Parabolic Trough Design

• Parabolic trough technology is currently the most proven solar thermal electric technology. Parabolic trough power plants use a curved, mirrored trough which reflects the direct solar radiation onto a glass tube containing a fluid (also called a receiver, absorber or collector) running the length of the trough, positioned at the focal point of the reflectors.

• The trough is parabolic along one axis and linear in the orthogonal axis. For change of the daily position of the sun perpendicular to the receiver, the trough tilts east to west (in case of N/S orientation) so that the direct radiation remains focused on the receiver. However, seasonal changes in the angle of sunlight parallel to the trough does not require adjustment of the mirrors, since the light is simply concentrated elsewhere on the receiver.

• The receiver may be enclosed in a glass vacuum chamber. The vacuum significantly reduces convective heat loss. The Heat transfer fluid passes through the receiver and becomes very hot. The fluid containing the heat is transported to a heat engine where about a third of the heat is converted to electricity.

• In regions with good solar resources where coal plants are currently used, parabolic trough plants can be integrated into the coal plant to either reduce coal consumption or add solar peaking, much like the ISCCS configuration.

• ISCCS (Integrated Solar Combined Cycle System):
  This is a new design concept that integrates a parabolic trough plant with a gas turbine combined-cycle plant. The ISCCS has generated much interest because it offers an innovative way to reduce cost and improve the overall solar-to-electric efficiency. Due to the higher temperature and pressure steam conditions used in modern coal plants, the solar steam may need to be admitted in the intermediate or low-pressure turbine

Advantages and Disadvantages of a Parabolic Trough Power System

Advantages of Solar Parabolic Troughs:

• Solar parabolic trough systems are the most developed and commercially tested concentrating solar power technology.
• Since solar parabolic trough systems produce steam to generate electricity with a conventional Rankine steam cycle, these systems can be readily hybridized, that is, they can be set up to use a fossil fuel (typically natural gas) as a supplementary fuel, so that electricity can be generated when the sun isn't shining.
• The solar parabolic trough system is suitable for use in an Integrated Solar Combined Cycle System (ISCCS) with potential to reduce the cost and increase the overall solar to electric efficiency.

Disadvantages:

• The solar parabolic trough system doesn't produce fluid temperature as high as some of the other concentrating solar power technologies, which makes its efficiency for electricity production lower.

Status of Commercialization of Parabolic Trough Power System

As mentioned above, the solar parabolic trough system is the most commercially developed of the concentrating solar power technologies. Over 40 solar parabolic trough power plants that are in operation, nearing completion, or are in planning around the world. Some of the SEGS solar parabolic trough plants in California have been operational for over 20 years