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What is Solar Energy?

Solar energy, radiant light and heat from the sun, has been harnessed by humans since ancient times using a range of ever-evolving technologies. Solar radiation, along with secondary solar-powered resources such as wind and wave power, hydroelectricity and biomass, account for most of the available renewable energy on earth. Only a minuscule fraction of the available solar energy is used. Solar powered electrical generation relies on heat engines and photovoltaics. Solar energy's uses are limited only by human ingenuity. A partial list of solar applications includes space heating and cooling through solar architecture, potable water via distillation and disinfection, daylighting, solar hot water, solar cooking, and high temperature process heat for industrial purposes.To harvest the solar energy, the most common way is to use solar panels. Solar technologies are broadly characterized as either passive solar or active solar depending on the way they capture, convert and distribute solar energy. Active solar techniques include the use of photovoltaic panels and solar thermal collectors to harness the energy. Passive solar techniques include orienting a building to the Sun, selecting materials with favorable thermal mass or light dispersing properties, and designing spaces that naturally circulate air.

Solar Power System Efficiency

Efficiency in photovoltaic solar panels is measured by the ability of a panel to convert sunlight into usable energy for human consumption. Knowing the efficiency of a panel is important in order to choose the correct panels for your photovoltaic system. For smaller roofs, more efficient panels are necessary, due to space constraints. How do manufacturers determine the maximum efficiency of a solar photovoltaic panel though? Read below to find out.   Let us first start out by saying that the maximum power, also known as Pmax, of a 200W panel is 200W regardless of the panel efficiency. It is the area the solar panels use up to get those 200W that determines how efficient the panel is. The panel efficiency determines the power output of a panel per unit of area. The maximum efficiency of a solar photovoltaic cell is given by the following equation:   ηmax (maximum efficiency) = Pmax (maximum power output) / (ES, γsw (incident radiation flux) * Ac (area of collector))   The incident radiation flux could better be described as the amount of sunlight that hits the earth's surface in W/m2. The assumed incident radiation flux under standard test conditions (STC) that manufacturers use is 1000 W/m2. Keep in mind though, that STC includes several assumptions and depends on your geographic location.   Now, we'll make a sample calculation to determine how manufacturers calculate the maximum solar panel efficiency under STC.   Assume you have a 400W system with an area of 30 ft2 and you want to determine the maximum efficiency of your solar panels under STC. Your first step would be to convert the area of your panels' to units of square meters which is:   30 ft2 x 1 meter / (10.76 ft2) = 2.79 m2   (In determining the efficiency, I would personally include the dimensions of the frames in your calculations. Although they are there for structural purposes, they are necessary components that do take up area)   Now that you have your Pmax (400W), ES, γsw (1000W/m2), and Ac (2.79 m2), you can plug your numbers into the efficiency equation where all units will cancel out and then multiply the value by 100% to give you your efficiency percentage:   ηmax (in percentage) = 400 W / (1000W/m2 x 2.79 m2) = 0.143 x 100 % = 14.3%   This would be the maximum efficiency of your solar panel, not to be confused with the minimum that may be found on the panel's specification sheet.   So when you are determining what solar panels are right for you, think about how important the efficiency of panels are in paying a premium price. Perhaps you have a roof with a large area that would be ideal for the placement of solar panels, and therefore, lower cost and less efficient panels would work for you. If your rooftop area is limited though, you may want to determine the efficiency you will need for your panels to achieve the desired power output over a limited area.

