I learned this today. There are two ways of making electricity from solar panels. Directly, by using sunlight to make electricity, or indirectly, by using the sunlight to make heat.
The sun releases energy in the form of photons. Photons are massless so they travel at the speed of light, 299,792,458 m/s. They travel from the sun to Earth in 499 seconds, 8 minutes and 19 seconds. 1 photon carries about 10-19 Joules of energy. The global energy use of the world per year is 580 million terajoules. This much energy comes to Earth from the sun every hour. If we could harness the power of the sun by using something like a Dyson sphere, we would have more energy than we could use. We can’t build something that complicated. The best we can do is to try to capture the energy when it hits Earth.
There are two main ways to do this. The first way is to convert the solar energy into heat. This is called concentrated solar power. They work by concentrating a large area of sunlight onto a receiver. The concentrated light is converted to heat and used to drive a conventional steam turbine to make electricity. Concentrated solar power is good because the heat can be stored to be used later when the sun has gone down, producing electricity whenever it is needed. The receiver is usually on a tower and contains either steam or molten salt. It is heated to about 1000℃ and then used to power the steam turbine. The panels used to concentrate the sunlight onto the receiver are usually computer controlled so that they can change their angle to keep the sunlight concentrated on the receiver.
This type of solar power station was incredibly popular in the 1980s and was predicted to be a growth industry, but it has stalled in recent years because it is still expensive. The price hasn’t come down and regular solar panels are more economical. There are plans for giant concentrated solar power stations, but it seems unlikely.
The second way of generating electricity from sunlight is with a photovoltaic cell. Solar panels can directly convert sunlight into electricity without having to heat any medium.
A solar panel is made up of many photovoltaic cells. A photovoltaic cell is made up of two pieces of a semi-conducting material, which is usually silicon. The silicon has phosphorous added to its top layer and boron to the bottom layer. The phosphorous negatively charges the top of the silicon and the boron positively charges the bottom. This makes an electric field because the opposite charges are separated. When a light photon hits the photovoltaic cell, it knocks an electron free from one of the atoms in the silicon. This electron would just wander off into space, but it is caught in the electric field and directed downward. Underneath the photovoltaic cell is a metal conductive plate that collects the free electrons and transfers them to a wire as electricity.
Photovoltaic cells are getting cheaper to produce and far more efficient. A solar panel in 1954 would have been 6% efficient and produced 20 watts of power a week. The same size solar panel now would be 20% efficient and would produce 300 watts a week. The efficiency, size, and cost are all slowly improving. That is why photovoltaic cell solar panels are more popular than concentrated solar power.
The ability of some materials to make an electrical charge when exposed to sunlight was discovered in 1839 by Alexandre-Edmond Becquerel. In 1881, Charles Fritts made the first commercial solar panel, but it was very inefficient and couldn’t produce enough electricity to be viable. In 1939, Russel Ohl came up with the solar panel design that is still used today. The first silicon solar panel was created in 1957.
There are some more advances that will appear in the near future. Silicon may well be discarded in favor of perovskites, a mineral made of calcium, titanium, and oxygen, which is far more efficient. As battery storage improves, it will be easier to store the power generated for days when there is little or no sunlight. Solar panels may be floated on the ocean. The water would keep the panels cool and increase efficiency by 10%. Right now 3% of the world’s electricity is generated from solar power. By 2035, this is predicted to be 40%.
So, you can make electricity from sunlight by focusing the photons on a central receiver to heat up a liquid and turn a steam generator. However, this isn’t the best method. Solar panels made of photovoltaic cells are much better. When a photon hits the cell, it knocks an electron loose. This electron is directed by an electric circuit toward a conductive plate where the electron is transferred to a wire, making electricity. And this is what I learned today.
Sources
https://en.wikipedia.org/wiki/Solar_panel
https://en.wikipedia.org/wiki/Photovoltaic_effect
https://www.livescience.com/41995-how-do-solar-panels-work.html
https://en.wikipedia.org/wiki/Concentrated_solar_power
https://en.wikipedia.org/wiki/Photon
https://www.solarreviews.com/blog/how-much-electricity-does-a-solar-panel-produce
https://sciencebusiness.net/climate-news/news/future-solar-four-problems-we-need-solve-fast