Photovoltaic Cells

As the world advances, new technologies arise - or, in some cases, older technologies are exhumed and improved upon.

Although most people are under the impression that the field of photovoltaics is a new subject, based on recent invention, this is not actually the case. But first of all lets take a look at what "photovoltaic" means.

The word "photovoltaics" can be split up in to two parts: "photo" and "voltaic". The term "photo" is derived from the Greek word "phos" which means "light." A "volt" is a measurement unit for electrical force. So, literally, "photovoltaic" means "electricity through light." And that is exactly what the word means: "capturing solar energy in the form of light and converting it into electricity."

So how do we convert sunlight into solar energy and electricity?

In order to convert sunlight into electricity you need to use a material called a "semiconductor".

In simple terms, a semiconductor is a material that acts as an insulator, but is also able to conduct electricity under certain conditions. We employ the characteristics of semiconductors when we convert solar energy (in the form of sunlight) into electricity. It is done as follows:

When a semiconductor (such as silicon) is exposed to light, it releases small amounts of electrical energy. This is due to the process of electrons (bits of electricity) leaving the surface of the semiconductor, in response to being hit by light. We call this the "photoelectric effect."

Sunlight is made up of "photons", which are particles of solar energy. Not all photons are the same and not all carry the same amount of energy. A simple explanation for this is that light comes in many colors. Some forms of light are visible to the eye, while some forms are invisible (such as ultraviolet or infrared light). But, regardless of color or visibility, the fact remains that light is still light and the basic particle of light is still a photon.

When a photon hits a photovoltaic cell (also called a "PV cell" for short) one of three things occurs:

1. The photon can be reflected by the photovoltaic cell
2. The photon can be absorbed by the photovoltaic cell
3. Or (believe it or not) the photon can even pass right the photovoltaic cell. Only the photons which are absorbed by the photovoltaic cell are converted into solar energy (in the form of electricity).

When a photon is absorbed by the semiconductor (the material in the photovoltaic cell which produces electricity) the solar energy of the photon is passed to an electron in one of the atoms of the semiconductor. With this additional energy the electron is able to break away from its atom. Thus an electrical current is generated.

This is the simplicity of what occurs in a photoelectric cell, when sunlight is converted into electricity. The electricity so produced can now be power an electrical device.

As you can see, the field of photovoltaics consists of the technology and the principles we use to convert solar energy into a usable form.

Photovoltaic Systems

Now that we know what a photovoltaic cell is and how it works, lets take this a step further and take a look at what a photovoltaic system is.

A photovoltaic system has consists of the following components:

• A "photovoltaic module", or "pv module". This is a group of photovoltaic cells connected together, commonly referred to as a solar panel, though the terms "PV module" and "solar charger" are used to describe it as well.
• One or more batteries to collect and store the solar energy, which was converted into electricity by the PV modules (or solar panels, solar chargers, or whatever you choose to call them).
• A "charge controller". This an electrical device which prevents the batteries from being ruined through overcharging, and which also prevents electrical current from flowing back out of the battery into the PV module or solar panel.
• "An inverter." An inverter an electrical device which changes the electricity produced by the PV modules into alternating current. Alternating current is the type of electricity you get from your wall sockets at home. An inverter is only used with PV systems when you want to produce alternating current as your end result. If you run your house on solar energy, the inverter is installed between the batteries and the fuse panel.

A good quality PV system will operate for more than twenty years. The PV module, having no moving parts, has an expected lifetime exceeding thirty years. Most system problems occur due to poor or sloppy installation.

So how much electricity is generated by a photovoltaic system?

The average PV system will generate about 180 kilowatt-hours per square meter, in most areas of the United States.

A PV system rated at 1 kilowatt will produce 1800 kilowatt hours per year.

What's a Kilowatt Hour? In case you are not clear on what a "kilowatt-hour" is, this is a way of measuring the amount of electricity produced or consumed.

Let me put it in monetary terms, which might be easier to understand. Many PV panels are guaranteed to last twenty years or more - most even claim to last thirty years. Even if we factor in the natural loss of efficiency in the PV modules over a period of twenty to thirty years, a PV system will generate close to 36,000 Kilowatt-hours in twenty years and 54,000 kilowatt hours over thirty years.

This is the equivalent of $10,000 worth of electricity at current energy prices.

Therefore, though initial installation of a PV system might seem a little costly, in the long run it is far cheaper to run on solar energy.

There are different types and sizes of solar panels (photovoltaic cells) which produce varying amounts of solar power.

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