The Origin of Solar Energy

Energy from the Sun, called solar energy, comes from chemical reactions that release energy. These are nuclear fusion reactions, which combine multiple atoms to form new elements.

The Sun is composed almost entirely of two elements: hydrogen (H) and helium (He). Four atoms of hydrogen can combine through nuclear fusion to form one atom of helium and release energy in the process.

Every second, 4 × 10 38 hydrogen atoms are converted into helium, releasing enormous amounts of energy. On average, the Sun emits 63,000,000⁢W / m2.

W/m2, which stands for watts per square meter, is a unit of energy flux. Energy itself is often measured in units called joules (J), and a watt (W) is one joule per second. Flux is the rate at which energy is emitted or transferred per unit area, so it has units of energy per time per area—in this case, joules per second (W) per square meter (over m2).

The Sun emits 63,000,000 W/m2, which means each square meter of the Sun’s surface emits 63 million watts (joules per second). A typical laptop or home gaming system has a power requirement of 200 watts. Think about how many laptops could be powered by just one square meter of the Sun!
The Sun’s energy is generated through a series of nuclear fusion reactions in which atoms collide and fuse to form a new element, giving off energy in the process.

Question 1

Guess how much of the Sun’s energy makes it to Earth

Not quite. The Sun emits energy with a flux of 63,000,000⁢W / m2, but only 1360⁢ W / m2 reaches Earth. What percentage is this? Try again.

Not quite. The Sun emits energy with a flux of 63,000,000⁢W / m2, but only 1360⁢ W / m2 reaches Earth. What percentage is this? Try again.

Not quite. The Sun emits energy with a flux of 63,000,000⁢W / m2, but only 1360⁢ W / m2 reaches Earth. What percentage is this? Try again.

Correct! The energy that reaches Earth (flux of 1360⁢ W / m2) is only 0.00216% of the energy emitted by the Sun (flux of 63,000,000⁢W / m2).