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"Renewable resources can be replaced as quickly as they are used. Renewable resources may also be so abundant that running out is impossible," while "Non-renewable resources are used faster than they can be replaced."

These definitions and a lot more can be found by clicking the word "attachment," below:

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Now, using what you know, let's see if you can save the Earth in this free online game about renewable energy resources:

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Wonderville is online STEM software providing hands-on STEM Resources with curriculum to teach K-12 students STEM, Robotics, Electronics, Alternative Energy, 3D Printing, Drones, Rocketry & Beyond! Wonderville's hands-on educational software is a perfect resource for underrepresented & at-risk students to develop an understanding of STEM subjects through project-based learning...inspiring the students to pursue STEM careers.

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According to ASU.edu:

- Solar panels provide shade for nearly 5,500 parking spots and over 800 stadium seats.

- In 2013 ASU's solar installations generated 29,530,506 kilowatt hours of electricity. That's enough to make 29.5 million cupcakes!

- In addition to shaded parking and seats ASU sites "building heat-load reduction, extended life of roofs that have shade, living lab for academics and research and sustainability initiatives," as additional benefits to it's use of solar installations.

All stats and info found at:

https://cfo.asu.edu/solar

or

https://cfo.asu.edu/solar-faq

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Not only are we reducing our use of non-renewable resources, but the implementation of solar energy has helped to reduce water use and energy costs for consumers.

According to Arizona Solar Industries Association:

- 330 Solar companies in AZ employ close to 9,000 people.

- 25,000 swimming pools could be filled with the amount of water-use reduced by using solar.

- "Distributed solar generation (DG) and net energy metering will provide Arizona Public Service (APS) customers with $34 million in benefits each year."

All stats from: http://www.seia.org/state-solar-policy/Arizona

or

http://www.seia.org/research-resources/benefits-costs-solar-distributed-generation-arizona-public-service

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Want to know more about how solar panels convert the sun's rays into electricity? 

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Want to know more about how solar panels convert the sun's rays into electricity? 

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Visit this How Stuff Works page.

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You've probably seen calculators with solar cells -- devices that never need batteries and in some cases, don't even have an off button. As long as there's enough light, they seem to work forever. You may also have seen larger solar panels, perhaps on emergency road signs, call boxes, buoys and even in parking lots to power the lights.

Although these larger panels aren't as common as solar-powered calculators, they're out there and not that hard to spot if you know where to look. In fact, photovoltaics -- which were once used almost exclusively in space, powering satellites' electrical systems as far back as 1958 -- are being used more and more in less exotic ways. The technology continues to pop up in new devices all the time, from sunglasses to electric vehicle charging stations.

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The hope for a "solar revolution" has been floating around for decades -- the idea that one day we'll all use free electricity from the sun. This is a seductive promise, because on a bright, sunny day, the sun's rays give off approximately 1,000 watts of energy per square meter of the planet's surface. If we could collect all of that energy, we could easily power our homes and offices for free.

In this article, we will examine solar cells to learn how they convert the sun's energy directly into electricity. In the process, you will learn why we're getting closer to using the sun's energy on a daily basis, and why we still have more research to do before the process becomes cost-effective.

The solar cells that you see on calculators and satellites are also called photovoltaic (PV) cells, which as the name implies (photo meaning "light" and voltaic meaning " electricity"), convert sunlight directly into electricity. A module is a group of cells connected electrically and packaged into a frame (more commonly known as a solar panel), which can then be grouped into larger solar arrays, like the one operating at Nellis Air Force Base in Nevada.

Photovoltaic cells are made of special materials called semiconductors such as silicon, which is currently used most commonly. Basically, when light strikes the cell, a certain portion of it is absorbed within the semiconductor material. This means that the energy of the absorbed light is transferred to the semiconductor. The energy knocks electrons loose, allowing them to flow freely.

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PV cells also all have one or more electric field that acts to force electrons freed by light absorption to flow in a certain direction. This flow of electrons is a current, and by placing metal contacts on the top and bottom of the PV cell, we can draw that current off for external use, say, to power a calculator. This current, together with the cell's voltage (which is a result of its built-in electric field or fields), defines the power (or wattage) that the solar cell can produce.

That's the basic process, but there's really much more to it. On the next page, let's take a deeper look into one example of a PV cell: the single-crystal silicon cell.

Before now, our two separate pieces of silicon were electrically neutral; the interesting part begins when you put them together. That's because without an electric field, the cell wouldn't work; the field forms when the N-type and P-type silicon come into contact. Suddenly, the free electrons on the N side see all the openings on the P side, and there's a mad rush to fill them. Do all the free electrons fill all the free holes? No. If they did, then the whole arrangement wouldn't be very useful. However, right at the junction, they do mix and form something of a barrier, making it harder and harder for electrons on the N side to cross over to the P side. Eventually, equilibrium is reached, and we have an electric field separating the two sides.

