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How Do Photovoltaic Cells Actually Work?

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SOLAR PANELS
TEMISTOCLE LUCARELLI via Getty Images
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Solar power is an abundant renewable source that could be the solution to our future energy needs, but just how does a solar array produce the electricity that powers our lives? The short answer is that, through a solar panel, photons (light particles) are able to knock electrons off atoms and this causes a flow of electricity. The long answer is a little more complex.

A "photovoltaic" cell is the basic building block which converts sunlight to electric energy that we can utilize to power our homes and businesses. In 1839, Edmund Bequerel noted that certain materials were photoelectric, which meant that they were able to absorb photons, causing them to release electrons and produce a mild electric current when exposed to sunlight.

It was Einstein who explored this photoelectric effect at an atomic level which earned him the Nobel prize in 1921. The first photovoltaic cell was produced by Bell Laboratories in 1954, but it wasn't until the 1960s that the technology really gained traction as a way of powering space exploration.

Each solar panel is constructed from many photovoltaic cells connected together. The photovoltaic cells consist of a thin wafer of semi-conductive material (usually silicon) which includes two 'doped' layers of opposing charge. The top layer contains phosphorous which gives that layer a negative charge as it has extra electrons which don't fit well within the silicon crystal structure. This is called the phosphorous doped or N-type layer.

The rest of the wafer lacks phosphorous doped, and instead includes an excess of Boron atoms which contain fewer electrons than is typical in a silicon crystal structure. This lack of electrons effectively creates positive charge carriers known as 'holes' and forms a P-type layer.

The boron-doped wafer is 1,000 times thicker than the thin phosphorous-doped layer within the wafer. Now your photovoltaic cell has a negative top layer and a positive bottom layer which creates an electric field where the two layers meet in the middle, known as the P-N 'junction.' The P-N junction is essential to extract electricity off of the solar cell.

When sunlight hits the photovoltaic cell, it knocks or excites electrons and holes from within the wafer. The electric field between the layers forces those electrons to the edges of the cell where conductive contacts collect the electrons and sweep them into wires. The negative electrons are attracted to one side of the solar cell and holes are attracted to the opposite side. These solar cells are connected front to back the same way that batteries are connected in a flashlight. In this way, each solar cell can be thought of as a battery which is powered by the sun. In a commercial panel, 60 or 72-cells are connected in series and resultant voltage in the module is correspondingly higher than a single cell.

How much current a photovoltaic cell will create depends on is efficiency, its size and the intensity of the sunlight. These factors must all be taken into account when calculating how many solar panels you need to adequately address your energy requirements.

This flow of electrons is the electricity that powers our homes and businesses. Photovoltaic arrays produce direct or DC current. This means that they can be connected in both series and parallel arrangements to produce any voltage or current combination that is required.

DC power isn't what is commonly used in homes and businesses as it's a continuous stream of electrons flowing in one direction and it's expensive to step up and down DC voltages, which is a requirement for the transmission grid. This means that the DC power produced by your solar array needs to be converted to alternating current or AC power. With AC power, the electrons oscillate in an electrical field which alternates 60 times per second. AC electricity can efficiently change between higher and lower voltage levels, and high voltages allow for long-distance transmission.

Your solar array will require a converter to change the DC current to AC. These inverters are usually very efficient, so you only lose a little of your energy in the conversion. Converting your DC current to AC will also allow you to feed in to your local grid in the event that you are eligible to receive potential rebates or incentives for the electricity you feed back to the grid (feed-in-tariff).

Many home and business owners are turning to the sun's rays, a renewable and free energy source. Not only does it typically reduce their monthly utility expenses, it could make the building more marketable and, in some cases, allows the owner to earn credits for electricity they feed back to the grid. Photovoltaic panels produce energy that is renewable and good for the planet.

Many local governments offer incentives and tax credits that experts claim could in some cases make solar an investment that beats the stock market in many states.

This blog was originally posted on NRG Home Solar.

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