Feed In Tariff (FIT)

 A feed-in tariff (FiT, feed-in law, advanced renewable tariff[1] or renewable energy payments[2]) is a policy mechanism designed to encourage the adoption of renewable energy sources and to help accelerate the move toward grid parity. FiTs typically include three key provisions[3]: guaranteed grid access long-term contracts for the electricity produced purchase prices that are methodologically based on the cost of renewable energy generation and tend towards grid parity. Under a feed-in tariff, individual ratepayers (homeowners and businesses) are paid for any renewable electricity they produce. If they produce more than they can use themselves, then regional or national electric grid utilities are obligated to buy the excess from them.[4] The cost-based prices therefore enable a diversity of projects (wind, solar, etc.) to be developed, and for investors to obtain a reasonable return on renewable energy investments. This principle was first explained in Germany's 2000 RES Act: “The compensation rates…have been determined by means of scientific studies, subject to the provision that the rates identified should make it possible for an installation – when managed efficiently – to be operated cost-effectively, based on the use of state-of-the-art technology and depending on the renewable energy sources naturally available in a given geographical environment.” (RES Act 2000, Explanatory Memorandum A)[5] As a result, the rate may differ among various sources of power generation, installation place (e.g. rooftop or ground-mounted), projects of different sizes and, sometimes, by technology employed (solar, wind, geothermal, etc.). The rates are typically designed to ratchet downward over time to track technological change and overall cost reductions. This is consistent with keeping the payment levels in line with actual generation costs over time. In addition, FITs typically offer a guaranteed purchase for electricity generated from renewable energy sources within long-term (15–25 year) contracts.[6] These contracts are typically offered in a non-discriminatory way to all interested producers of renewable electricity. As of 2009, feed-in tariff policies have been enacted in 63 jurisdictions around the world, including in Australia, Austria, Belgium, Brazil, Canada, China, Cyprus, the Czech Republic, Denmark, Estonia, France, Germany, Greece, Hungary, Iran, Republic of Ireland, Israel, Italy, the Republic of Korea, Lithuania, Luxembourg, the Netherlands, Portugal, South Africa, Spain, Sweden, Switzerland, Thailand, Turkey,[7] and in some (nowadays, a dozen) states in the United States,[8] and is gaining momentum in other ones as China, India and Mongolia. In 2008, a detailed analysis by the European Commission concluded that "well-adapted feed-in tariff regimes are generally the most efficient and effective support schemes for promoting renewable electricity", going to grid parity.[9] This conclusion has been supported by a number of recent analyses, including by the International Energy Agency,[10][11] the European Federation for Renewable Energy,[12] as well as by Deutsche Bank.[13]

Photovoltaic (PV)

 Photovoltaics (PV) is a method of generating electrical power by converting solar radiation into direct current electricity using semiconductors that exhibit the photovoltaic effect. Photovoltaic power generation employs solar panels comprising a number of cells containing a photovoltaic material. Materials presently used for photovoltaics include monocrystalline silicon, polycrystalline silicon, amorphous silicon, cadmium telluride, and copper indium selenide/sulfide.[1] Due to the growing demand for renewable energy sources, the manufacturing of solar cells and photovoltaic arrays has advanced considerably in recent years.[2][3][4] As of 2010, solar photovoltaics generates electricity in more than 100 countries and, while yet comprising a tiny fraction of the 4800 GW total global power-generating capacity from all sources, is the fastest growing power-generation technology in the world. Between 2004 and 2009, grid-connected PV capacity increased at an annual average rate of 60 percent, to some 21 GW.[5] Such installations may be ground-mounted (and sometimes integrated with farming and grazing)[6] or built into the roof or walls of a building, known as Building Integrated Photovoltaics or BIPV for short.[7] Off-grid PV accounts for an additional 3–4 GW.[5] Driven by advances in technology and increases in manufacturing scale and sophistication, the cost of photovoltaics has declined steadily since the first solar cells were manufactured.[8] Net metering and financial incentives, such as preferential feed-in tariffs for solar-generated electricity, have supported solar PV installations in many countries.

CPV/CSP (Concentrated Photo Voltaic or Concentrating Solar Power)

 Concentrated solar power (CSP) are systems that use lenses or mirrors to concentrate a large area of sunlight, or solar thermal energy, onto a small area. Electrical power is produced when the concentrated light is converted to heat which drives a heat engine (usually a steam turbine) connected to an electrical power generator. CSP should not be confused with photovoltaics, where solar power is directly converted to electricity without the use of steam turbines. The concentration of sunlight onto photovoltaic surfaces, similar to CSP, is known as concentrated photovoltaics (CPV).

