Humans have been working to harness the sun’s heat since the 7^th Century BC. Using glass, mirrors and other polished surfaces our ancestors concentrated the sun’s rays to start fires and signal their communities. Do you remember using a magnifying glass to ignite straw or paper? That action captured solar energy via a secondary device and is an example of active solar energy usage.

Concern for our environment, the desire for energy independence and a declining cost of solar technologies has fostered renewed interest in solar energy from the end of the last century to today. New technologies have enabled the use of this limitless source of energy in both large and small scale applications. Since the sun touches the entire earth in cycles of 12 hours, it is one of the more abundant forms of power that we can utilize for energy.

Scientifically, this is a rudimentary explanation of how solar energy is harvested. This energy source contains molecules that include electrons and protons – essential elements in the life cycles found in plants, animals, weather and, really all biological processes. In the case of utilizing solar power as an energy source, electrons are the ones that we are interested in. Those electrons can be gathered and manipulated with the use of materials which can be purchased at most hardware stores or electrical supply houses.

Types of Solar Energy

There are two ways to categorize solar energy:

• you can categorize by how it is converted into energy: passive solar and active solar
• you can categorize it by the type of energy it is converted into: solar thermal energy, photovoltaic solar energy or concentrating solar power

Passive Solar Energy - harnesses the sun’s energy without the use of mechanical devices. Orienting a building’s walls and windows is the first act of passive solar usage. In cooler seasons, using the sun’s path to heat exterior walls and to allow direct sunlight into the structure harnesses heat energy gained from the sun to warm the building and reduces dependence on mechanical heating systems. This works against the desired energy use in warmer months where interior cooling is desired.

Water and “Trombe” walls are another example of passive the use of solar energy. Water wall systems store water in pods arranged from the top to the bottom of a wall area. There are insulating screens arrayed on both the inside and outside of the wall.  During the day, the exterior shade is raised and the inside shade is lowered, allowing the sun to heat the water pods.  At night, when it is cooler outside, the outer screen is lowered and the inside one is raised to allow the stored heat to radiate into the building. A “Trombe” wall works in a similar fashion, heating a block or concrete wall and allowing cool air to be warmed as it passes between glazing and the black-painted wall, then being returned to the interior room by convection.

Solar ovens use an array of polished/reflective surfaces used to concentrate sunlight onto pots and baking dishes – are much more in use today around the world. They are easily carried on treks or stored in one’s home and are very effective in focusing the sun’s rays into the center of the oven. Because they are portable and lightweight they are perfect for camping, boating, picnicking and hiking and can also be used during power outages. Solar ovens maintain a steady temperature between 210 and 260 degrees in most areas and can even reach temperatures up to 300 degrees. The ovens cook food slowly and evenly – similar to your crock pot.  You can purchase a ready-made solar oven or make your own!

Passive Solar water heating – a passive solar water heating system uses natural convection or household water pressure to circulate water through a solar collector to a storage tank or to the point of use. The batch system is the simplest of all solar water heating systems. This system uses one or more metal water tanks painted with a heat absorbing black coating. It uses an insulating container with a cover made of glass or plastic to allow sunlight to strike the tank directly. The storage tank in this system is the collector as well and allows existing house pressure to move water through the system. Every time a hot water valve is used, heated water from the batch system tank is removed and is replaced by incoming cold water. The pipes leading from the heater need to be substantially insulated and the batch heater itself will need to be covered on cold nights to retain heat. The water will be at its highest temperature in late afternoon and evening and therefore the most efficient time to use your warmed water.

Another type of passive solar water heating is the thermo-siphon system. This system is more expensive and complex than the batch system. It uses a flat plate collector and a separate storage tank that must be located higher than the collector. The collector is similar to those used in active systems. Heated water from the top of the collector flows into the top of the storage tank. The colder water from the bottom of the storage tank will be drawn into the lower entry of the solar collector to replace the heated water that was thermo-siphoned upward. The storage tank may or may not use a heat exchanger but of course is not considered passive if used.

