8. manuel collares

8/8/2019 8. Manuel Collares

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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

8. manuel collares

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