CHP (combined heat and power)

Cogeneration (also combined heat and power, CHP) is the use of a heat engine or a power station to simultaneously generate both electricity and useful heat. All power plants must emit a certain amount of heat during electricity generation. This can be into the natural environment through cooling towers, flue gas, or by other means. By contrast CHP captures some or all of the by-product heat for heating purposes, either very close to the plant, or—especially in Scandinavia and eastern Europe—as hot water for district heating with temperatures ranging from approximately 80 to 130 °C. This is also called Combined Heat and Power District Heating or CHPDH. Small CHP plants are an example of decentralized energy.[1] In the United States, Con Edison distributes 30 billion pounds of 350 °F/180 °C steam each year through its seven cogeneration plants to 100,000 buildings in Manhattan—the biggest steam district in the United States. The peak delivery is 10 million pounds per hour (corresponding to approx. 2.5 GW)[2][3] This steam distribution system is the reason for the steaming manholes often seen in "gritty" New York movies. Other major cogeneration companies in the U.S. include Recycled Energy Development[4] and leading advocates include Tom Casten and Amory Lovins. By-product heat at moderate temperatures (212-356°F/100-180°C) can also be used in absorption chillers for cooling. A plant producing electricity, heat and cold is sometimes called trigeneration or more generally: polygeneration plant. Cogeneration is a thermodynamically efficient use of fuel. In separate production of electricity some energy must be rejected as waste heat, but in cogeneration this thermal energy is put to good use.

Sunlight Irradiance

Sunlight, in the broad sense, is the total frequency spectrum of electromagnetic radiation given off by the Sun. On Earth, sunlight is filtered through the Earth's atmosphere, and solar radiation is obvious as daylight when the Sun is above the horizon. When the direct solar radiation is not blocked by clouds, it is experienced as sunshine, a combination of bright light and radiant heat. When it is blocked by the clouds or reflects off of other objects, it is experienced as diffused light. The World Meteorological Organization uses the term "sunshine duration" to mean the cumulative time during which an area receives direct irradiance from the Sun of at least 120 watts per square meter.[1] Sunlight may be recorded using a sunshine recorder, pyranometer or pyrheliometer. Sunlight takes about 8.3 minutes to reach the Earth. Direct sunlight has a luminous efficacy of about 93 lumens per watt of radiant flux, which includes infrared, visible, and ultraviolet light. Bright sunlight provides illuminance of approximately 100,000 lux or lumens per square meter at the Earth's surface. Sunlight is a key factor in photosynthesis, a process vital for life on Earth.      

Peak sun hours

The equivalent number of hours per day when solar irradiance averages 1 kW/m2. For example, six peak sun hours means that the energy received during total daylight hours equals the energy that would have been received had the irradiance for six hours been 1 kW/m2.

ST Solar Thermal

Solar thermal energy (STE)[1] is a technology for harnessing solar energy for thermal energy (heat). Solar thermal collectors are classified by the USA Energy Information Administration as low-, medium-, or high-temperature collectors. Low temperature collectors are flat plates generally used to heat swimming pools. Medium-temperature collectors are also usually flat plates but are used for heating water or air for residential and commercial use. High temperature collectors concentrate sunlight using mirrors or lenses and are generally used for electric power production. STE is different from photovoltaics, which convert solar energy directly into electricity. While only 600 megawatts of solar thermal power is up and running worldwide in October 2009 according to Dr David Mills of Ausra, another 400 megawatts is under construction and there are 14,000 megawatts of the more serious concentrating solar thermal (CST) projects being developed.[2]  

Solar Stepper Motor Backlash

The motion control world has its jargon and buzzwords. Some are used interchangeably leading to ambiguity and possible confusion. Backlash and stiffness are both important but have different impacts, and those differences deserve attention. Backlash and stiffness are two important properties associated with motion control systems. Backlash is a characteristic of a mechanical drive system; clearances among the elements create slop when stationary, and dead play during reversals. Stiffness, on the other hand, is a property of a mechanism or a component and is simply the resistance to deformation or deflection when under a load.      

