity is limited. A lot of energy is needed to build a battery and when its useful life is over the old battery contributes to pollution.

The process of electricity generation by hydrogen is illustrated in the demonstration model of a fuel cell device.

The components of this hydrogen fuel cell are (from left to right):

-       First the solar panels. The panels convert solar energy to electric current. This current goes through the two connecting wires to the electrolyser (second component).

-       This second component, the electrolyser, has a thin membrane. Distilled water is fed by plastic tubes from a water reservoir (between the solar panel and the electrolyser) to the membrane. At the membrane, the water is dissociated by the current from the solar cells into hydrogen and oxygen (electrolysis). The oxygen escapes into the air and the hydrogen accumulates in the third component, a cylindrical reservoir.

-       In the reservoir water prevents the hydrogen from escaping into the air. The accumulated hydrogen is then fed into the fourth component, a hydrogen fuel cell.

-       In the fuel cell (fourth component), as a result of the working of the membrane in the cell, the hydrogen combines chemically with oxygen in the air to form water and electricity. The water is allowed to escape freely.

-       The electricity generated by this fuel cell is then used to drive a fan (far right). The fan is last of the five components of interest in this demonstration model.

This method of electricity generation may, in future, make a significant contribution to the supply of clean, renewable energy.

This demonstration model can be scaled up to generate considerable amounts of electric energy.

What are the main advantages of this method of electricity generation?

What are the challenges faced at present?

Try to answer these questions before referring to the lists below.

Main advantages:

1      The Sun’s energy is available in abundance in most parts of the world. In South Africa the average annual radiation is about 700 W/m² at noon.

2      Hydrogen is also available in abundance in water, in seas, dams, lakes, rivers and in the atmosphere, clouds and mist.

3      The energy generated by hydrogen fuel cells is clean. No environmental pollution results. The only interaction with the environment is the release of oxygen into the atmosphere. Exactly the same amount of oxygen is needed to recombine again with the hydrogen in the fuel cell where electricity is generated and water is released. It is thus a clean energy carrier for renewable energy.

4      An advantage of this method over solar cells (on their own) is that the hydrogen can be stored for use when the Sun does not shine. It is more practical and more economic than storage of solar generated electric energy in batteries.

Challenges:

1      Fuel cell membranes are still in the research and development stage. More economic, more efficient, longer lasting fuel cells and electrolysers with greater capacity to generate electricity than those in use at present need to be developed. Research and development is already being done. The Department of Science and Technology (DST) is financing such research in South Africa.

2      Safe storage of large quantities of hydrogen is a challenge. At present the hydrogen is stored as gas. It is compressed by the generating cell to about 20 bar. Other methods of storage  are continuously being researched.

At the heart of this method of electricity generation is the fuel cell. How does a fuel cell work? Is there as difference between the electrolyser and fuel cell used in our demonstration?

These and other relevant questions will be addressed in a future article.

Professor Jan Smit is Manager, Science Centre, NWU, Potchefstroom campus.

Acknowledgements

The author wishes to acknowledge Mr. Frikkie van der Merwe: Chemical Engineer, Involved in Research on Hydrogen Fuels Cells and Dr. Dmitri Bessarabov Director: DST Hydrogen Infrastructure Center of Competence.

SAASTA, NRF and DST provided financial assistance.