‘Desert Bounty’ Where can one find an oasis?


Solar Thermal Central Receiver Systems (SIREC, Spain)
Solar Thermal Central Receiver Systems (SIREC, Spain)

Where there is no life, no food or drink, no shops, no entertainment, or a general absence of anything of value, we may say “It’s a desert!” But at some point in the future, perhaps not too far off, that phrase may come to represent a cornucopia of goodies, a treasure- trove of benefits for mankind.

So says an international group of scientists and engineers, the ‘Trans-Mediterranean Renewable Energy Cooperation’ (TREC). Each year, they say, each square kilometre of hot desert receives solar energy equivalent to 1.5 million barrels of oil. Multiplying by the area of such deserts around the world, this is several hundred times as much energy as the world currently consumes.

This is not merely some remote theoretical idea with no bearing on practicalities: direct tropical sunlight may be converted into electricity using an effective, mature technology called ‘concentrating solar power’ (CSP), and it is feasible and economic to transmit solar electricity for 3000 km or more using highly-efficient ‘HVDC’ transmission lines. Since 90% of the world’s population lives within 2700 km of a hot desert, CSP could become a major source of clean energy for the world, helping to cut emissions of CO2 and fight climate change. The ‘TRANS-CSP’ report from the German Aerospace Centre calculates that CSP electricity, imported from the Middle East and North Africa, could become one of the cheapest sources of electricity in Europe, including the cost of transmission.

CSP, which is quite different from the better-known photovoltaic ‘solar panels’, is the remarkably simple technique of concentrating sunlight using mirrors to create heat, and then using the heat to raise steam to drive turbines and generators, just like a conventional power station. A neat feature of this technology is that it is possible to store solar heat in melted salts so that electricity generation may continue at night or on cloudy days. It is also possible to use gas as a stop-gap source of heat when there is not enough sun. These things mean that CSP plants can provide base-load power and they can also respond flexibly to peaks in demand. The cost of collecting solar heat equivalent to one barrel of oil is now about US$50 (already less than the current world price of oil) and it is likely to fall to about US$20 in the future.

Parabolic trough mirrors with maintenance workers at Kramer Junction, California
Parabolic trough mirrors with maintenance workers at Kramer Junction, California

This technology is not something like fusion nuclear power that might, with luck, work at some point in the future. CSP plants have been operating successfully in California since the mid 1980s and currently provide power for about 100,000 homes. Quite recently, a new CSP plant went on stream in Nevada and another one started producing power in Spain. New plants are now being planned or built in several different places around the world.

So far, so conventional: a CSP plant is much like an ordinary power station except that it uses the sun as a source of heat. But the quantities of electricity that are potentially available are quite startling. It has been calculated that, if it was covered with CSP plants, an area of desert measuring about 25,000 square miles – less than 1% of the area of the Sahara and about half the size of England – would produce as much electricity as the world currently consumes. About one fifth of that area would produce as much electricity as the European Union is using. In a report published in January this year, the American Solar Energy Society says that ‘… analysts evaluated the solar resource in the Southwest [of the US] and … found that CSP could provide nearly 7,000 GW of capacity, or about seven times the current total US electric capacity.’

Although the potential of CSP is huge, the TREC group is keen to stress the importance of diversity in supplies of renewable energy. For example, wind power in northern Europe – which is greatest in the winter – would complement supplies of solar electricity – which would be greatest in the summer. In the scenario up to 2050 described in the TRANS-CSP report, there would be a wide variety of renewable sources of energy in Europe with CSP providing no more than 15% of the total. An overall reduction in imports of energy and an increase in the diversity of sources of energy would mean greater resilience and security in energy supplies than what we have now.

Plentiful, inexhaustible, inexpensive and carbon-free supplies of electricity are not the beginning and end of CSP. Waste heat from the steam turbines of CSP plants may be used for the desalination of sea water, thus creating supplies of fresh water in the hot arid regions where they would be most welcome. Clearly, there is not much sea water in the middle of the Sahara but large areas of desert around the world are close to the sea and supplies of brackish water may sometimes be found further inland.

