AZ-TH, 80KWE SOLAR DISH-STIRLING FACILITY

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1 AZ-TH, 80KWE SOLAR DISH-STIRLING FACILITY Rafael Osuna a, Juan Enrile a, Marcelino Sánchez a, Valerio Fernández-Quero a, José Barragán a, Valeriano Ruiz b, Manuel Silva b, Francisco Bas c, Germán López-Lara c, Fernando Fernández-Llebre c. a Solúcar R&D, Sevilla, Spain b Departamento de Ingeniería Energética-Termodinámica, Escuela Superior de Ingenieros, Universidad de Sevilla, Sevilla, Spain c Agencia Andaluza de la Energía. Consejería de Innovación, Ciencia y Empresa. Junta de Andalucía. Ing. José Barragán, Solúcar R&D, Avda. Buhaira 2, E Sevilla, Spain, Tel: ; Fax: ; jose.barragan@solucarrd.abengoa.com Abstract. An initiative to promote a 80kWe dish-stirling facility is being carried out by Solúcar, an Abengoa company working on solar energy, with the support of the Renewable Energies Program of Andalusia Government through the Agencia de Innovación (IDEA), and the Agencia Andaluza de la Energía (AAE). The plant consists of 7 stirling dishes of 11,2kWe unitary power, that will generate 104MWh of electricity in a year, and will sell it to the grid in a commercial basis under the frame of solar thermal renewable energy production regulations in Spain, that consider up to 0,18 /kwh over pool market price for electricity. To achieve the feasibility of the project, a new concentrator based on single spherical 0,5 m2 curved mirrors has been proposed. It has been developed following the schemes of the traditional pedestal/arms heliostats. Foreseen cost for concentrator reaches 450 /m2 when completely installed and in operation. The facility will be installed in the area of PS10 and Sevilla PV plants, in the solar park that Abengoa is promoting in Sanlúcar la Mayor, in order to share maintenance, supervision, vigilance and operation costs with other bigger plants. The operation of the 7 units is foreseen for the end General Overview of the Project It is the objective of the AZ-TH project to build and operate a solar thermal power plant for electricity production of 80 KWe gross power. Based on Dish Stirling technology, this plant will be able to generate around 104 MWh of electricity every year running on a commercial basis. The plant is promoted by Solúcar Energía, S.A. hereafter Solúcar, the head company of the solar business group of Abengoa. Copyright by SolarPACES 1

2 The plant will be placed in Casaquemada (37,2º N and 6,23º W) in the municipality of Sanlúcar la Mayor, 36 kilometres far from Seville. The AZ-TH plant is being built in a free area between Sevilla PV and PS10 plants (Figure 1). PS10 Sevilla PV Figure 1. The AZ-TH emplacement. AZ-TH Solúcar was successful in 2003, - thanks to the support of Agencia de Innovación (IDEA former IFA)-, in applying for a subsidy to the Consejería de Innovación Ciencia y Empresa (CICE) of the Andalusia Government for the grid connection of a small demonstration plant based on dish-stirling technology. The project was finally granted by the Agencia Andaluza the la Energía, (AAE), dependant from CICE. The project is being developed from March 2004 till December [1] Description of the AZ-TH Plant The 80kWe power using dish-stirling technology for the AZ-TH plant is achieved with the installation of 7, -15hp-, generation units. Each of these units consists of a solar concentrator, a cavity receiver, a Stirling engine, and a generator. All these components are mounted in a 2 axis tracking system driven by an electronic control system, in order to focus the sun in every moment during operation. Additionally, the Stirling engine has its own control system integrated in the electric power board for the supervision of alarms, the transmission of signals to control the specific engine functions (valves, operation modes, etc ), and the monitorization of engine variables such as pressure, temperature, power, etc Main characteristics of the AZ-TH project are summarized in the Table 1. Emplacement Sanlúcar la Mayor, (Sevilla), Lat 37,4º, Lon 6,23 Technology Dish-Stirling Gross Electric Power 78,4 kwe, 11,2 kw per Unit (15,0h)p Units 7 Concentrator Area 60 m2 per Unit Focal Length 5 m Reflectivity 94% Receiver Cavity Working Gas Hydrogen Generator 1500 rpm Grid connection 400 V, 50 Hz, 3-phase Land 1 Ha Table 1 Main characteristics of the AZ-TH Project. Copyright by SolarPACES 2

