Energy from the Sun
The Sun sends Earth more energy in about an hour and a half than all of humanity uses in a year. Solar power captures some of this energy to make electricity or heat. It’s now the fastest-growing source of electricity in the world.
Photovoltaic cells
A photovoltaic cell (PV cell) turns sunlight directly into electricity. Photo means light and voltaic means electricity.
How it works
- A solar cell is made of two thin layers of silicon, a semiconductor.
- The layers are treated with tiny amounts of other elements so one has extra electrons and the other has "holes" (spaces for electrons).
- When sunlight hits the cell, its energy knocks electrons loose.
- The boundary between the layers pushes these electrons in one direction, creating a current.
- Metal contacts collect the electricity.
Many cells are connected in a solar panel (module); many panels make a solar array.
From panel to plug
- Solar panels produce direct current (DC).
- An inverter changes it to alternating current (AC), which homes use.
- Extra electricity can go into batteries or back to the power grid.
Efficiency
| Type | Typical efficiency |
|---|---|
| Common rooftop silicon panels | About 18–23% |
| Best lab cells | Over 40% (multi-layer cells used in space) |
| Plants (photosynthesis) | About 1–2% |
Solar panel costs have dropped by about 90% since 2010, making solar one of the cheapest sources of new electricity in many places.
Solar thermal
Solar thermal systems capture the Sun’s heat rather than making electricity directly.
| System | Use |
|---|---|
| Solar water heaters | Rooftop collectors heat water for homes and pools |
| Solar air heaters | Dark wall panels warm air for buildings |
| Concentrated solar power (CSP) | Mirrors focus sunlight to boil water and drive turbines |
| Solar cookers | Reflective surfaces focus sunlight to cook food |
The Drake Landing Solar Community in Okotoks, Alberta, stored summer solar heat underground and used it to heat about 50 homes through the winter.
Passive solar design
Passive solar design uses a building’s shape and materials to collect the Sun’s heat without machines:
- large south-facing windows (in the Northern Hemisphere) to let in winter sun
- overhangs that block high summer sun but let in low winter sun
- materials like concrete, stone or tile that absorb heat during the day and release it at night
- good insulation
Solar power in Canada
People sometimes think Canada is too cold or dark for solar power, but:
- Many Canadian cities get as much sunshine as Germany, a world leader in solar.
- The Prairies, especially southern Alberta and Saskatchewan, are among the sunniest places in Canada.
- Cold temperatures actually make solar panels more efficient.
- Snow reflects sunlight, which can boost output from panels that aren’t covered.
- Remote northern communities use solar to reduce reliance on diesel fuel.
Some provinces offer net metering: homeowners with panels send extra electricity to the grid and get credits on their bills.
Space and solar
Satellites and the International Space Station are powered by solar panels. NASA’s Mars rovers Spirit and Opportunity ran on solar power; Opportunity worked for nearly 15 years.
Advantages and disadvantages
| Advantages | Disadvantages |
|---|---|
| Renewable and abundant | No production at night |
| No emissions while operating | Less output on cloudy days and in winter |
| Quiet, few moving parts | Needs batteries or other sources for nighttime |
| Can be installed on rooftops, near where energy is used | Large arrays take up space |
| Low maintenance; panels last 25–30 years | Making panels uses energy and materials; recycling is still developing |
Common mistakes
- Thinking solar panels need heat. They need light; cold weather helps.
- Thinking solar doesn’t work in Canada.
- Thinking solar panels store energy. Batteries do that.
Try it yourself
- Connect a small solar panel to a motor or LED. Test it in sunlight, shade and under a lamp.
- Build a solar oven from a pizza box, foil and plastic wrap. Try melting chocolate or making s’mores.
- Use an online solar calculator to estimate how much electricity panels on your roof could make.
Quick recap
- Solar power turns sunlight into electricity or heat.
- Photovoltaic cells use semiconductors to make electricity directly.
- Inverters convert DC from panels to AC for homes.
- Solar thermal and passive solar design capture the Sun’s heat.
- Solar works in Canada and costs have fallen dramatically.