Daylighting -- the sun provides free, full-spectrum light all day and making use of this free source just makes sense. If you are building a new home or making renovations, plan to put as many south-facing windows in the plan as possible. Install skylights or solar tubes for additional daylighting in your home. Daylight sensors can be installed along with occupany sensors to turn lights off in a room if there are sufficient natural light levels or the room is unoccupied. 

Another daylighting strategy is the use of an interior light shelf. This horizontal overhang is made of a reflective material like metal or high-gloss paint, which uses a slightly curved or angled surface to reflect light from a window deeper into the room. It is installed directly below a clerestory window and redirects sunlight onto the ceiling, which diffuses it and distributes it more evenly.

You can even pipe in sunlight by fiber optics. Several companies are now manufacturing systems to capture sunlight and transmitting it into a building's interior spaces with fiber optic cables. This type of system can be used to illuminate spaces that cannot benefit from direct daylighting through windows.

Active Solar Energy - harnesses the sun’s energy with the use of mechanical devices to collect, store and distribute solar energy. This type of solar energy  is called active because one is actively gathering and using energy from the sun for your home's heating needs. These systems use focusing mirrors asnd metal plates to capture the sun's energy. Solar radiation is absorbed by the collectors and then transfers the heat to air or water. Active solar systems can be used to heat water in home, swimming pools, and commercial and industrial buildings. These systems can also be used to provide space heating. Using glazed collectors much like solar water heating systems heat is transferred to a radiant floor heating system. Fans or pumps can also be used to circulate heated air. 

Active Solar Space Heating - uses mechanical equipment such as pumps, fans and blowers to help collect, store, and distribute the heat throughout your home. Active systems also generally have an energy-storage system to provide heat on cloudy days. Active solar heating systems are most cost-effective when they are during most of the year - in cold climates that have good solar resources. They are most economical if they are replacing more expensive heating fuels like electricity, propane, and oil heat.

Active space heating systems are available as water systems or as air heating systems. Water-based systems are usually combination systems that supply domestic hot water and space heating. Liquid-based systems heat water or an antifreeze solution in a hydronic collector. Liquid-based systems use large water tanks or thermal mass for heat storage. The distrution of the heat is handles with radiant slab systems, hot-water baseboards or central forced air systems.

Air-based systems heat air in an air collector and use rock bins or thermal mass to store the heated air. The hot air is then distributed throughout the home using ducts and blowers. Air-based solar heating systems usually use an air-to-water heat exchanger to supply heat to the domestic hot water system, making the system useful in the summertime. Both systems collect and absorb solar radiation. Then the solar heat is transferred directly to the interior space or to a storage system.

Active solar water heating - uses pumps to circulate the water or a heat-transfer fluid through the system. Indirect systems use a heat transfer fluid which is usually a water-antifreeze mixture. After the heat-transfer fluid is heated in the solar collectors it is pumped to a storage tank where a heat-exchanger transfers the heat from the fluid to the household water. This type of system is also known as a closed-loop system.

Active Solar Pool Heating - can extend your swim season while reducing your pool heating costs. The systems are simple and relatively inexpensive - costing as little as $100. The solar pool systems usually use simple, low cost, unglazed plastic collectors and uses pumps to circulate the pool water throught solar collectors for heating and back into the pool. There is no need for water storage tanks because your pool is used as the storage medium for the heated water.

Another way to categorize solar energy is by the type of energy it is converted into:
solar thermal energy, photovoltaic solar energy or concentrating solar power.

Solar Thermal Energy -- uses energy from the sun directly to generate heat. Solar panels can be used to collect heat from the sun to capture its heat and transfer it for water and space heating in buildings.

The panels are positioned on a building to maximize the heat absorption of the sun during the day. They contain tubing called solar thermal collectors which circulate water. Alternatively, in the indirect method, a non-toxic anti-freeze liquid is used instead of water. The sun warms this liquid which in turn transfers this heat to water held in a tank.

