In today’s aggressive solar market, CSP parabolic trough innovations that increase parabolic trough plants’ operating efficiency are vital. Some innovations already promise to cut costs by up to 65%, according to the latest CSP Parabolic Trough Report: Cost and Performance now available is Spanish.
So which are the most promising innovations out there, and which of these will prove most bankable?
“Direct steam generation, compressed gas as a heat transfer fluid, advanced storage systems, large aperture troughs, and molten salt receivers” hold considerable allure according to the report, which provides up-to-the-minute information and detailed analysis of the most exciting novel alternatives and groundbreaking parabolic trough innovations that promise to put CSP back in the game.
Alternative HTF’s must prove their worth
Archimede Solar, using technology licenced from Italian research center ENEA, was built as the first pilot to use molten salt as heat transfer fluid (HTF) in a parabolic trough solar field. It came online in the summer of 2010.
There are multiple advantages of replacing traditional HTFs such as mineral or synthetic oil, with molten salts. “Its thermal properties enable the solar field to be operated at temperatures of up to 550ºC, making it possible to use more efficient, standardised steam turbines”, explains Carlos Marquez-Salazar, the report’s author.
Another benefit of using molten salt as the HTF in the solar field is that it eliminates the need for expensive heat exchangers. The molten salt medium has already proven to be a preferred choice for thermal energy storage for concentrating solar plants.
Other alternative HTFs highlighted in the report include compressed air and pressurized gas. “A key advantage of this approach is that it enables plants to operate at the high temperatures (around 1000oC / 1832oF) of today's most advanced power generation cycles, such as Brayton or supercritical Rankine”, explains Salazar.
However, there are tradeoffs, warns the report, which provides detailed analysis of the direct impact on cost and performance in Parabolic Trough technology. Much thicker walled piping must be used due to the need for increased pressure. In a parabolic trough plant where there are literally miles of HTF piping, that thicker piping presents a huge cost increase over the traditional piping used.
Direct steam generation (DSG) in parabolic trough plants is yet another novel concept singled out by the report. However, DSG’s main strengths have yet to be demonstrated. A Spanish consortium comprising CIEMAT, IDAE, and Iberdrola, aims to build a 3MW plant in the municipality of Puertollano, Spain, by 2012.
Thermal storage the keystone
Thermal storage is commonly cited as being the lynchpin to CSP’s competitiveness in global energy markets. As the report notes, molten salt storage methods are evolving, with single-tank thermocline storage set to rival the two-tank systems.
Single-tank systems using molten salt can significantly lower the cost of storage by replacing some of the salt with a low-cost quartzite rock and sand filler. According to the report, it can reduce the molten salt requirement to as little as 30 percent of the storage medium, driving down costs by as much as 65%.
Meanwhile, a host of other alternative novel storage mediums are currently being tested. The fully updated CSP Parabolic Trough Costs and Performance Report provides a comprehensive overview and analysis of novel parabolic trough and storage solutions currently being demonstrated.
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