03 Solar Collectors

Werner Weiss

SOLAR COLLECTORS

AEE - Institute for Sustainable Technologies (AEE IN TEC)A-8200 Gleisdorf, Feldgasse 19AUSTRIA

Conversion of solar radiation energy into other energy forms

Source: ENREL

TYPES OF COLLECTORS

Plastic Absorber

Flat plate collectors

FLAT-PLATE COLLECTOR

Source: IEA SHC Task 33


Transparent cover

Absorber plate

Tubes

Insulation

Source: Consolar


transparentcover

connection pipe

absorber

framework structure

connection pipefor

heat transfer medium pipe

insulation

ABSORBER - TYPES

Meander absorber

Harp absorber

Manufacturing of a Solar Collector

Manufacturing of a Solar Collector

Source:GREENoneTEC / ESTIF

Strip absorber

Strip Absorber

Local Production in Uganda

Thermographic Photographs of Various Absorber Types

Source: Treikauskas, Ingolstadt University

Absorber Material

37%

Aluminum or Copper?

Source: Sonne, Wind und Wärme, 2009

63%

Aluminum

Copper

Ultrasonic or Laser Welding?

43%

8%

5%

2%

Ultrasonic or Laser?


43%

Laser welding

Ultrasonic welding

Soldering

Mechanical

Other (Glue, Plasma welding)

Full Size or Strip Absorber

8%

Full Size or Strip Absorber

92%

Full Size

Absorber Strip


Absorber Colors

10%5%

Blue or black?


85%

Blue

Black Chrome

Other (AIOx, NiOx, etc.)

Snake Type or Register Absorber?

38%

11%

Snake Type or Register?

7%

44%

Snake

Double Snake

Register

Double Register


CPC - COLLECTOR

Evacuated Tube Collectors


Heatpipe, Vitosol 300 (left) / Direct coupled Sydney Collector (right)

Direct flow U-tube with cylindrical absorber

Detail Sydney collector

Direct flow U-tube with flat absorber

Source: Frei, U.: Kollektoren in solarthermischen Systemen, SPF Solartechnik Prüfung Forschung, TriSolar98

Lenz Tube

Source: SWW 08/20006 S.46


Detail Sydney collector

Evacuated Tube Collectors – Heat Pipe

Heat Pipe Principle – Wet Connection

Error–indication

Va cuu m fa ul ty Vac uu m p resen t

http://www.solardirect.com/

THERMOSYPHON SYSTEM - China


Source: Consolar

Concentrating Collectors

Parabolic Trough Collector

Working Principle - PTC

Tracking of the sun

Collector axis oriented north-south

Built Examples

50%

60%

70%

Wirk

ungs

grad

2. Prototyp 2. Prototyp (mit evakuiertem Hüllrohr)

AEE INTEC and Button Energy

Process Heat Collectors

2nd Prototype 2nd Prototype (evacuated glass tube)

0%

10%

20%

30%

40%

0,00 0,05 0,10 0,15 0,20 0,25 0,30

(Tm-Tu)/IDNI in m² K/W

Wirk

ungs

grad

1. Prototyp

PSE AG Germany

Fresnel Process Heat Collector

Aperture area: 88 m²

Working temperature: max. 200°C

CONCENTRATING COLLECTORS - CCSTaR

Universitat de les Illes Ballears

CPC Collector

0.60

0.70

0.80

0.90

1.00

Effi

cien

cy n

Air 1 barAir 0,01 barKrypton 0,01bar

Process Heat Collectors

LoCo EvaCo (Low concentrating evacuated flat collector), ZAE Bayern

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0 20 40 60 80 100 120 140

Temperature difference T_Coll_mid - T_Amb [K]

Effi

cien

cy n

Concentration: 1,8x

COLLECTOR MATERIALS

??

ABSORBER MATERIALS THERMAL CONDUCTIVITY

absorber material thermal conductivity[W/mK]

steel 50steel 50

aluminium 210

copper 380

ABSORBER COATING

Selective coating: 0 ≤ ε < 0.2, α > 0.9

Partially selective coating: 0.2 ≤ ε < 0.5, α > 0.9

Non selective coating: 0.5 ≤ ε < 1.0, α > 0.9

Plain copper black paint galvanic coating physical vapour deposition or sputtering