Photovoltaic Solar Energy -- these systems use sunlight to power ordinary electrical equipment like computers, lighting and household appliances. The photovoltaic (PV) process converts solar energy directly into solar power. Photovoltaic equipment has no moving parts, requires little maintenance and is nearly silent. This type of system generates solar electricity without producing emissions of greenhouse or any other gases. It uses solar cells – also known as photovoltaic cells or PV cells. The PV cell is made up of two or more thin layers of semi-conducting material to absorb the sun's light. The material is usually made of silicon which is the second most abundant elements on the earth's crust. However, in spite of its abundancy it does have to be refined to a purity factor of 99.999% to make it useful for application in solar panels. When silicon is exposed to light, electrical charges are generated and this can be conducted away by metal contacts as direct current (DC). Since the electrical output from a single cell is small, multiple cells are connected together and enclosed to form a module or solar panel. The solar panel is the main part of the system and they can be connected together to produce greater power. The electricity produced by the solar panel is in the form of direct current [DC]. However, direct current [DC] is not useable for most purposes. An inverter is used to transform the DC power to alternating current [AC] making it ready to distribute to use. The system can be connected to the regular power grid and even run any excess energy that your batteries cannot hold back to the grid and get credit for the extra energy your system has created.

Types Of Photovoltaic [PV]Cells


Amorphous Silicon [a-Si] Cells -- thin film amorphouse silicon [a-Si] solar cells are composed of non-crystalline form of silicon in a thin integrated layers that are micrometers thick and attached to a backing such as glass, stainless steel or a flexible plastic. Because it is attached to much less expensive backings and it uses  uses approximately 1% of the silicon needed for typical crystalline silicon cells, there can be a significant cost savings using this type of solar cell. Amorphous silicon can be deposited on a wide range of substrates, both rigid and flexible, which makes it ideal for curved surfaces and fold-away modules. A flexible backing allows them to be formed-fitted to applications such as roofing and prevents breakage during shipping and handling at the installation site.

Amorphous silicon has been used as a photovoltaic solar battery for calculators for a long time. Recent improvements in a-Si construction techniques have made them more attractive for large-area solar cell use as well. These cells absorbs light more effectively than crystalline silicon, so the cells can be thinner, lightweight, flexible and durable. However, they are less efficient than crystalline-based cells, with typical efficiencies of around six percent. This means that larger panels will be required for the same abount of power in other solar cell types. The cells suffer from significant degration of their power output in the range of 15-35% when exposed to the sun. This is the most well-developed thin film technology to date and their low cost makes them ideally suited for many applications where high efficiency is not required and low cost is important.

Monocrystalline Silicon [c-Si] Cells - made using cells saw-cut from a single cylindrical crystal  cut from an ingot of melted and recrystallized silicon, this is the most efficient of the photovoltaic (PV) technologies. Monocrystalline [single cell] technology are cut from a silicon boule that has grown from a single crystal [one that has grown in only one direction]. Because they are cut from a single silicon boule, they do not completely cover a square solar cell module without a lot of silicon waste. It also means that most c-Si panels have uncovered gaps at the four corners of the cells.

Monocrystalline photovoltaic panels are one of the oldest, most readily available, most efficient and most dependable of technologies. They are considered the workhorses of solar panels and are much more efficient than other crystalline panels with an efficiency level between 15 and 18 percent, though higher levels are possible. However, they are also the most expensive of solar panel choices. Each panel costs more because they’re made from just one crystal, not multiple crystals that are fused together, and therefore the manufacturing process is one of the most complicated and expensive ones around. If space is a concern, monocrystalline is the best type to use because more wattage per square foot can be delivered with these panels. The monocrystalline cells normally have a smoother uniform appearance, are a highly fragile product and require a rigid mounting to protect them.

The average monocrystalline panel outputs 175 watts, is about 63 inches long by 31 inches wide and about an inch high. They weigh approximately thirty-three pounds and have an aluminum frame. In spite of their high cost they can be a good investment because they have a minimum lifespan of 25 years and can last up to 50 years.