This electric field acts as a diode, allowing (and even pushing) electrons to flow from the P side to the N side, but not the other way around. It's like a hill -- electrons can easily go down the hill (to the N side), but can't climb it (to the P side).

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When light, in the form of photons, hits our solar cell, its energy breaks apart electron-hole pairs. Each photon with enough energy will normally free exactly one electron, resulting in a free hole as well. If this happens close enough to the electric field, or if free electron and free hole happen to wander into its range of influence, the field will send the electron to the N side and the hole to the P side. This causes further disruption of electrical neutrality, and if we provide an external current path, electrons will flow through the path to the P side to unite with holes that the electric field sent there, doing work for us along the way. The electron flow provides the current, and the cell's electric field causes a voltage. With both current and voltage, we have power, which is the product of the two.

There are a few more components left before we can really use our cell. Silicon happens to be a very shiny material, which can send photons bouncing away before they've done their job, so

an antireflective coating is applied to reduce those losses. The final step is to install something that will protect the cell from the elements -- often a glass cover plate. PV modules are generally made by connecting several individual cells together to achieve useful levels of voltage and current, and putting them in a sturdy frame complete with positive and negative terminals.

How much sunlight energy does our PV cell absorb? Unfortunately, probably not an awful lot. In 2006, for example, most solar panels only reached efficiency levels of about 12 to 18 percent. The most cutting-edge solar panel system that year finally muscled its way over the industry's long-standing 40 percent barrier in solar efficiency -- achieving 40.7 percent [source: U.S. Department of Energy]. So why is it such a challenge to make the most of a sunny day?

What would you have to do to power your house with solar energy? Although it's not as simple as just slapping some modules on your roof, it's not extremely difficult to do, either.

First of all, not every roof has the correct orientation or angle of inclination to take full advantage of the sun's energy. Non-tracking PV systems in the Northern Hemisphere should ideally point toward true south, although orientations that face in more easterly and westerly directions can work too, albeit by sacrificing varying degrees of efficiency. Solar panels should also be inclined at an angle as close to the area's latitude as possible to absorb the maximum amount of energy year-round. A different orientation and/or inclination could be used if you want to maximize energy production for the morning or afternoon, and/or the summer or winter. Of course, the modules should never be shaded by nearby trees or buildings, no matter the time of day or the time of year. In a PV module, if even just one of its cells is shaded, power production can be significantly reduced.

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If you have a house with an unshaded, southward-facing roof, you need to decide what size system you need. This is complicated by the facts that your electricity production depends on the weather, which is never completely predictable, and that your electricity demand will also vary. Luckily, these hurdles are fairly easy to clear. Meteorological data gives average monthly sunlight levels for different geographical areas. This takes into account rainfall and cloudy days, as well as altitude, humidity and other more subtle factors. You should design for the worst month, so that you'll have enough electricity year-round. With that data and your average household demand (your utility bill conveniently lets you know how much energy you use every month), there are simple methods you can use to determine just how many PV modules you'll need. You'll also need to decide on a system voltage, which you can control by deciding how many modules to wire in series.

You may have already guessed a couple of problems that we'll have to solve. First, what do we do when the sun isn't shining?

The thought of living at the whim of the weatherman probably doesn't thrill most people, but three main options can ensure you still have power even if the sun isn't cooperating. If you want to live completely off the grid, but don't trust your PV panels to supply all the electricity you'll need in a pinch, you can use a backup generator when solar supplies run low. The second stand-alone system involves energy storage in the form of batteries. Unfortunately, batteries can add a lot of cost and maintenance to a PV system, but it's currently a necessity if you want to be completely independent.

The alternative is to connect your house to the utility grid, buying power when you need it and selling it back when you produce more than you use. This way, the utility acts as a practically infinite storage system. Keep in mind though, government regulations vary depending on location and are subject to change. Your local utility company may or may not be required to participate, and the buyback price can vary greatly. You'll also probably need special equipment to make sure the power you're looking to sell the utility company is compatible with their own. Safety is an issue as well. The utility has to make sure that if there's a power outage in your neighborhood, your PV system won't continue to feed electricity into power lines that a lineman will think are dead. This is a dangerous situation called islanding, but it can be avoided with an anti-islanding inverter -- something we'll get to on the next page.

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If you decide to use batteries instead, keep in mind that they'll have to be maintained, and then replaced after a certain number of years. Most solar panels tend to last about 30 years (and improved longevity is certainly one research goal), but batteries just don't have that kind of useful life [source: National Renewable Energy Laboratory]. Batteries in PV systems can also be very dangerous because of the energy they store and the acidic electrolytes they contain, so you'll need a well-ventilated, nonmetallic enclosure for them.

