Is CSP the solution to global warming and climate change?

Solar power has long been touted as a form of clean energy that will meet the world's increasing demand for energy without causing pollution but in its most common form has failed to live up to its promises to date. Photovoltaic panels, which are increasingly popular, have an efficiency rating of about 17 - 18%, which is substantially lower than the 50 - 60% rate of the most efficient combined cycle power plants.

Two German scientists, however, believe that the sun's energy can be much more efficiently tapped without paving half the world with solar panels, by the adoption of CSP - or concentrating solar power technology. The idea behind CSP is simple: it is based on the same idea that allows us to burn a hole in a piece of paper by concentrating the sun's rays through a magnifying glass.

Designs may be different but essentially the technology uses mirrors to concentrate sunlight on a pipe or vessel containing a gas or liquid that becomes heated to around 400 deg C. This heat is then used to power conventional steam turbines. To generate sufficient energy the mirrors need to be very large but the scientists, Dr Gerhard Knies and Dr Franz Trieb, believe that covering an area equal to 0.5% of the world's hot deserts with these mirrors will generate enough energy to meet the entire world's electricity needs.

CSP is seen as a holistic technology with other benefits as well. Waste heat from power generation can be used for desalination, providing freshwater to the desert regions where the mirrors are most ideally suited. It is suggested that horticulture can be developed in the shaded areas under the mirrors, with the plants being irrigated by the desalinated water. The cold water can also be used to provide air conditioning. Finally, the hot liquid can be stored in large vessels to keep the turbines running for hours after sunset, which makes it superior to other solar power technologies.

"It is this triple use of the energy which really boost the overall energy efficiency of these kinds of plants up to 80% to 90%," Dr Knies told the UK's Guardian newspaper, which reported the scientists' study in November.

According to reports the scientists prepared for the German government, Europe should explore the possibility of collaborating with countries in the Middle East and Africa, where the deserts are located. They proposed the construction of a high-voltage direct current (HVDC) grid to transmit electricity to Europe to prevent electricity loss along the way, as would happen with alternating current cables. Dr Trieb, who works for the German Air and Space Agency, estimated the electricity loss of DC cables at 3% per 1,000 km, which translates into a loss of 10% between Africa and the UK. According to the reports, such an HVDC grid could fulfil all of Europe's electricity needs by 2050 and allow nuclear power to be phased out while the use of fossil fuels is also substantially reduced.

"Contrary to what is commonly supposed it is entirely feasible, and cost-effective, to transmit solar electricity over long distances. Solar electricity imported to Europe would be amongst the cheapest source of electricity and that includes transporting it," he said. "CSP imports would be much less vulnerable to interruption than are current imports of gas, oil and uranium."

According to the German reports, the capital cost of CSP would be around US$50 per barrel of oil (the current price is around US$60 per barrel) equivalent but that would fall to about US$20 when economies of scale lowers the production cost for the mirrors.

With desalination and the provision of air-conditioning factored in, CSP would be competitive against natural gas as well, especially with the cost of the carbon emissions from fossil fuels taken into account, Dr Knies said. It is also easily cheaper than nuclear energy: Dan Lewis, research director of the UK's Economic Research Council, reckons CSP costs US$3 - 5 million per installed megawatt or 20% the cost of fusion.

There are working CSP farms in the world. For example, there is a 15-year model in the Mojave desert of California, US and others in Spain and Australia; which means it is not an unproven technology.

An umbrella group of scientists called the Trans-Mediterranean Renewable Energy Cooperation (Trec) has been formed to push the concept. They hope that German chancellor Angela Merkel will use Germany's joint presidency of the EU and Group of Eight leading economies next year to push for an agreement on a European DC grid and the launch of a widespread CSP programme.

A parabolic trough CSP system uses parabolically curved, trough-shaped reflectors to concentrate sunlight on a receiver pipe running along the inside of the curved surface. This energy heats oil flowing through the pipe, and the heat energy is then used to generate electricity in a conventional steam generator. Source:

An alternative system uses large, sun-tracking mirrors (heliostats) to focus sunlight on a receiver at the top of a tower. A heat transfer fluid heated in the receiver is used to generate steam, which, in turn, is used in a conventional turbine-generator to produce electricity. Source:

A power tower system in Barstow, California. Source:

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