Fundamentals of Solar Thermochemical Processes
Prof. Aldo Steinfeld
ETH Zurich
Department of Mechanical and Process Engineering
ETH-Zentrum ML-J42.1
8092 Zurich
Switzerland
Tel: +41-44-632-7929
E-mail: [email protected]
Solar Concentrating Technologies
• Trough systems
• Tower systems
• Dish systems
SFERA Winter School Solar Fuels & Materials Page 2
Solar Radiation
Why Concentrated Solar Energy?
qsolar
qreradiation
T
quseful
SFERA Winter School Solar Fuels & Materials Page 3
Why Concentrated Solar Energy?
qsolar
qreradiation
T
quseful
C Tstagnation
1 364 K
10 648 K
100 1152
1000 2049 K
5000 3064 K
10000 3644 K
For:I = 1 kW/m2 (1 sun) = 5.67.10-8 W/m2K4
usefulFor q 0
1 solarq C I
0.25
stagnation
C IT
Thermal equilibrium:
useful absorbed reradiation
4solar
q q q
q T
8 2 4
Stefan-Boltzmann constant
5.67051x10 W /(m K )
Why Concentrated Solar Energy?
0
500
1000
1500
2000
2500
3000
3500
4000
0 2000 4000 6000 8000 1 104 1.2 104
Tem
per
atu
re [
K]
Concentration Ratio
C Tstagnation
1 364 K
10 648 K
100 1152
1000 2049 K
5000 3064 K
10000 3644 K
SFERA Winter School Solar Fuels & Materials Page 4
Maximum Solar Concentration
R
qsunqorbit
EARTH
SUND
8-1
11
R = 6.9599 10 m = sin R/D = 16' = 4.65 mrad
D = 1.505 10 m
2sun2 2
sun orbit 2orbit
q D 1q 4 R = q 4 D = 46,200
q R sin
0.2524sun sun orbit
sun2orbit
q = T qDT = 5780 K
Rq = 1353 W/m
,solarI ( ) 2
solar ,solar0
I I ( )d 1353 W/m
Solar Radiation
SFERA Winter School Solar Fuels & Materials Page 5
• Line focusing.
• C = 30 - 80.
• Unit 30 - 80 MW.
• Unidirectional trough curvature.
• 1-axis tracking N-S.
Parabolic Trough System
Heliostat Field
Tower
Receiver
• Point focusing.• C = 200 - 1000.• Unit 30 - 200 MW.• 2-axis tracking heliostats:
elements of different parabolas with varying focal length.
Solar Tower System
SFERA Winter School Solar Fuels & Materials Page 6
• Point focusing.
• C = 1000 - 13,000.
• Unit 7.5 - 100 kW.
• 2-axis tracking parabolic dish.
• Modularity.
• Remote applications.
Solar Dish System
In thermal equilibrium:
quseful = qabsorbed - qreradiation
quseful = qsolar - T4
Quseful = Qsolar - AT4
qsolar
qreradiation
T
quseful
SFERA Winter School Solar Fuels & Materials Page 7
Qsolar
Solar Receiver
absorption = [ ]
{
Solar Power Input
[ ] - [ ]
{Power absorbed {Power re-radiated
Qsolar
Qsolar A T4
= = 1
C =Qsolar
A.I}
Qreradiation
CConcentratedSolar Energy
T
I
4L
exergy,ideal absorption Carnot
TT1 1
C I T
4
absorptionT
1C I
For:I = 1 kW/m2 (1 sun) = 5.67.10-8 W/m2K4
C Tstagnation
1000 2049 K
5000 3064 K
10000 3644 K
Toptimal
1106 K
1507 K
1724 K
Carnot
1000
5,000
10,000
20,000
40,000
Fletcher and Moen, Science 197, 1050, 1977.
Toptimal
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Temperature [K]
0 500 1000 1500 2000 2500 3000 3500 4000
exergy,ideal
5 4exergy Loptimal L optimal
T IC0 T 0.75T T 0
T 4
0.25
exergy stagnation
C I0 T
4L
exergy,ideal absorption Carnot
TT1 1
C I T
SFERA Winter School Solar Fuels & Materials Page 8
OPTICAL CONCENTRATOR
SOLAR
RECEIVER
Electricity
HEAT
ENGINE
Heat
Concentrated Solar Radiation
Direct Solar Radiation
Rejected heat
Receiver losses
Concentrationlosses
absorption Carnot
solar to electrcity optics receiver heat to electricity
Solar FuelsReactants
HeatAbsorption
QH,TH
ChemicalReactor
H = 285 kJ/mol
FuelCell
W
QL,TL
G = 237 kJ/mol
H2OReactants H2 + ½ O2Solar Fuels
ConcentratedSolar Radiation
Solar Thermochemical Conversion
SFERA Winter School Solar Fuels & Materials Page 9
Solar FuelsReactants
HeatAbsorption
QH,TH
ChemicalReactor
FuelCell
W
QL,TL
ConcentratedSolar Radiation
Lmaximum Carnot
H
T1
T
Heat Engine
4H
absorption
T 1
C I
Solar Thermochemical Conversion
f
rim
= 16’ = 4.65 mrad
f.ab
2.f.(1+cosrim)cosrim
a =
2.f.(1+cosrim)
b =
Flux
f.r
a
C = sin2rim/2 = 4.65 mradrim = 45° } C 23,000
SFERA Winter School Solar Fuels & Materials Page 10
3D - CPC2D - CPC
CPC – Compound Parabolic Concentrator
Ref.: Welford, W. T., and Winston, R. (1989).High Collection Nonimaging OpticsAcademic Press, San Diego, USA.
rin
rout
L = (rin+rout).cot
For =1:
Axis ofParabola
2D-CPC in out
2 2 23D-CPC in out
C = r /r = 1/sin
C = r /r = 1/sin
SFERA Winter School Solar Fuels & Materials Page 11
= 16’ = 4.65 mrad
f
rim
inrim rim
in out rim
2D-CPC in out
2 2 23D-CPC in out
2fr
(1+cos ).cos
L = (r +r ) tan
C = r /r = 1/sin
C = r /r = 1/sin
Equations of the CPC
rin
rout
L = (rin+rout).cot
z
r
out
out in
out
2f sin( )r r
1 cos
2f cos( )z
1 cos
where :
r r sin
f r (1 sin )
22
SFERA Winter School Solar Fuels & Materials Page 12
x r[sin M() cos ]
y r[ cos M()sin ]
M( ) for 0
2 a
/ 2 a cos a 1 sin( a
for 2 a
32
a
Equations of the 2-D CPC + involute
a CPC‘s half acceptance angle and is taken equal to the rim angle of the primary parabolic concentrator.
r radius tubular receiver.
Tubular-Receiver
r
a
x
y
Receiver
Tower Reflector
CPCCompoundParabolic
Concentrator
Heliostat Field
Tower
• Heliostat field + TowerReflector (Cassegrain).
• Beam-down on CPC.
• C = 5,000 - 10,000.
• Major hardware on ground level.
SFERA Winter School Solar Fuels & Materials Page 13
DecarbonizationH2O/CO2-splitting
Solar Fuels
SolarCracking
SolarGasification
SolarReforming
SolarThermolysis
SolarThermochemical
Cycle
Solar Electricity
+Electrolysis
ConcentratedSolar Energy
Fossil Fuels(NG, oil, coal)
Optional CO2/C Sequestration
H2O CO2
Solar Fuels (H2, syngas)
SFERA Winter School Solar Fuels & Materials Page 14
