Nuts and Volts - August 2009

Solar Panel Construction

Individual solar cells are wired together in series-parallel arrangements to create the voltages and currents necessary for the solar panel’s application. This requires creating a grid of wires and supporting metallic traces for the interconnections which add to the area and also contribute electrical losses like any wires do in a DC circuit. The wires and traces also block light. Modern solar panels incorporate protective diodes that help prevent heavy current overloads if a portion of the panel is shaded. While effective, the diodes create their own electrical losses

Solar Array.

in terms of normal voltage drop and generated heat.

Solar cell and solar panel images courtesy Wikipedia.com

This value is generally 0.01 to 0.05 ohms — 10 to 50 milliohms — hardly anything in terms of adding to the load resistance. However, with such a small sense resistor the voltage drop is also small. To compensate, the multimeter adds a voltage amplifier across the sense resistor to boost the voltage to a measureable quantity for the A/D converter.

The gain of the voltage amplifier is used in calculating the voltage drop and resulting current value. So, if the voltage drop across a 0.01 resistor is one millivolt and the gain of the voltage amplifier is set at 100, the

The Experiments

Now, let’s get started on two of the solar panel experiments. You can find complete details on these and the other experiments including background information, equipment setup, and experiment procedures at www.learnonline.com. Just click on the Experimenter Kits menu selection. Then click on the selected experiment for your chosen processor.

Solar Experiment #1:

Sunlight versus Artificial Light

This experiment demonstrates the difference between sunlight and artificial light as it strikes a solar panel. It shows that sunlight provides a constant source of voltage and current while artificial light produces “ripples” due to its AC nature. The ripples are a result of the 60 Hz AC that powers the incandescent light bulbs and fluorescent lights.

Procedure:

Aim the solar panel at an open window with the sun shining (Figure 7). Notice the steadiness of the voltage output. Now expose the solar panel to artificial light from an incandescent bulb or overhead fluorescent light. Notice the ripples on the panel’s output. This is due to the 60 Hz AC that powers the artificial light. Go back to the window for another look at the steady voltage levels.

Now, expose the solar panel to a higher intensity of artificial light by moving it closer to the light source (Figure 8). Note the expected increase in voltage, as well as the increase in ripples. This is a simple experiment, but few people have ever seen artificial light and sunlight measured this way — this may include you, too.