Dual Axis Solar Tracker

Dual axis trackers have two degrees of freedom that act as axes of rotation. These axes are typically normal to one another. The axis that is fixed with respect to the ground can be considered a primary axis. The axis that is referenced to the primary axis can be considered a secondary axis. There are several common implementations of dual axis trackers. They are classified by the orientation of their primary axes with respect to the ground. Two common implementations are Tip - Tilt trackers and Azimuth-Altitude trackers. The orientation of the module with respect to the tracker axis is important when modeling performance. Dual Axis Trackers typically have modules oriented parallel to the secondary axis of rotation.    

Tracker Azimuth

An Azimuth – Altitude Dual Axis Tracker has its primary axis vertical to the ground. The secondary axis is then typically normal to the primary axis. Field layouts must consider shading to avoid unnecessary energy losses and to optimize land utilization. Also optimization for dense packing is limited due to the nature of the shading over the course of a year. This mount is used as a large telescope mount owing to its structure and dimensions. One axis is a vertical pivot shaft or horizontal ring mount, that allows the device to be swung to a compass point. The second axis is a horizontal elevation pivot mounted upon the azimuth platform. By using combinations of the two axis, any location in the upward hemisphere may be pointed. Such systems may be operated under computer control according to the expected solar orientation, or may use a tracking sensor to control motor drives that orient the panels toward the sun. This type of mount is also used to orient parabolic reflectors that mount a Stirling engine to produce electricity at the device.[7]    

Solar Concentration Factor


Multi-junction solar cells

Multi-Junction Solar Cells are the future of PV solar electricity generation. While the current industry average for solar panels is 12-18% efficiency, the latest multi-junction cells already offer efficiencies of 40% (for example, these 40% efficiency solar cells from Boeing subsidiary Spectrolab).   Common silicon PV solar cells can be understood by reading out short introduction to PV solar cells. Basically photons of sun light hit the cell and are absorbed and converted into electrical current. Around 85% of all solar cells manufacted today are still made in the this way with a p-n junction diode in a silicon wafer. Sunlight is made up of a broad spectrum covering infrared to ultraviolet with visibleligh in between. Photons of light have different energy levels depending on the wavelength of sunlight they are carrying. Common silicon cells are designed to absorb visible light, however they do not do so very well. High energy blue light photons do not have all of their energy converted into electricity - some is converted into electricity and the rest is wasted as heat. Low energy red light photons on the other hand pass straight through the solar cell and are not absorbed at all.   Multi-Junction Solar Cells A solar cell made of just one material cannot be more than about 30% efficient in theory and below around 25% in practice. Therefore researchers came up with multi-junction solar cells. A multi-junction solar cell is made up of a two or more layers of semi-conductor material - for example, one layer that can absorb blue light well, and a second layer that can absorb red light well. The overall efficiency of this multi-junction solar cell is therefore better than was possible when just one material was used.   The ideal solar cell in theory would have hundreds of different layers, each one tuned to a small range of light wavelengths all the way from ultraviolet to infrared. Although this would lead to fantastic efficiencies of over 70% it is not possible in practice due to difficulties in manufacturing such complicated crystals. Therefore researchers have focussed their attentions on multi-junction solar cells with just a few different layers - and they are now managing to reach efficiencies of 35-40% with improvements to come.   The ordering of the layers of a multi-junction solar device are decided by their individual band gaps - i.e. the wavelengths of light they will absorb. On the top - closest to the sun - goes the layer with the largest band gap. Subsequent layers are then positioned in descending order of their band gaps. The highest energy photons (e.g. ultra violet to blue light) are captured by the top layer, and the bottom layer captures the lower energy photons (red to infra red) which pass through the other layers.      


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