3 Description of the AZ-TH Stirling Concentrator In a first stage, AZ-TH project was intended to be approached with the installation of several Eurodish units for the generation of the 80kWe committed power. However, the relatively high cost of reflector concept in the Eurodish solution made Solúcar to go ahead in the study of a new concentrator. Mainly motivated by the large experience of Solúcar in T type heliostats, a solution considering central drive, pedestal and arms was proposed. In the Figure 2 is showed the Solucar s concentrator. Figure 2. Solúcar T type concentrator Figure 3. Mirrors of the concentrator. Solar Concentrator Solar concentrator designed by Solucar is based in a Spanish technology for manufacturing single spherically curved mirrors with relatively high image quality. The single mirror that has been originally considered is hexagonal shape, about 0,1m2 area each, and a first prototype will be assembled using this topology. Although this, a new version of about 0,5m2 per single mirror is being studied as a final solution for the 7 dishes manufacture. For the selection of this concentrating technology some of the small hexagonal spherical mirrors have been initially manufactured and tested under solar conditions. 20 single mirrors are assembled in a group called facet for the prototype solution. All mirrors in one facet are canted keeping the spherical shape for the set, so the facet keeps the same geometrical optics than the mirror. This solution is adopted to simplify the mirrors integration on the final concentrator solution. In the Figure 4 is showed a single spherical facet and single mirror and in the Figure 5 is displayed a solar image of a single facet on a target placed at focal distance on the top and solar image of a single mirror at the bottom. Copyright by SolarPACES 3

4 Figure 4. Single spherical facet and single mirror. Figure 5. Solar image of a single facet on a target placed at focal distance on the top and solar image of a single mirror at the bottom. The concentrator is composed by 30 facets, including over 600 hexagonal spherical mirrors in the prototype solution. For the final proposal in base to the consideration of 0.5m2 mirrors, the facet is composed by 4 units, and the concentrator in this solution is formed by 30 facets. Tracking System The proposed T concept for the concentrator tracking system allows the consideration of a central drive for the requested elevation and azimuth movements. The elevation drive is a linear actuator. The actuator and the joint are self-aligning to reduce the manufacturing tolerances. The system is driven by an induction motor and a variable frequency drive to allow smoother and more accurate movements. [2] The azimutal drive consists in a planetary gearbox acting on a precompressed large bearing. An additional anti-backlash device reduces the fatigue due to the wind loads. The variable frequency drive and the induction motor allow a smooth and accurate movement. The two axis drive has been developed by Solúcar, and keeps not only tracking accuracy requirements, (0.04 º in azimuth and zenith), but also quick speed requirements in order to defocus when alarm situations avoiding damages in receiver and engine (60º/min). The drive mechanism is finally, a block easy to assemble, to test, to transport and to maintain. The Figure 6 shows design and manufacture of proposed drive system for AZ-TH concentrators. Copyright by SolarPACES 4

5 Figure 6. Drive manufacture Overview for some other Components in AZ-TH Stirling Units Receiver and Stirling Engine The SBP/SOLO V-160/161 solar stirling engine is composed mainly by a receiver, a regenerator and a stirling engine coupled to them. The receiver is a cavity type with a 19 cm aperture. The heat exchanger for solar radiation absorption is placed behind the aperture at the required distance to reduce intensity of solar concentrated radiation flux below the limits. The regenerator is connected to the stirling engine cylinder head, where expansion of the heated gas is produced. [3] The SOLO Stirling 161 is a single acting engine, 90º type with a pressure less crankcase. A Stirling engine is an external combustion engine where the working fluid (hydrogen in this case) in gaseous phase is alternately heated and cooled inside a closed circuit. This engine works with temperatures in the range of 650 ºC achieving an efficiency around 30%. Electric Boards and Engine Control Systems Every concentrator unit is equipped with an electric board that provides power services to the engine. A CC 24 volts power supply source is implemented in this electric board. As valves for hydrogen pressure control are feed with this current. The electric cabinet also includes a microprocessor board (Motion Controller), an operator terminal (alternatively one handheld terminal for all systems), batteries, etc. The AZ-TH plant is supervised by a central computer that is placed in the control room. The central control system is at charge of the operation of all the 7 units. It executes the tracking system commands, the Stirling operation routines, user interfaces, data acquisition and visualization of operational functions for remote control. Energy Production Design Point Performance AZ-TH plant design power is 80kWe. The Table 2 shows a power balance in AZ-TH plant for design operation conditions. Copyright by SolarPACES 5

