HOW (PV) PHOTOVOLTAIC SOLAR WORKS
Photovoltaic: Electricity from light. Photo = light, voltaic = volts, a measure of electricity.
For billions of years, the sun has poured out massive amounts of energy in several forms; including light, heat, radio waves, and even x-rays. The planets, in orbit around the sun, intercept a very small part of the sun’s immense output. On Earth, direct sunlight is available from sunrise until sunset, except during the time of a solar eclipse. PV Solar collectors and modules are designed to capture some of the sun’s energy and convert it into more usable forms such as heat or electricity. In fact, sunlight is an excellent source of heat and electricity, the two most important forms of energy we consume.
Solar Energy
On planet Earth, sunlight is an incredibly important form of energy. Every day, the sun pours unimaginable amounts of energy into space. Some of it is in the form of infrared and ultraviolet light, but most of it is in the form of visible light. Some of this energy falls on the Earth, where it warms our planet's surface, drives ocean currents, rivers, and winds, and is used by plants to make food. Life on Earth depends totally on the sun.
Photovoltaic Cells
Visible light can be converted directly to electricity by a space-age technology called a photovoltaic cell, also called a solar cell. Most photovoltaic cells are made from a crystalline substance called silicon, one of the Earth's most common materials. Solar cells are typically made by slicing a large crystal of silicon into thin wafers and putting two separate wafers with different electrical properties together, along with wires to enable electrons to travel between layers. When sunlight strikes the solar cell, electrons naturally travel from one layer to the other through the wire because of the different properties of the two silicon wafers.
These photovoltaic (PV) cells are made up of special materials, particularly the element silicon, which allows them to absorb light. Silicon is known as a semiconductor due to its absorptive and insulative properties. A single cell can produce only very tiny amounts of electricity-barely enough to light up a small light bulb or power a calculator. In solar cells, silicon is placed under non-reflective glass to collect photons (units of electromagnetic energy) from the sun. The PV cells have one or more electric fields that essentially force the electrons harnessed by the absorption of sunlight to move in a certain direction. Nonetheless, single photovoltaic cells are used in many small electronic appliances such as watches and calculators. Individual solar cells are packaged into solar panels that can be mounted on your roof or on the ground to take advantage of the free energy landing there every day. On a sunny day, each square foot of PV cells generate approximately 12 watts of electrical power. A typical PV cell converts 15% of the incident solar energy to DC electricity. For our application, these PV cells are arranged into groups and mounted into solar panels, also called an array.
Photovoltaic Arrays
To capture and convert more energy from the sun, photovoltaic cells are linked to form photovoltaic arrays. An array is simply a large number of single cells connected by wires. Linked together in an array, solar cells can produce enough electricity to do some serious work! The solar array is installed on your roof or adjacent structure. Many buildings generate most of their electrical needs from solar photovoltaic arrays, including the Toronto Healthy House, which gets 80% of its power from the sun. Babcock Ranch in Florida is an entire community built around a huge PV array.
Photovoltaic arrays are becoming a familiar sight along roadsides, on farms, and in the city, wherever portable electricity is needed. They are commonly used to provide power for portable construction signs, emergency telephones, and remote industrial facilities. They are also becoming popular as a way of supplying electricity for remote power applications such as homes and cabins that are located away from power lines, for sailboats, recreational vehicles, telecommunications facilities, oil and gas operations, and sometimes entire villages-in tropical countries, for example.
Solar Electricity in Everyday Use
Photovoltaic panels, like computers and other technologies, are getting less expensive and easier to buy. In fact, many people consider them a great alternative to gas-powered generators or connections to the regular electricity supply. Some countries such as Japan have encouraged businesses and communities to install solar panels on the roofs of new buildings to reduce the need for electricity from other sources.
Many homes and businesses have both a connection to the commercial electrical supply system (often called the "grid"). The solar panels can provide all or most of the building's electrical supply during the day, and the grid supplies whatever other electricity may be needed during the night. During sunny days when your solar system generates more power than your home or business needs, your electric meter actually reverses direction and spins backwards as you lend that energy to the utility grid building up credit. When the sun goes down, you effectively retrieve that energy as you need it reducing your credit balance. This process is called net metering. In most PV Solar Systems, the panels make more electricity than is needed in the building and the excess is sent to the power company's grid.
This results in the power company giving the building owner a credit towards future bills!