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Physics
How Solar Panels Work
Solar Panels
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Solar panels turn sunlight into electrical energy using the photovoltaic effect. Sunlight arrives in small packets of energy called photons, and some photons have enough energy to free electrons inside a semiconductor. This matters because it lets a rooftop panel produce useful electric power without burning fuel. The process connects ideas from waves, quantum physics, electric fields, and circuits.
Key Facts
- Photon energy is E = hf = hc/λ, where h is Planck's constant, f is frequency, c is the speed of light, and λ is wavelength.
- A silicon solar cell works best when photon energy is at least the band gap energy, about 1.1 eV for silicon.
- The photovoltaic effect occurs when absorbed photons create electron hole pairs in a semiconductor.
- A p-n junction creates an internal electric field that separates electrons and holes, producing a voltage.
- Electrical power from a panel is P = IV, where I is current and V is voltage.
- Solar panel efficiency is efficiency = electrical power output / sunlight power input.
Vocabulary
- Photon
- A photon is a packet of electromagnetic energy that can be absorbed by matter.
- Photovoltaic effect
- The photovoltaic effect is the creation of voltage and current when light is absorbed in a material.
- Semiconductor
- A semiconductor is a material, such as silicon, whose electrical conductivity can be controlled by impurities and light.
- p-n junction
- A p-n junction is the boundary between positively doped and negatively doped semiconductor regions that creates an internal electric field.
- Inverter
- An inverter is a device that converts direct current from solar panels into alternating current used by most homes and the electric grid.
Common Mistakes to Avoid
- Thinking solar panels store energy by themselves, which is wrong because a panel mainly converts light to electricity and needs a battery or other system for storage.
- Assuming brighter sunlight only increases voltage, which is wrong because stronger light mostly increases current by creating more electron hole pairs.
- Forgetting that photon energy depends on frequency, which is wrong because E = hf means higher frequency light has more energy per photon.
- Confusing direct current with alternating current, which is wrong because solar cells produce DC while homes usually use AC after conversion by an inverter.
Practice Questions
- 1 A solar panel produces 8.0 A at 32 V in bright sunlight. What electrical power does it deliver?
- 2 Sunlight delivers 900 W/m^2 to a 1.6 m^2 panel. If the panel is 20 percent efficient, what is its electrical power output?
- 3 Explain why a solar panel can produce current when sunlight hits it, but not when it is completely covered by an opaque sheet.