Although several different kinds of batteries are commonly used, the one characteristic they should all have in common is that they are deep-cycle batteries. Unlike your car battery, which is a shallow-cycle battery, deep-cycle batteries can discharge more of their stored energy while still maintaining long life. Car batteries discharge a large current for a very short time -- to start your car -- and are then immediately recharged as you drive. PV batteries generally have to discharge a smaller current for a longer period of time (such as at night or during a power outage), while being charged during the day. The most commonly used deep-cycle batteries are lead-acid batteries (both sealed and vented) and nickel-cadmium batteries, both of which have various pros and cons.

On the next page, we'll dig a little deeper into the components that'll be needed for the sun to start saving you some cash.

The use of batteries requires the installation of another component called a charge controller. Batteries last a lot longer if they aren't overcharged or drained too much. That's what a charge controller does. Once the batteries are fully charged, the charge controller doesn't let current from the PV modules continue to flow into them. Similarly, once the batteries have been drained to a certain predetermined level, controlled by measuring battery voltage, many charge controllers will not allow more current to be drained from the batteries until they have been recharged. The use of a charge controller is essential for long battery life.

The other problem besides energy storage is that the electricity generated by your solar panels, and extracted from your batteries if you choose to use them, is not in the form that's supplied by your utility or used by the electrical appliances in your house. The electricity generated by a solar system is direct current, so you'll need an inverter to convert it into alternating current. And like we discussed on the last page, apart from switching DC to AC, some inverters are also designed to protect against islanding if your system is hooked up to the power grid.

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Most large inverters will allow you to automatically control how your system works. Some PV modules, called AC modules, actually have an inverter already built into each module, eliminating the need for a large, central inverter, and simplifying wiring issues.

Throw in the mounting hardware, wiring, junction boxes, grounding equipment, overcurrent protection, DC and AC disconnects and other accessories, and you have yourself a system. You must follow electrical codes (there's a section in the National Electrical Code just for PV), and it's highly recommended that a licensed electrician who has experience with PV systems do the installation. Once installed, a PV system requires very little maintenance (especially if no batteries are used), and will provide electricity cleanly and quietly for 20 years or more.

Related HowStuffWorks Articles

More Great Links

Sources

"About Solar Energy and Solar Power Systems." SolarEnergy.org. (1/21/2010) http://www.solar-estimate.org/index.php?page=solar-energy-systems

Beckman, William A. and Duffie, John A. "Solar Engineering of Thermal Processes 2nd Ed." John Wiley and Sons, Inc. 1991.

Beller, Peter. "Solar's Future Dims A Bit." Forbes. Jan. 15, 2010. (1/21/2010) http://www.forbes.com/2010/01/15/solar-power-subsidy-markets-equities-germany.html?boxes=marketschannelequities

Biello, David. "Why not spend $21 billion on solar power from space?" Scientific American. Sep. 2, 2009. (1/21/2010) http://www.scientificamerican.com/blog/post.cfm?id=why-not-spend-21-billion-on-solar-p-2009-09-02

Black, Ken. "What is a Solar Battery?" WiseGeek. (1/21/2010) http://www.wisegeek.com/what-is-a-solar-battery.htm

Bland, Eric. "Tobacco Plants Tapped to Grow Solar Cells." Discovery News. Jan. 25, 2010. (1/25/2010) http://news.discovery.com/tech/tobacco-plants-solar-cells.html

Darlin, Damon. "Financially, Solar Power for the Home Is a Tough Sell." New York Times. April 14, 2007. (1/25/2010) http://www.nytimes.com/2007/04/14/business/14money.html

"Enhancing Solar Cells With Nanoparticles." ScienceDaily. Dec. 26, 2008. (1/25/2010) http://www.sciencedaily.com/releases/2008/12/081223172705.htm

"Fast Solar Energy Facts." SolarBuzz.com. (1/21/2010) http://www.solarbuzz.com/Consumer/FastFacts.htm

"Glossary of Solar Energy Terms." SolarEnergy.org. (1/21/2010) http://www.solar-estimate.org/index.php?page=glossary

Goodall, Chris. "How long do solar panels last?" Scitizen. Aug. 5, 2009. (1/21/2010) http://scitizen.com/future-energies/how-long-do-solar-panels-last-_a-14-2897.html

"'Grapefruit Satellite' to Mark 45 Years in Space." Naval Research Laboratory. March 12, 2003. (1/25/2010) http://sse.jpl.nasa.gov/news/display.cfm?News_ID=4759

"How a Photovoltaic System Works." Ameco. (1/21/2010) http://www.solarexpert.com/solar-electric-how-it-works.html

