The Only Way Is Up: CSP Builds Up Heat

The International Energy Agency says the resource could account for 11% of global electricity demand by 2050, with North America as the largest producer, followed by North Africa and India. Emerging Energy Research (EER) forecasts the addition of 20 GW of CSP globally by 2020, up from about 1 GW today.

For now Spain continues to dominate the market. ‘Spain is driving the industry and it will likely do so for the next three to five years’, says Reese Tisdale, author of EER’s ‘Global CSP markets and Strategies 2010 to 2025’.

Concerned about run-away solar expansion, Spain has placed new controls on CSP and requires developers to pre-register projects to receive the feed-in tariff. Developers must also show the ability to secure financing and off-take contracts. Projects totalling about 2.3 GW have pre-registered, and of that about 500 MW will be granted feed-in tariffs over the next four years, Tisdale said.

The only utility-scale US project in construction is in the southeast, where Florida Power & Light is building a solar/gas hybrid. However, it is the southwest US where most future action will take place. The second major worldwide hotspot for CSP, the region is home to about three dozen project proposals that will generate almost 10,000 MW, according to the Solar Energy Industries Association. The Southwest is also home to the world’s first CSP plant, a series of projects developed in the Mojave Desert by Luz International in the mid-1980s and completed in the early 1990s.

On the plus side, utilities have signed long-term power purchase agreements with several projects, particularly in California. But because of a sour credit market and permitting delays, ‘you are not going to see a whole lot in the US until 2012’, Tisdale said.

US projects have also been delayed by the federal Bureau of Land Management (BLM), which owns large swathes of desert in Nevada, Arizona, New Mexico, Colorado, Utah, and California. ‘BLM hasn’t developed a process in which it can permit and award approval to applications yet’, Tisdale added. ‘That has been ongoing for several years now and is expected to continue through this year. They should have a draft process in place in the third or fourth quarter of his year and final approval in 2011.’

The first projects developed on BLM land will be those deemed by the federal agency as most ready-to-go and put on a fast track for approval. If cleared by December 2010, the projects will be eligible for federal economic stimulus money. The fast-track projects are listed in Table 1.

In June, 2010, BLM reached a milestone when it published rental rates for land use by solar projects, which includes both base rates set by the counties and a per megawatt capacity rate. Depending on location, the federal agency will charge about US$15–$313/acre ($6–$126/ha). In addition, once in operation, projects must pay a capacity rate of $6570/MW for CSP without storage capacity and $7884/MW for CSP with at least three hours per day of storage capacity. By way of example, the BLM said rental for 4000 acres (1616 ha) in Clark County, Nevada, would be $753,360 per year. Added to that is a capacity fee, which for a 400 MW CSP plant with storage would be about $3.2 million per year for five years.

CSP works best in the dry, remote deserts where there are large swathes of available land. But these areas lack the water needed to cool plants. They also require new transmission infrastructure. While dry technology exists to reduce water use, this approach adds costs to CSP’s already relatively high price tag, Tisdale said. Thus, CSP’s water and transmission needs put it at a disadvantage to concentrating solar photovolatics, which require little of either. Conversely, CSP offers energy storage capacity not available to PV.

Still, the IEA sees CSP becoming a competitive source of bulk power for peak and intermediate loads by 2020 and of base-load power by 2025 to 2030. While the US and Spain dominate in 2010, about a dozen other countries have projects under way. Plans are being made to build CSP in China, India, the Middle East, and Africa, with Northern Africa positioned as a possible exporter of CSP to Europe, according to the IEA. Australia also is making a move into CSP with a programme underway to develop 1 GW of solar through 2014. In May the Australian government’s Department of Resource, Energy, and Tourism shortlisted four CSP project developers for funding through its A$1.5 billion ($1.25 billion) solar programme.

Above: eSolar already operates the 5 MW Sierra SunTower in Antelope Valley, California. Credit: eSolar

Parabolic Troughs

By far the most proven and commonly used CSP technology, parabolic troughs typically consist of two rows of curved mirrors to focus the sun’s rays and steel tubes that act as heat collectors. The tubes are coated to absorb solar radiation and reach temperatures of around 700oF (371oC). In the heat exchanger, water is preheated, evaporated, and superheated into steam, which runs a steam turbine. The water is cooled, condensed, and reused in the heat exchangers. Most of these plants have little or no storage and use combustible fuels for backup to firm capacity. For example, in Spain natural gas produces 12%–15% of CSP generation, according to the IEA. Newer parabolic trough plants do often include significant storage capacity.

In the US, parabolic trough technology accounts for most of the new projects in the development queue. One of the largest is the 1000 MW Blythe Power Project, owned jointly by Solar Millennium and Chevron Energy Solutions and consisting of four adjacent 250 MW parabolic trough units. Under review before the California Energy Commission as of June 2010, and on fast-track for BLM approval, the project will occupy a little less than 6000 acres (2424 ha), eight miles (13 km) west of Blythe, California in an unincorporated part of Riverside County.

Meanwhile, in the Middle East, Abu Dhabi’s government-backed Masdar Initiative in June selected Abengoa Solar and French oil company Total to partner in its development of a 100 MW parabolic trough project. Called Shams I, the project is scheduled to begin construction in 2010 and take about two years to complete. Expected to be the largest solar plant in the Middle East with 6,300,000 ft² (585,900 m²) of parabolic trough collectors, its construction is in keeping with Abu Dhabi’s goal of reaching 7% renewable energy by 2020.

Abengoa Solar is no stranger to CSP. A Spanish multinational company, it also has projects in Algeria, Morocco and the US.

