Task I: Solar Thermal Electric Systems

Operating Agent: Mark S. Mehos
National Renewable Energy Laboratory

Task I addresses the design, testing, demonstration, evalua-tion, 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.  These are separated into sub sectors, as designated by the Operating Agent and approved by the Executive Committee.  Each sector is coordinated by a Sector Leader who is appointed by the Operating Agent and is responsible for coordinating activities within his Sector. Current Sectors are:

• Central Generation Systems: includes technology activities primarily associated with large-scale parabolic trough, linear Fresnel and power tower systems.  This sector is currently led by Mark Mehos of the National Renewable Energy laboratory in the USA.

• Distributed Generation Systems: includes technological activities associated with dish/engine, and other systems capable of providing power on a distributed basis like mini-towers and modular schemes for troughs and Fresnel collectors. The Australian CSIRO currently leads this sector.

• CSP Market Development: includes activities addressing financial, regulatory, environmental, marketing, dissemination and other largely non-technical issues.  Task 1.3 focuses on identifying, tracking, and facilitating entry into emerging markets by the worldwide Concentrating Solar Power industry.  Sandia National Laboratories, USA, leads this sector.

Task activities are cost-shared, task-shared (either through SolarPACES or between SolarPACES participants), and/or information-shared.  Cost-sharing and task-sharing activities involve cooperative efforts involving two or more participants where either the cost of the activities or responsibilities are mutually agreed and shared. Information sharing is used for the exchange and discussion of results of projects carried out independently by Participants, but whose results are of interest to all.

Creation of a Task activity is based on the request of one or more of the participants and must be approved by the OA.  Each activity has a lead individual designated by the Participants involved in the activity. The lead individual is responsible for coordinating the SolarPACES involvement, as well as regular reporting to the Task I OA.

Deliverables: The OA is responsible for general Task I reporting, including preparation of input to the IEA/SolarPACES Annual Report, and for maintaining a Program of Work describing ongoing and anticipated activities. Participants are responsible for detailed reporting on their respective activities. General reports (not containing proprietary information) are available to all Task participants, although the Participants in an activity may, at their option, limit the distribution of proprietary information. The activity lead is responsible for providing information to the OA for general reporting requirements. The OA is responsible for organizing one to two Task meetings per year to discuss activity status and progress. 

Task I Program of Work in 2006

As summarized in Table 3.1 , Task I activities are organized by Sector. The focus of our efforts is on the testing of integrated CSP systems and support of commercial deployment projects. Activities listed in the table below (with contact person) are currently part of our Program of Work. In the sharing column, “I” refers to information sharing; “M” to task sharing by member countries; “T” to task sharing through SolarPACES; and “C” to cost sharing.

Concentrating solar power today is basically represented by four technologies: parabolic troughs, linear Fresnel reflectors, power towers and dish/engine systems. Of these technologies, only parabolic troughs 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.  At the end of 2005 SolarGenix completed construction of a 1 MW parabolic trough plant for Arizona Public Service, the first new commercial CSP plant to begin operation in more than 15 years.  Three additional CSP plants are currently under construction, PS10 and Andasol One in Spain, and Nevada Solar One in the U.S.  PS10, a 10 MW saturated steam central receiver plant, and Nevada Solar One, a 64 MW parabolic trough plant, are expected to begin generating power in 2007. Andasol One, a 50 MW parabolic trough plant with 6 hours of thermal storage, is expected begin operating in 2008.  Numerous other projects, described later in this report, are expected to begin construction in 2007.  Many other projects are under various stages of development, primarily in Spain, northern Africa, and the southwest U. S.

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 with lower costs 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.

The Chapter dealing with solar thermal power plants by Becker et al. in “The future for Renewable Energy 2: Prospects and Directions” edited by the EUREC Agency in 2002 (See reference [3.05]), provides a thorough, up-to-date summary of the status of the technology, a look at the road to the future, market inroads, and goals for RD&D, as seen from the standpoint of selected experts of the SolarPACES community.   Chapter 6 of Volume 16 of the American Solar Energy Society (ASES) Advances in Solar Energy, written by Price and Kearney [3.06] provides a comprehensive discussion of the current status and future cost reductions related to parabolic trough technology. 

