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Linear-focusing Concentrator Facilities: DCS, DISS, EUROTROUGH and LS3

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The PSA has several parabolic-trough solar collector facilities. Some of them, such as the SSPS-DCS, were pioneers in Europe, while other more modern facilities, such as the DISS loop, are unique worldwide and place the PSA in a privileged position for research and development of new parabolic-trough collector applications. The main characteristics of these facilities are briefly explained below.

The DISS test loop

This facility was erected and put into operation in 1998 for experimenting with direct generation of high-pressure high-temperature (100 bar/400ºC) steam in the parabolic-trough collector absorber tubes. The DISS loop is the only facility in the world where two-phase flow (water/steam) processes in parabolic trough collectors can be studied under real solar conditions. It is very appropriate not only for the study and development of con-trol schemes, but also for the study and optimization of operating procedures, that must be implemented in direct steam generation solar fields.

The DISS loop consists of two subsystems: the Solar Field of parabolic-trough collectors, and the Power Block. In the solar field, the feed water is preheated, evaporated and con-verted into superheated steam as it is circulated through the absorber tubes of a 550 m long row of parabolic trough collectors having a total solar collecting surface of 2,750 m2. The facility can produce 0.8 kg/s of 100 bar 370ºC steam.

The Power Block is where the superheated steam generated in the solar field is con-densed, processed and reused again as feed water for the solar field (closed-circuit op-eration).

Facility operation is highly flexible and can work at three different pressure levels: 30, 60 and 100 bar and in any of the three basic direct steam generation modes: Recirculation, Injection and Once-Through, or any combination thereof. Furthermore, it is provided with a complete range of instruments that allows thorough system monitoring and evaluation.

The figure below shows a simplified diagram of the DISS loop in which the solar field is shown as one row of 11 parabolic-trough collectors with north-south-oriented rotating axes. Nine collectors are composed of 4 reflective parabolic-trough modules, while two collectors (nos. 9 and 10) have only 2 modules. Each module is 12 m long by 5.7 m wide. The solar field consists of two parts, the evaporating section and the superheating section. At the end of the evaporating section there is a recirculation pump and a water/steam separator which augments the operative flexibility of the system.

Simplified diagram of the PSA DISS loop.

The Power Block consists of water/steam separators, condensers, chemical-dosing sys-tem, preheaters, degasifier and water pumps.

One of the most important characteristics of the DISS loop is the possibility of measuring the thermal gradient in the cross sections of the solar collector absorber tubes.

View of the DISS solar field in operation

The LS-3 (HTF) test loop

The LS-3 test loop, also called the HTF test loop, which was erected in 1997, is an ideal facility for evaluating parabolic-trough collector components under real solar energy op-erating conditions. Mirrors, absorber tubes, solar tracking systems, etc., can be installed and evaluated on this system, which is provided with the appropriate measurement and monitoring instrumentation.

The facility consists of a thermal oil circuit connected in a closed loop to a solar collec-tor made up of four 12 m-long by 5.7 m-wide LS-3 parabolic-trough modules with a total collecting surface of 272.5 m2. The thermal oil used in this facility (Syltherm 800) has a maxi-mum working temperature of 400ºC, and a freezing point of –40ºC. The rotating axis of the solar collector is oriented east west, which increases the number of hours per year in which the angle of incidence of the solar radiation is less than 5º.

The facility’s oil circuit, which has a maximum working pressure of 16 bar, is made up of the following elements:

  • 1-m3-capacity oil expansion tank, with automatic nitrogen inertization system
  • Oil circuit sump tank
  • Mechanical draft oil cooler, with air speed control and 225-kW maximum cooling.
  • Centrifugal oil pump, with a flow rate of 0 – 2,8 liters per second
  • 40 kW, 3 x 380 V electrical oil heater.

General view of the LS-3 test loop

SSPS-DCS plant with solar desalination system

This 1.2 MWt-capacity facility consists of four main subsystems, as shown in the diagram below:

  • A solar field made up of 40 ACUREX 3001 parabolic-trough collectors in 10 parallel rows of 4 collectors connected in series. Its total solar collecting surface is 2,672 m2 and the rotating axis of the collectors is oriented east west. The fluid used by this col-lector field is Santotherm 55 oil, which has a maximum working temperature of 300ºC. The collector absorber tubes are not evacuated and have a black chrome selective coating. This solar field has an overall performance of 50%, with peak power of 1.3 MWt for direct solar radiation of 950 W/m2. The average daily thermal energy deliv-ered is 6.5 MWt.

General diagram of the SSPS-DCS plant

  • A 5 MWht-capacity thermal storage system consisting of a 140 m3 thermocline oil tank for charging/discharging temperatures of 295º/25ºC with automatic fire-extinguishing system, automatic venting valves and volatile-condensing system. It also has a water-cooled oil cooler for quick cooling during transient testing.
  • A 500 kWe water/steam Rankine cycle electricity generating system consisting of a steam generator fed by the hot oil delivered by the solar field and/or storage tank; degasifier; steam turbine; electric generator and mechanical draft closed-loop cool-ing tower.
  • The MED desalination plant, called the SOL-14, consists of a 14-stage multi-effect distil-lation plant, which is connected to the thermal storage system described above. For a nominal production of 3 m³/h distillate, plant consumption is 190 kWt, with an effi-ciency factor (number of kg of distillate produced for every 2,300 kJ of energy con-sumed) over 9. The saline concentration of the distillate is around 50 ppm. The nomi-nal temperature gradient between the first and last stages is 40ºC, with an operating temperature of 70ºC in the first stage. The vacuum system, which is made up of hydroejectors fed by 3 bar seawater, is used to evacuate the air from the unit at startup and to compensate for any small amounts of air and gas liberated from the feed water, as well as any slight losses that might be produced in the various connections.

    Capacity: 3 m3/hour
    Number of effects: 14
    Feed water: Seawater (35,000 ppm)
    Product: Distillate (£50 ppm)
    Recovery Factor: 38%
    Feedwater flow rate: 8 m3/hora
    Thermal consumption (FR): 63 kWh/m3 (>9)
    Electricity Consumption: 3 kWh/m3
    Solar field capacity: 1.2 MWp
    Solar field performance: 50%
    Collector surface: 2762 m2
    Type of collectors: ACUREX 3001 (CCP)
    Storage: 5 MWh (Therminol 55)
    Maximum oil temperature: 300ºC

Technical specifications of the PSA SOL-14 solar desalination plant and aerial view with ACUREX field in foreground, ther-mal storage tank at upper left and MED upper right

There is also a double-effect absorption heat pump, which represents the first real pro-totype of a device of its kind for this application. The connection of this device increases the performance ratio of the MED plant to 20 thanks to condenser heat loss recovery.

Descripción de las Instalaciones General Description of the PSA    
Proyección Europea Central Receiver Facilities : CESA-1 and CRS Linear-focusing Concentrator Facilities: DCS, DISS, EUROTROUGH and LS3 Centro Docente
Historia de la PSA Dish-Stirling Systems: DISTAL and EURODISH The Solar Furnace La PSA en el Congreso de los Diputados
Historia de la PSA Solar Chemical Facilities Other Facilities La PSA en el Congreso de los Diputados


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