HT instruments PVCHECK - Manual (Page 64)

PVCHECK
EN - 62
11. APPENDIX – THEORETICAL OUTLINE
11.1. EFFICIENCY TEST ON PV INSTALLATIONS
According to the requirements of the laws in force, DC efficiency test on a PV installation
depends on the type of correction used to compensate the effects of the module’s
temperature and on the mathematical relationship used to calculate the nDC parameter
(see § 5.2.3).
Corr. Tcel value
Mathematical relationship for nDC
calculation
Standar
d
Result
Tmod
Tcel = Measured module temp.
value




  
 

C) 40 Tcel (se
100
40) - (Tcel - 1
C) 40 Tcel (se 1
fv2

R
hence






 

n
STC
p
dc
P
G
G
Rfv
P
nDC
2
Italian
guideline
CEI
82-25
OK/NO
Tenv
Tcel = Calculated module temp.
value
 
800
G
20 Tamb Tcel p    
NOCT
nDC
Tcel = Measured module temp.
value
 
n
dc
cel
p
STC
P
P
T
G
G
nDC
 





    
25
100
1

- - - - - -
where:
Symbol Description
Measurin
g unit
p
G
Irradiance measured on PV module surface
 
2 W/m
STC
G
Standard Irradiance = 1000
 
2 W/m
n
P
Rated Power = sum of all Pmax values of the section of the PV plant being
measured
 
kW
dc
P
DC power measured at the PV generator’s output
 
kW
2 Rfv
Correction factor depending on the Temperature of PV Cells (Tcel) measured or
calculated according to the type of selected correction relationship
 Absolute value of the thermal coefficient of Pmax of the PV modules included in the
plant section being measured.
 
C %/

NOCT
(Normal Operating Cell Temperature) = Temperature the cells under reference
conditions are brought to (800W/m
2
, 20°C, AM=1.5, air speed =1m/s).
 
C %/

The previous relationships are valid if Irradiance > Min Irradiance (see the User Manual of the MASTER
instrument) and the irradiance values are “steady”, i.e. for each sample taken, with IP
 1min, the
difference between the maximum and minimum irradiance values measured must be < 20W/m
2
The final OUTCOME can be:
 Non-displayable: if the obtained values are inconsistent (e.g. nDC >1.15) or if
irradiation has never reached a steady value > minimum threshold set.
 The maximum performance of the system
The highest performance (maximum value of nDC) is detected according with previous
relationships