Solar cell

A solar cell is a device that turns the energy in sunlight directly into electrical energy. It is usually made from a semiconductor such as silicon. When light hits the material, electrons inside it start to move, and that movement is an electric current.

Satellites have a hard time carrying fuel, so getting power from solar cells has been common for a long time. Solar cells are also seen as a key way to power bases on places like the Moon or Mars, where there is sunlight but no power grid.

A solar cell joins two layers with different properties onto a semiconductor layer that absorbs light, and this creates an electric field. When particles of light hit the semiconductor and knock electrons loose, the field pushes those electrons in one direction. That flow is the current.

Many cells are wired in series or in parallel to get the voltage and current you want. Arrays that fold up for storage and unfold later use this same basic principle. Only the structure is changed to make them lighter.

A satellite in orbit takes in sunlight to charge its batteries and to power its electronics. On the ground, the same principle produces electricity on house roofs and in large power plants.

In places where sunlight is fairly steady, such as a Moon base, solar cells are considered as a long-term power source. In regions with long nights, though, batteries or other ways of making power have to be designed in alongside them.

A solar cell makes electricity only when there is light, so its output falls close to zero at night or in shade. You should know first that you need a way to store energy if you want to keep using the power it makes.

A common misunderstanding is that a larger cell area always gives the same amount of power. In practice, the amount of power changes a lot with conditions such as the angle of the sunlight, dust, temperature and cosmic radiation in space.

Think of the thin solar panel on a small calculator. It shows numbers even under a lamp, because electricity flows as soon as light reaches it.

If people are going to stay on the Moon or in space for a long time, the first problem to solve is where the electricity will come from. Once you understand how a solar cell works, it is easier to see why power for a Moon base matters so much.