Werner Weiss
SOLAR COLLECTORS
AEE - Institute for Sustainable Technologies (AEE IN TEC)A-8200 Gleisdorf, Feldgasse 19AUSTRIA
FLAT-PLATE COLLECTOR
transparentcover
connection pipe
absorber
framework structure
connection pipefor
heat transfer medium pipe
insulation
Ultrasonic or Laser Welding?
43%
8%
5%
2%
Ultrasonic or Laser?
Source: Sonne, Wind und Wärme, 2009
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
Source: Sonne, Wind und Wärme, 2009
Absorber Colors
10%5%
Blue or black?
Source: Sonne, Wind und Wärme, 2009
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
Source: Sonne, Wind und Wärme, 2009
Direct flow U-tube with flat absorber
Source: Frei, U.: Kollektoren in solarthermischen Systemen, SPF Solartechnik Prüfung Forschung, TriSolar98
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
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
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
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
TRANSPARENT COVER MATERIALS
4% Reflection
(42)
4% Reflection
Standard Solar Glass
Standard Solar Glass
TRANSPARENT COVER MATERIALS
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
Source: Sonne, Wind und Wärme, 2009
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, ..), ..
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
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
eEnergieeingesetzt
eNutzenergi=η useful energy
solar energy
G
tta
G
tta amam )²()(
210
−⋅−
−⋅−= ηη
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
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