Solar cells for slideshare
- 1. SOLAR CELL Presenter: Damion Lawrence, M.Sc., B.Ed. 1
- 2. The Solar Cell • The most common type of solar cells are Photovoltaic Cells (PV cells) • Converts sunlight directly into electricity • Cells are made of a semiconductor material (eg. silicon) • Light strikes the PV cell, and a certain portion is absorbed • The light energy (in the form of photons) knocks electrons loose, allowing them to flow freely, forming a current • Metal contacts on the top and bottom of PV cell draws off the current to use externally as power
- 3. Why Use Solar Cells? • Low maintenance, long lasting sources of energy • Provides cost-effective power supplies for people remote from the main electricity grid • Non-polluting and silent sources of electricity • Convenient and flexible source of small amounts of power • Renewable and sustainable power, as a means to reduce global warming • In 2002, the global market for photovoltaic panels and equipment was valued at 3.5 billion dollars
- 4. The Single Crystalline Silicon Solar Cell • Pure silicon is a poor conductor of electricity • “Doping” of silicon with phosphorus and boron is necessary to create n-type and p-type regions • This allows presence of free electrons and electron-free ