Ahead of the curve

Technology moves fast in the renewable energy sector, and European engineering group SENER manages to demonstrate that single-handedly. The Spanish innovators have achieved a great deal since we spoke to them last at the start of the year, so we caught up with the company to discuss its latest news.

JL: When IRJ last spoke to SENER, you were trialling a prototype of SENERtrough®-2 at the Valle 1 and Valle 2 plants in Spain. What did the trials reveal?

SENER: The trials carried out with the SENERtrough®-2 prototype loop installed at the Valle 2 plant confirmed the performance we expected from this new trough. This prototype loop is equipped with specific devices – flow meters and temperature sensors – that have allowed us to monitor its performance and check its thermal output over a full year, thus covering a wide variety of conditions in terms of incidence of sunlight on the trough.

We also carried out a deflectometry measurement to assess the optical efficiency of the SENERtrough®-2. The results of these trials confirm the completely satisfactory performance of the SENERtrough®-2 prototype, installed at Torresol Energy’s Valle 2 plant, ever since its commissioning in the first quarter of 2012.

This satisfactory operating performance, together with the approval of the manufacturing and assembly processes carried out during the construction of the prototype, allow us to say that the new SENERtrough®-2 has a proven design.

JL: Are there plans to roll out SENERtrough®-2 more widely now?

SENER: Yes, SENERtrough®-2 has already been approved for commercial operation by SGS – a company with extensive and recognised experience in the inspection, verification, testing and certification sector. The assessment of its optical performance was conducted by CSP Services GmbH, a spin-off company from DLR Deutsches Zentrum für Luft- und Raumfahrt, which is a German research centre highly recognised in the field of solar thermal power.
Starting this year, SENERtrough®-2 is part of SENER’s product range and offered as yet another option in solar field technology.

JL: How does SENERtrough®-2 differ to the first SENERtrough®?

SENER: The new SENERtrough®-2 is based on the same SENERtrough® technology, but larger in size than its predecessor. It has been designed to reduce the solar field cost, while maintaining its operational efficiency. The aperture surface of the SENERtrough®-2 is 28% larger than that of the SENERtrough®-1, which enables a reduction in the number of troughs needed to capture the same amount of thermal energy in the solar field. The reduction in the total number of troughs, the optimisation of their basic parameters (aperture, focal distance and length) and the design of its components result in an overall reduction of the solar field cost.

This new development incorporates the knowledge acquired by SENER over the course of more than 20 solar thermal plants.

JL: You were also trialling a prototype single tank for holding both hot and cold molten salts. What did you discover?

SENER: The trials conducted with the single tank proved the feasibility of this new design of the molten salt thermal storage system, which uses a single tank for the simultaneous storage of cold and hot salts, but keeps them separated by a floating barrier that moves naturally along the splitting plane dividing the two volumes of salts (cold and hot).

Many loading and unloading tests have allowed us to check the proper operation of this barrier and its efficiency in the isolation of both volumes of salt, thus validating the proven performance of this new system.

JL: Which other companies have contributed to the development of these technologies?

SENER: As far as the SENERtrough®-2 is concerned, it has been important for us to cooperate with manufacturers of specific solar energy components (such as HCE tubes and mirrors). It is also noteworthy to mention that we have worked in close collaboration with manufacturers producing the main structural components, in order to achieve design optimisation from the manufacturing cost point of view.

Regarding the single tank, it is a development that is essentially focused on finding a solution for concept and design, both developed by SENER. The collaboration with other companies has followed the usual project terms, either as a supplier of existing equipment or as a construction subcontractor.

JL: After a number of years in operation, the Gemasolar plant is still attracting a lot of attention – for example, as a setting in Gran Turismo 6, scheduled for release in December. What is it about the plant that captures peoples’ imaginations?

SENER: Gemasolar is, worldwide, a pioneering plant; it is the first commercial plant to use high-temperature tower receiver technology together with molten salt thermal storage, which allows energy to be produced for 15 hours in the absence of solar radiation. This makes it the only solar power plant in the world capable of producing electricity for 24 uninterrupted hours, which is usually the case in the summer time. This facility is owned by Torresol Energy and was built by SENER, who also supplied all the technology involved and owns 60% of Torresol Energy.

