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”

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.

The Other Solar Power

Solar thermal power cuts a fascinating contrast with solar photovoltaics and wind turbines — today’s leading renewable energy technologies — besting one on price and the other on quality. Little surprise then that it is being selected for power plants equal in output to large wind farms and ten-times the size of the largest photovoltaic installations.

Whereas photovoltaics employ semiconductors to directly convert sunlight into electricity, solar thermal power stations convert sunlight into heat to generate steam and drive a turbine. This roundabout is, ironically, a huge money-saver. The Abengoa thermal solar power towers in Sevillemirrors, pipes, pumps and steam turbines that form a solar thermal plant cost less than half than an equivalently powerful array of photovoltaics.

Solar thermal cannot similarly challenge wind turbines on cost (at least not at present). But solar thermal plants can store some of the energy they capture and, as a result, produce a much steadier and more reliable supply of electricity than the famously variable wind turbine.

So why then did we hear so much about solar photovoltaics over the past decade and sol little of solar thermal? Because the latter is inherently utility-scale technology, whereas photovoltaic panels provide value one rooftop at a time. Fred Morse, a solar thermal pioneer and currently senior advisor to renewable energy developer Abengoa Solar, likens it to a bakery operating through the depression. “If you had a bakery and you sold cookies or big wedding cakes, during hard times you could sell a lot of cookies,” says Morse. “PV has little niche markets and it could grow and grow and as the price came down it expanded those markets to where it is today.”

These days, thanks to state and (albeit on-again-off-again) federal incentives and record fuel prices, solar power is back to wedding cakes.

For more, check out “Solar without the Panels”

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