Operating Agent: Mark S. Mehos National Renewable Energy Laborator
Nature of Work & Objectives
Task I addresses the design, testing, demonstration, evaluation, and application of concentrating solar power systems, also known as solar thermal electric systems. This includes parabolic troughs, linear Fresnel collectors, power towers and dish/engine systems. Through technology development and market barrier removal, the focus of SolarPACES Task I is enabling the entry of CSP systems into the commercial market place. The component development and research efforts of Task III (see Part 5 of this report) logically feed Task I as new components become parts of new systems. In return, the results of this Task I provide direction to Task III on new component needs.
Organization and structure
The Task I Operating Agent is responsible for organization and reporting of Task I activities. As described in the 2007 annual report for this task, Task I is currently focused on two subtasks, 1) the development and population of an international project database for commercial CSP systems under operation, construction, or development and 2) the development of acceptance test procedures and standards for CSP systems.
Status of the Technology
Concentrating solar power offers the lowest cost option for solar energy today, with expected production costs of less than 20¢/kWh for early commercial plants sited in locations with premium solar resources. Lower costs are expected where additional incentives for CSP systems are available (e.g. the existing U.S. Federal 30% Investment Tax Credit). As the cost of electricity from conventional generation technologies continues to rise, off-takers are becoming increasingly interested in CSP as a viable alternative to other renewable technology options. Concerns over global warming and the increasing likelihood of a global carbon constrained energy market, has further increased this interest.
Concentrating solar power today is represented by four technologies: parabolic troughs, linear Fresnel reflectors, power towers and dish/engine systems. Of these technologies, parabolic troughs, and more recently towers, have been deployed in commercial plants. Nine SEGS plants totaling 354 MW, originally built and operated by LUZ in California in the 1980s and 1990s, are continuing to operate today with performance of most of the plants improving over time. In 2006, two commercial CSP plants began full-scale operation. Acciona, formerly SolarGenix, completed construction of a 64-MW parabolic trough plant near Las Vegas, Nevada. The 64-MW plant was the first new commercial large-scale parabolic trough plant to begin operation in more than 15 years. Abengoa inaugurated PS10, an 11-MW saturated steam central receiver plant located near Sevilla, Spain. Numerous additional plants continued or began construction in 2008 (see below for list of plants in operation or under construction). Andasol One began start up operations near the end of 2008. Several additional plants, including Andasol Two, PS20, Ibersol, and several Abengoa Solnova plants are anticipated to begin operating in 2009. Many other projects are under various stages of development, primarily in Spain, northern Africa, and the southwest U.S. (see project database task for more information on CSP projects in operation, under construction, or under development).
Parabolic troughs are today considered to be fully mature technology, ready for deployment. Early costs for solar-only plants are expected to be in the range of 0.17-0.20 $/kWh in sunny locations where no incentives are offered to reduce costs. In recent years, the five plants at the Kramer Junction site (SEGS III to VII) achieved a 30% reduction in operation and maintenance costs, record annual plant efficiency of 14%, and a daily solar-to-electric efficiency near 20%, as well as peak efficiencies up to 21.5%. Annual and design point efficiencies for the current generation of parabolic trough plants under construction in the U.S. and Spain are expected to be even higher based on the current generation of heat collection elements being furnished to the plants by both Solel and Schott.
Hybrid solar/fossil plants have received much greater attention in recent years, and several Integrated Solar Combined Cycle (ISCC) projects are now under construction in the Mediterranean region and the U.S. New Energy Algeria (NEAL) selected Abengoa to build the first such project at Hassi-R’mel. The project will consist of a 150MW ISCCS with 30 MW solar capacity. A similar project is under construction in Morocco where again Abengoa has been selected to build the plant. Achimede is another example of an ISCCS project, however the plant’s 31,000m2 parabolic trough solar field will be the first to use a molten salt as a heat transfer fluid.
Advanced technologies like Direct Steam Generation (DISS) are under development at the Plataforma Solar de Almeria where researchers continue to compare direct steam, using a combination of sensible heat storage and latent heat storage, with oil based heat transfer fluids. Research on higher temperature heat transfer fluids and lower cost storage systems are also being pursued.
Linear Fresnel systems are conceptually simple, using inexpensive, compact optics, and are being designed to produce saturated or superheated steam. This technology may be suited for integration into combined cycle recovery boilers; i.e., to replace the bled extracted steam in regenerative Rankine power cycles or for saturated steam turbines. Extensive testing experience at a prototype-scale has been underway for several year at the Liddell power station in Australia. Systems are also under development by MAN/SPG (Germany).
Power towers technology, a.k.a. central receiver technology, have completed the proof-of-concept stage of development and, although less mature than parabolic trough technology, are on the verge of commercialization. The most extensive operating experience has been accumulated by several European pilot projects at the Plataforma Solar de Almería in Spain, and the 10-MW Solar One and Solar Two facilities in California.
Construction of PS10, the first commercial power tower, was completed by Solucar at its project site outside of Seville, Spain and has been operating successfully since 2007. The tower system uses a saturated steam receiver to deliver steam to an 11-MW saturated steam turbine. PS20, roughly double the size of PS10, is scheduled to become operational in 2009. Brightsource and ESolar are also developing steam-based receiver designs with the intent of delivering superheated steam at higher temperatures and pressures.
An alternative to steam receiver systems under development by Solucar, Brightsource, and ESolar is the molten salt tower. This approach offers the potential for very low-cost storage that permits dispatch of solar electricity to meet peak demand periods and a high capacity factor (~70%). A molten-salt power tower three times larger than Solar Two is being designed by Sener for southern Spain. This plant, named Germasolar, is a 17-MW molten-salt tower and is projected to start construction in 2010.
Dish/engine systems are modular units typically between 5 and 25 kW in size. Stirling engines have been pursued most frequently, although other power converters like Brayton turbines and concentrated PV arrays have been considered for integration with dish concentrators. The high solar concentration and operating temperatures of dish/Stirling systems has enabled them to achieve world-record solar-to-electric conversion efficiencies of 30%. However, due to the level of development of these technologies, energy costs are about two times higher than those of parabolic troughs. Dish/engine system development is ongoing in Europe and the USA. Reliability improvement is a main thrust of ongoing work, where the deployment and testing of multiple systems enables more rapid progress. Dish/Stirling systems have traditionally targeted high-value remote power markets, but industry is increasingly interested in pursuing the larger, grid-connected markets.
In Europe, Schlaich Bergermann und Partner have extensively tested several 10-kW systems, based on a structural dish and the Solo 161 kinematic Stirling engine at the Plataforma Solar de Almería. Follow-up activities based on the EuroDish design are being pursued by a European Consortium of SBP, Inabensa, CIEMAT, DLR and others. EuroDish prototype demonstration units are currently being operated in Spain, France, Germany, Italy and India.
In the USA, Stirling Energy Systems (SES) is developing a 25-kW dish/Stirling system for utility-scale markets. Six SES dish/Stirling systems are currently being operated as a mini power plant at Sandia National Laboratories’ National Solar Thermal Test Facility in Albuquerque, NM, USA. SES has two power purchase agreements to install 800 MW of these 25-kW systems in California, USA.
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