3.2 Types of solar collectors (parabolic trough, power tower, linear Fresnel, dish)
4 min read•august 9, 2024
Solar collectors are the heart of concentrated solar power systems. They come in four main types: parabolic troughs, power towers, reflectors, and parabolic dishes. Each design has unique features for focusing sunlight and converting it to usable energy.
Understanding these collector types is crucial for grasping how CSP systems work. We'll explore their designs, components, and operating principles to see how they concentrate sunlight and generate power on an industrial scale.
Parabolic Trough and Linear Fresnel Collectors
Parabolic Trough Design and Operation
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systems use a large field of sun-tracking mirrors (heliostats) to focus sunlight onto a central receiver
Central receiver mounted on top of a tall tower (typically 100-200 meters high)
Achieves very high concentration ratios (600-1000 suns) allowing for operating temperatures up to 1000°C
High temperatures enable more efficient power generation and
Single power tower plant can generate 50-200 MW of electricity
Heliostat Field Configuration
Heliostat field consists of thousands of individual mirrors each with two-axis tracking
Mirrors arranged in concentric circles or other optimized patterns around the central tower
Field layout designed to minimize shading and blocking between heliostats
Computer-controlled tracking system adjusts each heliostat to maintain focus on the receiver
Typical heliostat sizes range from 50-150 square meters
Receiver and Heat Transfer Systems
Central receiver designs include external cylindrical receivers and cavity receivers
External receivers exposed on all sides allow for simpler heliostat field layout
Cavity receivers have an opening facing the heliostat field reducing heat losses
Heat transfer fluids include water/steam, molten salts, and pressurized air
Molten salt systems allow for efficient thermal energy storage extending plant operation
Parabolic Dish Collectors
Parabolic Dish Design and Operation
Parabolic collectors use a dish-shaped reflector to focus sunlight onto a small receiver at the focal point
Dishes track the sun on two axes providing the highest concentration ratios of any collector type (1000-3000 suns)
Typically smaller in scale than other CSP technologies with dish diameters of 5-15 meters
Individual dishes often paired with Stirling engines or small turbines for distributed power generation
Modular nature allows for scalable installations from single dishes to large fields
Concentrator and Tracking Systems
Concentrator surface made up of multiple mirror facets or a single paraboloid reflector
High-precision tracking system required to maintain focus on the small receiver aperture
Tracking accuracy of 0.1 degrees or better needed for optimal performance
Structurally challenging due to wind loads on large dish surface area
Advanced materials like composites used to reduce weight and improve tracking
Receiver and Power Conversion
Receiver designs include directly illuminated tubular receivers and heat pipe receivers
Directly illuminated receivers use tubes arranged in a cavity to absorb concentrated sunlight
Heat pipe receivers use liquid metal to transfer heat from the absorber surface to the engine
Stirling engines commonly used for power conversion due to high efficiency at small scales
Brayton cycle turbines also being developed for dish-based systems
Typical electrical output for a single dish-engine system ranges from 3-25 kW
Key Terms to Review (16)
Central receiver system: A central receiver system, also known as a power tower, is a type of Concentrated Solar Power (CSP) technology that uses a large array of mirrors to focus sunlight onto a central receiver located at the top of a tall tower. This concentrated solar energy is then converted into heat, which is used to produce steam that drives a turbine to generate electricity. This system stands out for its efficiency and scalability in harnessing solar energy compared to other solar collector types.
Dish: A dish, in the context of solar collectors, refers to a type of concentrating solar power system that uses a parabolic reflector to focus sunlight onto a receiver, typically located at the focal point of the dish. This design captures solar energy efficiently, converting it into thermal energy, which can then be transformed into mechanical or electrical energy. Dishes are known for their high efficiency and ability to achieve high temperatures, making them suitable for various applications including electricity generation.
Distributed collector system: A distributed collector system refers to a solar thermal energy generation setup where multiple smaller collectors are spread out over a larger area, as opposed to a single, centralized collector. This approach allows for the harnessing of solar energy in a more flexible manner, improving efficiency and reducing land use impacts by integrating with existing structures or landscapes. It also enhances energy accessibility by allowing localized energy production close to where it is consumed.
