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7/24/2019 NCES Presentation on Solar Collectors
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SOLAR ENERGY COLLECTORSSOLAR ENERGY COLLECTORS
Non Conventional EnergyNon Conventional Energy
SourcesSources
References : G.D RAIReferences : G.D RAI
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SOAR COEC!ORS:
Collector is a device which absorbs the incoming solarradiation, converts it into heat, and transfers this
heat toa uid (usually air, water, or oil) owing through thecollector.
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COLLECTORS
Collecting FluidsMounting
Flat (or)
Nonconcentric AdjustableStationary Liquid as (or) Air
Concentric
(or)
Focussing
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Flat-plate collectors, developed byHottel and hillier in the !"#$s,
are the most common type ofsolar collector which are widelyused for domestic household hot-water heating , air heating
%emperature can be upto "$$
&n the 'on-concentrating type, thecollector area is the same as theabsorber area.
"lat or Non concentric ty#e collector
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Flat (or)
Non
concentric
Fluid Ty!e Air Ty!e
"$ID !%&E : 'eat !ransfer (e)iu( is *ater or any ot+er li,ui)
AIR !%&E : 'eat !ransfer (e)iu( is air or gas.
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A ty#ical )iagra(s of""lat #late solar
t+er(al collectors#
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Co(#onents of "lat #late collectorCo(#onents of "lat #late collector
LAZIN
ABSORBER
HEADERS
INSULATION
CONTAINER
-- !+ese can asor ot+ )irect an) )i/use)
ea( ra)iations
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GA0ING:GA0ING:
o 1a)e of one or (ore covers of trans#arent (aterial like glass or #lastic..
o It is use) to re)uce convective an) ra)iative +eat losses fro( t+e asorer.
o It is o#a,ue to t+e infrare) ra)iations.
A2SOR2ER :A2SOR2ER :
o It is usually (a)e of co##er or steel (etal.
o !+e surface is covere) *it+ a t+in coating of #ri(er an) t+en 3at lack #aint of +ig+asor#tance +uge
#aint (ay increase t+e resistance to +eat tranfer
o Coating is a##lie) on t+e surface to (a4i(i5e t+e asor#tance of solar energy an)(ini(i5es t+e
ra)iation e(itte) y #late.
!$2ES OR 'EADERS :!$2ES OR 'EADERS :
o A tue t+at is attac+e) to asorer or so(eti(es it is a #art of asorer #late.
o If t+e *orking 3ui) is air 6 t+e 3o* #assage s+oul) e elo* t+e asorer #late to(ini(i5e +eat losses.
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Insulation:Insulation:
!+ese are so(e (aterials suc+ as 7erglass an) t+ey are #lace) at t+e ackan) si)es of
t+e collector to re)uce +eat losses. eg. *ool6 7er etc...
Container :Container :
8+ic+ encloses t+e ot+er co(#onents toget+er an) #rotects fro( t+e *eat+er.
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"lat #late collectors"lat #late collectors
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"lat #late collector "lui) !y#e"lat #late collector "lui) !y#e
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Cross sectional arrange(ents t+roug+Cross sectional arrange(ents t+roug+
t+e collector #latest+e collector #lates!ue in stri# ty#e!ue in stri# ty#e
GlazingRiser
Absorbing plate
Insulation
A
BBGlazing
Riser
Absorbing plate
Insulation
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CGlazing
Riser
Absorbing plate
Insulation
DD
Glazing
Riser
Absorbing plate
Insulation
!ues ra5e) to!ues ra5e) toasorerasorer
Cross sectional arrange(entsCross sectional arrange(ents
t+roug+ t+e collector #latest+roug+ t+e collector #lates
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8orking &rinci#le
unlight passes through theglaing and stri*es the
absorber plate, which heatsup, and solar energy isconverted into heat energy.%his the heat is transferred to
the uid passing through pipesattached to the absorber plateby means of convective heattransfer.
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Gla5ing )esign
Due to t*o glass s+eets are use) losses )ue to air convection arefurt+er re)uce) 6 t+is is (ainly use) an) i(#ortant in *in)y areas.
Ra)iation losses in infrare) s#ectru( are re)uce) to 9; fro(ciency)ecreases.
!+e air s#ace et*een t+e cover an) t+e asorer #revents +eatloss y convection
'o*ever if one *atc+es t+e electro(agnetic s#ectru(
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As cover is made of glass
It allows the solar radiations of wavelength < 2m
and is opa!ue for wavelength " 2m
$t is seen %ro& electro&agnetic s!ectru& t'at in%rared
radiations 'aing aelengt' * 2m
As a result infrared are opa!ue and does not pass
#oo heat is trapped inside the space between the cover and
absorber plate similar to green house effect and $eeps it hot%
&owever some of heat occurs due to conduction ' convection ' and
radiation thereb( effecting the overall efficienc(overall efficienc(%
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)his can be met b( following steps *++
It can be reduced b( using ,water white glass, with low iron content
Reflection which is order of -./ can be met b( gentll( itching the
glass surface h(dro flouric acid%
Gla5ing )esign consi)erationsGla5ing )esign consi)erations
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Asorer )esignAsorer )esign
Coating done on the absorber surface is called ,selective coatings ,
,Blac$ chrome, is e0tensivel( used coating which is of 2m
thic$ness
'eat trans#ort syte('eat trans#ort syte(
&eat generated in the absorber is continuosl( ta$en b( the flow of
medium through tubes%
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111
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Non !orus absorberNon !orus absorber * Air flows above and beneath the absorber%
+orus Absorber+orus Absorber * Air flows through the absorber%
Air ,eaters
Non !orus
Absorber+orus
Absorber
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Non &orus Air +eaterNon &orus Air +eater
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Air !y#e "lat #late collectorsAir !y#e "lat #late collectors
$se) co((only for s#ace +eating an)
agricultural +eating a##lications.
