Other solar thermal designs, like solar towers, are also gaining traction. This is where sun-tracking mirrors, called heliostats, focus light on a central tower. "Troughs are a tried and true technology, but you also have these new central receiver plants that achieve higher temperatures and, in theory, lower costs," said Mark Mehos the CSP program manager at NREL.
The Ivanpah Solar Electric Generating Station near the California-Nevada border is one such design. The 377-megawatt plant will use 170,000 heliostats and power 140,000 homes. When it comes online in October, it will double solar thermal production capacity in the United States. The project received a $1.6 billion loan guarantee from DOE.
Spain, Italy and Saudi Arabia gearing up
Compared to photovoltaic plants, CSP generators require sunshine that is more reliable, so they are limited geographically to sun-soaked locales. Photovoltaic panels are also modular, so developers can construct plants faster. However, mirrors are more durable than panels and do not degrade over time. As these plants get larger, power variability becomes a greater concern with photovoltaics but not with CSP.
On the back end, solar thermal plants have more in common with coal- and gas-fired generators than with photovoltaic farms. Thermal plants, both renewable and fossil-fueled, generally use the Rankine Cycle to produce electricity. This is where a heat source heats steam in a closed loop that spins a turbine to generate electricity. The steam then condenses and recirculates.
However, solar thermal systems, because of their high temperatures, could also use a power block driven by supercritical carbon dioxide, according to Gleckman. These turbines use a Brayton Cycle, which is similar to how jet engines work, except the turbines use a hot liquid -- in this case, carbon dioxide -- instead of air. This power block would use 30 times less space than Rankine turbines, substantially cutting materials and maintenance costs.
"If you could use a different way of producing the electricity that is less expensive, then you have a potentially disruptive approach," Gleckman said. "It's very challenging to come to cost parity [with fossil fuels] without doing things on the power block cycle."
Despite their steady performance, Mehos said, solar thermal plants would likely serve on the grid to absorb demand surges rather than provide baseload power. "In today's market, my belief is, really, there is no market for baseload CSP systems. The value of that energy in non-peak or shoulder times is low," he said. Part of the reason is that grid operators do not generally price energy storage, but CSP developers are trying to change that.
Many other countries are also developing CSP plants. Spain leads the way, with more than three dozen running or under construction.
"The two biggest markets are expected to be India and Saudi Arabia," said Gleckman, pointing out that Saudi Arabia wants to move away from burning oil for electricity so it can sell the oil instead, while India wants low-carbon energy to power its development.
Reprinted from Climatewire with permission from Environment & Energy Publishing, LLC. www.eenews.net, 202-628-6500