Heat Transfer Fluid: Heat transfer fluid is a medium used to transfer heat between different parts of a thermal energy system, playing a crucial role in the efficiency and effectiveness of concentrated solar power systems. These fluids are essential for collecting, storing, and delivering thermal energy, impacting the overall performance and design of various solar collector technologies, thermal storage integration, and system configurations.
Industrial heat applications: Industrial heat applications refer to the use of thermal energy in various industrial processes to provide heat for manufacturing, processing, and other operational needs. These applications often leverage renewable energy sources, such as concentrated solar power systems, to produce steam or hot fluids that can be used for heating, drying, or chemical processes, enhancing energy efficiency and reducing reliance on fossil fuels.
Linear Fresnel: Linear Fresnel is a type of solar collector system that uses long, flat mirrors to concentrate sunlight onto a fixed receiver. This technology allows for the capture of solar energy through a series of linear arrangements of mirrors, which follow the sun's path to maximize energy collection while minimizing land use. Linear Fresnel systems are known for their simplicity and efficiency in converting solar radiation into thermal energy.
Optical Efficiency: Optical efficiency refers to the effectiveness with which a solar collector converts incident solar radiation into usable thermal energy, taking into account losses due to reflection, absorption, and scattering. It plays a critical role in determining the overall performance of Concentrated Solar Power (CSP) systems, influencing design choices and optimization strategies.
Parabolic Trough: A parabolic trough is a type of solar collector that uses curved, parabolic-shaped mirrors to focus sunlight onto a receiver tube running along its focal line. This design is effective in converting solar energy into thermal energy, which can be used to generate electricity or for other heating applications.
Power Tower: A power tower is a type of concentrated solar power system that utilizes a central tower with a field of mirrors, known as heliostats, to focus sunlight onto a receiver at the top of the tower. This concentrated sunlight generates heat, which is then used to produce steam that drives a turbine for electricity generation. The power tower design allows for high thermal efficiency and can store heat energy for use when sunlight is not available, making it a promising technology in renewable energy production.
Reflective Materials: Reflective materials are surfaces designed to reflect solar radiation efficiently, maximizing the capture of sunlight for conversion into thermal energy in solar power systems. These materials play a crucial role in various types of solar collectors, enhancing their performance by directing sunlight onto a receiver where it can be converted into usable energy. The effectiveness of reflective materials significantly influences the overall efficiency and output of solar energy systems.
Solar Receiver: A solar receiver is a crucial component in concentrated solar power systems that captures and absorbs solar energy concentrated by mirrors or lenses, converting it into heat. This heat is then used to generate steam, which drives a turbine for electricity production. The efficiency and design of the solar receiver directly impact the overall performance of the power generation system, making it essential for both thermal and thermodynamic efficiency.
Steam generation: Steam generation refers to the process of converting water into steam, which is a critical component in various energy systems, including concentrated solar power (CSP) applications. This process involves heating water to its boiling point, allowing it to expand and create pressure that can drive turbines to produce electricity. In CSP systems, the efficiency of steam generation is influenced by heat transfer mechanisms and fluid dynamics, as well as the design of different solar collectors.
Thermal efficiency: Thermal efficiency is the measure of how well a system converts thermal energy into useful work or output. It indicates the effectiveness of energy conversion processes in power generation, highlighting how much of the input energy is transformed into usable energy while minimizing waste.
Thermal energy storage: Thermal energy storage is a technology that allows for the storing of excess thermal energy for later use, typically in concentrated solar power systems. This technology enhances the efficiency and reliability of solar energy by allowing power generation even when sunlight is not available, supporting grid stability and providing dispatchable energy.
Tracking systems: Tracking systems are mechanisms that allow solar collectors to follow the sun's path across the sky, maximizing the amount of sunlight captured throughout the day. By continuously adjusting their position, these systems enhance the efficiency of various solar technologies, including parabolic troughs, power towers, linear Fresnel collectors, and dish systems, ultimately improving energy output and reducing costs.
Utility-scale power generation: Utility-scale power generation refers to large-scale electricity production that is typically connected to the grid and can supply power to a wide range of consumers, including residential, commercial, and industrial users. This form of generation often involves significant investments in infrastructure and technology, allowing for the efficient conversion of renewable resources into electricity, including solar energy through various collector systems. By harnessing solar energy at a large scale, utility-scale systems contribute significantly to energy sustainability and the transition to cleaner power sources.