Home Solar Energy: How the Electrical Current is Created (part 11)
Popped from their “holes” in the silicon atom, electrons flow through solar PV cells connected in series to produce useful electric voltage. This concept and a little more is the focus of this article. The United States is at the beginning of a huge, wide-spread, pervasive switch to solar energy as a primary energy source for our homes. The manufacturing costs are down, awareness and need is up, and new options to rent solar systems versus having to buy them all line up perfectly.
How do solar PV cells create an electric current?
The remainder of this article explains some of the details related to the internal workings of solar cells and how their arrangement, when placed into a solar array mounted on your roof can make a big difference in the energy output of your solar system.
The internal electric field of the silicon diode creates a flow of electric charges only when sunlight photons strike the silicon. As the photons hit electrons in silicon bonds, they create hole-electron pairs that are free to separate and wander around the silicon lattice or crystalline structure. Free electrons wandering near the p/n junction are pushed in one direction by the internal electric field.
This movement of electronics as a result of the photoelectric effect results in a steady flow of electric charges moving in a circuit within the silicon structure, i.e. an electric current. The flow is directly proportional to the intensity of light and the energy conversion efficiency of the solar cells included in the solar PV panel. The greater the sunlight hitting the silicon atom the greater the number of electrons bumped free. Ultimately, this creates a greater number of electrons flowing in and out of the silicon and into the solar inverter.
This whole continuous movement of electrons illustrates why it is so important for all solar cells in a module or solar array to get the same intensity of sunlight. It is important for the solar panels to receive the sunlight from the same direction and not to be shaded by trees or buildings. The exact number of photons from the sun must must strike each solar cell in order to bump the corresponding number of electrons in the next solar cell. In essence, the photons from the sun hit the silicon and cause a chain reaction within the silicon.
The additional movement of free silicon electrons, in and out of the holes produced in the silicon atoms, creates the electric current and flow of energy. Think of a game of billiards; the pool player hits the white ball which in turn hits the green ball into the pocket. This occurs in a chain reaction fashion as you add more balls each hitting each other. The little twist here is the fact that the sun will continually hit the white ball (i.e. the sun photon hitting the silicon atom) as long as the sunlight hits the solar cell.
Solar PV Cells Connected in Series
Individual solar cells produce only a small amount of voltage. They are most commonly connected together in series, positive to negative poles within a solar array, to produce a useful electric voltage.
When photons of sunlight strike solar cells in a string, the internal electric field pushes the electrons out of the cells in a continuous flow through the string. The electrons moving through the silicon structure each gain about one half of a volt during the photoelectric process. The displaced electrons are collected in a grid pattern of wiring printed on the cells.
Module manufacturers connect enough solar cells in series in a single module to produce a useful voltage. The typical high voltage grid tied module has 72 cells in series. Electrons moving about the solar cells get about one half of a volt from each solar cells. After moving through 72 solar cells connected in series gain enough electric voltage to account for about 40 volts.
If more voltage is needed to produce useful electric current for home use, then solar modules can be connected in series. The most common solar energy unit configuration has a solar array connected in series with 8 other solar modules. This results in a final operational electric voltage of about 320 volts.
Solar Cells, Arrays, and Solar Modules Connected in Series
In the previous article, we explained a little about the Photoelectric Effect, where photons of light hit electrons in the silicon lattice and provide energy to flow. We also described how electrons flowing from one cell into the next cell in a module gain about 1/2 volt from each cell.
To Rent a Home Solar Energy System or Buy It
The Option to Rent a Home Solar Energy System is fast approaching as a viable option for home electricity needs. The American homeowner has the option to produce renewable energy from the sun by renting a complete solar energy system versus having to purchase one outright. This is an exciting solar rental service that allows the average homeowner to created their own solar generated electricity from the son and keep the energy savings they create.
Those who have a suitable location (i.e. good sun, enough roof space, and moderate energy needs), who follow the reservation steps, and who complete the requirements have a home solar system installed have good chance of getting a solar unit installed on their home on a rental basis.
Daniel Stouffer
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