Concentrating Solar Power

Concentrating Solar Power is the process of focusing sun light rays into a reduced area by using mirrors and/or lenses to either make PV panels more efficient or to generate heat.
This procedure is tipically used on large Solar Power Plants and it is not yet designed for domestic use. It is usually used in combination with solar trackers, which are devices that follow the sun trajectory through the sky, much like artificial sunflowers.
Even though the process name may sound complicated, the basic concept is really a very simple thing. Anyone that has used a magnifying glass on a sunny day to burn something, has used and seen the potential of concentrated Solar Power.

When combined with PV panels, it is simply used to maximize the system electrical efficiency by augmenting the amount of light rays (photons) that are received by the panels surfaces.

The most common use in large Solar Power is called Conentrating Solar Thermal. This means using the heat generated by the concentrated sunlight instead of the photons energy. The high temperatures generated (up to 1000 °C) are used to heat fluids -generally salt water- that are the source for a power generation or energy storage system.
There are several methods to achieve this. Most Representative are: Parabolic trough, Concentrating Linear Fresnel Reflectors, Dish Stirling and Solar Power Tower.

Parabolic Through.jpg

Parabolic trough.
Parabolic trough is an energy collector that functions with the combination of a long and very reflective parabolic/convex mirror and a long thermally insulated tube placed at the area of highest concentrated heat. A fluid, generally oil, runs trough the tube and it is heated to around 400°C. The fluid is then used to heat steam in a standard turbine generator.
Solar Power Plants that use this technology: Solana Plant, Solel, SEGS III-VII, SEGS VIII-IX, Beacon Solar Energy Project, Nevada Solar One plant, Saguaro Solar Power Plant

Concentrating Linear Fresnel Reflectors

Concentrating Linear Fresnel Reflectors (CLFR).
CLFR functions in a similar way as Parabolic Through. It is also a combination of mirrors to reflect and concentrate solar heat and transfer it to a thermal fluid that is then used on a heat exchanger to power a steam generator.
The difference is that CLFR uses Fresnel reflectors' lens effect to improve the concentration to around 30 times its normal intensity. It also includes the use of absorber plates and insulated tubes that transport the thermal fluid on top of an air cavity. This highly improves the temperature distribution and the absorbtion efficiency.
Solar Power Plants that use this technology: Carrizo Energy Farm

Dish Stirling

Dish Sterling.
Dish Sterling systems use mirrored parabolic dishes wich concentrate sunlight into a reduced area above the dish. This system also includes the use of thermal fluids, but in this case the engines are placed directly on the light concentration point. The engines used are Striling engines, which are heat engines that operate by cyclic compression and expansion at different temperature levels.
While the generated heat is higher, the necessary structure for this designs require higher maintanance and solar tracking devices must be used.
Solar Power Plants that use this technology: Solar One, Solar Two

Solar Power Tower

Solar Power Tower.
Solar Power Tower (a.k.a. Thermal Central Power Tower, Heliostat Power Plants) is a design that uses a large number of movable mirrors that focus or concentrate the sunlight into a Central tower, also called collector. As on the above explained designs the heat 'collected' on the central tower is tranfered to a thermal fluid - currently liquid sodium- that stores the heat an then is used to boil water to drive steam engines. The main advantage of this system is that the heat is stored by liquid sodium so energy an be temporarily generated withouth sunlight.
Solar Power Plants that use this technology: eSolar, BrightSource

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