Andasol III

Andasol III · Project Sheet

  • TEMPORARY JOINT VENTURE: RwE, Solar Millennium, Ferrostaal, Swm y Rheinenergie
  • PROMOTER: Solar Millenium, Duro Felguera
  • CSP TECHNOLOGY: Parabolic trough collector CSP, oils (HTF) and steam.
  • LOCATION: Calahorra (Granada-Spain).
  • 2 engineers and 30 fitters
  • 18 km of mineral insulation heating cable
  • 50 active circuits in oils (HTF)
  • 35 active circuits in steam (BOP)
  • 164 active circuits in oils (HTF)
  • 125 active circuits in molten salts (TES)
  • Over 1,500 control i/o


Andasol is the first solar thermal complex in the world with heat storage. Andasol, formed by Andasol 1, Andasol I and Andasol II, is located in the Guadix Region in the municipality of Aldeire and La Calahorra, in the province of Granada, Spain. Andasol I, Andasol II and Andasol III, each with 50 MW, have been built on one of the highest and largest plateaus in the Iberian Peninsula (the average height is 1100 m). Thanks to this height it has one of the best direct solar radiation resources in Spain.

Its location near to a 400 kV high voltage line, the availability of water for cooling from the northern slopes of the Sierra Nevada, the nearby road and railway infrastructures and the availability of flat land not protected for environmental reasons, makes it the perfect enclave for the implementation of the solar thermal project.

The most important characteristics are that Andasol III has included better techniques than the two previous ones, which have make it possible to reduce its construction costs, as it uses less land surface, and therefore, less surface of parabolic trough collectors. This optimises its production and efficiency in the electricity production process (from 38.5% of turbines efficiency to 41.2%).

  • Rated electrical power: 50 MW
  • Total electricity production: 170 GWh/year
  • Salt accumulator capable of operating at full capacity for 7.5 hours, 640 solar collectors, each with a length of 150 m
  • 500,000 m² of mirror surface
  • Thermal oil system that includes main and auxiliary pumping installations, tanks, oil boilers and steam generation equipment.
  • Water-stream cycle auxiliary installations (BOP)

The Andasol Temporary Joint Venture has been in charge of the design and construction of the plant and will also manage its operation. The Temporary Joint Venture is made up of Duro Felguera Energía, Ferrostaal, Solar Millennium and Flagsol.

The Andasol III plant has almost 205,000 parabolic mirrors that capture sunlight. These huge curved mirrors concentrate the heat and transmit it to a heat transfer fluid. Using heat exchangers, the energy is taken to a steam circuit that activates the power generating turbine.

With the integration of a heat storage device, the power generated during the day can be made available to the grid according to the planning. The accumulator contains up to 30,000 tonnes of a special salt compound and has a storage capacity of over seven hours. This allows Andasol III to continue to generate electricity reliably and power the electricity network even at night. Thus, as a whole, the plants can supply electricity, annually, to around half a million people, preventing the emission of 450,000 tonnes of carbon dioxide.

The relevant factor this project has provided is that it is the first thermo-solar project in which a scale prototype has been included, the storage of cold and hot salts in the same tank, called "single-tank". A Research and Development Project headed by the Engineering Firm SENER in which AKO has participated adapting its AKOTRACE® solution to the new requirements of this innovation, demonstrating its high degree of involvement in new technologies, its application in thermoelectric energy and investment in the R&D&i area to be able to prepare studies, field tests and to be able to make technological progress in this type of facilities.

Project Challenge

Technical requirements, although already largely resolved by AKO in the dozens of projects implemented in solar thermal power plants with parabolic trough technology.

  • Maximum operating and process temperatures of the materials in this type of plants with a risk of fire and explosion. In this case, in the circulation of HTF oil, water and salts (BOP) where the maximum maintenance temperatures range from 260-300 ºC
  • Tracing of critical points such as valves, pump heads and vertical pipelines, providing in the first case, a specific and improved solution to the one used up to date.
  • The scope and capacity of AKO 's management in a 50 MW solar thermal power plant, applying its extensive knowledge, experience, guarantee of efficiency and profitability. As done before with its predecessors, Andasol I and Andasol II.

AKOTRACE® Solution

The scope of the AKO solution has been the execution of the electrical heat-tracing system, AKOTRACE® for the three installations. This project involves AKO in the Solar Thermal Power Plant with the highest production in Europe, consolidating the AKOTRACE® solution as the world leader in the electrical-heat tracing sector. AKO's Innovation Director, Miguel Angel González, referring to this project:"In this project we have improved the control strategies, improving coordination aspects between regulation of the trace circuits to even out the power consumption of the heat-tracing system and we have introduced higher alarm levels to increase the installations safety".

In the AKOTRACE® solution, it is worth mentioning that we have chosen different key technical characteristics for this project:

  • Mineral insulating cable for the Salt and HTF area and constant, self-adjusting and mineral insulated power for the BOP area and low exposure (80 ºC)
  • PT100 probes applied in the entire installation
  • Additional safety temperature control protections
  • Specific design of heaters for singular points in the safety valves of the salt tanks, as a temp. of 290 ºC has to be maintained to guarantee that the valves operate correctly.
  • Installation of AKODUO Control Trace PLC's in the TES area basically made up of a salt circuit that runs between the hot and cold salts tank
  • Connectivity with the DCS in the TES area
  • Operator interface displays in the plant for quick identification of the system's status.


AKO started the Andasol I and Andasol II Solar Thermal Power Plant project and continued with the same good results obtained in the implementation of the AKOTRACE® solution in Andasol III:

  • Assurance of the criticality of the system with an efficient investment, guaranteeing the circulation of the fluid at high temperatures, to prevent undesired Plant shutdowns or a loss of performance in its operation
  • Increase of the application of the AKOTRACE® solution in HTF, BOP and TES circuits; unlike its predecessors, Andasol I and Andasol II, plants where the solution was only applied in the HTF and BOP circuits
  • Strict compliance of safety, health and hygiene standards
  • Specialised training of the plant's staff on the correct operation of the tracing system and its installation.
  • Perfect control of the behaviour of each circuit thanks to the management and monitoring software (included in the AKOTRACE® system) that manages the operating data of the heat-tracing control system guaranteeing the detection and solution of anomalies in the plant at all times

The execution of this project complements the experience and knowledge acquired by AKO throughout its over 30 years of experience, which has positioned it as the world leader, committed to renewable energy future technologies in CSP parabolic trough and concentration tower Solar Thermal Power Plant Projects.

About AKO

Over 30 years of innovation and with 130 people team of in-house professionals AKO Electromecànica, S.A.L. is a Spanish company leader in the Regulation and Control of Temperature with Electrical Heat Tracing Solutions for Concentrated Solar Power Plants (CSP), that offers comprehensive support from project design and manufacturing, to technical assistance, to the System commissioning (turnkey projects) and after-sales service. Electrical Heat Tracing System AKOTRACE® based the heating cable technology, providing advantages and savings on energy and the overall cost of the installation, with a reliable and secure management, ensuring the health, safety and respect for the environment.

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