Solar Cell:
Solar cells have many applications. Historically solar cells have been used in situations where electrical power from the grid is unavailable, such as in remote area power systems, Earth orbiting satellites, consumer systems, e.g. handheld calculators or wrist watches, remote radiotelephones and water pumping applications. Recently solar cells are particularly used in assemblies of solar modules (photovoltaic arrays) connected to the electricity grid through an inverter, often in combination with a net metering arrangement. Solar cells are regarded as one of the key technologies towards a sustainable energy supply.
Solar Panels - Solar Panel Arrays:
An array is an assembly of solar-thermal panels or photovoltaic (PV) modules; the panels can be connected either in parallel or series depending upon the design objective. Solar panels typically find use in residential, commercial, institutional, and light industrial applications.
Solar-thermal panels saw widespread use in Florida and California until the 1920's when tank-type water heaters replaced them. A thriving manufacturing business died seemingly overnight. However, solar-thermal panels are still in production, and are common in portions of the world where energy costs, and solar energy availability, are high.
Recently there has been a surge toward large scale production of PV modules. In parts of the world with significantly high insolation levels, PV output and their economics are enhanced. PV modules are the primary component of most small-scale solar-electric power generating facilities. Larger facilities, such as solar power plants typically contain an array of reflectors (concentrators), a receiver, and a thermodynamic power cycle, and thus use solar-thermal rather than PV.
Solar Car:
A solar car is an electric vehicle powered by solar energy obtained from solar panels on the surface of the car. Photovoltaic (PV) cells convert the sun's energy directly into electrical energy. However, solar cars are not currently a practical form of transportation. Although they can operate for limited distances without the sun, the solar cells are generally very fragile.
Using solar car technology, development teams have focused their efforts toward optimizing the functionality of the vehicle, with little concern for passenger comfort. Most solar cars have only enough room for one or two people. Solar cars compete in races (often called rayces) such as the World Solar Challenge and the American Solar Challenge. These events are often sponsored by government agencies, such as the United States Department of Energy, who are keen to promote the development of alternative energy technology (such as solar cells). Such challenges are often entered by universities to develop their students' engineering and technological skills, but many professional teams have entered competitions as well, including teams from GM and Honda.
Solar Power Classifications:
Direct or Indirect
In general, direct solar power involves a single transformation of sunlight which results in a useable form of energy.
* Sunlight hits a photovoltaic cell creating electricity. * Sunlight warms a thermal mass. * Sunlight strikes a solar sail on a space craft and is converted directly into a force on the sail which causes motion of the craft. * Sunlight strikes a light mill and causes the vanes to rotate as mechanical energy, little practical application has yet been found for this effect. * In a direct solar water heater the water heated in the collector is used in the domestic water system. * Sunlight which is not reflected provides direct lighting.
In general, indirect solar power involves multiple transformations of sunlight which result in a useable form of energy.
* Vegetation uses photosynthesis to convert solar energy to chemical energy. The resulting biomass may be burned directly to produce heat and electricity or processed into ethanol, methane, hydrogen and other biofuels. * Hydroelectric dams and wind turbines are powered by solar energy through its interaction with the Earth's atmosphere and the resulting weather phenomena. * Ocean thermal energy production uses the thermal gradients present across ocean depths to generate power. These temperature differences are produced by sunlight. * Fossil fuels are ultimately derived from solar energy captured by vegetation in the geological past. * In an indirect solar water heater the fluid heated in the collector transfers its heat through a heat exchanger to a separate domestic water system. * Sunlight reflected off a ceiling or other surface provides indirect lighting.
Passive or Active
Passive solar systems use non-mechanical techniques of capturing, converting and distributing sunlight into useable forms of energy for heating, lighting or ventilation. These techniques include selecting materials with favorable thermal properties, designing spaces that naturally circulate air and referencing the position of a building to the sun.
* Passive solar water heaters use a thermosiphon to circulate fluid. * A Trombe wall circulates air by natural circulation and acts as a thermal mass which absorbs heat during the day and radiates heat at night. * Clerestory windows, light shelves, skylights and light tubes can be used among other daylighting techniques to illuminate a building's interior. * Passive solar water distillers may use capillary action to pump water.
Active solar systems use electrical and mechanical components such as photovoltaic panels, pumps and fans to process sunlight into useable forms of energy.
Concentrating or Non-Concentrating
Concentrating solar power (CSP) systems use lenses or mirrors and tracking systems to focus a large area of sunlight into a small beam capable of producing high temperatures and correspondingly high thermodynamic efficiencies. Concentrating solar is generally associated with solar thermal applications but concentrating photovoltaic (CPV) applications exist as well and these technologies also exhibit improved efficiencies. CSP systems require direct insolation to operate properly.
Concentrating solar power systems vary in the way they track the sun and focus light.
* Line focus/Single-axis * A solar trough consists of a linear parabolic reflector which concentrates light on a receiver positioned along the reflector's focal line. These systems use single-axis tracking to follow the sun. A working fluid (oil, water) flows through the receiver and is heated up to 400 °C before transferring its heat to a distillation or power generation system. Trough systems are the most developed of the CSP technologies. The Solar Electric Generating System (SEGS) plants in California and Plataforma Solar de Almería's SSPS-DCS plant in Spain are representatives of this technology. * Point focus/Dual-axis A power tower consists of an array of flat reflectors (heliostats) which concentrate light on a central receiver located on a tower. These systems use dual-axis tracking to follow the sun. A working fluid (air, water, molten salt) flows through the receiver where it is heated up to 1000 °C before transferring its heat to a power generation or energy storage system. Power towers are less advanced than trough systems but they offer higher efficiency and energy storage capability. The Solar Two in Daggett, California and the Planta Solar 10 (PS10) in Sanlucar la Mayor, Spain are representatives of this technology. A parabolic dish or dish/engine system consists of a stand-alone parabolic reflector which concentrates light on a receiver positioned at the reflector's focal point. These systems use dual-axis tracking to follow the sun. A working fluid (hydrogen, helium, air, water) flows through the receiver where it is heated up to 1500 °C before transferring its heat to a sterling engine for power generation. Parabolic dish systems display the highest solar-to-electric efficiency among CSP technologies and their modular nature offers scalability. The Stirling Energy Systems (SES) and Science Applications International Corporation (SAIC) dishes at UNLV and the Big Dish in Canberra, Australia are representatives of this technology.
Non-concentrating photovoltaic and solar thermal systems do not concentrate sunlight. While the maximum attainable temperatures (200 °C) and thermodynamic efficiencies are lower, these systems offer simplicity of design a have the ability to effectively utilize diffuse insolation. Flat-plate thermal and photovoltaic panels are representatives of this technology.
