How solar energy actually works

The sun radiates a phenomenal amount of light and heat energy in our direction. In fact, the amount of solar energy hitting earth’s surface in just two hours would be enough to cover all of our energy needs for an entire year.

There are two key ways of capturing and using this energy from the sun: solar panels (photovoltaics), which convert light into electricity, and solar thermal power, which transforms the sun’s energy into heat.

Inside a solar panel you’ll find a neat arrangement of solar cells, each around the size of a coaster, made of two thin slices of material (usually silicon), with opposing electrical charges. As the Sun shines on the cell, photons (minuscule packets of light energy) knock electrons off the silicon atoms, in what’s known as the photoelectric effect. The resulting flow of electrons forms a small electrical current in each cell.

Another way of capturing the sun’s energy is converting it into heat. Concentrating solar-thermal power plants, for instance, use mirrors and lenses to reflect and focus sunlight to heat water or other liquids. The resulting heat is used to provide hot water to homes and businesses, or to drive a turbine to generate electricity.

The downside of solar power? It can only be generated during the day. This means that it needs to be used alongside other energy sources – or stored – in order to provide a steady supply of electricity day and night. PV solar panels generate direct current (DC) electricity. With DC electricity, electrons flow in one direction around a circuit. This example shows a battery powering a light bulb. The electrons move from the negative side of the battery, through the lamp, and return to the positive side of the battery.

With AC (alternating current) electricity, electrons are pushed and pulled, periodically reversing direction, much like the cylinder of a car's engine. Generators create AC electricity when a coil of wire is spun next to a magnet. Many different energy sources can "turn the handle" of this generator, such as gas or diesel fuel, hydroelectricity, nuclear, coal, wind, or solar.

AC electricity was chosen for the U.S. electrical power grid, primarily because it is less expensive to transmit over long distances. However, solar panels create DC electricity. How do we get DC electricity into the AC grid? We use an inverter.

However, as a clean, versatile and increasingly affordable form of renewable energy, solar power is set to take the world by storm. Solar panels currently produce just 2.7 per cent of the world’s electricity, but our total capacity to generate solar power is expected to more than triple in the coming decade.

Science Focus