Parabolic trough basics and heat conversion
Parabolic troughs use curved mirror arrays shaped like a parabola to focus sunlight onto a long receiver tube running along the focal line. The concentrated sunlight heats a fluid inside the tube, and that thermal energy is then used to produce steam or transferred to a storage medium for later use.
Steps in energy conversion:
- Collection: Parabolic mirrors track the sun on one axis (typically east–west) to keep sunlight focused on the receiver throughout the day.
- Absorption: The receiver tube, often coated with selective absorber coatings and covered with a glass envelope to reduce convection losses, absorbs concentrated light and heats the working fluid.
- Heat transfer: Heat transfer fluids (HTFs) such as thermal oil, pressurized water/steam, or molten salts carry the heat to a heat exchanger or steam generator.
- Power generation: Heated fluid produces steam that drives a turbine and generator, creating electricity. Excess heat can be stored in thermal storage.
Advantages of parabolic troughs:
- Mature technology: Proven in commercial plants with established supply chains.
- Moderate temperatures: Typical operating temperatures (around 300–400°C) are well-suited for Rankine steam cycles.
- Simpler tracking: Single-axis tracking reduces mechanical complexity compared to dual-axis systems.
Design considerations and challenges:
- Thermal losses: Insulation and glass covers help reduce convective and radiative losses from the receiver.
- Fluid selection: HTFs must remain stable at operating temperatures and transfer heat efficiently; molten salts allow higher storage temperatures but require freeze protection.
- Field layout: Mirror alignment, spacing, and maintenance access influence performance and lifetime costs.
Parabolic troughs remain a robust option for utility-scale CSP, offering predictable performance and straightforward integration with thermal storage and steam turbines.