The solar power plant 'Gemasolar' situated near Seville in Spain was commissioned in 2011 and uses unique innovations which made it not only more efficient than other thermoelectric solar plants, but also able to continue producing electricity without sunlight.
Because its central tower receiver and molten salt storage technology enables it to produce electricity for 15 hours without the sun (and even 24 hours in summertime), Gemasolar can continue to operate during the night or cloudy weather. This meant, for the first-time solar energy became manageable, and capable of responding to large scale commercial demand.
Beating The Heat Of More Than 1,000 Suns
Fine Tubes worked with SENER for 4 years 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 - which can absorb 95% of radiation in the solar spectrum and transmitting this energy to be stored in the molten salt compound in its interior.
Santiago Arias, Technical Director from Torresol Energy and Project Management of SENER:
“SENER values highly the contribution of Fine Tubes to this project. The service conditions of components required high quality and reliable products - which Fine Tubes has rigorously fulfilled. Other remarkable aspects during the manufacturing process were meeting deadlines, and continuous information transfer, two points where the collaboration with Fine Tubes was crucial and essential for the successful development of the project."
Backgrounds
SENER has been working in the solar field industry since the 1980’s when the company was developing solar technology, including the first heliostats (mirrored panels which reflect sunlight). During 2001-2005 the company worked on two ground-breaking solar power plant projects, Solar Tres and Andasol-1, which provided them with enormous research and development opportunities resulting in the creation of Gemasolar.
The Gemasolar project itself began in 2006, when SENER designed and installed an experimental unit in the Almeria Solar Platform which demonstrated the validity of the receiver design and the molten salts system. Together with Abu Dhabi’s alternative energies company MASDAR, the company formed Torresol Energy in 2008 and Gemasolor started commercial production in 2011.
Innovative Molten Salt Technology
The 185-hectare site near Seville boasts 2,650 heliostats which aim solar radiation at the tower’s receiver system. The radiation heats molten salts that circulate inside the tower to temperatures of more than 500 °C. These salts are used directly as the heat absorption fluid: they are pumped from the cold molten salt tank to the receiver at the top of the tower, where they are heated to extreme temperatures, after which they descend to the hot molten salt tank or directly to the heat exchanger where they generate steam.
When excess of energy is received, i.e., when the received heat radiation is more than the turbine demand, the level in the hot tank increases, enabling the power plant to generate electricity for up to 15 hours without any incoming solar radiation.
Challenges
Because Gemasolar was a first-of-its-kind; challenges were present at every project stage. It was unique due to its innovative design and cutting-edge equipment developed by SENER; notably the central tower and receiver, the solar field and the control system.
The central receiver is the main component for this type of thermosolar plant and its component parts need to perform reliably in extreme conditions throughout the plant’s lifetime. Fine Tubes needed to provide extremely robust tubes made from a material with a high resistance to corrosion, thermo-mechanical fatigue and creep to be capable of holding the molten salt. High quality and durability for these tubes was vitally important because the receiver availability is continuous, absorbing an enormous amount of solar energy - the equivalent of more than 1,000 suns.
SENER also required heat exchanger tubing to operate effectively within the steam generator units. Once again quality and durability were imperative, the units work at very high pressure turning the turbines to generate electrical power for over 27,500 homes per year.
Solutions
There were no ‘off the shelf’ solutions in a project such as this and Fine Tubes first went to work with SENER creating prototype panels. Because we were able to exceed the standard definitions required for these component parts, SENER selected us to be the exclusive supplier of tubes for the manufacturing panels of the central receiver.
We produced over 15 km of high-performance seamless tubing for the system, which holds the 565°C molten salt (nitric salt), housed in the 140-metre high Gemasolar tower. Made from a corrosion-resistant nickel-chromium alloy, the tubing has superior resistance to very high temperatures and the extreme service conditions.
We also provided over 300m of heat exchanger tubes manufactured from the same nickel-chromium alloy, but with a thicker wall to withstand the high pressures present within the steam generators.
Producing Electricity with No Sunlight
The plant was officially opened in October 2011. The results achieved in the first year of Gemasolar operation broke all expectations. Since then, its available production hours are increasing significantly, and it is hitting all production goals.
After a routine annual maintenance stop at the beginning of 2012, the plant achieved continuous 24-hour production for 12 straight days in winter, successfully delivering the projected energy supply to the grid.
For more information about the latest developments go to https://www.group.sener/