PV Gap

Stella Said:

how the solar panel works?

We Answered:

How Solar Cells Work

In the 1950s scientists tinkering with semiconductors found that by introducing small, minutely controlled amounts of certain impurities called dopants to the semiconductor matrix, the density of free electrons could be shepherded and controlled. The dopants, similar enough in structure and valence to fit into the matrix, have one electron more or less than the semiconductor; for example, doping with phosphorus, which has five valence electrons, produces a (negative) n-type semiconductor, with an extra electron which can be dislodged easily. Aluminum, boron, indium, and gallium have only three valence electrons, and so a semiconductor doped with them is (positive) p-type, and has holes" where the missing electrons ought to be. These holes behave just like electrons, except that they have an opposite, positive charge. (Holes are theoretical, but so are electrons, and either or both may or may not exist, but we know for sure that if one exists, they both do, because we can't create something out of nothing in the physical world.) It is important to understand that, although loosely bonded or extra carriers exist in a substance, it is still neutral electrically, because each atom's electrons are matched one for one by protons in the nucleus.

The fun begins when the two semiconductor types are intimately joined in a pn-junction, and the carriers are free to wander. Being of opposite charge, they move toward each other, and may cross the junction, depleting the region they came from, and transferring their charge to their new region. This produces an electric field, called gradient, which quickly reaches equilibrium with the force of attraction of excess carriers. This field becomes a permanent part of the device, a kind of slope that makes carriers tend to slide across the junction when they get close.

When light strikes a Photovoltaic cell, atoms are bombarded with photons, and give up electrons. When an electron gets lopped off an atom, it leaves behind a hole, which has an equal and opposite charge. Both the electron, with its negative charge, and the hole, with its positive charge, begin a random walk generally down the gradient. If either carrier wanders across the junction, the field and the nature of the semiconductor material discourage it from recrossing. A proportion of carriers which cross this junction can be harvested by completing a circuit from a grid on the cell's surface to a collector on the backplane. In the cell, the light pumps" electrons out one side of the cell, through the circuit, and back to the other side, energizing any electrical devices (like the battery in the diagram) found along the way.

This information was reprinted from The Independent Home, by Michael Potts. You may purchase this book and many others from our On-Line Catalog.

Anita Said:

i need to know on how a solar panel works in a simple to explain to my class for a project?

We Answered:

I know solar panels...My work has 3.5 million dollars of them on there buildings...This link might help...

Photovoltaic Cells: Converting Photons to Electrons
The solar cells that you see on calculators and satellites are photovoltaic cells or modules (modules are simply a group of cells electrically connected and packaged in one frame). Photovoltaics, as the word implies (photo = light, voltaic = electricity), convert sunlight directly into electricity. Once used almost exclusively in space, photovoltaics are used more and more in less exotic ways. They could even power your house. How do these devices work?

Photovoltaic (PV) cells are made of special materials called semiconductors such as silicon, which is currently the most commonly used. Basically, when light strikes the cell, a certain portion of it is absorbed within the semiconductor material. This means that the energy of the absorbed light is transferred to the semiconductor. The energy knocks electrons loose, allowing them to flow freely. PV cells also all have one or more electric fields that act to force electrons freed by light absorption to flow in a certain direction. This flow of electrons is a current, and by placing metal contacts on the top and bottom of the PV cell, we can draw that current off to use externally. For example, the current can power a calculator. This current, together with the cell's voltage (which is a result of its built-in electric field or fields), defines the power (or wattage) that the solar cell can produce.

That's the basic process, but there's really much more to it. Let's take a deeper look into one example of a PV cell: the single-crystal silicon cell.