A parabolic trough is a type of concentrating solar power (CSP) collector that uses long, curved mirrors to concentrate sunlight onto a slim receiver tube running along the focal line. By focusing solar radiation, the trough raises the temperature of a heat-transfer fluid inside the receiver, which can then be used to produce steam or to supply process heat. In principle it serves the same purpose as other solar technologies — such as flat-plate solar panels — but it concentrates rather than converts sunlight directly to electricity.

How it works

Parabolic troughs are mounted on single-axis trackers that follow the sun from east to west, keeping the mirrors aligned so that solar energy is reflected onto the receiver. The receiver is usually a metal tube with a selective coating and often an evacuated glass envelope to reduce heat loss. A heat-transfer fluid (HTF) circulating through the tube — historically thermal oil, and in some designs molten salt or pressurized water — carries the captured heat to a heat exchanger or boiler. The thermal energy is then converted to mechanical energy with a rotary turbine and finally to electricity via a generator. Early thermal machines used reciprocating steam pistons in engines, but modern utility-scale plants use turbines and electrical transformers (transformer) for grid integration.

Main components

  • Parabolic mirror arrays mounted on a supporting structure and tracking system.
  • Receiver (absorber) tube with selective coating and often an evacuated envelope.
  • Heat-transfer fluid loop, pumps, and heat exchangers.
  • Power block (steam generator, turbine, generator) and electrical equipment.

History and development

The parabolic trough concept has evolved from early laboratory concentrators to large field installations. Commercial development accelerated in the late 20th century with utility-scale plants demonstrating the feasibility of trough-based CSP. Advances in mirror manufacture, selective coatings, and tracking control have improved efficiency and reduced costs, while newer receiver materials and working fluids allow higher operating temperatures.

Uses, advantages and limitations

Parabolic troughs are used primarily for utility-scale electricity generation and for industrial process heat where high-temperature thermal energy is required. They can be paired with thermal energy storage to provide dispatchable power and combined with fossil backup in hybrid plants. Advantages include proven technology, relatively simple construction, and mature supply chains. Limitations include large land use, sensitivity to direct sunlight (reduced performance in cloudy regions), and the need for water in some cooling and steam cycles.

Distinguishing features and notable facts

Parabolic troughs are one of several CSP geometries; others include power towers and parabolic dishes. Compared with linear Fresnel systems, troughs typically have higher optical efficiency but can be costlier to build. Their widespread use in several large plants worldwide has helped demonstrate CSP's role in low-carbon electricity systems that benefit from thermal storage and hybrid operation.

For further technical details and plant examples, see sources that cover CSP technology and parabolic trough design in depth (overview, thermal cycles, power conversion, historical engines, electricity, transformers).