FACT SHEET 15:
HYDROGEN
At present the world has a fossil fuel economy. There is a growing demand
for energy to fuel this economy and 80% of the world’s energy comes from
fossil fuels. Reduced availability of oil and gas, together with global
warming and other environmental problems, is likely to make this
dependence on fossil fuels unsustainable.
A hydrogen economy is one where hydrogen is used: to carry and store
energy, fuel transport, enable continuous electricity supply and drive other
machines. If a hydrogen economy is to work we need to be able to:
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produce sufficient hydrogen to meet our needs;
store large quantities of hydrogen for long periods of time;
transmit hydrogen over long distances and distribute it to
customers; and
convert the energy stored in hydrogen to the type of energy needed
by the consumer.
Production of hydrogen
Hydrogen is the second most abundant element on the earth’s surface, in
terms of the number of atoms. However, only a trace of free hydrogen is
found naturally. The major portion of hydrogen is combined with oxygen in
water. Hydrogen is also a constituent of all animal and vegetable tissue,
fossil fuels and some rocks and minerals.
Hydrogen can be separated from oxygen in water by electrolysis (see fact
sheet Energy Storage for more information). If electricity from renewable
sources were to be used to make hydrogen by electrolysis the hydrogen
economy could be sustainable.
Figure 1. Possible future energy generating system using solar energy and a
hydrogen energy storage system (Stevens 1992)
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Sea water contains a virtually inexhaustible supply of hydrogen.
Furthermore, enormous amounts of electricity can be generated from
renewable sources, like wind farms, solar PV farms (Figure 1), tidal
generators and wave energy systems. However, electricity from these
renewable sources is presently expensive.
It has also been proposed that hydrogen can be made using off-peak
electricity from nuclear power plants. While this will not add to global
warming there are challenging environmental problems associated with
nuclear power.
Large amounts of hydrogen are already being produced and shipped
around the world. It is used as a raw material in the chemical industry,
mainly for nitrogen fertilisers and in oil refining. World consumption is 50
million tonnes per year, growing at about 10% pa (World Nuclear
Association). Virtually all this hydrogen is made from oil or natural gas,
giving rise to carbon dioxide emissions. Hydrogen made in this
conventional way is cheaper and could be used in a transition to renewable
fuels.
The purity requirements for hydrogen for fuel cells are much higher than for
most industrial requirements which adds to the cost.
An alternative proposal it to produce hydrogen from biomass. This, together
with improved electrolysis efficiency, is the subject of considerable research
interest.
Storage of hydrogen
Although hydrogen has been safely handled by the chemical industry over
many years, it does present different handling difficulties to natural gas or
liquid fuels. Hydrogen is very reactive and pipes and containers need to be
made of materials that do not react with it. It is a very small molecule and
can diffuse through extremely small holes so leakage can be a problem.
Nevertheless, a small leak in the open air does not present an
environmental problem because hydrogen diffuses so rapidly and does not
add to global warming.
Hydrogen has a high energy density per unit of weight, but low energy
density per unit of volume. Unless it is compressed it requires a lot of space
for storage. It is gaseous unless cooled to very low temperatures. It can be
stored as a gas in pressurised containers and in underground caverns.
Research and development is taking place into higher storage pressures
and the materials needed to store hydrogen under these pressures
Liquid hydrogen can be stored at temperatures below minus 254°C in
cryogenic tanks. This is a much lower temperature than the minus 160°C
required to liquefy natural gas. Liquefying hydrogen requires a large
amount of energy and this cost has to be balanced against the advantages
of storing and transporting it as a liquid.
Hydrogen cannot easily be turned into a solid but it can be stored with solid
materials so effectively it can be handled as a solid. There are three main
focuses for research in this field: gas-on-solid adsorption, glass
microspheres (small spheres which contain hydrogen) and metal hydrides.
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Using metal hydrides to store hydrogen is still in the experimental stage but
looks promising. The hydrogen is absorbed into a metal alloy and some
heat is given off. The alloy then has to be heated to release the hydrogen.
The desired properties of an efficient metal hydride storage material are:
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It can hold a lot of hydrogen.
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The metal hydride should not need to be heated to more than
100°C for it to give up the hydrogen.
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The hydrogen can be absorbed quickly and released quickly.
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Very little heat is given off when the metal hydride is formed.
