Operating Agent: Mark S. Mehos National Renewable Energy Laboratory
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. Additional subtasks will be implemented as the needs are raised by the Task I membership and approved by the SolarPACES Executive Committee.
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 (see http://www.solarpaces.org/News/Projects/projects.htm for additional information on CSP plants that are operational, under construction, or under development).
Parabolic troughs are today considered to be fully mature technology, ready for deployment. Early un-incentivized 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 in operation in the U.S. and Spain have 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. (see http://www.nrel.gov/csp/solarpaces/parabolic_trough.cfm for additional information on hybrid ISCCS CSP plants that are operational, under construction, or under development).
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. Linear Fresnel systems have the potential for a lower upfront capital cost than systems based on parabolic mirrors because they use flat rather than deeply curved mirrors, and the mirrors are located close to the ground giving them a lower wind profile. However, linear Fresnel systems have lower operating efficiencies than parabolic trough systems. Operational experience from operational linear Fresnel is necessary before it becomes clear whether the lower upfront capital cost will outweigh the lower operational efficiency.
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.
Construction of PS10, the first commercial power tower, was completed by Abengoa 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 became operational in 2009. Several other companies are similarly developing steam-based receiver designs with the added intention of delivering superheated steam at higher temperatures and pressures.
An alternative to steam receiver systems under development by 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%). Molten-salt power tower are now under construction or under development (see http://www.nrel.gov/csp/solarpaces/power_tower.cfm for additional information on central receiver plants that are operational, under construction, or under development). .
Dish/engine systems are modular units typically between 3 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%. 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. Numerous dish/engine projects are under development, primarily in the U.S. (see http://www.nrel.gov/csp/solarpaces/dish_engine.cfm for additional information on dish/engine plants that are operational, under construction, or under development).
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Modeling guidelines
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