6 Direct normal irradiance DNI for design power operation has been selected in 875W/m2. This value is high enough to avoid frequent defocusing strategies because of higher energy inputs at Casaquemada site, but allows the plant to work near design conditions during many hours in a year, as direct irradiance values around 850 to 900W/m2 are rather common in the area for central sunny hours. 1 Unit 7 Units DNI [W/m2] 875 Effective Collecting Surface [m2] Power onto Collecting Surface [kwth] Reflectivity [%] 87.00% 87.00% Power reflected to Receiver [kwth] Spillage [%] 95.00% 95.00% Receiver Efficiency [%] 87.25% 87.25% Power to Working Fluid [kwth] Engine Efficiency [%] 33.00% 33.00% Generator Efficiency [%] 95.00% 95.00% Electric Power to the Grid [kw] KW 300 KW 200 KW 100KW Balance of Pow er in the AZ-TH: Seven Dish-Stirling KW η Reflectivity = 87% KW = 82.9% Receiver + spillage η KW Engine + generator =31.4% η Table 2. Design Point Performance. 78,2 KW Solar Radiation Hydrogen St eam Electricity Figure 7. Balance of power in the AZ-TH solar thermal power plant. Each concentrator unit effective reflecting surface is about 56,5m2. Total collecting surface for 7 units is near 400m2. Mean operational reflectivity is evaluated in 87%, as mirrors are 93% reflectivity when clean. (Figure 7). Power sent towards receiver from a concentrator is 43.0kWth, that is, just over 300kWth for the complete 7 units plant. Receiver efficiency including spillage losses is close to 83%. In this sense every unit is sending 35,7kWth towards the working fluid, that is, nearly 250 kwth for the 7 units. Stirling engine efficiency is for the selected working fluid temperature and pressure evaluated in 33% for design conditions operation. This figure allows a 27.35% efficiency for the receiver-engine-generator set. Final power for every unit reaches 11.2kWe, with overall efficiency of 22.6% from concentrated solar thermal radiation to electricity. The complete plant is sending 78,2kWe to the grid. [4] Annual Balance Performance The annual energy production estimations for the AZ-TH plant are presented as a breakdown in the Table 3. Main considerations to take into account for the annual basis estimations are related to efficiency reductions because of Off Design conditions. Copyright by SolarPACES 6

7 1 Unit 7 Units Yearly DNH [kwh/m 2 ] 2012 Yearly Usable DNI [kwh/m 2 ] 1700 Collecting Surface [m 2 ] Energy onto Collecting Surface [MWh th ] Mean Annual Reflectivity [%] 87.00% 87% Energy reflected to Receiver [MWh th ] Mean Annual Spillage [%] 92.5% 92.5% Mean Annual Receiver Efficiency [%] 80.00% 80.00% Energy to Working Fluid [MWh th ] Mean Annual Engine Efficiency [%] 28.00% 28.00% Mean Annual Generator Efficiency [%] 95.00% 95.00% Mean Annual Operation Efficiency [%] 90.00% 90.00% Electric Energy to the Grid [MWh] Table 3 Annual energy production breakdown in the AZ-TH solar termal power plant Final electricity annually generated by every unit reaches nearly kWhe, with overall efficiency of 15,4% from concentrated solar thermal radiation to electricity in annual basis, what is undoubtfully a quite promising starting value for future plants. The complete plant is sending over kWhe to the grid, that are sold at solar tariff of 0,18 /kwh + electric pool value (about 0,04 /kwh for solar hours) to the distribution company, to achieve incomes over per year. Current Status, Development of in Site Erection Tasks, Planning for Future Activities Several activities are being developed nowadays regarding the erection and construction of the plant. In this sense, all the three main subsystems of the plant (tracking system, reflectors, and Stirling units) are under manufacture and assembly. Solar trackers pedestals have been installed in site as it can be identified in the Figure 8. Installation of some pedestals Figure 9.Current status of the AZ-TH Plant Drives are ready for installation, and structures have been also manufactured and delivered. Copyright by SolarPACES 7

8 Figure 10.Drives Figure 11. Structures Stirling engines will be delivered between June and September. Tests will begin in November and the plant will be finished at the end of Acknowledgements AZ-TH project is being subsidized by Junta de Andalucía, Consejería de Innovación Ciencia y Empresa, through its initiative for Clean Renewable and Energetic Efficiency Program. References 1. Osuna R., Fernández V., Romero, S., Romero, M, Sanchez, M., PS10: A 11.0-MW Solar Tower Power Plant with Saturated Steam Receiver. 2. Enrile, J., Cerón, F., Valera, P., and Osuna, R. Prothelios: Heliostat for large PV plant. 3. Schlaich Bergermann und Partner GbR. EuroDish Stirling. System Description. A new decentralised Solar Power Technology. Stuttgart, June Design news. Sun Rises on Solar. High-efficiency Stirling engines key to energy conversion. January p Ministerio de Educación y Ciencia, Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas, Plataforma Solar de Almería. Informe Anual Plataforma Solar de Almería, p Copyright by SolarPACES 8

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