The sun has almost infinite capacity for electric current generation on earth. Movement is the name of the game for electric power. With traditional power generation methods, some fuel is burned or some river is exploited to turn (move) a turbine, thereby releasing electrons, which can be stored in a battery or fed to a community power grid for immediate use by home owners and businesses. Renewable power generation works basically the same. You can use wind to directly drive a turbine, generating electricity. You can use the sun in several ways to create electricity. One way is to use the sun to heat a surface hot enough to boil water or some other liquid. Then use the steam to power a turbine. Another way is to use the sun to create a cold and hot boundary. When cold air and hot air come together, wind is created, which can be used to turn a turbine. A third way to create movement of electrons is to shine sunlight onto the surface of some semiconductor material that is doped positive on one side and negative on the other. Electrons on the outer valence of the semiconductor material will be released and made available for electric current. So rather than moving air, steam, or water to move a turbine, you are moving electrons on a microscopic level. In physics terms, you are converting phonons into electrons. The process of converting light into electricity with semiconductors is called photovoltaics.
Here is a neat 3-d animated video explaining the semiconductor concept.
Photovoltaic Solar Electric Systems use the principals of semiconductor electronics explained above to generate electricity for home use. You can use this power to offset (grid-tied) or replace (off-grid) the power sold to by your local utility company. Here is a simple video showing how PV systems are used.
Prior to now the main stumbling block to home solar electric installations has been cost. However, the prices for solar panels are falling off a cliff. Sunelec is currently offering un-finished laminate solar panels for 50 cents a watt. These are panels that only three years ago went for more than $4.00 per watt. These prices are before your federal and local rebates and tax credits In other countries, governments have enacted, what's called a Feed-In Tariff, meaning there are no up front costs to installing a PV system. And, you receive a constant rate for selling your excess power to your local utility. So now is the time to get excited about solar electric PV system installation. Here is a short list of advantages of installing a solar PV system on your home.
There are several components to a small scale solar panel system that most people can build. The basic building block of a photovoltaic system is a solar cell. It is made of silicon semiconductor material and converts light into electricity. A matrix of solar cells are wired together to make a solar panel, which typically outputs 12, 24, or 48 volts direct current (Vdc). A single solar panel can be used individually for small charging chores such charging a 12 volt battery or charging electronic equipment such as cell phones. However, to supply electricity to a whole household, several or many solar panels must be wired together to form a solar array. This solar array is usually mounted on an equator facing roof top or a metal post. The electrical output of your solar array is totally dependent on the amount of direct sunlight that hits the panels. Any obstructions, such as trees or clouds, will severely reduce the amount of electricity produced.
Solar cells have been used for many years on a small scale. We've all seen and used solar powered clocks, calculators, and watches. Those devices used very small solar cells that could extract fractions of a watt from ambient light. These low power applications were perfect because of the costs of solar PV technology at the time.
So what is a solar cell? It is a device that uses light to generate electricity. Today's photovoltaics industry is an offspring of 1950s solid-state electronics, and was greatly stimulated by the need to find power sources for America's space satellites. Its beginnings, though, can be traced back to 1839, when French scientist Edmund Becquerel observed that light falling on certain material created a difference in electric response. In other words, it created electricity. He further discovered that the amount of electricity produced varied with the amount of light and intensity. This is called the Photovoltaic Effect. "Photo" for light and "voltaic" for electric charge.
Solar cells are very thin (about 1/100 of an inch thick, usually expressed in millimetres or nanometres). These cells are made of sand that is super-heated much the same way glass is made, into silicon semiconducting material. The same material is used for most electronics today, including micro-processors for personal computers, remote controls, IPhones, and the like.
Solar cells work by allowing light to excite freely available electrons in the outer band of doped semiconductor material. Once electrons are released from the atoms they are free to move in an electric current.
A solar module is a configuration of PV cells laminated between two pieces of glass.
A solar panel is made up of one or more solar modules fastened together. The terms solar panel and solar module are often used to mean the same thing.
A solar array is one or more solar panels wired together for a specific voltage output and attached to a mounting foundation.
If you are going to attempt to install the system yourself make sure follow all instructions including precautions. A manual highly recommended and used as training material for solar installers is
Photovoltaics Design and Installation Manual Produced by Solar Energy International. The manual highlights key National Electric Codes (NEC) that apply to solar electric installations.