+ %ypicalFlat plate collectorolar air heater
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Collectors *it+ #orus asorersCollectors *it+ #orus asorers
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Design of Air #late collectorDesign of Air #late collector
&eavil( insulated material li$e mineral wool is coated beneath the
surface of absorber
)he most favourable orientation of the panel is facing due south with
an inclination of -.o
latitude with the horizontal%
Air as medium of heat transfer eliminates the corrossion and
freezing problems which are more when water is used%
Air is passed through the baffles arranged in zig zag pattern
between the absorber and insulation where fins provides the morecontact area thereb( more amount of heat to transfer%
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A##licationsA##lications
"lat &late"lat &late
collectorscollectors
Air collectorsAir collectors
&eating Buildings
Dr(ing Agricultural roducts
&eating Green houses%
&eat source for heat engines%
Both Beam and Diffuse radiations
orientation need not be towards sun
little maintaince
simplier than concentric plate t(pe
A)vantagesA)vantages
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!+er(al Analysis of "lat &late Collectors!+er(al Analysis of "lat &late Collectors
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!+er(al Analysis of "lat &late!+er(al Analysis of "lat &lateCollectorsCollectors If I is the intensit( of solar radiation' in 34m 2' incident on the aperture plane of the
solar collector having a collector surface area of A' in m2
)hen the amount of solar radiation received b( the collector is *
&owever' as it is shown 5igure 2' a part of this radiation is reflected bac$ to the s$('&owever' as it is shown 5igure 2' a part of this radiation is reflected bac$ to the s$('
another component is absorbed b( the glazing and the rest is transmitted through theanother component is absorbed b( the glazing and the rest is transmitted through theglazing and reaches the absorber plate as short wave radiation%glazing and reaches the absorber plate as short wave radiation%
)herefore the conversion factor indicates the percentage of the solar ra(s penetrating)herefore the conversion factor indicates the percentage of the solar ra(s penetrating
the transparent cover of the collector 6transmission7 and the percentage beingthe transparent cover of the collector 6transmission7 and the percentage being
absorbed%absorbed%
Basicall(' it is the product of the rate of transmission of the cover and the absorptionBasicall(' it is the product of the rate of transmission of the cover and the absorptionrate of the absorber and is given b(rate of the absorber and is given b(
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!+er(al Analysis of "lat &late!+er(al Analysis of "lat &lateCollectorsCollectors As the collector absorbs heat its temperature is getting higher than that ofthe surrounding and heat is lost to the atmosphere b( convection and
radiation%
)he rate of heat loss 68o7 depends on the collector overall heat loss
coefficient 69:7 and the collector temperature%
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9nder stead( state conditions
)he rate of useful energ( e0tracted b( the collector 68u7' e0pressed as
!+er(al Analysis of "lat &late!+er(al Analysis of "lat &lateCollectorsCollectors
It is also $nown that the rate of e0traction of heat from the collector ma( be
measured b( means of the amount of heat carried awa( in the fluid passed
through it' that is*
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It is convenient to define a !uantit( that relates the actual useful energ(
gain of a collector to the useful gain if the whole collector surface were at
the fluid inlet temperature% )his !uantit( is $nown as ;the collector heat
removal factor 65R7 and is e0pressed as*
!+er(al Analysis of "lat &late!+er(al Analysis of "lat &lateCollectorsCollectors
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Concentric ty#e collector :Concentric ty#e collector :
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si(#le concentric collectorsi(#le concentric collector
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\
Ty!es o% concentric collectorsTy!es o% concentric collectors
a7 5lat plate collector with ad=ustable mirrors
b7 Compounded parabolic collector
c7 C(lindrical parabolic collector
d7 >irror strip reflector 6or7 >oving reflector with fi0ed concentrator
e7 5resnel lens collector
f7 arabolic trough collector
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Beam radiation is reflected from the
number of individual mirrors called
heliostatsto the central receiver at the top%
9pto 2???9pto 2?????CC
Cylin)ricalCylin)rical#araolic#araolictroug+troug+collectorcollector
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"resnel ens Collector"resnel ens Collector
&t is at on one side and has ne
longitudinal grooves on the
other
%he angles of these grooves are
such that the radiation is
brought to the focus
ens are made of plastic sheets.
sed upto /$$$C
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&araolic troug+ collector&araolic troug+ collector
solar radiation coming in a
particular direction is collected
and is collected on the focus of
the parabola
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!+er(al Analysis of concentrate collectors!+er(al Analysis of concentrate collectors
$n)er t+e stea)y state con)itions *e +ave :$n)er t+e stea)y state con)itions *e +ave :
@!uation is written assuming that the contribution of diffuse beam
radiations are negligible
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And 8-the overall loss coefficient can be given as *
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CONC$SION
:ong lasting
Cheaper than other water heating s(stems%
&owever'the( re!uires large areas
Also solar energ( is free
If we do not include the initial cost for installation and the maintenance%
5inall( besides these we should remember b( using solar energ( we canprotect nature
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!+e En)!+e En)