Cu stp 10_clfr

SOLAR THERMAL POWER!GEEN 4830 – ECEN 5007!

Manuel A. Silva Pé[email protected]!

10. Concentrating Linear Fresnel Reflectors!

Fresnel reflectors }  Geometrically, ideal reflectors for solar energy collection are

continuous reflectors (PD, PT) }  Large continuous reflectors (or lenses) can be approximated

by smaller elements distributed over a plane (CRS, LFR) }  The design enables the construction of lenses of large aperture

and short focal length without the weight and volume of material that would be required in conventional lens design.

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The Fresnel reflector principle

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Ref. p. 278] 4 Solar power

Landolt-Börnstein New Series VIII/3C

251

Focal point

P

1

1

H

z

xP2

2

P

0

Paraboloid slices

!

!

Fig. 4.1.10. Fresnel geometry using three confocal parabolas P0, P1 and P2.The height of the Fresnel optics is H.The curvature of the elements is de-creasing with the distance from the central line.

4.1.2.6 Fresnel geometry

Building a large single piece paraboloid is expensive, so other designs would be preferable for the pur-pose of energy collection. An alternative is the Fresnel reflector which is composed of parabola slices mounted on a flat surface. The flat mounting surface has advantages with regard to practical engineering and construction. The simplest geometry is shown in Fig. 4.1.10. A set of parabolas with a common focal point are superimposed. Three parabolas P0, P1 and P2 are shown, P0 being the base parabola. The focal lengths obey the equation

)cos(2

)cos(1

i

ii ff

!!+= ,

where f is the focal length of the base parabola. The outer parabolas have a larger aperture and a smaller curvature. Therefore the curvature is most important for the inner parts. Furthermore, the images of the parabola segments become more and more degraded for the outer parts. The size of the parabola segments is defined by the array’s thickness, respectively the height H. The angles !i can be determined as

Hf

xii "

= "u

1)tan(! .

The term xu is the x-value of the respective parabola for z = H. Again, rotation around the z-axis produces a point focusing device, linear extension gives a line focusing array.

The Fresnel geometry principle also found application as a refractive device, the Fresnel lens. The re-fractive material can be a plastic film and the active surfaces may be manufactured by pressing grooves into this film. This method can produce low-cost optical elements.

4.1.2.7 Non-imaging optics

If the approach of concentrating light using principles of image formation is given up, many different design schemes of non-imaging optics appear. One of them is the compound parabolic concentrator (CPC). A two-dimensional line focusing geometry is shown in Fig. 4.1.11. Two parabolas R and L are joined so that the focal point of the parabola R lies on the end of the parabola L and vice-versa. The axes

}  Source: Neumann, A.:  4.1 Solar thermal power plants. Heinloth, K. (ed.). SpringerMaterials - The Landolt-Börnstein Database (http://www.springermaterials.com). DOI: 10.1007/10858992_10

First LFR prototypes

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}  1964 Giovanni Francia (IT) }  1970’s FMC }  1993 University of Sydney }  1998 Solarmundo (BE)

Concept }  Line focus concentrating system }  Array of nearly-flat reflectors (mirrors) that concentrate

sunlight onto elevated linear receivers

Sun rays

2nd stage concentrator

Primary fresnel reflectors

Absorber tube

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Advantages }  Low cost for structural support and reflectors }  Fixed fluid joints }  Receiver separated from reflector }  Long focal length (allows for nearly flat mirrors) Ø LOW COST ALTERNATIVE TO PARABOLIC TROUGHS

Disadvantages •  Low concentration -> limited maximum

temperature Ø LOW EFFICIENCY

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Nova 1 LFR Module (source: Novatec)

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4

#

'

9

Fresnel collector

n  Base module of 513 m2 •  128 Primary Reflector Units track sun

using 2 x 40 Watt motors •  Land use factor = 50% •  Thermal Power Capacity = 306 kW •  Solar-to-Thermal Conversion Factor:

68% (?) n  Direct steam production n  Saturated steam at 270°C, 55bar

n  (next product generation for superheated steam at 350° in 2011)

Compact linear fresnel reflectors }  Efficient land use by using 2 parallel receivers

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AUSRA CLFR module

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Applications

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}  Stand-alone }  Solar booster }  Thermal energy generation }  Solar cooling

Basic configuration of a DSG CLFR power plant

Cooling Tower

Steam Turbine Electric

Generator

Condenser

Solar field

High Pressure Cycle Supply Pump

Hotwell

To Grid

Cooling Water

Steam Dryer

Water

Steam

Steam

Sun

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Prototype CLFR mirrors (AUSRA / SHP)

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Pre Phase 1: 2002 Prototype CLFR main componentry Develop absorber design Phase 1: 2003 1MW(th) Research Pilot. Vent to atmosphere Phase 2: 2004 5MW(e) Connect to Liddell Phase 3: 2005/6 36.5MW(e) Rollout

Liddell CLFR 36.5MW Pilot Project

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Lidell (Ausra)

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Kimberlina (Bakersfield, CA), 2008. 5 MWe, 25 MWth,

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Kimberlina (Ausra)

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Puerto Errado (Murcia, Spain) 2009. 1.4 Mwe (Novatec Biosol - Prointec)

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Puerto Errado

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Puerto Errado

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Puerto Errado 2 (under construction)

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SPG Pilot plant at PSA (Spain)

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Hybrid solar-gas cooling installation at ETSI Seville

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