presented at Material Research Society (MRS) conference, Boston MA, 2009

1. 1
Thermoelectric Topping Cycle for
Trough Solar Thermal Power Plants
Presenter: Andy Muto
Advisor: Gang Chen
NanoEngineering Group, MIT
MRS Conference, 12/2/09
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2. 2
Solar Thermal Power
-most attractive solar technology for
utility scale
-uses conventional steam Rankine cycle
-allows for 6-15 hrs thermal storage
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3. Solar Thermoelectric Topping Cycle 3
Vacuum Heat Transfer fluid outlet
Enclosure temperature is limited to 400°C
Thermoelectric Characteristics:
Low Temp Absorber
Fluid -high power densities
-reliable, no moving parts, no
Thermoelectric Elements maintenance
-inexpensive
High Temp Absorber -low efficiency
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4. 4
Thermoelectric Conversion Efficiency
Carnot Limit
ZT=15
Solar Rankine
ZT=3
ZT=2
ZT=1
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5. 5
Thermoelectric Conversion Efficiency
Carnot Limit
Topping ZT=15
Cycle
Solar Rankine
ZT=3
ZT=2
ZT=1
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6. 6
Thermoelectric Conversion Efficiency
Carnot Limit
Topping ZT=15
Cycle
Solar Rankine
ZT=3
ZT=2
ZT=1
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7. 1-D Model 7
fluid
tube wall
P N
absorber
Csolar  qloss
glass  Abs 
Csolar
Csolar qloss
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8. 1-D Model 8
fluid
tube wall
ZTeff 1 1
W TE AbsC,TE
P N TE Tf
ZTeff 1 
Tabs
Carnot efficiency
absorber
Csolar  qloss
glass  Abs 
Csolar
Csolar qloss
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9. 1-D Model 9
WTE  WRankine
Rankine  sys 
WRankine Csolar
fluid
 Rankine  C , Rankine II , Rankine  Abs  TE 
tube wall
ZTeff 1 1
W TE AbsC,TE
P N TE Tf
ZTeff 1 
Tabs
Carnot efficiency
absorber
Csolar  qloss
glass  Abs 
Csolar
Csolar qloss
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10. 10
Surfacevs. Wavelength
Intensity
Properties
1.4
Absorptivity=0.96
1.2
Glass transition λ=2700 nm
Transmissivity=0.963 (λ<2700 nm)
1 Emissivity=0.89 (λ>2700 nm)
Solar Intensity [W/m2/nm]
Intensity [W/m2/nm]
Surface Emissivity
0.8
0.6
0.4
0.2
Emissivity=0.05
0
500 1000 1500 2000 2500 3000 3500 4000
Wavelength [nm]
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11. 11
Optimal Transition Wavelength
Intensity vs. Wavelength
60
Solar at 40 times concentration
50
transition TAbs , Csolar 
Intensity [W/m2/nm]
40
30
20
Black Body 700°C
10
Blackbody 400-700°C
by 50°C increments
0
500 1000 1500 2000 2500 3000 3500 4000
w avelength [nm]
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12. Absorber Efficiency
Intensity vs. Wavelength Rankine Topping Cycle
60
[W/m2/nm]
1.4
1.2 Topping cycle 55
1800 nm
0.9
1
0.92
0.88
95.6%
Solar Intensity/nm]
50
0.8
0.82
Concentration [suns]
0.86
0.8
0.84
2
Intensity [W/m
0.6 Original cycle 45
0.7 0.76 .78
2500 nm
0
concentration
0.4
99.1% 40
0.2
35
4
0
500 1000 1500 2000 2500 3000 3500 4000
30
Wavelength [nm]
25
20 Absorber Efficiency
15
Absorber Efficiency decreases
rapidly with increasing temperature 10 200 300 400 500 600 700
due to blackbody overlap with solar absorber Temperature [C]
spectrum Absorber Temperature [C]
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13. Decision to Implement TE Topping Cycle
with TE Topping cycle should produce 10% more
Pratio 
without power to justify added engineering costs
