By Granada Hernández Pacheco

The Plataforma Solar of Almería (PSA-CIEMAT) has held the DUKE Project facility (Durchlaufkonzept – Entwicklung und Erprobung, in English, the “once-through” concept – Development and Demonstration) since June last year. The launch of this new infrastructure is in response to the need for further research into the technology of Direct Steam Generation (DSG) for solar power plants with parabolic trough solar collectors, using the "once-through" operating mode.

This project is the result of long term collaboration between CIEMAT and the German Aerospace Agency (DLR) in the area of concentrating solar systems fields - and in particular in DSG technology.

CSP Today interviewed Dr. Eduardo Zarza, the man responsible for concentrating solar systems at CIEMAT, for whom DSG technology is a very viable option to lower the cost of electricity produced by thermal power plants with parabolic trough collectors. In fact, several studies have shown that up to 10% reduction can be achieved, but to accomplish this, it is necessary to investigate those technical issues that are still outstanding such as the availability of a suitable heat storage system.

CSP Today: What are the advantages of DSG compared to other technologies?
Eduardo Zarza: DSG can replace the thermal oil that is currently used in parabolic troughs with water. This replacement eliminates the risks associated with the use of thermal oil. Another advantage is that it simplifies the overall configuration of the CSP plant, eliminating the need for heat exchanger oil/water to produce steam for the turbine.

CT: Is this technology already in use in any commercial plant? If this is not the case, when will it be applied?
EZ: DSG is installed at a commercial level only on a 5 MW solar power plant in Thailand. But this plant uses the operating mode “recirculation”, while the DUKE Project will study the technical and commercial feasibility under the “once-through” operating mode - which simplifies the configuration of the solar field and reduces the investment cost of the plant, resulting in a lower cost of electricity. “Once-through” carries some significant technological challenges, especially the control of steam parameters in the plant output when solar irradiation is interrupted. These challenges need to be studied to find a viable commercial response.

CT: What is the status of this technology in the world?
EZ: As I mentioned in the previous question, there is only one commercial CSP plant of DSG in the world, which has a nominal output of 5 MW and is located in Thailand. The DUKE project will last a couple of years, so until the project is not finished you cannot think about implementing 'once-through' technology on a commercial level. Although there are currently no concrete plans to install the technology in new thermal power plants, the path for commercial use will be clear if the results obtained in the DUKE project are positive.

CT: How has the collaboration with the DLR been?
EZ: The collaboration between CIEMAT and DLR in the field of DSG technology started in 1994 and has been very fruitful. This collaboration has placed both entities at the forefront of DSG technology, currently being undisputed world leaders.

CT: Once the project is completed in 2014, what technological challenges or work will continue to be tackled by the DLR and CIEMAT?
EZ: We are already talking about the possibility of joint projects on new thermal storage systems for DSG, as thermal storage systems for DSG solar fields must meet certain special requirements that make them different to storage systems used in existing plants.
We are also talking about the possible installation of a second row of the current solar pilot plant at DUKE and the connection of the DSG solar field to a turbo-group to check the operation of DSG multi-solar fields rows under real solar conditions and with the system connected to the national grid.

To comment on this article please contact the editor, Jennifer Muirhead