ABSORBER COATING

Source:Alanod-Sunselect / ESTIF

TRANSPARENT COVER MATERIALS

cover thickness [mm]

weight [kg/m²]

solar transmittance

Standard glass *) 4 10 0.84

*) danger of breaking determined by high collector temperatures

Standard glass *) 4 10 0.84

Standard glass, tempered 4 10 0.84

Iron free glass, tempered 4 10 0.91

Antireflective coated glass 4 10 0.95

PMMA, ducted plate 16 5.0 0.77

PMMA, double ducted plate 16 5.6 0.72

Collector test


4% Reflection

(42)

4% Reflection

Standard Solar Glass

Standard Solar Glass


Solar glass Solar glass with antireflective coating


AR coated

Sol

ar tr

ansm

issi

on

(42)

Incident angle

Uncoated

Sol

ar tr

ansm

issi

on

Market Share of Clear and Structured Glass

33%

9%

59%

clear glass

structured glass

AR-glass


Glass Thickness

30%

70%

3,2 mm

4 mm


INSULATING MATERIALS

insulatingmaterial

max. allowabletemperature

[ ° ]

density[kg/m³]

conductivity[W/mK] at 20°C

Mineral wool > 200 60 - 200 0.040

Glass wool > 200 30 - 100 0.040

Glass wool > 200 130 - 150 0.048

Polyurethanefoam < 130 30 - 80 0.030

Polystyrol foam < 80 30 - 50 0.034

Absorber Manufacturing Processes

Production Process Deficiencies

Spot Welding - not possible with all metals, susceptible to corrosion, ...

Soft-Soldering - low processing temperature (stagnation!!!), - emission of flux residues, …

Ultrasonic Welding - no continuous substance-to-substance connection, …

Laser Welding - very high processing temperature,

micro-cracks in welding spots

ub

stan

ce-t

o-

sub

stan

ce

con

nec

tio

ns

Laser Welding - micro-cracks in welding spots su co

Plasma Welding - very high processing temperature, …

Splicing - low processing temperature (stagnation!!!), - low heat conductivity of adhesive, …

no

n

sub

stan

ce-

to-

sub

stan

ce

con

nec

tio

ns

Clamping (various designs)

- low heat conductivity of clamping (non uniform contact pressure, ..), ..

FLAT-PLATE COLLECTOR – Simple Design

Modul Collector Roof Integrated Collector

FLAT-PLATE COLLECTOR – Advanced Design

Module Collector Roof Integrated Collector

Physical Processes inside a Flat-Plate Collector

reflection on thepane of glass

heat loss through the pane of glass

reflection on absorber

occurrenceof solar radiation heat loss through the

rear and side walls

Losses of a basic Flat-plate Collector

Source: Source: Wagner & Co.

Characteristic Values of Flat-plate and Evacuated Tube Collectors

Qcoll is the energy collected per unit collector area per unit time

FR is the collector’s heat removal factor

ττ is the transmittance of the cover

α is the shortwave absorptivity of the absorber

G is the global incident solar radiation on the collector

UL is the overall heat loss coefficient of the collector

T is the temperature differential between the heat transfer fluid entering the collector and the ambient temperature outside the collector.

Collector Efficiency Curve

(tm – ta)/G [Km²/W]

Collector Efficiency

eEnergieeingesetzt

eNutzenergi=η useful energy

solar energy

G

tta

G

tta amam )²()(

210

−⋅−

−⋅−= ηη

Collector Efficiency

s. T-Sol Collector data

Collector efficiency curve

0,5

0,6

0,7

0,8Optical Losses

Thermal Losses

0

0,1

0,2

0,3

0,4

0 0,04 0,08 0,12 0,16

(TKm-TA) / GT [Km²/W]

eta

Useful Energy

Stagnation Point

Efficiency of different collector types (calc)

Evacuated Tube Collector

(tm – ta)/G [Km²/W]

Simple Flat-plate Collector

Uncovered Absorber

Selective Flat-plate Collector

Area Definitions

Apertur area

Possible Improvements of FPC

• Hermetically sealed collectors with inert gas fillings;• Double covered flat-plate collectors;• Vacuum flat-plate collectors; and• combinations of the above mentioned

0.5

0.6

0.7

0.8

0.9

effic

ien

cy (

ba

sed

on

ap

ert

ure

are

a) operating temperature

80° to 120°C

0

0.1

0.2

0.3

0.4

0 0.05 0.1 0.15

(Tm-Ta)/G in Km²/W

effic

ien

cy (

ba

sed

on

ap

ert

ure

are

a)

1 AR

2 AR

3 AR

standard flat-platecollector

Source: IEA SHC Task 33


?

Register-Type Absorber

00

11 pipes (d= 10 mm)

1100

1630

1700

28


12 m²

Hydraulic connection of collectors

03 Solar Collectors

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