Grade by Grade
E. Earth and Space Science: Space Exploration · Space Exploration: The Sun, the Solar System and the Universe

From Sunlight to Electricity: The Sun and Renewable Energy

E2.2 A1.3 A2.4About 75 minutes
Learning goals
  • I can explain how solar, wind, hydroelectric and biomass energy all come from the Sun.
  • I can describe how a photovoltaic (solar) cell turns light into electricity.
  • I can tell which energy sources are renewable and which are not, and explain why.
  • I can calculate energy produced from power and time.
  • I can design, build and test a device that uses solar energy.

Words to know

renewable energy source
A source that is naturally replaced on a human timescale, such as sunlight, wind and flowing water.
non-renewable energy source
A source that takes millions of years to form and can run out, such as coal, oil, natural gas and uranium.
photovoltaic (PV) cell
A device, usually made of silicon, that converts light directly into electricity.
solar thermal energy
Using the Sun's energy to heat water, air or buildings.
passive solar design
Designing a building so it collects, stores and spreads the Sun's heat without pumps or fans, for example with large south-facing windows.
hydroelectric power
Electricity generated by moving water turning a turbine.
biomass
Plant and animal material, such as wood or crop waste, used as fuel.
efficiency
The percentage of input energy that is turned into useful output energy.

Remember from Grade 5

In Grade 5 you compared renewable and non-renewable energy sources and thought about how to conserve energy. In this course, the Electricity strand looks at how electricity is produced and used. In this lesson you will see that most renewable energy on Earth is really solar energy in disguise.

A puzzle to start

A wind turbine near Lake Huron, a dam on the Niagara River and a pile of wood pellets seem to have nothing in common. But follow the energy backwards and you will find the same source for all three. Can you guess what it is before you read on?

How the Sun's phenomena become renewable energy

In the last lesson you learned that the Sun causes wind, the water cycle and photosynthesis. Each one can be turned into useful energy:

  • Solar photovoltaic (PV): sunlight is converted directly into electricity by solar cells.
  • Solar thermal: sunlight heats water or air. Solar water heaters use dark absorbers; passive solar buildings in Canada use large south-facing windows to let in winter sunlight.
  • Wind: the Sun's uneven heating makes wind, which turns turbines.
  • Hydroelectric: the Sun evaporates water, which later falls as rain or snow on high ground. As it flows downhill, its energy turns turbines in dams and generating stations. Ontario has many hydroelectric stations, including large ones on the Niagara River.
  • Biomass and biofuels: plants store sunlight's energy by photosynthesis. Wood, crop waste, and fuels made from them release that energy when burned or digested.
  • Wave energy: waves are made by wind, so they also come from the Sun.

Not from the Sun: geothermal energy (heat from inside Earth), tidal energy (mainly the Moon's gravity) and nuclear energy (uranium formed long before our Sun was born).

What about fossil fuels? Coal, oil and natural gas formed from ancient living things that got their energy from sunlight millions of years ago. So they are stored sunlight, but they are non-renewable: they took millions of years to form and we use them much faster. Burning them also releases carbon dioxide, which contributes to climate change.

SunSolar panelslight → electricitySolar heatinglight → heatWinduneven heating → windHydroelectricwater cycle → riversBiomassphotosynthesis → fuelelectricity and heat for homes, schools and industry
Five renewable energy sources that all begin with the Sun. Each one uses a different natural phenomenon caused by the Sun's energy.

How a solar cell works

A photovoltaic (PV) cell is a thin wafer made mostly of silicon, with two specially treated layers (called n-type and p-type).

  1. Light hits the cell and gives energy to electrons in the silicon, knocking them loose.
  2. The boundary between the two layers pushes the loose electrons in one direction.
  3. Metal contacts collect the electrons, and they flow through a circuit as direct current (DC).
  4. Many cells are joined into a panel. An inverter changes DC to the alternating current (AC) used in homes.

A typical modern panel converts about 20% of the sunlight that hits it into electricity. That number is its efficiency. Engineers keep working to improve it.

sunlightn-type silicon layerp-type silicon layerlight bulb (load)electronsmetal contact on the backLight knocks electrons loose in the silicon. The layers push them one way,so they flow through the wire as direct current (DC).
A simplified solar cell (not to scale). Light frees electrons in the silicon; they travel through the external circuit and can light a bulb.

What affects how much electricity a solar panel makes?

  • Angle: panels produce the most when sunlight hits them straight on. In Canada, panels usually face south and are tilted.
  • Season and latitude: summer days are longer and the Sun is higher, so a panel in Ontario makes much more in June than in December.
  • Weather: clouds reduce output, and snow covering a panel can stop it until it slides off.
  • Shade: even partial shade from a tree or chimney can cut output a lot.
  • Temperature: surprisingly, PV panels work slightly better when cool, so a sunny, cold, clear day can be very good.

Pros and cons of Sun-powered energy

Every energy source has advantages and challenges. The table below compares four of them.