Multicrystalline Silicon [mc-Si] Cells -- made from cells cut from an ingot of melted and recrystallised silicon. Also known as polycrystalline cells, they are cut from a silicon boule grown from a crystal that grows in multiple directions.  Multicrystalline cells are cheaper to produce than monocrystalline ones because of  the simpler manufacturing process. The multicrystalline silicon can be produced in a number of ways. The most common manufacturing method used the process  of pouring liquid silicon into blocks [ingots] of polycrystalline silicon and then saw-cut into very thin wafers and assembled into complete cells.

The starting material for manufacturing the multicrystalline cells can be a refined lower-grade silicon, as opposed to the higher-grade semiconductor grade required for the single-crystal material. The cooling rate is one of the factors that determines the final size of crystals in the ingot and the distribution of impurities. During the solidification process of the material, varying sizes of crystal structures are formed giving them that shattered glass appearance. This also creates defects around the borders and therefore making it less efficient. Additionally, the mold for producing the ingot is usually square. This allows the ingot  to be cut and sliced into square cells that fit more compactly into a PV module. These square cells fit together better than the monocrystalline cells with a minimum of wasted space

Thick-film Silicon: is another multicrystalline technology where the silicon is deposited in a continuous process onto a base material giving a fine grained, sparkling appearance. It is created by drawing flat thin films from the molten silicon and results in a multicrystalline structure.  Like all crystalline photovoltaics [PV], this is encapsulated in a transparent insulating polymer with a tempered glass cover and usually bound into a strong aluminium frame. These types of cells are not as efficient as multicrystalline but production costs are lower because there is not as much silicone water and does not require sawing the silicon ingots.

Other Thin Films: A number of other promising materials such as cadmium telluride (CdTe) and copper indium diselenide (CIS) are now being used for photovoltaic [PV] modules. The thin film term comes from the method used to deposit the film, not from the thinness of the film.

The attraction of these technologies is that they can be manufactured by relatively inexpensive industrial processes, certainly in comparison to crystalline silicon technologies, yet they typically offer higher module efficiencies than amorphous silicon. New technologies based on the photosynthesis process are not yet on the market.  [Check back later for additional information on Other Thin Films]check back for information on this solar cell type]

 
 Concentrating Solar Energy --  uses lenses and mirrors to reflect and concentrate the sun's light to receivers that collect the solar energy and convert it into heat. Electrical power is produced when the concentrated light is directed onto photovoltaic surfaces or used to heat a transfer fluid for a conventional power plant.  There are three main types of Concentrating Solar Power [CSP] technology:.

Linear/Concentrator Systems -  collect the sun's energy using long rectangular, curved (U-shaped) mirrors. The mirrors are tilted toward the sun, focusing sunlight on tubes (or receivers) that run the length of the mirrors. The reflected sunlight heats a fluid flowing through the tubes. The hot fluid then is used to boil water in a conventional steam-turbine generator to produce electricity. There are two major types of linear concentrator systems: parabolic trough systems, where receiver tubes are positioned along the focal line of each parabolic mirror; and linear Fresnel reflector systems, where one receiver tube is positioned above several mirrors to allow the mirrors greater mobility in tracking the sun.

Dish/Engine Systems -  uses a mirrored dish similar to a very large satellite dish. The dish-shaped surface directs and concentrates sunlight onto a thermal receiver, which absorbs and collects the heat and transfers it to the engine generator. The most common type of heat engine used today in dish/engine systems is the Stirling engine. This system uses the fluid heated by the receiver to move pistons and create mechanical power. The mechanical power is then used to run a generator or alternator to produce electricity.

Power/Tower Systems -  uses a large field of flat, sun-tracking mirrors known as heliostats to focus and concentrate sunlight onto a receiver on the top of a tower. A heat-transfer fluid heated in the receiver is used to generate steam, which, in turn, is used in a conventional turbine generator to produce electricity. Some power towers use water/steam as the heat-transfer fluid. Other advanced designs are experimenting with molten nitrate salt because of its superior heat-transfer and energy-storage capabilities. The energy-storage capability, or thermal storage, allows the system to continue to dispatch electricity during cloudy weather or at night.  

Solar Energy Cost and Pricing Guides

A free solar panel price comparison chart from EcoBusinessLinks.com
http://www.ecobusinesslinks.com/solar_panels.htm

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