A solar cell is a renewable energy machine that converts light directly into electrical energy. It works without burning fuel, so it can generate electricity with very low air pollution during operation. The key idea is the photovoltaic effect, where incoming light gives energy to electrons inside a material.
Silicon solar cells are common because silicon is abundant, stable, and can be engineered to control electric charge.
Key Facts
- Photon energy is E = hf, where h is Planck's constant and f is light frequency.
- A silicon solar cell uses a p-n junction to create an internal electric field.
- The photovoltaic effect occurs when absorbed photons free electrons and create electron-hole pairs.
- Electric current is charge flow, I = Q/t.
- Electrical power from a solar cell is P = IV.
- Solar cell efficiency is efficiency = useful electrical power output / light power input.
Vocabulary
- Photovoltaic effect
- The photovoltaic effect is the process in which light absorbed by a material produces a voltage and electric current.
- Photon
- A photon is a packet of electromagnetic energy that can transfer energy to electrons in a solar cell.
- P-n junction
- A p-n junction is the boundary between p-type and n-type semiconductor regions where an internal electric field forms.
- Electron-hole pair
- An electron-hole pair is a freed electron and the positive vacancy it leaves behind after absorbing energy.
- Semiconductor
- A semiconductor is a material with electrical conductivity between that of a conductor and an insulator, allowing its charge flow to be controlled.
Common Mistakes to Avoid
- Thinking solar cells store energy, which is wrong because a solar cell converts light to electricity while a battery stores chemical energy.
- Assuming heat is what makes a solar cell work, which is wrong because useful current comes mainly from photon energy freeing electrons, not from heating the panel.
- Forgetting the role of the p-n junction, which is wrong because the junction's electric field separates charges and helps produce a usable voltage.
- Using P = IV with the wrong units, which is wrong because voltage must be in volts and current must be in amperes to get power in watts.
Practice Questions
- 1 A small solar cell produces a current of 0.40 A at a voltage of 5.0 V in sunlight. What electrical power does it output?
- 2 Sunlight delivers 800 W of power to a solar panel, and the panel converts 160 W into electrical power. What is the panel's efficiency as a percent?
- 3 A photon enters a silicon solar cell and creates an electron-hole pair near the p-n junction. Explain how the cell's internal electric field helps turn this event into current in an external circuit.