Tomorrows Power Grids - Desert Power - Andreas Kleinschmidt – Fall 2009

By 2050, electricity generated at solar-thermal power plants and wind farms in Africa and the Middle East is expected to cover 15 to 20 % of Europe’s energy needs. That’s the goal of the Desertec Industrial Initiative. Siemens is a founding member and technology partner.

Suddenly, he no longer had a quiet moment. There were calls from the Chancellery, ministries, ambassadors, and company representatives by the minute—and although Prof. Hans Müller-Steinhagen from the German Aerospace Center (DLR) in Stuttgart, Germany, is used to acting more like a manager than a researcher, he was still overwhelmed. "When you’ve got 250 people working for you, you can’t just hide in the lab," he says. Still, what he experienced in the summer of 2009, when the whole world started talking about Desertec, was something completely different. In fact, just as Müller-Steinhagen finishes describing this, the phone rings—this time it’s the German Embassy in London, asking if he’d be willing to do a presentation.

Along with the Desertec Foundation and the German Association for the Club of Rome, Müller-Steinhagen’s Institute of Technical Thermodynamics is one of the nerve centers for a project that has been compared in size with the Apollo space program—which culminated in the 1969 moon landing. Desertec, however, focuses on the sun rather than the moon—more specifically on the sun’s energy. In conjunction with the Trans-Mediterranean Renewable Energy Cooperation (TREC), a team of researchers in Stuttgart under the direction of Müller-Steinhagen’s colleague Dr. Franz Trieb has determined that solar-thermal power plants could meet the world’s entire energy requirements. To achieve that, however, it would be necessary to cover an area measuring around 90,000 km²—that’s about the size of Austria—with mirrors.

But, according to the DLR, which has studied the associated technology for over 30 years, if only 15 to 20 % of Europe’s energy demand—the goal of the Desertec project—were covered, an area of around 2,500 km² would be sufficient. An additional 3,600 km² would be needed for the high-voltage power lines that would transmit electricity to Europe.

This vision is now gaining traction because a dozen European companies joined together in July 2009 to form the Desertec Industrial Initiative (DII) and lend additional momentum to the €400 billion project. According to DLR estimates, €350 billion will be needed for the power plants and €50 billion for associated transmission technology.

Partners in the initiative include companies that are normally rivals, as well as a major bank and the Münchener Rück insurance company, one of the largest reinsurers in the world. Siemens is one of the driving forces in the initiative—which should be no surprise given that its portfolio of solutions for solar-thermal power plants includes key components such as steam turbines and receiver tubes, power plant control technology, and systems for transmitting high-voltage direct current with low losses (see HVDC Transmission, HVDCT Converters).

"Solar-thermal power works—there’s no question about it," says Müller-Steinhagen. In fact, a cluster of power plants in California’s Mojave Desert has demonstrated for over 20 years that a huge amount of electricity can be generated with solar energy. The facilities feed some 350 MW into the grid—enough electricity to power 200,000 households.

There are many reasons why this technology is now being widely discussed in the context of Desertec, with increased awareness of the need for climate-friendly power being chief among them. In addition, technology for low-loss transmission of electricity over long distances has now established itself, while recent innovations have made solar-thermal power plants even more efficient. When oil prices begin rising again, as is expected after the economic crisis, solar-thermal electricity may quickly become competitive. In fact, its production in favorable regions already costs less than €0.20 per kWh.


90 % of the earth’s population lives within less than 3,000 km from the earth’s sunbelt (Source: Solar Millenium)

Major Alliance. If there’s one person who might be called the father of Desertec, it’s Dr. Gerhard Knies. Knies is Chairman of the Supervisory Board of the Desertec Foundation, which developed the Desertec concept that is now being refined in the DII. A retired physicist, Knies’ favorite quote is from Albert Einstein, who said: "We can’t solve problems by using the same kind of thinking we used when we created them." Knies believes this logic fits in very well with the issue of climate change brought about by CO2 emissions, as this development can only be counteracted by revamping the energy supply system. Over the years, he has put together an impressive group of supporters, including TREC, the Club of Rome, DLR, and Prince Hassan of Jordan.

"We all understood that putting a halt to climate change would require CO2-free technologies like wind power, geothermal systems and, above all, solar-thermal facilities—all on a mass scale," he says. Whereas Müller-Steinhagen is one of Desertec’s technology designers, Knies got the associated political process moving. His work culminated in the launch of the implementation phase in the summer of 2009, when a consortium was established and support was obtained from companies such as Siemens.

The DII intends to develop business plans and financing concepts for the biggest-ever solar power project within three years. The goal is to build a belt of solar-thermal power plants in North Africa and the Middle East, which would be linked via high-voltage lines with local consumers and European countries. Plans call for achieving a capacity of 100 GW and the supply of 700 TWh per year by 2050, which would cover 15 to 20 % of Europe’s electricity needs.

