How to check the closed-circuit current on a PV array

Written by peter johnson
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Solar photovoltaic (PV) cells produce their maximum current when the cell is closed or short-circuited. Producing a closed-circuit and measuring the current does not damage the cell. The short-circuit current is usually given the symbol "Isc" and is measured in amps. This value, together with the open-circuit voltage, "Voc," are two of the principal parameters that define the performance of a solar cell. The closed-circuit current of an array of solar panels can be calculated from the closed-circuit current of a single panel.

Skill level:
Moderate

Things you need

• Digital multimeter capable of measuring DC up to 10 amps

Instructions

1. 1

Examine one of the solar panels in the array and look for the short-circuit current shown on the back of the panel, or given in the installation manual that came with the panels. Make a note of this "Isc" value in amps.

2. 2

Verify that the short-circuit current of one of the solar panels is less than 10 amps --- which is generally the case. Switch the dial on the multimeter to measure up to 10 amps DC. Make sure the red and black probes are plugged in correctly. Use alligator clip probes for this measurement.

3. 3

Measure the current at a time when there is sunshine full on the solar panel. Disconnect the panel from the array and cover the front surface. Connect the red alligator clip from the multimeter to the positive terminal of the solar panel, and the black clip to the negative terminal. Uncover the panel and read the short-circuit current in amps on the multimeter. Make a note of this value. Repeat this procedure for the other panels in the array. The closed-circuit current should be the same for each solar panel --- unless one of the panels is damaged.

4. 4

Repeat the measurements at least twice to check that your readings are reliable.

The short-circuit current will change with the level of insolation --- the measure of solar radiation energy on a surface. This may vary even on a bright sunny day.

5. 5

Calculate the closed-circuit current for the entire array. Solar panels connected in series "strings" will have the same closed-circuit current as a single panel. When the "strings" of panels are connected in parallel, the closed-circuit current of each string should be added together to obtain the closed-circuit current of the entire solar array.

Tips and warnings

• The voltage produced by an array of solar panels can be dangerously high. Do not try to measure the short-circuit current of the entire array. If you are unsure of the procedure to be followed, consult a qualified electrician.

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