"How Solar Cells Work." GE Energy. (1/20/2010) http://www.gepower.com/prod_serv/products/solar/en/how_solar_work.htm

Knier, Gil. "How do Photovoltaics Work?" NASA. (1/20/2010) http://science.nasa.gov/headlines/y2002/solarcells.htm

Milton, Chris. "The Solar Powered Plane: It Flies!" Scientific American. Dec. 7, 2009. (1/21/2010) http://www.scientificamerican.com/article.cfm?id=the-solar-powered-plane--it-flies-2009-12

Montoya, Randy. "Advancements in Solar Power Grids." Popular Mechanics. September 2000. (1/20/2010) http://www.popularmechanics.com/science/research/1281986.html

National Center for Photovoltaic Research Web site. The National Renewable Energy Laboratory. (1/21/2010) http://www.nrel.gov/pv/ncpv.html

Nave, C. R. "The P-N Junction." Georgia State University. (1/20/2010) http://hyperphysics.phy-astr.gsu.edu/hbase/solids/pnjun.html

"New Generation of Solar Cells Promises Efficiency." ScienceDaily. July 24, 2009. (1/21/2010) http://www.sciencedaily.com/releases/2009/07/090723201446.htm

"New World Record Achieved in Solar Cell Technology." U.S. Department of Energy. Dec. 5, 2006. (1/20/2010) http://www.energy.gov/print/4503.htm

Noufi, Rommel and Zweibel, Ken. "High-Efficiency CdTe and CIGS Thin-Film Solar Cells: Highlights and Challenges." National Renewable Energy Laboratory. September 2007. (1/21/2010) http://www.nrel.gov/docs/fy06osti/39894.pdf

"Own Your Own Power! A Consumer Guide to Solar Electricity for the Home." The National Renewable Energy Laboratory. January 2009. (1/21/2010) http://www.nrel.gov/docs/fy09osti/43844.pdf

Pandolfi, Keith. "Boost home value, get cheaper bills." This Old House. March 4, 2008. (1/25/2010) http://www.cnn.com/2008/LIVING/homestyle/03/04/solar.power/index.html

Pandolfi, Keith. "Solar Shingles." This Old House. (1/25/2010) http://www.thisoldhouse.com/toh/article/0,,1205726,00.html?partner=yes&xid=cnn-0208-solar-shingles

Pollick, Michael. "How Do Solar Panels Work?" WiseGeek. Jan. 3, 2010. (1/20/2010) http://www.wisegeek.com/how-do-solar-panels-work.htm

Shahan, Zachary. "1st Solar-Powered Electric Vehicle (EV) Charging Station in NYC." Scientific American. Dec. 20, 2009. (1/21/2010) http://www.scientificamerican.com/article.cfm?id=1st-solar-powered-electric-vehicle-2009-12

"Solar Cell." Encyclopedia Britannica. (1/21/2010) http://www.britannica.com/EBchecked/topic/552875/solar-cell

SolarPanelInfo.com Web site. (1/21/2010) http://www.solarpanelinfo.com/

"Solar Photovoltaic Technology." The National Renewable Energy Lab. Sept. 29, 2009. (1/20/2010) http://www.nrel.gov/learning/re_photovoltaics.html

"Types of Solar Energy Systems." SolarBuzz.com. (1/21/2010) http://www.solarbuzz.com/Consumer/SolarSystem.htm

Welch, William. "Air Force embraces solar power." USA Today. April 18, 2007. (1/20/2010) http://www.usatoday.com/tech/science/2007-04-17-air-force-solar-power_N.htm

Whitney, Ryan. "Nellis activates nation's largest PV array." Nellis Air Force Base. (1/20/2010) http://www.nellis.af.mil/news/story.asp?id=123079933

Wright, Sarah. "Getting wrapped up in solar textiles." MIT. June 9, 2008. (1/21/2010) http://web.mit.edu/newsoffice/2008/solar-textiles-0609.html

Yago, Jeffrey. "The care and feeding of solar batteries." Backwoods Home Magazine. (1/21/2010) http://www.backwoodshome.com/articles2/yago95.html

Zweibel, Ken. "Harnessing Solar Power: The Photovoltaics Challenge." Plenum Press, New York and London. 1990.

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You've probably seen calculators with solar cells -- devices that never need batteries and in some cases, don't even have an off button. As long as there's enough light, they seem to work forever. You may also have seen larger solar panels, perhaps on emergency road signs, call boxes, buoys and even in parking lots to power the lights.

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Energy created by the sun. A renewable alternative to non-renewable energy resources.

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Because many of the energy resources we are currently using are not renewable and will run out. Bill Nye the Science Guy explains more in this video:

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Safety Smart® Science with Bill Nye the Science Guy®: Renewable Energy -- PREVIEW

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This diagram briefly explains how solar energy funtions: