Abstract on solar energy tracking system — Document Transcript

1. Solar Energy Tracking SystemIntroductionConceptPhotovoltaic’s (PV) is a method of generating electrical power by converting solarradiation into direct current electricity using semiconductors that exhibit thephotovoltaic effect.MaterialsMaterials presently used for photovoltaic’s include monocrystalline silicon,polycrystalline silicon, amorphous silicon, cadmium telluride, and copper indiumselenide/sulfide.Photovoltaic effect & Photoelectric effectThe photovoltaic effect is the creation of a voltage (or a corresponding electriccurrent) in a material upon exposure to light. Though the photovoltaic effect isdirectly related to the photoelectric effect, the two processes are different andshould be distinguished. In the photoelectric effect, electrons are ejected from amaterials surface upon exposure to radiation of sufficient energy. Thephotovoltaic effect is different in that the generated electrons are transferredbetween different bands (i.e., from the valence to conduction bands) within thematerial, resulting in the buildup of a voltage between two electrodes.Solar TrackerA solar tracker is a generic term used to describe devices that orient variouspayloads toward the sun. The optics in concentrated solar applications acceptsthe direct component of sunlight light and therefore must be orientedappropriately to collect energy. Tracking systems are found in all concentratorapplications because such systems do not produce energy unless oriented closelytoward the sun.

2. PayloadsPayloads can be photovoltaic panels, reflectors, lenses or other optical devicesTracker TypesPhotovoltaic trackers can be grouped into classes by the number and orientationof the tracker’s axes. Compared to a fixed amount, a single axis tracker increasesannual output by approximately 30% and a dual axis tracker an additional 6%.Single Axis TrackersSingle axis trackers have one degree of freedom that acts as an axis of rotation.The axis of rotation of single axis trackers is typically aligned along a true Northmeridian. It is possible to align them in any cardinal direction with advancedtracking algorithms.There are several common implementations of single axis trackers. These includeHorizontal Single Axis Trackers, Vertical Single Axis Trackers, and Tilted Single AxisTrackers. The orientation of the module with respect to the tracker axis isimportant when modeling performance.Horizontal Single Axis Tracker (HSAT)The axis of rotation for Horizontal Single Axis Tracker is horizontal with respect tothe ground. The posts at either end of the axis of rotation of a Horizontal SingleAxis Tracker can be shared between trackers to lower the installation cost.Vertical Single Axis Tracker (VSAT)The axis of rotation for Vertical Single Axis Trackers is vertical with respect to theground. These trackers rotate from East to West over the course of the day. Suchtrackers are more effective at high latitudes than are horizontal axis trackers.

3. Tilted Single Axis Tracker (TSAT)All trackers with axes of rotation between horizontal and vertical are consideredTilted Single Axis Trackers. Tracker tilt angles are often limited to reduce the windprofile and decrease the elevated end’s height off the ground.Polar Aligned Single Axis Trackers (PASAT)One scientifically interesting variation of a Tilted Single Axis Tracker is a PolarAligned Single Axis Trackers (PASAT). In this particular implementation of a TiltedSingle Axis Tracker the tilt angle is equal to the latitude of the installation. Thisaligns the tracker axis of rotation with the

earth’s axis of rotation. These are rarelydeployed because of their high wind profile.Dual Axis TrackersTip – Tilt Dual Axis Tracker (TTDAT)A Tip – Tilt Dual Axis Tracker has its primary axis horizontal to the ground. Thesecondary axis is then typically normal to the primary axis. The posts at either endof the primary axis of rotation of a Tip – Tilt Dual Axis Tracker can be sharedbetween trackers to lower installation costs.Field layouts with Tip – Tilt Dual Axis Trackers are very flexible. The simplegeometry means that keeping the axes of rotation parallel to one another is allthat is required for appropriately positioning the trackers with respect to oneanother.Azimuth-Altitude Dual Axis Tracker (AADAT)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 tooptimize land utilization. Also optimization for dense packing is limited due to thenature of the shading over the course of a year.

4. This mount is used as a large telescope mount owing to its structure anddimensions. One axis is a vertical pivot shaft or horizontal ring mount, that allowsthe device to be swung to a compass point. The second axis is a horizontalelevation pivot mounted upon the azimuth platform. By using combinations ofthe two axis, any location in the upward hemisphere may be pointed. Suchsystems may be operated under computer control according to the expectedsolar orientation, or may use a tracking sensor to control motor drives that orientthe panels toward the sun. This type of mount is also used to orient parabolicreflectors that mount a Stirling engine to produce electricity at the device.[Drive typesActive trackerActive trackers use motors and gear trains to direct the tracker as commanded bya controller responding to the solar direction.In order to control and manage the movement of these massive structures specialslewing drives are designed and rigorously tested.Active two-axis trackers are also used to orient heliostats - movable mirrors thatreflect sunlight toward the absorber of a central power station. As each mirror ina large field will have an individual orientation these are controlledprogrammatically through a central computer system, which also allows thesystem to be shut down when necessary.Passive trackerPassive trackers use a low boiling point compressed gas fluid that is driven to oneside or the other (by solar heat creating gas pressure) to cause the tracker tomove in response to an imbalance. As this is a non-precision orientation it isunsuitable for certain types of concentrating photovoltaic collectors but worksfine for common PV panel types. These will have viscous dampers to preventexcessive motion in response to wind gusts.

