Turning the Sun’s Energy Into 24/7 Electricity or Heat
Harnessing the Sun’s Power 24/7
Concentrating solar thermal systems use mirrors to concentrate sunlight by hundreds or even thousands of times its normal intensity. The concentrated sunlight, in the form of heat, is then transferred into a thermal energy storage (TES) system, such as molten salt. The heat in the TES stays in storage until required. Systems typically have capacity to provide 8 – 15 hours or more of full output.
For power generation heat is used to produce superheated steam to run a steam turbine with a synchronous generator. CSTs synchronous generators also provide system benefits as they deliver essential grid support services – inertia, system strength and frequency control – currently provided by coal and gas generators.
CST Use Cases
Concentrating solar thermal systems with built in long duration storage are ideal solutions for:
CST offers long duration storage, providing renewable electricity to the grid 24/7 complementing intermittent PV and wind.
CST is ideal as part of off-grid 100% renewable electricity systems for mining and remote area locations.
CST provides a pathway to generate and store large amount of heat with zero emissions, which can then be used, as required, to meet industry’s 24/7 process heat needs.
CST’s renewable heat and electricity can power the production of low-cost green fuels, including methanol, ammonia and hydrogen.
CST Designs
There are four types of CST design, each with particular strengths
Where a series of large trough-shaped mirrors that reflects the sun’s rays onto an inline receiver tube running along the centre of the trough arrays. The receiver tube can contain water, oil or molten salts. These are the most commercially mature and reliable version and have been deployed in many utility scale systems around the world for over 35 years.
Many individual heliostats (tracking mirrors) reflect the sun onto a thermal receiver sitting at the top of a tower. These are a newer commercial development increasingly favoured for their higher temperatures and more cost-effective storage.
Focuses the sun’s rays onto a thermal receiver or Stirling engine located at the focal point of the parabola. These offer the highest efficiencies but are still in the R&D phase.
Uses modular flat reflectors to focus the sun's heat onto elevated receivers containing water; the concentrated sunlight boils the water or heats molten salt in the tubes, generating high-pressure steam for use in power generation and industrial steam applications. These are at an early stage of commercialisation but offer potential for cost reduction.
Concentrating solar thermal systems are often referred to by different acronyms that have overlapping meanings.
Concentrating solar thermal (CST) is used in place of CSP, sometimes interchangeably. In precise use it implies concentrating solar that produces high temperature whether for use in power generation or for direct use of heat.
Concentrating solar thermal power (CSP) is used where the system is for electric power generation. In some interpretations CSP is also used to cover systems with solar concentrators that have high efficiency PV cells at the focus (also called concentrating pV or CPV).
In Europe the phrase Solar Thermal Electric (STE) is also widely used interchangeably with CSP.