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It does not cost too much to make the metal alloy.
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It is light weight.
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It does not react with oxygen or water.
Transmission and Distribution
Existing shipping, road and rail transport networks can be used for
transporting hydrogen. Gaseous hydrogen can be distributed via pipelines
and in pressurised vessels on conventional forms of transport. Liquid
hydrogen can also be distributed on conventional forms of transport in
cryogenic vessels and liquid hydrogen tankers. Similarly, solid hydrogen
can be transported using conventional means.
Fuel companies are interested in modifying their existing distribution
systems for hydrogen. The fuel cell bus trial being conducted worldwide,
which includes Perth in Western Australia, is testing hydrogen distribution
technology as well as fuel cells.
Distribution and transmission costs could be reduced if hydrogen were to
be produced at re-fuelling stations rather than in central plants. It is still an
open question if more central production and distribution to local re-fuelling
stations or on site production would prevail in a hydrogen economy.
Conversion to useful energy
Energy is needed to generate electricity and provide power for transport.
Heat is also needed, both at low temperatures for room and water heating
and at high temperatures for cooking and chemical and mineral processing.
Hydrogen can be used to meet these needs. Furthermore, it is a clean
burning fuel, with the only emission being water vapour.
TRANSPORT
Hydrogen can be burnt in a normal internal combustion engine or reacted
chemically in a fuel cell to power a vehicle. Fuel cell cars and buses are
already being tested. Liquid hydrogen fuel tankers, either road or sea, could
be powered by gas boil off, as are LNG tankers. Boil off is the small amount
of gas that evaporates because of heat leakage into a heavily insulated
cryogenic vessel.
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ELECTRICITY GENERATION
Electricity can be generated from hydrogen using standard technology (e.g.
boilers and steam turbines) or fuel cells. Fuel cells show promise of great
efficiency (see fact sheet Fuel Cells).
Electricity can then be used to provide power for machines,
communications, cooking, light, refrigeration and other modern
requirements.
HEAT
Waste heat from the electricity generation process can be used to provide
both low and high temperature heat. Low temperature fuel cells can provide
domestic water heating as a by-product of electricity generation. High
temperature fuel cells can provide steam. Heat can also be obtained
directly by burning hydrogen.
Iceland’s hydrogen economy
Iceland has begun to work towards a hydrogen economy. Iceland has large
reserves of geothermal and hydro electric power and plenty of water but no
reserves of fossil fuels. It plans to fuel its large number of cars, boats and
other transport vehicles with hydrogen and become completely
independent of fossil fuels. It already has hydrogen fuelled cars and buses
on the road.
References
Dr Trevor Pryor, MUERI, Murdoch University
Energy: A Guidebook, New Edition by Janet Ramage, Published by Oxford
University Press, 1997. ISBN 0-19-288022-5, Chapter 15
Justi 1987
Boyle, G. (2002).. Oxford, Oxford University Press in Renewable Energy
Power for a Sustainable Future association with the Open University.
Carl Jochen-Winter 1988
Stevens 1992
K Fueki, World Energy Conference
Icelandic New Energy Ltd
Department for Planning and Infrastructure Perth Fuel Cell Bus Trial
Government of Western Australia
http://www.dpi.wa.gov.au/fuelcells/index.html
DaimlerChrysler
Shell Hydrogen
IEA / OECD Conference - Towards Hydrogen March 2003
World Nuclear Association (http://www.world-nuclear.org/info/inf70.htm)
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Further Reading
The Use of Hydrogen for Energy Transportation
"Fuel Cell Handbook", A J Appleby & F R Foulkes, Van Nostrand Reinhold,
New York, 1989
Check out some of the properties of hydrogen at:
Chemistry: Periodic Table: hydrogen: key information
Read about the hydrogen economy at:
Howstuffworks "How the Hydrogen Economy Works"
The Online Fuel Cell Information Centre
International Energy Agency
Iceland launches energy revolution
Acknowledgements
This information was taken from Murdoch University Unit M190 Introduction
to Energy Studies Week 12, Unit M292 Energy in Society Topic 20, Unit
M390 Energy Systems Topic 8 and reworked by Christine Creagh (2003,
Murdoch University) and edited by Philip Jennings (Murdoch University)
and Mary Dale (Australian Institute of Energy).
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