Solar PV systems use cells to convert sunlight into electricity. The PV cell consists of one or two layers of a semi conducting material, usually silicon. When light shines on the cell it creates an electric field across the layers causing electricity to flow. The greater the intensity of the light, the greater the flow of electricity. PV cells are referred to in terms of the amount of energy they generate in full sunlight; know as kilowatt peak or kWp.
The solar cell is the basic building block of Solar PV technology. Most people are familiar with PV Solar Cells that power calculators. These cells are wired together to form a module (PV solar panel). The PV modules gather solar energy in the form of sunlight and convert it into direct current (DC) electricity. An inverter can convert this DC power into alternating current (AC power, which is the type of electricity used in your home).
PV modules are joined together to form a PV Solar Panel system. Large PV systems can be integrated into buildings to generate electricity.
Check out the excellent Solar Spark website (http://www.thesolarspark.co.uk/) which includes a wealth of resources, animations, talks and experiments related to solar power.
Experiment to investigate the variations in electrical power generated with changes of a) Solar Panel angle b) Solar Panel direction c) Shade?
Solar panels; ammeters, voltmeters, or multimeters; alligator clips; small electric motors, lamps or resistors (the load); recording sheet
Methodand Data Analysis
- Attach the motor, or lamp to the solar panel using the alligator clips in a complete circular circuit. Set it out in the sun and watch the motor or lamp run off the sunlight.
- Use a voltmeter and ammeter or a multimeter to measure the current in the circuit and the voltage across the solar panel. Remember you must connect the voltmeter in parallel with the solar panel, while the ammeter must be connected in series. See http://www.bbc.co.uk/bitesize/ks3/science/energy_electricity_forces/electric_current_voltage/revision/5/ for some further help. Record your measurements. Note that power is the product of voltage (V) and current (I), i.e. P (Watts) = V (Volts) x I (Amps).
- Now connect two solar cells together first in series and then in parallel. Does that change how fast the motor runs or how brightly the lamp shines? What happens to the values of the voltage and current?
- When circuits are wired in series, the voltage (V) of each panel is added together, but the current (I) remains the same. In a series circuit, every device must function for the circuit to be complete, so if one device stops working or is disconnected, the all other devices in the series circuit will stop working.
- When circuits are wired in parallel, the voltage of each panel remains the same and the current of each panel is added. In a parallel circuit, each device has its own circuit, so if one or more device stops working or is disconnected, electricity can still flow to the other devices (provided they are not connected in series with the broken/disconnected devices).
- With a load and your meters connected, point the panel towards the sun. Vary the angle of the panel from 0 to 90 degrees to the horizontal. Comment on the results, particularly the variations around the 30 degree position, which is the angle used for the solar farm panels. Discuss why this is the chosen angle.
- Now set the panel to 30 degrees. Change the direction of the panel by rotating horizontally through 360 degrees using a compass to help you. Comment on the results, particularly the variations around the due South direction, which is the direction in which solar farm panels are set. Discuss why this is the chosen direction.
- Note the time of day, set the panel to face the sun in its current position. Record the direction and comment on the result. You could leave your panel circuit set up and return to it at different times of day to see the change in your meter readings, as the sun moves around the panels.
- Shade the front surface of the panel. Record the meter readings while doing this. Discuss the effect of shadow on the panel output.
Can you summarise how you would design a solar panel array to maximise the amount of energy generated? Give your evidence for your conclusion. Can you identify any roofs or other locations at your school which would be suitable for mounting solar panels?
Evaluate how you carried out the solar panel efficiency experiment and what could be improved.