Parabolic troughs are today considered to be a 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.  Several commercial trough projects are being pursued in Spain, the first one under construction is the 50‑MW Andasol project that will use EUROTrough collectors and will have a 6-hour molten-salt heat storage system.  Construction of the Andasol project near Granada began in 2006, with commissioning planned for 2008.

In the United States two commercial parabolic trough power plant projects are underway. The first is a 1‑MW organic-rankine-cycle plant built by SolarGenix for Arizona Public Service. An organic Rankine cycle operates at lower temperature and efficiency than a steam-Rankine cycle and, potentially, will require lower operating and maintenance staffing.  Construction was completed in December of 2005 and the plant startup started in January of 2006.  SolarGenix is also nearing completion of a 64‑MW trough project (conventional hot oil with a Rankine cycle power block) in Boulder City, Nevada (near Las Vegas) with operation scheduled for Spring of 2007.

Several options for hybrid solar/fossil plants exist. The integrated solar combined-cycle system (ISCCS) using trough technology has received much attention the past few years. Its advantage is lower solar electricity cost and risk in the near term, but this design’s small annual solar fraction of about 10% is a concern to some [3.28].  New Energy Algeria (NEAL) selected Abener to build the first such project at Hassi-R’mel.  The project will consist of a 150‑MW ISCCS with 30 MW solar capacity.  Similar project are under consideration in Egypt, Mexico, Morocco, and India. 

Advanced technologies like Direct Steam Generation (DISS) are under development at the Plataforma Solar de Almería where research continues 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 [3.17] are also being pursued.

Linear Fresnel systems are conceptually simple, using inexpensive, compact optics, and are being designed to produce saturated steam at 150-360 C with less than 1 Ha/MW land use. 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. The most extensive testing experience at a prototype-scale is underway at the Liddell power station in Australia with very compact designs using multi-tower aiming of mirror facets. The first large proof-of-concept facility will be a commercial project started by the Solar Heat & Power Company, now Ausra, to integrate 36 MW of solar into an existing coal-fired power plant.  In this hybrid plant, the 132,500‑m² reflector field will supply 270°C heat to replace bled steam in the regenerative feed water heaters of the Rankine power cycle.  Late in 2006, a 300‑m-long array (5 MW_th delivery) was installed at the site.  This is the first of three such arrays planned for this project stage.  Connection to the Liddell plant is expected in 2007.

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. After continuous technology improvement, CRS technology is predicted to reach efficiencies of 23% at design point and 20% annual performance.

Construction of PS10, the first commercial power tower, was completed by Solucar at its project site outside of Sevilla, Spain. The tower system uses a saturated steam receiver, producing 40 bar/250ºC saturated steam to power a 10‑MW saturated steam turbine. For cloud transients, the plant incorporates a thermal-oil storage system with a 20-MWh thermal capacity (1/2 hour at 70% load).

A likely more cost effective alternative to the saturated steam system developed for PS10 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 is projected to achieve energy costs similar to trough technology, but with higher investment risk.  Larger increases in plant size are projected to reduce energy costs significantly, achieving costs below that of advanced trough technology.  Solar Tres, a 17‑‑MW molten-salt tower under development by Sener, is projected to start construction late in 2007.  Another 100‑MW molten-salt plant is also under consideration in South Africa.

The use of volumetric air receivers for efficient integration into gas turbine cycles has been promoted in Europe and Israel using either open or closed loops, intermediate storage, and hybridization approaches in the SOLGATE, SOLAIR and Consolar pilot projects, but a commercial project is not yet underway.

Dish/engine systems are modular units typically between 5 and 25 kW unit size. Stirling engines have been used 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 their level of development, energy costs are about twice as high as those of parabolic troughs  REF _Ref68253757 \r \h [3.05]. 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. The EnviroDish project aims to transfer the former Eurodish system into small series production and deploy systems around the world. 

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 units in California, USA.

Participation and National Contributions

Task I is open to all IEA/SolarPACES member.  Participation requires active involvement in an appropriate activity as described by the scope of Task I.  Currently, all SolarPACES member countries except Switzerland participate in Task I.

Cooperation with Industry

Industry involvement is key to the system-level nature of Task I activities.  Involvement can take forms ranging from a self-funded project lead to contractor status.  Current participants are listed alphabetically by country in  REF _Ref34627944 \r \p \h below.