Iaremenko Sergii/Shutterstock
Until now, these two separate pieces of silicon were electrically neutral; the interesting part begins when you put them together. That's because without an electric field, the cell wouldn't work; the field forms when the N-type and P-type silicon come into contact. Suddenly, the free electrons on the N side see all the openings on the P side, and there's a mad rush to fill them.
Do all the free electrons fill all the free holes? No. If they did, then the whole arrangement wouldn't be very useful. However, right at the junction, they do mix and form something of a barrier, making it harder and harder for electrons on the N side to cross over to the P side. Eventually, equilibrium is reached, and we have an electric field separating the two sides.
Advertisement
This electric field acts as a diode, allowing (and even pushing) electrons to flow from the P side to the N side, but not the other way around. It's like a hill — electrons can easily go down the hill (to the N side), but can't climb it (to the P side).
When light, in the form of photons, hits the solar panel, its energy breaks apart electron-hole pairs. Each photon with enough energy will normally free exactly one electron, resulting in a free hole as well. If this happens close enough to the electric field, or if a free electron and free hole happen to wander into its range of influence, the field will send the electron to the N side and the hole to the P side.
This causes further disruption of electrical neutrality, and if we provide an external current path, electrons will flow through the path to the P side to unite with holes that the electric field sent there, doing work along the way. The electron flow provides the current, and the cell's electric field causes a voltage. With both current and voltage, we have power, which is the product of the two.
There are a few more components left before the cell can really be used though. Silicon happens to be a very shiny material, which can send photons bouncing away before they've done their job, so an antireflective coating is applied to reduce those losses.
The final step is to install something that will protect the cell from the elements — often a glass cover plate. PV modules are generally made by connecting several individual solar panels together to achieve useful levels of voltage and current, and putting them in a sturdy frame complete with positive and negative terminals.
Unfortunately, the process for converting solar light into usable power is not perfect. As of 2023, commercially available solar panels have less than 30 percent efficiency, meaning two-thirds of the potential concentrated solar power is wasted. In lab settings, some researchers have been able to reach 47 percent efficiency, but they were using a directed light beam that is several times more powerful than our ambient outdoor sunlight.
As of yet, the only practical solution to this efficiency problem is to install more solar panels over larger areas, but this greatly increases the cost of creating a solar farm in both real estate and natural resources. From a monetary standpoint, solar used to be one of the most expensive power sources to build in comparison with the energy collected. However, prices have trended downward in recent years, and brought photovoltaics more in line with the cost of wind turbine construction.
An effective alternative to the photovoltaic system is known as the concentrated solar plant. This method does away with silicon panels and instead uses a massive array of polished mirrors to capture sunlight. These mirrors are programmed to follow the sun's movement and direct the light to a large tower known as a central receiver. The receiver contains a large tank of chemical solution known as molten salt, which heats up to temperatures in excess of 1,000 degrees Fahrenheit (538 degrees Celsius). The heat can then be siphoned off in order to drive traditional steam turbines throughout the day, and at nighttime as well.
Concentrated solar is able to generate several times more power than the typical solar cell array, but it requires a huge swathe of flat ground and the heat involved presents hazards to both people and wildlife. For these reasons, the power plants tend to be located in relatively uninhabited areas, like the Mojave desert.
Advertisement
The amount of sunlight that strikes the earth's surface in an hour and a half is enough to handle the entire world's energy consumption for a full year. Solar technologies convert sunlight into electrical energy either through photovoltaic (PV) panels or through mirrors that concentrate solar radiation. This energy can be used to generate electricity or be stored in batteries or thermal storage.
Below, you can find resources and information on the basics of solar radiation, photovoltaic and concentrating solar-thermal power technologies, electrical grid systems integration, and the non-hardware aspects (soft costs) of solar energy. You can also learn more about how to go solar and the solar energy industry. In addition, you can dive deeper into solar energy and learn about how the U.S. Department of Energy Solar Energy Technologies Office is driving innovative research and development in these areas.
Solar radiation is light – also known as electromagnetic radiation – that is emitted by the sun. While every location on Earth receives some sunlight over a year, the amount of solar radiation that reaches any one spot on the Earth’s surface varies. Solar technologies capture this radiation and turn it into useful forms of energy.