TedEd: How do solar panels work?

A TedEd by Richard Komp

The Sun produces a lot of energy. The Earth gets as much as 173,000 terawatts of it every day. That’s 10,000 times more than the entire planet uses. So could we become entirely dependent on solar energy? A solar panel is made up of smaller solar cells. Each cell is typically made of silicon, a semiconductor. Silicon is put between two conductors. There are two types of silicon used - N and P. N type has extra electrons, while P is missing some. When photons from the Sun hit the solar cell, something called P/N Junction occurs. A photon with enough energy will knock an electron out of its spot, leaving a hole behind. Because of the electric field at the P/N Junction, the electrons will go toward the N silicon and the remaining spaces to the P. Then, the electrons run through a circuit, eventually returning to the P silicon to fill the holes. Because it cycles through, the solar cells don’t wear out, lasting for many years. Each cell only produces 1/2 volt, but many of them can be put together to make a solar panel. So why can’t the entire world run on solar power? There are many physical and logistical challenges to making that work. First, not all parts of the world receive enough solar energy. Also, clouds and nighttime make sunlight less readily available, so effective storage and movement of energy would be needed to make this work. Secondly, solar cells aren’t very efficient yet. If a photon is reflected, or an electron returns to a hole before going through the circuit, energy is lost. The most efficient solar cell so far only makes use of 46% of total available energy, and widely available ones are 15~20% effective. Still, with enough space and infrastructure, it would be possible. As much as hundreds of thousands of square miles of space would be needed, which isn’t actually very much. In fact, solar panels are already competing with electricity from the grid, and floating solar farms at sea could take things even further. There are also billions of developing communities, many of which have ample sunlight with little to no electricity who could benefit. But in places with many cloudy days or little daylight, solar power could be a little way off.