SPECTRUM: China Stumbles on Path to Solar Thermal Supremacy

In the final days of 2018 a 100-megawatt solar thermal generating station capable of running around-the-clock, 365-days-a-year connected to the Northwest China regional power grid. It was a race against time to commission the plant in temperatures as low as -20 celsius—and one that plant designer and builder Beijing Shouhang Resources Saving Co could not afford to lose.

“We must finish on time. Otherwise we may face a heavy financial problem,” says Chen Han, Shouhang’s director for international markets.

Shouhang was racing to beat the Chinese government’s December 31, 2018 deadline to secure a guaranteed price for the plant’s power. The deadline was part of an aggressive demonstration program launched in September 2016 to slash the cost of solar thermal power and catapult Chinese firms to the head of the global pack—much as China did with solar photovoltaics.

Alas, a little more than two years later, China has stumbled on the path to solar thermal supremacy. While Shouhang’s and two more of the program’s 20 approved projects met the deadline, four others were cancelled last year and the remaining 13 projects are in limbo. Continue reading “SPECTRUM: China Stumbles on Path to Solar Thermal Supremacy”

Solar Towers Not Avian Annihilators

Solar power towers have had a reputation as alleged avian vaporizers since preliminary reports of birds being burned in mid-air at California’s Ivanpah solar thermal plant. Their reputation was muddied even more during tests early this year at SolarReserve’s Crescent Dunes power tower, whose intense beams of reflected light recently began generating power in Nevada. California public radio station KCET reported that as many as 150 birds were killed during one six-hour test in January. It is obviously upsetting to imagine birds ignited in the name of renewable energy. But avian mortality is a downside common to many modern human creations—including buildings, highways, and powerlines. Full data on bird mortality at Ivanpah, macabre as it might be, shows the death rate to be small and likely of little ecological significance. “The data does support a low level of avian mortalities and hopefully, through adaptive management and deterrence, it will go even lower,” says Magdalena Rodriguez, a senior environmental scientist with the California Department of Fish and Wildlife. Continue reading “Solar Towers Not Avian Annihilators”

Return of the Solar Power Tower

Last week Spectrum Online ran my profile of Andasol 1, a solar thermal power plant that’s set to startup in Andalucia with the largest installation built expressly for storing renewable energy: a set of molten salt storage tanks that will hold enough heat energy to run its 50 MW steam turbine for 7.5 hours after dark. This week brought decisive evidence that another solar thermal design that makes even better use of energy storage — a so-called ‘power tower’ whereby sunlight is focused on a central tower — will also have its moment in the Andalucian sun.

The project, dubbed Gemasolar, will employ sun-tracking mirrors covering an area equal to 40 soccer fields to focus light at the top of a roughly 120-meter-high tower. There the sunlight will heat a solar receiver full of molten salt. In contrast, Andasol 1 (like most of the solar thermal plants under construction in the U.S., Spain, North Africa and the Gulf) uses thousands of square meters of trough-shaped mirrors to focus light on a synthetic oil; energy is stored via heat exchangers that transfer the synthetic oil’s heat to a molten salt.

One advantage of the power tower is thus obvious: heating salt directly eliminates the need for heat exchangers, reducing installation and operating costs. Another lies in the fortuitous thermodynamics of heating molten salts, whose maximum safe temperature of 565 C is about 165 C higher than the synthetic oil’s.

Sandia National Lab researchers verified these power tower advantages in the second half of the 90s, but also suffered through a series of operational difficulties. Five years ago the European Commission provided funding for the Gemasolar project (then known as the Solar Tres) to demonstrate that the difficulties could be overcome, but the project foundered on legal issues and changes in Spain’s renewable energy law. But engineering continued and this March the project sprung back to life when its lead proponent, Spanish engineering firm Sener, clinched a solar thermal joint venture with Abu Dabi’s alternative energy program.

With Abu Dabi’s deep pockets Gemasolar’s financing just might survive the current financial crisis. Siemens confirmed that the tower was moving forward this week by disclosing that it would supply the steam turbine to convert the tower’s solar-generated heat into up to 19 MW of electricity for the Spanish grid. 

For further details on Gemasolar, see this frank telling of its origins, design and goals on Sener’s website. For details on a competing power tower design that directly produces steam, see this white paper from Spains’ Abengoa Solar.

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This post was created for Tech Talk – Insights into tomorrow’s technology from the editors of IEEE Spectrum.

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