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Home Solar Energy: How the electrical current is created (Part 11)

By Daniel Stouffer

Republish: EasyPublish™ Published: 27Jul2008 Word count: 804 Viewed: 808 time(s) Get Free Content For Your Site

How free electrons, popped from their "holes" in the silicon, flow through solar PV cells connected in series is mentioned as it relates to the buildup of useful electric voltage. We are at the starting gate of wide-spread, pervasive adaption of solar as an energy source for United States homes.

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 more photons following into the silicon lattice results in more electrons following out of the solar cells and into the 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 same amount of photons must fall on each cell connected in series to energize the same number of electrons in each successive cell. In essence, the photons from the sun hit the silicon and cause a chain reaction within the silicon.

The successive bumping of electrons in and out of the silicon lattice creates the current flow. Think of a game of billiards; the player strikes the white ball to hit a green ball into the corner pocket. 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. Electrons leave each solar cell with a net potential gain of one half of a volte (V). 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 passing through each cell gain a little more than 1/2 volt so after passing through 72 cells the operational voltage of the module is about 40 volts.

If more voltage is needed to produce useful electric current for home use, then solar modules can be connected in series. For example, a typical residential solar energy system and arrangement of the solar array has 8 solar modules connected in series. 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. It is an attractive option allowing homeowners to self-produce their own energy and keep the savings every month.

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.

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