A photovoltaic cells consists of a thin piece of specially coated silicon, with wires attached to capture the flow of electricity.

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.

This calculator is powered by a single photovoltaic cell.

A single cell can produce only very tiny amounts of electricity-barely enough to light up a small light bulb or power a calculator. Nonetheless, single photovoltaic cells are used in many small electronic appliances such as watches and calculators.

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! 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.

Many single photovoltaic cells are connected by wires and mounted on a flat panel to form a photovoltaic array. Photo courtesy of Solar Futures International

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.

Storing Electricity
Solar panels make electricity in all kinds of conditions, from cloudy skies to full sunlight, in all seasons of the year. But they don't work at all during the nighttime! To make electricity available after sundown, the energy must be stored during the day for later use. The usual storage device is a rechargeable battery.

This battery is designed for use with a photovoltaic system, and can be discharged and recharged many times. Photo courtesy of Solar Futures International

The batteries used with solar arrays must be able to discharge and recharge again many times. They contain special parts and chemicals not found in disposable batteries. They are also usually larger and more expensive than their disposable cousins.

Besides solar panels and rechargeable batteries, modern photovoltaic systems are usually equipped with some kind of electronic charge controller. The main job of the charge controller is to feed electricity from the solar panel to the battery in the most efficient manner and to prevent the solar panel from overcharging the battery. The charge controller also protects the solar panels from electrical damage.

An electronic charge controller used to maintain the health of a rechargeable battery connected to a solar panel. Photo courtesy of Solar Futures International

In many cases, people need the electricity stored in the rechargeable batteries for use with normal household appliances. The problem is that most of those appliances require 110 volts of alternating current ( 110V AC), whereas the battery puts out only direct current (DC), usually at a much lower voltage. A device called a power inverter solves this problem by converting the battery's low-voltage direct current to 110 volts of alternating current. Modern charge controllers often come equipped with their own built-in power inverters.

Photovoltaic arrays are becoming popular with rural and urban homeowners who want to avoid monthly power bills. Photo courtesy of Solar Futures International

Solar Electricity in Everyday Use
Photovoltaic panels, like computers and other technologies, are getting cheaper 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 "electricity 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. In some cases, the panels make more electricity than is needed in the building, and the excess is sold to the power company. This results in the power company sending the building owner a cheque instead of a bill!

How Photovoltaic Panels Work:   The Pembina Institute Photovoltaic cells are marvels of sub-atomic physics. They are constructed by layering special materials called semiconductors into thin, flat sandwiches, called solar cells. These are linked by electrical wires and arranged on a panel of a stiff, non-conducting material such as glass. The panel itself is called a module. A ray of light consists of a stream of photons-tiny packets of light energy-moving along at around 300,000 kilometres per second. When these energy packets strike the top layer of a solar panel, they bump electrically charged particles called electrons away from their "parent" atoms. These electrons are collected by another layer in the sandwich and passed along to wires that connect to batteries and other appliances. The amount of electricity the panel can produce depends on the intensity of the light.

Questions List all the appliances in your home, school, or neighbourhood that have a photovoltaic cell or array on them. What are the advantages of solar electricity over electricity made from fossil fuels, nuclear fuels, or hydroelectricity? What are the problems or disadvantages of solar electricity? Make a list of companies that sell solar electricity equipment in your community or region. Try to locate companies that sell photovoltaic panels, batteries, and charge controllers.