Post on 10-Apr-2018
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Solar Energy and Non
Imaging Optics for theproduction of clean water
by
Manuel Collares Pereira(Investigador Coordenador-INETI)
(Professor Catedrtico Convidado- IST)(Director de I&D-Ao Sol Energias Renovveis, lda)
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Why Non Imaging Optics?
(Solar thermal applications)Low temperatures T
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Advantages of flat plate
technology The collectors are fully stationary , i.e. theydo not need to track the apparent dailymotion of the sun
they collect diffuse solar radiation
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What if we want highertemperatures? T>50C
With more sophisticated materials: a moreexpensive product
One possible
alternative solution :Vaccuum technology
Again the cost is much higher for the same quality
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Is there another solution?Can we have higher temperatures?
Thermal losses from large absorbers arelarge :losses are proportional to absorberarea
If we reduce the absorber area ,incomparison with the glass area....
Concentration Aabs
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Classical Concentrators and imagingor focussing optics
they only collect beam(direct) radiation
they must track the sun!
Is there an alternative ( better) solution ?
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The problem is: given radiation incident on anaperture a within a certain angular range ( ) , how
much can it be concentrated - Cmax ?
the solution calls for a new typeoptics: non -imaging optics ; giveup the imaging part , i.e. the opticsmust scramble the incidentradiation, and then it can
concentrate the energy to the limit - Cmax( )-established by firstprinciples in physics
+
?
C=a/b
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+
CPC with mirrors
dielectric CPCn=1 air
n>1
dielectricCPC with mirrors
2 parabolic mirrors with Foci at the
edges of segment b , with each axisparalel to the edge rays from ( )
C=Cmax=a/b= 1/sin( )
Dielectric CPCsame geometry, but now
taking into account totalinternal reflection
C=Cmax=a/b= n /sin( )
One solution to the problem -
CPC type optics
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Acceptance angle function and theconcept of truncation
c
+
+ c + c
a c c e p t a n c e a n g l ef u n c t i o n
f u l l C P C t r u n c a t e d C P C
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Assymetric CPCs
Cmax=a/b= 2/ ( sin( 1) +sin( 2))
1
2
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Other features of Non Imaging orAnidolic Optics
2D; also 3D solutionsin 3D Cmax= (n/sin( ))
other absorber shapes ( tubes, shaped fins,cavities, etc.)
2
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Advantages of Non Imaging Optics in Solar
collectors are concentrators but: 1) they are stationary ( or require few
adjustments through the year...)2) they collect diffuse radiation
3)they retain the potential for low costof flat plate collectors
i.e. the best of both worlds!
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Does Nature use this typeof optics?
Yes! The Limulus optical system
(...) the cones in our retina(...)
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Low temperature applications(T
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simulation of a roof system with CPCs 1.5X: demonstration of air conditioningwith solar and gas as back-up, at INETI
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Other applications: solar cooking
Box type cookers, 2 X 2D CPCs
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High concentration cooker:a 3D solution
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Other applications: still highertemperatures -T>>
Combine non-imaging optics with focussing type optics:
second stage concentration3 D solution
2 D solution
Solar Furnace at PSA+TERC>2800C
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Other applications
Electricity, via PV conversionillumination: interior lighting, car lights, etc.
radiation collection/detection : defense ,astronomy, particle physics,etc.(....)
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Other applications: Solar U.V. for Photocatalysis
detoxification of contaminated wastes, with UV and acatalyst- TiO2(...) added to the waste water circulating intubes
Ci=Ct=1.0 Ra=14.6mm e=1.4mmL=0.92% Lr = 0% H=37.5mm W=91.7mm
-30
-20
-10
0
10
20
-60 -40 -20 0 20 40 60
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Catalyst in suspension-Cadox project (EU)
Pro t o t ype t e s t ed a t INETI and PSA
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Final version for a collectorfield with 100m2
Module of Cadox collector
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SOLWATER: the fixedcatalyst fin case
Application: drinking waterproduction from contaminated surfacewaters
Optimal, butnot ideal
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The case of the fin Examples of raytracing
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Conclusions
Non Imaging Optics can solve many
problems in all sorts of differentapplications. It does so in an ideal way, i.e. In the limits
allowed by first principles in Physics