Samlex America SC-10 - Manual (Page 6)

6
3
PRINCIPlES OF OPERATION
Electrical operating parameters of a solar panel
A solar panel can be considered as a current limited source of electrical power with a
voltage versus current relationship as shown in Fig. 1.
Voltage - Current Characteristics
Voltage (V), Volts
Cu
rr
en
t
(I)
, A
m
p
s
0.0
0.2
0.4
0.6
0.8
1.0
0 5 10 15
V
MP
= 16 V
V
OC
= 20.2 V
V
OC
= 21.5 V
V
MP
= 17 V
I
SC
= 0.6 A
I
SC
= 0.33 A
20 25
SC-05
SC-10
Fig. 1. Voltage versus Current characteristics.
When exposed to the sun and without any load connected, the solar panels will generate
an Open Circuit Voltage (V
oc
). As soon as a load is connected to the panel, the voltage at the
load will drop and the value of the voltage at the load will be determined by the current (I)
drawn by the load. Please note that at the Open Circuit Voltage Voc, the output current (I) is
zero.
The electrical power (P) in Watts fed to the load = Voltage (V) X Current (I).
If the output of the panel is short circuited, the output current will be limited to the
maximum current that the panel can provide. This Short Circuit Current is designated as I
sc
.
The maximum power P
mp
is fed to the load when the operating point is near the knee
of the curve as shown. At this operating point for maximum power output, the voltage is
designated as V
mp
and the current is designated as I
mp
.
Please note that for the portion of the curve between V
oc
to V
mp
, the current drops at a
faster rate. After that, the current is almost constant and equal to the Short Circuit Current
I
sc
.