Obviously, these plants could meet an even higher share of the energy requirement in the dynamically growing countries in which they would be located. The electricity requirement in the MENA Region (Middle East and North Africa) is expected to increase five-fold over the next 30 to 40 years, to 3,500 TWh. "Solar-thermal plants and wind power facilities could, for example, play a key role in the energy-intensive desalination of seawater," says Knies. Moreover, because as much as 80 % of the value created through construction of the power plant facilities will remain in the MENA countries themselves (e.g. through the production of mirrors, foundations, and frames), a project like Desertec would also greatly boost development in the region. According to estimates by Greenpeace, Desertec would lead to the creation of some two million jobs in participating countries by 2050.

Dr. René Umlauft, CEO of Siemens’ Renewable Energy Division, has supported the initiative from the start. "Desertec can make a key contribution when it comes to establishing a sustainable energy supply system," he says. "And with the solutions from its Environmental Portfolio, Siemens is the right technology partner for this visionary project, many of the elements of which have already been implemented in Europe."


Reliable and highly flexible steam turbines from Siemens, such as the SST-700, are ideal for the special requirements of solar-thermal power plants (right: the Andasol plant)

For instance, Siemens is the market leader in the construction of new offshore wind turbines, many of which can be found on European seas (see Offshore Wind). Siemens technology can also be found in European solar power plants. At the beginning of 2009, for example, the Andasol parabolic trough plant went online in Andalusia in Spain.

Just Follow the Sun. The Andasol plant is equipped with curved parabolic mirrors laid out in long rows covering an area of 500,000 m². These mirrors will enable the plant, which will consist of three complexes in its final expansion stage, to generate 150 MW in all, and 176 GWh per complex and year. To optimize the facility’s yield, the mirrors continuously track the sun to within one-tenth of a degree of arc. The light they reflect is channeled into vacuum-insulated receiver tubes that contain a special oil that is heated to nearly 400 °C. The oil later transfers its heat to water in heat exchangers, thereby creating steam.

"At that point, a solar-thermal plant begins operating like a conventional facility," says Umlauft. That’s because the downstream "power block," in which electricity is generated from steam, employs the proven technology used in steam-turbine plants.

But solar-thermal plants have special requirements with regard to turbine size and flexibility. For one thing, turbines in certain types of solar plants need to be able to start up very quickly when the sun rises. That’s one reason why many solar power plant operators opt for customized Siemens technology. In May 2009, Siemens opened a new turbine production hall in Görlitz, Germany, that produces the SST-700, the world market leader when it comes to parabolic trough power plants. In fact, Siemens’ share of this market is more than 90 %.

Together with control systems from Siemens, the SST-700 turbine is also being used in another power plant in Andalusia: Solnova 1 in Sanlúcar la Mayor, near Seville. Power generation is scheduled to begin at the facility in late 2009.

SST-700 turbines are already in operation in many CSP plants around the world. The model is popular due to its reliability and specifications—which are very well-suited to the size class currently in operation—and its flexibility. "This is important because in Seville we have light cloud cover about 90 days a year. The plant’s output can fluctuate considerably on such days," says Valerio Fernandez, Director of Operations and Maintenance at Abengoa Solar, which operates Solnova. "The turbine therefore has to be flexible enough to make up for these fluctuations."

As the morning sun rises, Fernandez inspects the Solnova construction site, where workers are busy tightening bolts and assembling and polishing equipment. "Here in Seville we have very good conditions for solar-thermal power plants: about 210 days a year of perfect sunshine, from morning to evening," says Fernandez. The Spanish feed-in law for subsidizing solar-thermal power has triggered a real boom. Since 2006, producers have been entitled to receive a maximum of nearly €0.28 per kWh from the government, and civil servants are being buried in applications.

Big Up-front Investment. Depending on the location and sunlight intensity, it now costs up to €0.23 to produce 1 kWh of electricity, which is relatively high. Electricity from wind power, on the other hand, can already be produced at competitive prices in many regions in Europe. But things weren’t always this way. Thirty years ago, it cost around €3 million to install one MW of onshore wind-power output, while today it costs only €1 million. Experts expect a similar development with regard to solar-thermal power. Here, the high cost at the moment is mainly due to the initial investment. For example, a 50-MW facility with heat storage costs around €300 million, which has to be paid off over the plant’s useful life, which can extend up to 40 years.

Heat storage isn’t cheap, as indicated by existing systems at the European Center for Solar Energy Activities, the Plataforma Solar de Almería, as well as in Andasol. But by storing heat produced during the day, both locations can generate electricity at night as well. Up until now, large insulated tanks containing liquid salts with a melting point of around 200 °C have mostly been used as storage media. Researchers at DLR and other facilities are now trying to find ways to reduce costs by altering the storage media or fine- tuning power plant components to ensure that as little heat as possible is lost during the heat exchange process between the hot heat transfer agent and the steam.