SourceAdvantagesChallenges
Solar PVNo emissions while running; works on rooftops; few moving partsMakes no power at night; less in winter; needs storage or backup
WindNo emissions while running; large amounts of powerWind varies; turbines affect views; must be placed carefully to protect birds and bats
HydroelectricReliable and can be adjusted to demandDams flood land and change river ecosystems and fish migration; can affect communities that rely on the river
BiomassCan use waste; available any timeBurning releases carbon dioxide and air pollutants; needs land and must be harvested sustainably
All four depend on the Sun, but each has trade-offs. Choosing an energy mix means weighing them.
Worked example

Example 1: Energy from a solar panel

A 400 W solar panel produces its full power for the equivalent of 4 hours on a sunny day. How much energy does it produce in kilowatt-hours (kWh)?

  1. Use energy = power × time.
  2. Convert power to kilowatts: 400 W = 0.4 kW.
  3. Energy = 0.4 kW × 4 h = 1.6 kWh.

1.6 kWh for the day. (You learn more about kWh and energy costs in the Electricity unit of this course.)

Worked example

Example 2: Efficiency

On a clear day, about 1000 W of sunlight strikes each square metre of a solar panel at noon. The panel delivers 200 W of electrical power per square metre. What is its efficiency?

  1. Efficiency = useful output ÷ input × 100%.
  2. 200 W ÷ 1000 W = 0.20.
  3. 0.20 × 100% = 20%.

The panel is 20% efficient. The other 80% of the energy is reflected or turned into heat.

Hands-on activity

Engineering design challenge: a pizza-box solar oven

You need: a clean pizza box, aluminum foil, black construction paper, clear plastic wrap, tape, a ruler or stick to prop the lid, a kitchen thermometer, scissors, and a sunny day.

Grown-up note: an adult should do any cutting with a craft knife. The inside of the oven gets hot; use oven mitts. Only warm safe foods such as melting chocolate on a cracker.

Design problem: build an oven that reaches the highest temperature in 30 minutes using only sunlight.

  1. Plan: sketch your design. Think: How will you reflect more light in? How will you absorb it? How will you trap the heat?
  2. Build: cut a flap in the lid (leave one edge attached). Cover the inside of the flap with foil (reflector). Line the bottom with black paper (absorber). Cover the opening with plastic wrap (traps warm air, like a greenhouse).
  3. Test: put the thermometer inside. Aim the oven at the Sun and prop the flap so it reflects light inside. Record the temperature every 5 minutes for 30 minutes. Also record the outdoor air temperature.
  4. Improve: change one thing (the flap angle, a second layer of plastic, insulation such as newspaper around the sides) and test again.
  5. Communicate: write which change helped most and why.

What to look for: a working oven gets clearly warmer than the outside air, often by several tens of degrees on a sunny day. The best explanations use the words reflect, absorb and insulate, and say that only one variable was changed per test.

Just for fun

Solar panels are fans of cold, sunny Canadian days: they actually work a little more efficiently when they are cool. Finally, something that likes January!

Your turn

1

Trace the energy in a hydroelectric dam back to the Sun.

2

Name three renewable energy sources that come from the Sun and one that does not.

3

Why are fossil fuels non-renewable even though their energy came from the Sun?

4

What does an inverter do?

5

A 300 W panel runs at full power for 5 hours. How many kWh does it make?

6

Give one advantage and one challenge of wind power.

7

Why do solar panels in Canada usually face south?

More practice: warm-up

1

What material are most solar cells made of?

2

What does PV stand for?

3

What kind of current does a solar cell produce: AC or DC?

4

Is tidal energy caused mainly by the Sun or the Moon?

5

What process stores the Sun's energy in plants?

More practice: on your own

1

A panel receives 1000 W of sunlight and delivers 180 W. What is its efficiency?

2

Why does a solar panel in Ottawa produce much less energy in December than in June?

3

Explain why hydroelectric power is considered renewable but still has environmental impacts.

4

How does a passive solar house use the Sun without any solar panels?

5

In the pizza-box oven, what are the jobs of the foil, the black paper and the plastic wrap?

Challenge

1

A family's home uses about 25 kWh of electricity per day. Their rooftop panels total 5 kW and produce full power for the equivalent of 4 hours on an average summer day. What fraction of their daily use do the panels supply in summer? What about the night?

2

Explain why solar and wind energy are often combined with batteries or with hydroelectric reservoirs.

3

A remote northern community gets its electricity from diesel generators. List two benefits and one challenge of adding solar panels.

Check your understanding

Quiz

1.

Which energy source does NOT come from the Sun?

2.

A solar cell converts:

3.

A 250 W panel works at full power for 4 hours. How much energy does it produce?

4.

Why are fossil fuels non-renewable?

5.

What makes wind, ultimately?

6.

A panel receives 800 W of sunlight and delivers 160 W. Its efficiency is:

For parents and teachers

Big idea: the second half of E2.2 asks how the Sun's phenomena contribute to renewable energy production. The ministry notes that this connects to the Biology strand (ecosystems, climate change) and the Physics strand (electricity), so this lesson links forward to the Electricity unit. The solar oven is an engineering design task (A1.3); weighing trade-offs supports scientific literacy (A2.4).

Common difficulties:

  • Thinking all renewable energy is 'solar panels'. Help your teen see wind, hydro and biomass as indirect solar energy.
  • Unit mix-ups (W vs kWh). Watts measure power (rate); kilowatt-hours measure energy (power × time).
  • Thinking renewable means 'no impact'. Every source has trade-offs.

Safety: supervise cutting and remind your teen the oven interior gets hot.

How to help: look at your home's electricity bill together and find the kWh used. Ask: how many solar panels would it take to supply that?