5. Shader/reflectors are used to reflect early morning sunlight to "wake up" thepanel and tilt it toward the sun, which can take nearly an hour. The time to do thiscan be greatly reduced by adding a self-releasing tie down that positions thepanel slightly past the zenith (so that the fluid does not have to overcome gravity)and using the tie down in the evening. (A slack-pulling spring will prevent releasein windy overnight conditions.)Chronological trackerA chronological tracker counteracts the Earths rotation by turning at an equalrate as the earth, but in the opposite direction. Actually the rates arent quiteequal, because as the earth goes around the sun, the position of the sun changeswith respect to the earth by 360° every year or 365.24 days. A chronologicaltracker is a very simple yet potentially a very accurate solar tracker specifically foruse with a polar mount (see above). The drive method may be as simple as a gearmotor that rotates at a very slow average rate of one revolution per day (15degrees

per hour). In theory the tracker may rotate completely, assuming there isenough clearance for a complete rotation, and assuming that twisting wires arenot an issue.Sun tracking control systemA control circuit for tracking of a heat radiation source which functions tomaintain heat collection structure in optimum alignment with the source therebyto enable maximum efficiency of heat collection; the control circuit includes athreshold circuit for sensing ambient light level to provide enablement control toA-C power circuitry which energizes the heat collector orienting drive system, andthe threshold circuit also functions to automatically invert the heat collector to aprotected position upon detection of insufficient threshold voltage; and, thecircuit further comprises a tracking section energized by a radiation sensor tocause intermittent energization of the drive system to further enable intermittentbi-directional tracking movement of the heat collector, such tracking circuitrybeing enabled by detection of sufficient threshold voltage.

6. Automatic guidance system for radiation-responsive systemsThe invention concerns a guidance, or tracking, arrangement which automaticallyadjusts the alignment of a radiation responsive system in accordance with theposition of a movable radiation source.The arrangement utilizes two bodies able to transmit heat expansion forces intolinear movements to rotate a rocker about an axis perpendicular to the pathplane of the source. The bodies are partially shaded such that exposure to theradiation source controls the extent to which the bodies rotate the rocker.Resilient support means compensate the arrangement for undue forces arisingfrom expansions of the bodies.Photovoltaic array with two-axis power maximization trackingA control system for maximizing the power supplied by an array of solar cellssenses the current and voltage produced and multiplies these to determine theinstantaneous power. The array is tilted slightly in a first direction and the effecton the instantaneous power is noted. If an increase in power was produced, afurther movement in the same direction is executed; but if the first movementproduced a reduction in power, a movement in the opposite direction isexecuted. The process continues until no increase in power is obtained in eitherdirection. Thereafter, the same process is carried out with respect to a secondaxis of the solar array.

7. Advantages • Solar tracking systems continually orient photovoltaic panels towards the sun and can help maximize your investment in your PV system. • One time investment, which provides higher efficiency & flexibility on dependency. • Tracking systems can help reducing emissions and can contribute some help against global warming. • Bulk implementations of tracking systems help reduced consumption of power by other sources. • It enhances the clean and emission free power production.Disadvantages • Initial investment is high. • It’s a bit of difficult for servicing, as the systems are not quite popular regionally. • Moving parts and gears which will require regular maintenance. • May require repair or replacement of broken parts over a long run. • It has to be built reliably, against damages caused by heavy rainsConclusion • With Global Warming constantly affecting the world in numerous ways, it is essential we begin taking care of our environment in whatever way possible. • Present day technologies stresses on everything to be clean & green. • Being environmentally friendly, solar power generators and panels are reasonably easy, safe, and convenient to install. • A life cycle analysis proves that solar cells are cleaner than conventional fossil fuel power generation. • With Global Warming constantly knocking on our door, solar energy takes a step in the right

direction by emitting no waste products whatsoever. • Hence enhancing the solar powered systems with advanced intelligent trackers proves to be optimal and grab every possible opportunity to gain advantage of the solar power

8. References http://www.solarpoweristhefuture.com http://www.scientificamerican.com http://www.linak.com/products http://www.thesolarguide.com http://www.patentstorm.us http://www.free-power.org http://en.wikipedia.org

SolarEnergyTrackingSystemIntroductionConceptPhotovoltaic’s(PV)isamethodofgeneratingelectricalpowerbyconverting so lar radiat i o n intod irec t c u rren t ele c tric ity usingsem ic ond u c tors thatexhibitthephotovoltaiceffect