Vacuum
Enclosure
Low Temp Absorber
Fluid
Thermoelectric Elements
High Temp Absorber
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14. Decision to Implement TE Topping Cycle
with TE Topping cycle should produce 10% more
Pratio 
without power to justify added engineering costs
60
55
50
Power Ratio
concentration [suns]
45
ZT=1
40
1.1 5
1.0 5
1.1
35
concentration [suns]
30
Implement Do Not Implement
25
20
15
10
150 200 250 300 350 400 450 500
fluid temperature [C]
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15. Decision to Implement TE Topping Cycle
with TE Topping cycle should produce 10% more
Pratio 
without power to justify added engineering costs
60
55
50
Power Ratio
concentration [suns]
45
ZT=1
40
1.1 5
1.0 5
1.1
35
concentration [suns]
30
Implement Do Not Implement
25
20
15
10
150 200 250 300 350 400 450 500
fluid temperature [C]
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16. Decision to Implement TE Topping Cycle
with TE Topping cycle should produce 10% more
Pratio 
without power to justify added engineering costs
60
55
1.4
1.1 5
1.0 5
1.3
1.1
1.2
50
1.45
concentration [suns]
45
1.35
1.2 5
40
35
concentration [suns]
1.5
30 Power Ratio
ZT=3
25
20
15
10
150 200 250 300 350 400 450 500
NanoEngineering Group fluid temperature [C]

17. Optimal Absorber Temperature, ZT=3
60
55
65 0
50
concentration [suns]
45
625
40
35
60 0
30
57 5
25
Optimal Temperature ZT=3
55 0 500-600°C
20
52 5
15 500
10
150 200 250 300 350 400 450 500
fluid temperature [C]
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18. 18
Conclusions
•investigated a thermoelectric topping cycle for
parabolic trough solar thermal power plants
•current materials with ZT=1 will not work in this
application
•ZT=3 or greater is needed, with operating
temperatures around 500-600°C
•other applications may exist within solar thermal
energy at lower temperatures
Acknowledgements: KFUPM
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19. Power Ratio ZT=3 Emissivity=0 with TE
Pratio 
without
60
55
1.5
1.4
50
concentration [suns]
45
1.25
1.3 5
1.4 5
1.2
1.1 5
40
1.3
1.1
35
30
25
1.05
20
15
10
150 200 250 300 350 400 450 500
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20. Limits to ZT=1 applications 20
3 Power Ratio ZT=1, emissivity=0
10
1.2
1.1
1. 05
1. 2
1. 1
1. 05
concentration [suns]
2
10
1.2
1
1.
5
1. 0
1
1
1
10
100 200 300 400 500 600 700
fluid temperature [C]
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21. Efficiency Gain ZT=3
 gain   with TE   without
60
55 0.1 2
50
2
concentration [suns]
45
0.0
0.0 8
0.0 6
0.0 4
0.1
40
35
30
25
20
15
0
10
150 200 250 300 350 400 450 500
fluid temperature [C]
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22. 1-D Heat Loss 22
Tabs absorber
1 
1 
 A
 A
1
1
AVF
AglassVF
1   glazing
 glazing Aglazing qloss A
Tglazing glass
1 1    , glazing
UAglazing   , glazing Aglazing
1
AglazingVF
1    , 1    ,
  A   A
T
qloss  qabs  glazing  qtransmit  qglazing   qtransmit  qconvection
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23. 1-D Model 23
WTE  WRankine
 sys 
Csolar
 II , Rankine  0.65  Rankine  C , Rankine II , Rankine  Abs  TE 
 ZT  15
ZTeff 1 1
 II ,TE TE AbsC,TE
ZT ZTeff 1 
Tf
Tabs
1 0.20 Carnot efficiency
2 0.30
3 0.37 Csolar  qloss
 Abs 
Csolar
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24. 24
U.S. Concentrating Solar Resource
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