Among Abengoa’s parabolic trough projects are:

• The 280 MW Solana station, outside of Gila Bend, Arizona. The plant is expected to be operating in 2013.
• The Solúcar Platform, a 300 MW trough and tower project in Seville, Spain, which will consist of 250 MW in troughs and 50 MW of towers. Currently producing about 90 MW from its various solar technologies, the plant is expected to be fully operational in 2013.
• Abengoa also is participating in the construction of two integrated solar-combined-cycle plants, or ISCC, which are hybrid solar/fossil fuel facilities. The ISCC projects, 150 MW in Algeria and 470 MW in Morocco, will each supply some 20 MW from parabolic troughs.

Power Towers

Solar tower central receiver systems use thousands of moving mirrors or heliostats to track the sun in two dimensions and reflect the light to a boiler on top of a tower. When the concentrated sunlight strikes the boiler, it heats the fluid inside to about 1000°F (538°C). Some towers use molten salts for both the heat transfer fluid and thermal storage capacity.

After parabolic troughs, solar towers represent the largest number of new CSP projects underway in the US. eSolar already operates the 5 MW Sierra SunTower in Antelope Valley, California. And about a dozen others are in development, including BrightSource Energy’s 400 MW Ivanpah installation, a project fast-tracked on BLM land in the Mojave Desert. Ivanpah received $1.4 billion in loan guarantees from the US government earlier in 2010.

‘We expect to receive final permits this summer and begin construction in the fall. Ivanpah will be the first commercial-scale solar thermal power plant constructed in California in nearly two decades. Once constructed, Ivanpah will represent the world’s largest solar energy project, nearly doubling the amount of solar thermal electricity produced in the US today’, said Keely Wachs, BrightSource’ senior director of corporate communications.

BrightSource chose tower technology because of its efficiency, relatively low cost and environmental benevolence, according to Wachs. ‘We have lower capital costs due to commodity-based inputs – heliostat mirrors are simpler to manufacture and less costly to install than parabolic mirrors’, he said. ‘We use air instead of water for cooling – dry cooling – which reduces water consumption by 90%, up to 25 times less than other solar technologies’, he added.

Meanwhile, Pratt & Whitney Rocketdyne, a United Technologies Corporation company, received $10.2 million in 2010 from the Department of Energy to design and develop power tower technologies that lower solar electricity costs. Currently, solar electricity is significantly more expensive than fossil fuels and this project is considered a step towards competitive solar pricing.

The IEA Technology Roadmap Report predicts that CSP technologies will become competitive with fossil fuel-based generation in the sunniest countries by 2020 for intermediate loads and 2030 for base loads.

Dish/Engine Systems

Parabolic central receiver dishes reflect sunlight onto a focal point above the dish, while also tracking the sun. Most dishes have a small generator at the focal point. They do not require a heat transfer fluid or cooling water, and boast the best solar-electric conversion rate among CSP systems. The dish recievers reach up to 1200oF (649oC). However, they are relatively small in size, which means that many dishes must be combined for large-scale energy production.

Stirling Energy Systems, a pioneer in CSP dish-engine technology, manufactures the SunCatcher solar dish, which has an estimated daily energy generated per unit area of 629 kWh/m² (parabolic troughs typically produce 260 kWh/m² and power towers some 327 kWh/m²). The technology also lays claim to significantly lower water usage than other CSP technologies.

When built, the company’s Imperial Valley Solar project (previously known as Solar Two) is expected to generate 750 MW on more than 6000 acres (2424 ha) of land in Imperial County, California. The caveat of dish systems is, of course, that you need a lot of them – phase I of the planed construction would include 12,000 SunCatchers and phase II a further 18,000. That’s 30,000 individual dishes each producing 25 kW. This project is also on BLM’s fast-track for approval.

Linear Fresnel Collectors

Fresnel collector systems, which still represent a relatively small portion of the market, consist of long, parallel, rows of flat mirrors (in contrast to the curved mirrors used by parabolic troughs) that track sunlight throughout the day, and reflect sunlight onto a central receiver in a fixed focal line above the mirrors. Operational Fresnel collectors currently use water instead of oil or molten salts as the heat transfer medium, so steam can be generated directly inside the receivers. While Fresnel collectors are generally considered less efficient than other CSP technologies, in their favour they also offer lower initial investment costs due to the use of cheaper flat mirrors and a simplified design.

Schott Solar, which manufactures high-performance evacuated receivers, recently signed a deal with Fresnel specialist Novatec Bisol. Schott’s receivers will be used in the high-temperature area of Novatec’s collectors. In April Novatec broke ground on its first Fresnel project, the 30 MW Puerto Errado 2 plant in Murcia, Spain.

Ausra, acquired by Areva this year, operates the 5 MW Kimberlina Solar Thermal Energy in Bakersfield, California and a 3 MW plant in New South Wales, Australia, that supplies solar-produced steam to the Liddell Power Station. The company touts the ability to offer efficient heat storage with natural gas backup systems, ensuring reliability and smooth integration into the grid. Ausra says it can achieve 50% more energy production per unit area than competing technologies.

Given the range of developments underway, and in particular in the hotspots of the southwestern US and Spain, it is evident that CSP technology in all of its various guises continues to attract the attention of technology companies, developers and policy-makers. Certainly, the market has developed enough for the IEA to believe that CSP has a significant role to play in securing future supplies of low carbon energy. And, with a range of competing technologies under development, it seems that the winning players have already likely taken a seat at the table and stake in the game.