The Desertec concept: Solar power in the desert, wind on the coasts, and a network of transmission lines (Source: Desertec Foundation)

Fernandez thus expects that the initial investment per MW of installed generating capacity will soon decrease. "So far we’ve been producing mostly one-of-a-kind equipment and procuring special components, like receiver tubes, from small production series. But when mass production for solar-thermal plants begins, investment and power generation costs will fall dramatically," he predicts.

Siemens is now in a good position to supply receiver tubes, as the company acquired a 28 % interest in Archimede Solar in March 2009. The Italian company produces tubes through which molten salt rather than special oil flows. The advantage of this setup is that unlike oil, which ages with frequent temperature changes and thus must be replaced, molten salt can remain in the cycle. It also allows operation at temperatures up to 550 °C, which boosts efficiency because the steam that drives the turbine can also be brought to higher temperatures and pressures.

What’s more, the use of salt eliminates the need for high-loss heat exchangers because the salt in the receiver tubes can also be used as the storage medium and can be pumped into an insulated tank as well. After it cools, the salt flows back into the receiver, where it again "harvests" solar energy. Construction of a new factory for producing Archimede receivers is expected to begin in northern Italy this year; the facility is expected to enter service in 2010. Archimede tubes are already being used at a solar field in southern Italy. "By acquiring an interest in Archimede Solar, Siemens is underscoring its intention to become the leading supplier of solutions for solar-thermal power plants," says Umlauft.

Instead of using special oil or molten salt, it’s also possible to produce steam directly in absorber tubes. This eliminates the need for an expensive heat transfer agent, as water can be used to generate steam directly. Together with the DLR, Siemens has been working on the associated technology for many years. Thanks to the major advances achieved so far, it will be possible to operate some of the parabolic collectors at the Andasol-3 power plant with such a direct steam generation system.

Conditions for solar power generation are even more favorable in the deserts of the U.S. and North Africa than in southern Spain. Egypt, for example, is considered to be ideal for solar power because the Nile can provide sufficient cooling water for the condensers in the steam cycle. However, condensers can also be cooled in dry regions using air, although efficiency in this case is 20 % lower. Such an approach might make sense in parts of Algeria, for example, where stone deserts offer an optimal location for solar-thermal power plants for a different reason: There are no sand storms that can damage mirrors. Algeria is the site for the future Hassi R’Mel power plant, a 160-MW facility currently under construction that combines a conventional gas and steam turbine plant with solar technology. The facility will initially generate electricity for the local market. However, with the construction of more and more power plants, North Africa will eventually have an electricity surplus, which could be transmitted to Europe. Clearly, in such a case, losses must be minimized—and this is where high-voltage direct current transmission (HVDC) comes in.

Electricity Highway. "Transferring power via conventional AC lines over thousands of kilometers from Africa to Europe would lead to huge losses," says Dr. Dietmar Retzmann, Siemens’ leading expert for HVDC transmission technology. "Such losses can be greatly reduced by using HVDC lines and undersea cables." HVDC loses only around 10 % of power over 3,000 km—that’s roughly the distance from the southern end of the Sahara to Central Europe. Siemens is now building the most powerful HVDC connection in the world in China, where 5,000 MW of power will be transported 1,400 km (see HVDC Transmission). "Such HVDC lines are like electricity highways," says Retzmann. "We’re going to need them in Europe when we expand our grid and large amounts of electricity from wind power facilities will have to be moved great distances."

Desertec might therefore become a key component of tomorrow’s energy networks. The project provides solutions in three key areas, according to Michael Weinhold, chief technologist at Siemens Energy. "Energy systems must be effective in terms of three dimensions," he says, "economy, environment, and security. Desertec will be good for the environment, it will be designed in an economical manner, and it will enhance European energy security because it will substantially reduce dependence on fossil fuel imports."

The key issue with solar-thermal power today is no longer feasibility but the ability to achieve efficiency in large-scale applications. The main issue for the MENA Region is to ensure continued stable economic development and a reliable supply of energy for drinking water systems. The water table in Sanaa, Yemen, for example, is sinking at the rate of 6 m per year, according to Müller-Steinhagen. In Egypt, new water sources with a volume equivalent to the entire flow of the Nile need to be tapped by 2050. Desalination at solar-thermal facilities could meet a large portion of this requirement. In conjunction with modern technology, the sun that relentlessly beats down on this region, could one day be bringing water, electricity, and life to the desert.

Source:http://www.siemens.com/innovation/en/highlights/
energy/update_02/desertec.htm

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