european journal of social sciences issn: 1450-2267 - EuroJournals

European Journal of Social Sciences – Volume 5, Number 3 (2007)
Figure 1 (a): PV/T collector with CPC, (b) PV/T collector without CPC
Glass cover Solar cell
Fin
Results and Discussions
The efficiency of the combined photovoltaic thermal collector is defined as the sum of thermal
efficiency and electrical efficiency as:
η pv / t = ηthermal
+ ηelectrical
The thermal efficiency of the collector with CPC and fins is as follows:
η th =
.
m c p ∫ ( T 0 - T i ) dt
A c CR ∫ I tot dt
The electrical efficiency is as follows:
η elect =
∫ τ g I u η pv α pv
'
2 n
' ρ pv ρ g ρ
n
R
P CR d ρ R [ 1 + (
CR
CR ∫ I tot dt
) dt
The thermal efficiency of the collector without CPC is as follows:
η th =
.
m c p ∫ ( T 0 - T i
A c ∫ I tot dt
) dt
The electrical efficiency is as follows:
η elect = ∫ τ g I tot η pv α pv P
∫ I tot dt
Where:
I
u
I tot
=
CR
Absorber plate
Air in
Air in
CPC
(a) (a)
Insulator
ηpv is solar cell efficiency which defines as follows:
η = η [ 1 - 0.0045 ( T - T ) ]
pv ref
pav ref
ηref is the reference efficiency of the solar cell at Tref = 25 Cº which is 15 %.
Figure 2 show the comparative on the photovoltaic efficiency of the collectors with and without
CPC. It can see that the photovoltaic efficiency is quite close between two collectors at flow rates less
than 0.0316 kg/s, but the deviation becomes more pronounced for mass flow rate greater than or equal
0.09 kg/s. the comparative on the thermal and combined efficiency of the collectors with and without
121
Fin
Glass cover
Air in
Insulator
(b)
Solar cell
Air in
Absorber plate