Innovative Lives

Experiments with Solar Shingles

The Story of Inventor Subhendu Guha


How does a photovoltaic panel work?

A photovoltaic cell is a semiconductor. When light hits the photovoltaic (or PV) cell, the light can be reflected or absorbed or it can pass through the cell.

If the light is absorbed into the cell, the light's energy is transferred to the electrons in the semiconductor. This causes the electrons to flow, creating an electrical current.

Sun and PV panel

Both PV cells and LEDs are semiconductors

Light Emitting Diodes

We can learn how PV cells work by experimenting with light emitting diodes (LEDs), because both are semiconductors.

What is a diode?

Diodes are semiconductors that allow electricity to flow in one direction but not the other like a one way valve for electricity. The positive side of the diode is called the anode. The negative side is called the cathode. Current always flows from the anode to the cathode.

Cathode | AnodeA Light-Emitting Diode (LED) is a diode that emits light. The two small arrows pointing away from the diode represent light energy being emitted.

How many LEDs can you light?

 Materials and Tools
  • Yellow, red and green light-emitting diodes
  • Insulated test leads with alligator clips at each end
  • 2 "AA" batteries
  • "AA" battery holder (holds 2 batteries)
LEDsTest leads
AA Batteries


  1. Arrange one LED, 2 wires and two batteries in a holder to make the LED glow. Does it matter which way the LED is connected? Why?
  2. Now try adding more wires (but still only 2 batteries) to make 2 LEDs glow.
  3. How many LEDs can you make glow with two batteries?
  4. Sketch a picture of each arrangement that makes the LED glow. Compare your sketches with series and parallel circuits below.

Battery/LED diagram

This activity was created by Emily Wilson, Lemelson Center

All text and images © Smithsonian Institution. Updated 26 February 1999.

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