Solar concentrator
A solar concentrator is a technology that enhances the efficiency of solar energy systems by focusing sunlight onto a small area to generate intense heat. Utilizing mirrors or lenses, solar concentrators have evolved from ancient applications, such as the use of convex lenses, to modern designs that include parabolic dishes, Fresnel reflectors, troughs, and solar towers. These systems can be paired with photovoltaic cells to improve energy production or used to create steam for electricity generation. Notably, parabolic dishes function similarly to satellite dishes, while solar troughs can heat a working fluid, and solar towers utilize a field of reflectors to generate high temperatures efficiently.
Solar concentrators are also employed in solar ovens, contributing to sustainable cooking solutions in developing regions, as they use no fuel and produce no smoke. While current advancements have made solar concentrators competitive in terms of cost with fossil fuels, challenges remain, particularly in terms of efficiency and the need for solar tracking mechanisms. Future innovations may focus on eliminating tracking needs through the use of advanced materials, though stability remains a concern. Overall, solar concentrators represent a crucial component in the ongoing development of renewable energy technologies.
Subject Terms
Solar concentrator
Summary: Solar concentrators represent major advancements in solar electricity efficiency by concentrating the sun’s energy into a focal point to generate intense heat.
Solar concentrators are systems that use mirrors to focus the sun’s energy onto a small focal point, creating intense heat. Solar concentrators have been used since ancient times, especially in the form of convex lenses, to increase the heat delivered from the sun. In more recent times, solar concentrators have been used in conjunction with photovoltaic cells or to generate steam cheaply and efficiently. Modern designs typically fall into four main categories: parabolic dishes, Fresnel reflectors, troughs, and solar towers. Novel uses of concentrating solar energy include solar ovens and parabolic mirrors for starting fires.
The first mention of concentrated solar power comes from Greek legends that tell how Archimedes repelled an invading fleet by using a “burning glass” of several large mirrors to concentrate the sun’s energy to ignite the ships. However, the legitimacy of this claim has been repeatedly brought into question, and experiments conducted in 2005 proved that while it was theoretically possible under ideal conditions, it would have been far easier to ignite ships with a catapult or flaming arrows.
The first use of concentrating solar power into energy was in the 19th century, when a parabolic trough design was used to generate steam to run the world’s first solar steam engine. Following this advancement, concentrated solar power was commonly put to use for irrigation, locomotion, and refrigeration.
Modern Designs
Four main types of solar concentrators are in use today for electricity generation and are either used in conjunction with modern silicon photovoltaic cells or steam energy to generate electricity. Solar concentrators, in order to obtain maximum efficiency, must be directly facing the sun and must therefore shift their orientation throughout the day, a hurdle in the small-scale deployment of concentrated solar energy.
The four types of solar concentrators are parabolic dishes, Fresnel reflectors, troughs, and solar concentrator towers. Parabolic dishes reflect sunlight back toward a photovoltaic cell in a similar fashion to satellite TV dishes. Larger parabolic dishes can be used with a small Stirling engine to generate electricity. A Fresnel reflector is a single lens with concentric rings that allows for a higher concentration of light with lighter material than a simple convex lens. Solar troughs are similar to dishes but instead focus energy on a tube filled with a working fluid, such as molten salt, that is heated, and the heat is used to generate electricity. One advantage of troughs is that they only have to track the sun on a single axis. Concentrated solar towers are the largest of the concentrated solar technologies, with a single tower placed in a field of solar reflectors, all of which reflect the sun’s energy back to the tower, creating intense heat for electricity generation. Concentrated solar towers are the most efficient of the concentrated solar technologies and are able to generate electricity for several hours after daytime.
Parabolic dishes and Fresnel reflectors are commonly used in conjunction with photovoltaic cells to improve their efficiency by increasing the intensity of the sunlight hitting the cell. This drastically reduces the cost of photovoltaic solar arrays, as the cells are far more expensive than mirrors and lenses. Since about one-tenth as many silicon chips are needed, the cost per kilowatt-hour is dramatically reduced, putting solar energy closer to the cost of coal and natural gas electrical generation. However, with these two systems, heat is a major hurdle, as the concentrated solar energy also produces significant heat.
Solar concentrators are also used as solar ovens or cookers, often as part of development schemes in poorer countries to slow deforestation and desertification. Basic models are simply a foil arranged in a parabolic shape to concentrate the sun’s energy, while more complex models are box-shaped with a combination of reflectors and black surfaces to generate heat. These solar ovens use no fuel, produce no smoke, and can be used in a similar manner as a slow cooker; however, they are most efficient during the hottest time of the day and take a long time to cook food, requiring advance planning.
Current and Future Applications
Since the cost of fuel for solar energy is free, the most important factor in reaching grid parity is the cost of building solar concentrators. Current technology has brought the cost per kilowatt-hour to levels roughly equal to both natural gas and coal, but still roughly 10 times higher than nuclear energy.
The United States initially led in concentrated solar energy with the 354-megawatt SEGS concentrated solar energy station in the Mojave desert (comprising 99 percent of total U.S.-installed solar capacity in 1992); it was once the largest solar plant in the world. In 2024, the largest solar plant in the world was China's 3.5 gigawatt Midong photovoltaic (PV) farm.
Potential future developments include dyes that can diffuse and redirect the sun’s energy to eliminate the need for solar tracking. Solar tracking adds significant cost and maintenance to solar concentrators. However, the dyes are somewhat unstable and do not last as long as typical solar panels.
Bibliography
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