For a solar electric system to be compatible with standard household devices such as lamps, an inverter is needed between the solar and load devices.
In urban areas where homes are powered by a centralized utility grid, you can connect your solar PV system to the utility. There are several advantages to this. Namely, you are using the utility has a battery storage. You system produces more electricity than need during the day. Any excess electricity can be sold to the utility, usually at top rates in the summer when everyone is running the air conditioners. At night when the panels are not producing, you buy back electricity from the utility at much lower rates. A grid-tie system usually does not have batteries. However, batteries are possible. You may want to add batteries for back-up in case the grid goes down.
If you have a cabin in the country side where no power lines are available, you can install an off-grid PV system. This system must have batteries to provide electricity at night.
Batteries in a stand-alone PV system allow the storage of electricity from the PV array for use at night. The battery input and output DC electricity. Battery voltages come in 6, 12, and 24 volt capabilities. Typically the 6 volt batteries are for higher wattage applications.
Batteries also come in several chemistries, including Nickel Metal Hydride, Lithium Ion, and Lead Acid. Both NiMH and LI are very expensive technologies for high power use, just as solar panels were not so long ago. Lead Acid is the most popular battery chemistry for solar electric systems.
There are several types of Lead Acid batteries. The most popular is Sealed Lead Acid (SLA). There are two distinct types of SLA: starting and deep cycle. Batteries designed to start car engines should not be used for solar electric applications, unless they are hybrid batteries. Only deep cycle SLA batteries should be used in this application. Some SLA batteries need their water levels checked periodically. Being that Lead Acid batteries exhaust vapours while powering appliances, they need to be in a location with adequate ventilation. And they have an optimal temperature range. If you are in a climate with excessive summer heat or winter cold, then you may need to locate them in a temperature controlled shelter.
Be sure there is a blocking diode between the batteries and the solar panels. This will prevent battery discharging back into the solar panels at night when there is no sun.
A charge controller matches the output of the solar electric producing panels to a voltage that the batteries can handle. It prevents the batteries from being overcharged and too much voltage being appied to the battery contacts.
What is required from a PV system is dependent on your home energy needs. There are several ways to determine this. The most popular way is to pull out all of your electric utility bills for the previous year. Each invoice should show the monthly kilowatt hour usage. The procedure is to add up all of your kilowatt usage for the 12 statements. Once you find your annual electricity usage in kilowatt hours, you can size your PV system. By sizing, we mean how many solar panels you will need.
The installation of the PV system is straight forward. You have a couple of options depending on the amount of space you have to mount the solar panels. They can be mounted on a post, which can be stationary or rotating. If the stand rotates, it can move in one, two, or three axis. It can move manually, closed loop automation, or open loop automation. In closed loop automation, the panels sense the strength of the sun and rotate in concert with the sun's movements across the sky. Then in the evening, the panels reset to where the sun will rise the next morning.
Photovoltaic systems require a substantial economic investment, with the typical systems costing $7,000 to $15,000 before any incentives are applied. Over the life of the system, you'll pay about 12 cents per kilowatt-hour of electricity produced, compared to about 1 to 20 cents per kilowatt-hour for electricity currently purchased from the utility company. But as the cost of retail electricity increases, the financial return on photovoltaic systems will improve.
Some sites are better than others for producing photovoltaic power. The size and orientation of your home, the presence of shade, and possible zoning restrictions all effect the viability of PV systems for your site.
The size of your investment in photovoltaic power will depend primarily upon the output of your system. This peak output is usually measured in watts. Residential systems can usually range from one to five thousand watts, will commercial systems range up to thirty kilowatts or more.
Many utilities allow their customers to connect properly installed photovoltaic systems onto the existing electrical grid. These grid-tied systems can feed excess PV power back into the power grid any time the customer uses less power than the systems produces. This typically happens during the day when the sun is out and the occupants are not home or have minimal demands. These systems then draw power back from the utility grid when the customer consumes more than the PV system produces, such as during cloudy weather, at night, or when the system is out of operation.
Almost all PV systems are installed by electrical contractors. Your understanding of PV basics will help you choose a competent contractor and effectively supervise their work. This is the best approach unless you have a lot of experience with complicated electrical installations.
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