Published on April 8th, 2015 | by Steve Hanley
How A Solar Panel Works
The sun is a gigantic nuclear furnace that puts off incredible amounts of energy. Even 93,000,000 miles away, enough of that power strikes the surface of the Earth in just 90 minutes to meet the energy needs of every human being on Earth for an entire year, according to the scientists at Sandia National Laboratories. If we could better harness that energy, we could eliminate hunger, eradicate poverty, and bring the thinking of billions of minds to bear on global problems via the internet.
What Is A Solar Panel?
A solar panel is a device that converts sunlight into electricity by a process known to scientists as photovoltaic action, or PV for short. Albert Einstein was one of the first to describe how this process works way back in 1905. His early experiments that helped to explain the nature of light eventually led to a Nobel Prize in physics. Many think he won the Nobel Prize for his Theory of Relativity, but he actually won primarily for his discovery of the photoelectric effect.
Today, we know that when sunlight hits a thin layer of silicon, an electric current is created which can be harvested by electrodes attached above and below it and used to power electric devices like light bulbs, motors, and such. But that wasn’t always the case.
Early solar panels had low efficiency rates. That means only a small percentage of the sunlight coming in was converted to electricity. They were heavy, expensive, and difficult to install. But scientists and engineers have learned how to conquer most of those concerns over the last 30 years. Today, some commercially produced solar cells are up to 25% efficient, meaning almost a quarter of the sunlight hitting them is converted to electricity. (Solar cells in the lab are approaching 50% efficiency.)
What Are Solar Panels Made Of?
A solar panel consists of a rectangular aluminum frame holding a white background material. An arrangement of solar cells made from thin layers of silicon is placed over the background and covered with a sheet of non-reflective glass that lets sunlight through so that it can interact with the silicon.
Now, time for a short chemistry lesson: A silicon atom has four electrons in its outer shell but can hold eight. When two silicon atoms combine, they form a strong, stable bond and create pure crystalline silicon.
However, pure silicon is a poor conductor of electricity since it has no electrons that are free to move about. In other words, the silicon is better off with impurities. To create these impurities, silicon is combined with something else, usually phosphorous or boron, which has free electrons to give.
When sunlight strikes the impure silicon, it shakes everything up. The free electrons from the silicon/phosphorous compound are released and flow to to the silicon/boron compound, and that flow of electrons gives us electricity.
Each solar panel is made up of many solar cells arranged in rows. Some perform better in direct sunlight. Some are more suited to climates with diffuse light because of clouds or other atmospheric conditions that cut down on the amount of available sunlight.
As a general rule, the more efficient a solar panel is, the more costly it will be.
Types Of Solar Panels
There are three basic types of residential solar panels available today. For this discussion, we are going to rely on the folks at Energy Informative to give us the basics.
Monocrystalline panels use solar cells that are cut from purely drawn crystalline silicon bars. The entire cell is aligned in one direction, which means that when the sun is shining brightly on them at the correct angle, they are extremely efficient. These panels work best in direct sunshine such as is normally found in the American Southwest. The silicon bars are octagonal in shape, so panels made this way have a little bit of wasted space between the cells.
Polycrystalline panels are made from blocks of less-uniform silicon molded into rectangular cells. Because the individual crystals are not all perfectly aligned, they are not quite as efficient. But the cells work better with light at all angles or in low light conditions, making them a better choice for locations that do not have constant exposure to strong sunlight, like most northern states.
Hybrid panels add a special substrate material behind the silicon layer to capture more of the sun’s energy. They are the most efficient solar panels available but cost much more than other panels. They are useful when the available space for a solar installation is limited but are not cost effective for most residential applications. They do have the advantage of working well in low light environments.
All-black panels are popular for some specialized situations, such as preserving the visual appearance of historic properties with slate or dark-colored roofs. They use a black background behind the solar cells instead of the white background found on conventional panels. They also use black anodized aluminum frames instead of the bright finished aluminum usually used. They may make for a better appearance when installed but they absorb much more heat from the sun, causing them to overheat and lose efficiency. They may be trendy but should be avoided if at all possible.
We Have Electricity. Now What?
The electricity created by a solar panel is in the form of direct current, commonly known as DC. But the electricity we use in our homes is alternating current, also known as AC. The two are incompatible with each other, so the current coming from the solar panel has to be converted to AC before we can use it.
You would think the device performing that operation would be called a converter, but in fact it is known as an inverter. It transforms the DC current into AC current so it can operate our appliances (like air conditioners, refrigerators, and water heaters). The inverter performs another essential service. Most electric companies allow us to sell excess electricity from our solar panel system to the utility, but first it must meet all the criteria necessary to be compatible with the electrical grid. The inverter takes care of this chore for us.
For most solar panel users, the solar electricity system on the roof provides much of the electricity needed to run the home during the day while the sun is shining. In the US, any extra energy is typically sold to the local utility company. At night, when the output of the solar system declines as the sun sets, the homeowner buys that excess power back to cool or heat the house, cook dinner, and run the lights and entertainment devices used by the members of the household. However, some solar panel users are off the grid and store their solar-generated electricity in batteries for use when the sun isn’t shining. Also, in some locations, solar panel users may be on the grid but unable to sell excess electricity to the grid.
In many other countries, all electricity generated by solar panels is sold to the grid for a designated price. Meanwhile, for the electricity the home or business uses, it pays the grid operator or utility just like anyone else.
In other articles, we will talk about the cost of solar, whether it is better to lease or own a solar system, and how to claim the many federal, state, and local incentives available for residential solar power.