About Solar Thermal Energy
Solar thermal energy systems – known as Concentrating Solar Thermal or ‘CST’ systems - are versatile, reliable and flexible. Solar thermal delivers power to meet peak electricity demand, it can include thermal energy storage to deliver power day or night, it can be coupled with other fuels such as gas and biomass for fully dispatchable electricity supply. And solar thermal can also reduce coal consumption in coal-fired electricity plants, by delivering solar generated steam to augment existing steam systems.
Solar thermal energy harnesses the sun’s heat to generate power. Reflectors concentrate the sun’s energy onto a thermal receiver; a fluid (such as water, oil or molten salt) or a gas passes through the receiver where the concentrated solar energy heats it to very high temperatures – from 350°C to over 1,000°C depending on the system. The fluid or gas is referred to as a ‘heat transfer medium’ – HTF.
Where the HTF is a fluid, the fluid is used to boil water to create super-heated steam, which in turn drives a highly efficient traditional steam turbine, the same as those used in coal-fired power stations. Where the HTF is a gas, the turbine is like an aircraft jet engine, or the turbines used in gas-fired power stations – this is known as a Brayton cycle system.
There are four types of CST design:
- Linear Fresnel design, which uses modular flat reflectors to focus the sun's heat onto elevated receivers containing water; the concentrated sunlight boils the water in the tubes, generating high-pressure steam for direct use in power generation and industrial steam applications .
- Central receiver or ‘power tower’ design, where many individual heliostats (tracking mirrors) reflect the sun onto a thermal receiver sitting at the top of a tower. Power towers can drive Carnot (steam turbine) systems, or Brayton cycle (air turbine) systems.
- Parabolic trough design, where a series of large dish-shaped troughs 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, and drive a Carnot (steam turbine) system.
- Parabolic dish, which focuses the sun’s rays onto a thermal receiver or Stirling engine located at the focal point of the parabola.
Each has particular strengths and efficiencies which make it well-suited to particular electricity generation or industrial steam applications.