Gemasolar’s many innovations create a lot of excitement, both in the renewable energy field and in other sectors of society. The plant has received numerous awards, including the prize at the 2011 European Business Awards and, recently, the FIDIC [International Federation of Consulting Engineers] Award of Merit, recognising the plant among the world’s best engineering projects of the last 100 years. Besides, several trademarks have shown interest for using it as setting in their advertising, because it is appreciated as an example of pioneering and innovative work.

Gemasolar requires many bespoke technologies – including the panels of the central receiver on which we worked with Fine Tubes in the UK. The central receiver is the main component for this type of thermosolar plant, which is capable of absorbing 95% of radiation in the solar spectrum and transmitting this energy to be stored in the molten salt compound in its interior. We have been working with Fine Tubes for more than four years on developing and producing the corrosion-resistant heat exchanger tubes for the steam generators, as well as the high-performance tubing that make up the receiver of the Gemasolar central tower. The over 140m-high tower houses more than 15km of high-specification seamless tubing designed to hold the 565°C molten salt (nitric salt). Made from the highly corrosion-resistant nickel-chromium alloy 625, the tubing has superior resistance to thermo-mechanical fatigue and creep. The same alloy has also been used for the thicker wall tubing in the high-pressure steam generator units. The service conditions of these components require high quality and reliable products, which were crucial and essential for the successful development of the project.

As a side note, we would like to mention that on the 4 October 2013 it has been two years since the official opening of the Gemasolar plant. During this time, the plant’s operation has exceeded expectations and demonstrated the robustness of SENER’s design – the equipment designed by SENER is achieving the performance expected and demonstrating a much higher degree of automation than other solar thermal plants currently in operation. Another significant figure is the very low number of incidents occurring since the start of production, due in large part to the experience of the operating personnel: the Torresol Operations and Maintenance (Torresol O&M) professionals.

JL: In our last interview, you mentioned Ouarzazate – a solar thermal project in Morocco set to be the biggest plant of its kind in the world. Is it still on track to achieve this accolade?

SENER: Yes, the Ouarzazate solar thermal complex is located on a site with excellent solar and environmental conditions, and will have an installed capacity of 160MW and thermal storage of 3.5 hours. The facility will involve an investment of more than 500 million Euros. The project is currently in progress, with a scheduled construction period of 28 months.

JL: What will SENER’s scope of work on the project involve?

SENER: SENER has a 25% share in the consortium to be responsible for the engineering, construction and commissioning of the plant. In addition, we are in charge of plant engineering in relation to the solar field, the HTF System, the thermal storage system and the power island.

The technology to be implemented in the Moroccan plant includes the SENERtrough® parabolic trough, designed and patented by SENER. The design of the energy storage system using molten salts, which allows electricity to be generated in the absence of solar radiation, will also be our responsibility.

JL: What challenges do you anticipate facing in this project?

SENER: The major challenge of this project is the size of the solar field, because the plant is much larger than the parabolic trough plants that SENER has built so far. It is very important that all project completion conditions are satisfactorily met.

JL: Also in our last interview, you mentioned a plant in South Africa. Are you able to tell me more about it now?

SENER: We are part of the construction consortium awarded the turnkey contract to develop a 50MW solar thermal plant, which complies with the specifications of this South African bid in particular.

Bokpoort will be a parabolic trough plant where SENER’s SENERtrough® technology, in addition to its molten salt storage technology with nine-hour capacity, will be implemented.

South Africa is set to become a country with great opportunities for developing further solar thermal plants, in a relatively short period of time.

JL: What’s next in terms of SENER’s technology development and company progression?

SENER: From our point of view, it’s not about the ‘next’ technology development, but rather the continuous technology development on which SENER has been working for many years in parallel with the SENERtrough®-2 collector and single tank achievements: the development of the central tower salt receiver technology. In this respect, we can now highlight the high-power salt receivers, and a new heliostat shape configuration with more efficient use of land and a lower cost per square metre of mirror aperture surface.

SENER has been working for some time now on both developments, which are intended for tower plants with higher output capacity.

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