FIRE - Solar Energy
Solar energy is the light and radiant heat from the Sun that influences Earth's climate and weather and sustains life. Solar power is sometimes used as a synonym for solar energy or more specifically to refer to electricity generated from solar radiation. Since ancient times solar energy has been harnessed for human use through a range of technologies. Solar radiation along with secondary solar resources such as wind and wave power, hydroelectricity and biomass account for most of the available flow of renewable energy on Earth.
Solar energy technologies can provide electrical generation by heat engine or photovoltaic means, space heating and cooling in active and passive solar buildings; potable water via distillation and disinfection, daylighting, hot water, thermal energy for cooking, and high temperature process heat for industrial purposes.
Type of Different Technologies
The installation uses parabolic trough solar thermal technology along with natural gas to generate electricity. 90% of the electricity is produced by the sunlight. Natural gas is only used when the solar power is insufficient to meet the demand from Southern California Edison, the distributor of power in southern California.
Mirrors
The parabolic mirrors are shaped like a half-pipe. The sun shines onto the panels made of glass, which are 94% reflective, unlike a typical mirror, which is only 70% reflective. The mirrors automatically track the sun throughout the day. The greatest source of mirror breakage is wind, with 3000 typically replaced each year. Operators can turn the mirrors to protect them during intense wind storms. An automated washing mechanism is used to periodically clean the parabolic reflective panels.
Heat transfer
The sun bounces off the mirrors and is directed to a central tube filled with synthetic oil, which heats to over 400 °C (750 °F). The reflected light focused at the central tube is 71 to 80 times more intense than the ordinary sunlight. The synthetic oil transfers its heat to water, which boils and drives the Rankine cycle steam turbine, thereby generating electricity. Synthetic oil is used to carry the heat (instead of water) to keep the pressure within manageable parameters
There are many emerging technologies that use variations of the concept above to achieve highest level of efficiency.
Photovoltaic cell is a wide area electronic device that converts solar energy into electricity by the photovoltaic effect. Photovoltaics is the field of technology and research related to the application of solar cells for solar energy. Sometimes the term solar cell is reserved for devices intended specifically to capture energy from sunlight, while the term photovoltaic cell is used when the source is unspecified. Assemblies of cells are used to make solar modules, or photovoltaic arrays.
Solar cells have many applications. Cells are used for powering small devices such as electronic calculators. Photovoltaic arrays generate a form of renewable electricity, particularly useful in situations where electrical power from the grid is unavailable such as in remote area power systems, Earth-orbiting satellites and space probes, remote radiotelephones and water pumping applications. Photovoltaic electricity is also increasingly deployed in grid-tied electrical systems. Similar devices intended to capture energy from other sources include thermo-photovoltaic cells, beta-voltaic cells, and opto-voltaic nuclear batteries.
First Generation
Crystalline silicon and Vacuum deposition
First generation cells consist of large-area, high quality and single junction devices. First Generation technologies involve high energy and labor inputs which prevent any significant progress in reducing production costs. Single junction silicon devices are approaching the theoretical limiting efficiency of 33% and achieve cost parity with fossil fuel energy generation after a payback period of 5-7 years. They are not likely to get lower than USD $1/W.
Second Generation
Thin-film cell
Second generation materials have been developed to address energy requirements and production costs of solar cells. Alternative manufacturing techniques such as vapor deposition and electroplating are advantageous as they reduce high temperature processing significantly. It is commonly accepted that as manufacturing techniques evolve production costs will be dominated by constituent material requirements, whether this be a silicon substrate, or glass cover. Second generation technologies are expected to gain market share in 2008.
Such processes can bring costs down to a little under US$0.50 but because of the defects inherent in the lower quality processing methods, have much reduced efficiencies compared to First Generation.
The most successful second generation materials have been cadmium telluride (CdTe), copper indium gallium selenide, amorphous silicon and micromorphous silicon. These materials are applied in a thin film to a supporting substrate such as glass or ceramics reducing material mass and therefore costs. These technologies do hold promise of higher conversion efficiencies, particularly CIGS-CIS, DSC and CdTe offers significantly cheaper production costs.
Third Generation
Third generation solar cell
Third generation technologies aim to enhance poor electrical performance of second generation (thin-film technologies) while maintaining very low production costs.
Current research is targeting conversion efficiencies of 30-60% while retaining low cost materials and manufacturing techniques. They can exceed the theoretical solar conversion efficiency limit for a single energy threshold material, that was calculated in 1961 by Shockley and Queisser as 31% under 1 sun illumination and 40.8% under maximal concentration of sunlight (46,200 suns, which makes the latter limit more difficult to approach than the former).
There are a few approaches to achieving these high efficiencies:
- Multijunction photovoltaic cell (multiple energy threshold devices).
- Modifying incident spectrum (concentration).
- Use of excess thermal generation (caused by UV light) to enhance voltages or carrier collection.
- Use of infrared spectrum to produce electricity at night.
Technologies includes:
- Silicon nanostructures
- Up/Down converters
- Hot-carrier cells
- Thermoelectric cells
