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VERY HIGH EFFICIENCY CONCEPTS 137
Efficiency h
[%]
100
6000
90
80
85.4%
5500
5000
70
60
50
4500
4000
40
3500
30
3000
20
2544 K
10
2500
0
1 10
100 2000
(∆eH rc )/(eH rs )
Temperature of the radiator T r
[K]
Figure 4.8 TPV ideal converter efficiency versus H rc ε/H rs ε. The energy ε and the cell voltage
V are optimised
Hot cell
(LED)
Cold cell
·
E s
·
E r
Hot cell (LED) T r
·
E r ′
·
E c
·
W r
W·
A i inlet A r A c
Cold
cell
·
W c
Concentrator
Cavity
·
Q c
Environment at T a
(a)
(b)
Figure 4.9 Diagram of the TPH converter with cavity. In (b), the energy fluxes are given
by Ė s ≡ E(T s , 0, 0, ∞,H rs ), Ė r ≡ E(T r ,qV r , 0, ∞,H rs ), ˙Q r = Ė s − Ė r , Ė ′ r ≡ E(T r,qV r , 0, ∞,H rc ),
Ė ′ c ≡ E(T a,qV c ,ε g , ∞,H rc )
emitted by a heated light emitting diode (LED) into electricity. A diagram of this device
is found in Figure 4.9. As in the TPV device, the LED can be heated with a fuel, but in
our context it is heated as well with radiation absorbed from the sun. To emit luminescent
radiation, the LED absorbs electric power, Ẇ r , in addition to the power delivered from
the photons that illuminate the absorber. This power is to be subtracted from the electric
power converted by the solar cell Ẇ c .