Although CSP plants would need only a small part of the world’s deserts, the fields of mirrors for CSP plants need quite a lot of land and some people have suggested that this is a problem. But one of the most fascinating spin-offs from CSP plants is that the solar mirrors provide areas of shade that are protected from the full glare of the tropical sun. Since the shaded areas are not totally dark – there is still plenty of light filtering past the mirrors – and since there may be supplies of fresh water from desalination of sea water, those shaded areas could be used for growing plants that would not otherwise be able to survive. Thus land that is now unproductive from a human perspective could become a horticultural powerhouse, producing marrows, maze, melons or macadamia nuts, helping to feed the world.

Solar Two tower and heliostats in Daggett Barstow, California
Solar Two tower and heliostats in Daggett (Barstow), California

Where people are living in desert regions, CSP plants and their fields of mirrors can be put to other uses. Buildings can be designed with roofing that doubles as CSP fields of mirrors and it may even be possible to retrofit CSP mirrors on top of existing buildings. Either way, the mirrors provide protection from the sun, helping to keep buildings cool and the CSP plants provide the electricity that people need where they are living or working. But if waste heat from CSP plants is not needed for the desalination of sea water, it can be used for air conditioning, reinforcing the cooling effect of shading under the solar mirrors. Naturally, that solar air conditioning would be greatest at the times of day when it is most needed.

Since the energy potential of hot deserts is so large, they may provide at least some of what is needed for energy-intensive industrial processes – and it may not always be necessary to convert solar heat into electricity. For example, CSP could provide the large amounts of heat and electricity needed to create aluminium from bauxite, and this could be done in the Australian desert, close to where the bauxite is mined.

Apart from the direct material benefits that have been mentioned, CSP can mean the creation of jobs and earnings in large new industries throughout EUMENA. CSP may also have a more subtle but potentially more important contribution to make. In a recent speech to the UN (April 2007), Margaret Beckett, UK Foreign Secretary, identified climate change and consequent shortages of energy, water, food and usable land as potential sources of conflict in the world. By alleviating those shortages, CSP may help to reduce the risks of conflict. More generally, the development of a CSP collaboration amongst countries of Europe, the Middle East and North Africa, with benefits for all, may help to improve relations and develop understanding amongst different groups of people, a positive alternative to the confrontational policies of recent years. It is also very much in line with the recent call by French President-elect Nicolas Sarkozy for a new trans-Mediterranean partnership to speed economic development in Africa countries.

Although the potential benefits of CSP are great, there are few technologies that are totally positive in their effects, without some offsetting negatives. So it is natural to ask what snags or problems there might be with CSP. Some people worry about the security implications for Europe of importing electricity from abroad. There is not enough space here for a full discussion of that issue here but the risks are probably much less than they may superficially appear, certainly less than the risks arising from the energy supply systems that we have now. Another concern is the effect of solar power stations on fragile desert ecosystems. These things would have an impact on the areas where they are set up but, since only a small proportion of the world’s deserts would be needed, there would be plenty left for wildlife. Another possible worry is that CSP might turn out to be another case where rich countries take what they need from poor countries, leaving little for them except pollution. But host countries have much to gain from CSP and several of the benefits are purely local and cannot easily be expropriated.

Hot deserts around the world cannot yet deliver theatre tickets, designer jeans or limousines. But carbon-free electricity (helping to cut CO2 emissions), fresh water in arid regions, new food supplies, new areas of usable land, new jobs and earnings, and enhanced global security, are not bad for starters.

Further information may be found at www.trec-uk.org.uk

An overview of concentrating solar power is at www.trec-uk.org.uk/csp.htm

Dr Gerry Wolff is the coordinator of Desertec-UK and the Kyoto2 Support Group. He writes about alternative energy.