What are photovoltaics (solar electricity), or "PV"?

What do we mean by photovoltaics? The word itself helps to explain how photovoltaic (PV) or solar electric technologies work. First used in about 1890, the word has two parts: photo, a stem derived from the Greek phos, which means light, and volt, a measurement unit named for Alessandro Volta (1745-1827), a pioneer in the study of electricity. So, photovoltaics could literally be translated as light-electricity. And that's just what photovoltaic materials and devices do; they convert light energy to electricity, as Edmond Becquerel and others discovered in the 18th Century.

History of Solar Power

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The photoelectric effect

The photoelectric effect occurs when a beam of UV light, composed of photons (quantized packets of energy), strike one part of a pair of negatively charged metal plates. This causes electrons to be "liberated" from the negatively charged plate. These free electrons are then attracted to the other plate by electrostatic forces. This flowing of electrons is an electrical current. This electron flow can be gathered in the form of direct current (DC). This DC is then coverted to AC (alternating current) by an inverter so that the enrgy can be used in your home.

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PV systems today

Did you know that PV systems are already an important part of our lives? Simple PV systems provide power for many small consumer items, such as calculators and wristwatches. More complicated systems provide power for communications satellites. Many road and traffic signs along highways are now powered by PV.

Mariner 5 is shown in flight. Photovoltaic systems were an important power source for that mission. Solar cells have not only enabled America to explore space, the solar system, and the Earth in great detail, they also have enabled the emergence of the telecommunications industry. (Credit: NASA and NSSDC Photo Gallery)

What Percentage of Solar Power Do We Use in the US?

The amount of solar power that is currently part of the electricity mix in the U.S. is unfortunately quite small. According to the Annual Energy Review of 1999 provided by the EIA, 0.076 quadrillion BTU's of energy were produced by solar power. This is about 0.1% of the overall 72.523 quadrillion BTU's produced in the U.S. This percentage is dwarfed by the 57.673 quadrillion BTU's, or 80% of the total, produced using fossil fuels. Coal alone produced 52% of the electricity produced in the US in 1999. From an environmental perspective, this is troubling, since coal is the most potent emitter of lead and mercury as well as a leading emitter of CO2, NOx, and SO2. The process of mining the coal is itself harmful in a number of ways. 95% of acidic mine drainage is a product of coal mining along with 18.8 million metric tons of methane (CH4) each year.

History

You would probably guess that any discussion about the early use of electricity would have to include Thomas Alva Edison, and you'd be right. Although knowledge of electricity dates back to the ancient Greeks, it wasn't until Edison's pioneering work with electricity in the late 19th century that we were able to harness electricity in a useful way. Edison's invention of the incandescent light bulb in 1879 revolutionized our way of life and we have him to thank for the last 125 years of electric innovation. **

**From The Edison Electric Institute

Invention of the Light Bulb

On October 21, 1879, Edison created his now famous incandescent light bulb, which burned for 40 hours. During 1880, Edison continued work to refine his light bulb. He also began exploring ideas for an equally important invention: a way to generate and transmit the electricity his light bulb would need. A practical and reliable electricity supply was essential if the light bulb was ever to become a practical appliance for homes and businesses. **

**From The Edison Electric Institute

Edison's Pearl Street Station

By the end of 1880, Edison had formed the Edison Electric Illuminating Company to build central station electric generating plants in New York City. The first central power plant - Pearl Street Station in lower Manhattan - began generating electricity on September 4, 1882.  With the success of Pearl Street Station, Edison created the Edison Company for Isolated Lighting. This company was formed in May 1883 to build and sell electric power stations, like Pearl Street Station, to towns and cities throughout the United States. .**
**From The Edison Electric Institute

AC vs. DC

Edison's method for generating and transmitting electricity was called direct current, or low voltage. George Westinghouse, a consolidator of his time, built Westinghouse Electric by purchasing other inventor's patents, including the polyphase alternating current (AC) system invented by Nikola Tesla.

In an alternating current system, transformers were used to step up, or increase the voltage that left the power plant. This enabled the electricity to travel over long-distance wires. When the electricity reached its destination, another transformer would then step down, or decrease the voltage so that power could be used in homes and factories.

Edison's direct current system was unable to use transformers. With Edison's system, the voltage dropped as it traveled further and further from the generator. To overcome this disadvantage, power plants would have to be built close to the power users - a costly solution.

Soon, the Westinghouse alternating current system — rather than Edison's more expensive, higher-maintenance, and less efficient direct current system — began to get most of the orders.

In 1893, the Westinghouse AC system was chosen to move electric power from Niagara Falls to Buffalo. Shortly after that, the Westinghouse AC "universal" system became the new standard for transmitting electricity. **
**From The Edison Electric Institute

Note: The solar photovoltaic panels and wind turbine on The Greenius create DC (direct) current, which is converted into AC (alternating) current for your home by the inverter we install with your system.

Modern Electricity

Electricity is an essential part of modern life. In our homes we use it for lighting, running appliances and electronics, and for heating and cooling. Most consumers do not think much about their electricity until a power outage, or when they are “shocked” by a high utility bill. Fortunately in the United States, power outages are relatively infrequent and short in duration. Electricity bills, however, are frequent, unavoidable and growing ever higher. The dollar amount charged each month is a function of the price per kilowatthour (kWh) and the amount of kilowatthours consumed; other add-ons to your bill include State and local taxes and costs for maintaining the overall “grid”.

Where Does Your Electricity Come From Today?

Electricity is delivered to you by the local utility through a network of existing transmission and distribution lines, often referred to as the “grid.” Transmission lines are the large, high-voltage power lines that move electricity from power plants to substations and are often supported by tall metal towers. Smaller, lower voltage distribution lines move power from substations and transformers, and are often seen along residential streets supported by wood poles. Most of the existing grid was built during a highly structured, highly regulated era designed to insure that everyone in the United States had reasonable access to electricity service.

What Are the Types of Power Plants that Generate Electricity on the Grid?

Power plants can be grouped into the types of fuel or energy source they use to produce electricity. These include fossil fuels (coal, natural gas, or a refined oil product), nuclear energy, and renewable energy sources such as water (hydroelectric power), biomass, waste-to-energy, geothermal, wind, and solar energy, as well as alternative fuels. Figure 2 shows the relative share of electricity generation by fuel/energy type. One of the features of electricity is that your television and stereo, heating system, air conditioning system, appliances and light fixtures cannot tell the difference between the types of generation, location, or fuel sources. This makes all the electricity on the system usable by all those connected to the grid.

Average household electricity usage

There is no quick answer to the question of what the average household electricity usage is in the United States.  Studies vary from a low of about 600 kWH per year, or 50 kWh a month, to 900 kWh, or 75 kWh a month.  Electricity usage is not necessarily connected to the size of your home.

What do I really pay now?

You can check your bill to determine your usage.  The simple way to determine your cost per kWh is to divide your total bill by the kWh used.  It is important to consider that the rate published by your local utility, say 8 or 9 or 10 cents, often does not include delivery, line maintenance, and other “surcharges” which bring the actual kWh rate up significantly from the published rate.

Electricity Consumption in Your Home

Energy Saving Tips

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