  Home     Chibobo     The Challenges     Activities     Gallery     Contact Us     Links

# Experimenting with Photovoltiac (Solar) Panels (Practical)

### Current-Voltage Characteristics of a Photovoltaic Panel (Solar Panel)

You will need the following equipment:

1. sunlight or a desk/lamp on a day where it is cloudless
2. a photovoltaic cell
3. a voltmeter, ammeter
4. light meter (measuring in watts per sq. m is preferable - some schools will have a lux meter instead)
5. potentiometer (with 10 ohm protective resistors) as follows
 Source of light Variable resistor required Sun light - maximum brightness (≈ 1000W/m2) (0 – 50 ohm) or possibly (0 – 100 ohm) Sun light – half sun brightness(dull) (≈ 500 W/m2) (0 – 250 ohm) or possibly (0 – 500 ohm)

Use a 10 ohm protective resistor in series with the variables so they don't overheat and burnout under high power output.

Method

Part A

• The experiment should be done outside under constant temperature and sunlight conditions – ie no clouds

• The experiment should also be performed quickly to avoid overheating of the panel that may then change the characteristics during the data-collection

• Make sure that you don’t cast any shadows or reflections over the panel during the experiment.

• Set-up the circuit below (using the middle and either of the outer pins of the variable resistor) in area of maximum sun • Once you have fixed the panel it is NOT TO BE MOVED DURING THE EXPERIMENT.

• Record the sunlight intensity using the light meter (in W/m2) by holding its face parallel with the face of the panel.
• Turn the axle of the variable resistor so that you can record current and voltage pairs increasing at approximately 1 V intervals. Include uncertainties.
• Determine the short-circuit current by removing the variable resistor from the circuit and measuring the current under no load. Check that the voltage is ZERO for this measurement and add this data to your table.
• Determine the open-circuit voltage by measuring the panel voltage without the load - connecting only the voltmeter across the panel – ZERO current.
• Measure the dimensions of the panel face or a cell so as to determine its area in m2

Part B

• Repeat for a position where the panel faces away from the sun.

Analysis

Enter the data on a spreadsheet as follows:

 Panel/Load voltage (V) Current output (A) Power output (W) Load resistance (ohms)
1. Enter your data onto a spreadsheet with the voltage column first according to the table above.
2. For each current-voltage pair determine the power developed by the photovoltaic panel by using the spreadsheet (Power = Measured Voltage x Measured Current)
3. For each current-voltage pair determine the load resistance developed by the photovoltaic panel by using the spreadsheet.
Resistance =
 Measured Voltage Measured Current
4. Plot the current (A) (y-axis) vs voltage (V) (x-axis) and power (W) (y-axis) vs voltage (V) for all trials - by producing an XY scatterplot for each one. You should have separate graphs with each graph showing the current and power developed vs voltage.
5. Locate the maximum power points produced by the panel by determining the maximum power points for each of the sets of data using the graphs that you have generated.
- determine the voltage, current, power and circuit resistance at the maximum power point.
6. Determine the maximum power supplied to the panel by the sunlight as follows:

Power Supplied by Sun (watts, W) = Irradiance (W/m2) x panel area (m2)

Questions

1. Compare the voltage (V) vs current (A) graphs for each panel position and note any differences.
2. Compare the different maximum powers, voltages, currents and external resistances for the different panel positions and comment on their comparison.
3. Comment on how power output is affected by the external resistance loaded to a photovoltaic panel.
4. Calculate the maximum output efficiency for each part as follows:

Maximum efficiency (%) =
 Maximum power output of panel (W) x 100 Power supplied by the Sun (W)

Comment on the significance of the size of the efficiency.