This project involved CSIRO working with Spanish company Abengoa to find cost-effective ways to collect and store heat from sunlight (solar thermal energy) in order to increase user confidence in solar energy, minimise disruption to the electricity grid and make it more economic for solar power plants to produce electricity.
Solar thermal energy (heat from sunlight) has the potential to play a significant part in the generation of Australia’s electricity, as well as helping to meet the energy requirements of Australia’s energy-intensive industries. One of the current limitations is that solar thermal energy is only available when there is sunlight, preventing solar-generated electricity from being produced during cloudy periods or overnight.
Technologies that can store solar thermal energy and discharge it on demand to meet user needs will help to make solar energy plants more reliable and improve consumer confidence in them as electricity generators.
The project involved the design and construction of a solar thermal energy storage system that can operate up to 750 degrees Celcius. By maximising the operating temperature and efficiency of the system, CSIRO aims to develop a cost-effective way to store solar thermal energy.
After identifying the most suitable materials to store the energy, work focused on the design of the system itself to reliably operate at a high temperature.
An important part of the project was to integrate the storage system with the concentrating solar thermal facility at CSIRO’s National Solar Energy Centre in Newcastle, NSW.
Ensuring solar-generated electricity is available on demand through the addition of storage technologies will make solar thermal energy an attractive power source option. Solar thermal energy storage will also improve user confidence in solar thermal energy, overcome some of the grid integration challenges posed by the intermittency of solar-generated electricity, and improve the commercial viability of solar thermal power plants in Australia.
Achievements and lessons learned
In spite of operational limitations of the plant as installed, the project provided valuable insights into the challenges involved in storing solar thermal energy at high temperatures. Thermal energy storage is a key factor in the feasibility of the CSP plants. At high operating temperatures the best thermal energy storage systems are ceramic regenerative systems, however the cost of the container is usually an impediment in their use at these temperatures.
A new storage vessel concept has been built and tested in the project to reduce the cost of the thermal energy produced. In these tests, hot spots in the top dome of the vessel were observed. Preferential flow channeling was also indicated, affecting the expected thermocline in the bed. These issues along with operational data are now being evaluated for future Improvement of the Storage Vessel design.
The performance of the Solar Receiver/Absorber does indicate that it is capable of performing according to design specifications. The pressure drop across it is not excessive and provided gas is heated to the design inlet temperature it is capable of producing gas with an outlet temperature of 750oC.
Further details of the lessons learned, including the design and operation of the thermal energy storage vessel, the use of molten salts for high temperature applications and the mechanical design and the construction of systems for handling gases at high temperatures and pressures with thermal cycling, is available in the report below.