Following a proposal from the Spanish NC (National Committee), a recommendation from the IEC SMB (Standardization Management Board) and a vote from IEC NCs, the SMB has established TC (Technical Committee) 117: Solar thermal electric plants, to draft International Standards in this field. The SMB has allocated the TC 117 secretariat to the Spanish NC. Three WGs (Working Groups) will be created after TC 117 is launched. They will cover the main needs for standardization: plant, components and storage.
As energy consumption keeps growing at an unprecedented rate, it is becoming a pressing strategic issue worldwide. Renewable energies, which help cut CO2 (carbon dioxide) emissions and mitigate the economic impact of higher oil and gas prices, are bound to play an increasing role in the overall energy consumption structure from 2020 and beyond. Within renewables, solar energies and in particular CSP (concentrating solar power) technologies, which are used in STE plants, present the greatest potential.
Unlike PV (photovoltaic) technology that uses semiconductor material to convert sunlight directly into electricity, CSP technologies use reflective material to concentrate the sun's heat to drive steam or gas turbines, or other engines, to produce electricity. They can also provide energy for other purposes such as water desalination, heating or the production of chemicals. To lessen problems arising from varying electricity demand and solar radiation, STE plants can use storage tanks and hybrid solar-fossil fuel systems to deliver electricity throughout day and night, at base and peak times, ensuring grid stabilization.
In addition to the increasing demand for renewable sources in the future energy mix, CSP technologies used in STE plants present unique and multiple advantages compared to other renewables:
- High degrees of predictability and reliability of production as installations are located in zones enjoying large and constant amount of sunshine
- Good dispatchability – that is, a good capacity to increase or reduce power generation, or to be brought on line or shut down as required, due to proven and highly cost-effective storage, and to the potential integration of backup firing
- Efficient storage and backup possibility
- Grid stability due to inertial features of STE power blocks
- Long-term supply security and independence from oil and gas supplies and prices
- Cost competitive compared to other renewables
- Potential for significant technological progress
Four main technologies
There are currently four main STE technologies being deployed, each presenting different characteristics and advantages, meaning that they can be used in different settings and for distinct purposes.
- Parabolic trough plants collect solar radiation energy reflected from the parabolic trough and direct it to absorber tubes located at the focal point. The solar radiation energy is transferred to the working fluid (oil), which is used in a heat exchanger to produce superheated steam, which in turn is converted into electricity in a conventional steam turbine engine.
- Tower plants use solar radiation concentrated from a field of heliostats (each made up of a mirror, a supporting structure and a solar tracking mechanism) onto the centralized receiver, which is located in a tower. This receiver transfers solar radiation energy to a working fluid, which is used to run a conventional power cycle (turbine).
- Fresnel plants use flat mirrors to heat water (rather than a thermo fluid) directly to produce steam and generate power in a steam turbine. No heat exchanger is needed.
- Dish/Stirling systems use reflectors (dishes) to concentrate solar radiation onto a small receiver area, where it is absorbed and converted to heat a fluid or a gas within a Stirling engine to generate electricity. A Stirling engine is an external combustion engine with a closed cylinder heated at one end by concentrated sunlight and cooled at the other end by air or water. Dish/Stirling systems are more suited to smaller installations.
After more than 25 years of testing STE plants are now entering a commercial ramp-up phase. Current installations in operation, mainly in Spain and the US (United States), have an overall capacity exceeding 3 000 MW (megawatts). Several large-scale STE projects in excess of 50 MW are now under construction in both countries as well as in the Middle East, North Africa and other regions. Various estimations forecast 23 000 MW and 140 000 MW of STE-generated capacity for 2015 and 2020, respectively.