General Description Of Solar System - Samlex Power SCC-30AB Manuel Du Propriétaire

SECTION 2 |

General Description of Solar System

Current (I),Voltage (V) and Power (P) Curves of a Solar Panel
and how the Solar Panel is rated - V , V , I , I , Pmax
oc mp sc mp
Fig. 2.1. Current (I),Voltage (V) and Power (P) Curves
A Current (I) versus Voltage (V) Curve of a Solar Panel ("I-V" Curve) shows the possible
combinations of its current and Voltage outputs. A typical I-V curve for a 12V Panel is
shown in Fig. 2.1.
The power in a DC electrical circuit is the product of the Voltage and the current.
Mathematically,
• Power (P) in Watts (W) = The Current (I) in Amperes (A) X the Voltage (V) in
Volts (V) i.e. W = V x A
A Solar Panel produces its maximum current when there is no resistance in the circuit,
i.e. when there is a short circuit between its Positive and Negative terminals. This
maximum current is known as the Short Circuit Current and is abbreviated as I . When
sc
the Panel is shorted, the Voltage in the circuit is zero.
Conversely, the maximum Voltage occurs when there is a break in the circuit. This is
called the Open Circuit Voltage (V ). Under this condition, the resistance is infinitely
oc
high and there is no current, since the circuit is incomplete. Typical value of the open-
circuit Voltage is located about 0.5 – 0.6V per cell for Crystalline Cells and 0.6 – 0.9V
for Amorphous Cells. Normally, 12V nominal panel consists of 36 cells in series and a
24V nominal panel consists of 72 cells in series. Hence, the Open Circuit Voltage (V oc )
of panels with crystalline cells will be as follows:
- 12V panel: 36 cells x (0.5 to 0.6V per cell) = 18V to 21.6V
- 24V panel: 72 cells x (0.5 to 0.6V per cell) = 36V to 43.2V
These two extremes in load resistance, and the whole range of conditions in between
them, are depicted on the I-V Curve. Current, expressed in Amps, is on the vertical
Y-axis. Voltage, inV, is on the horizontal X-axis.
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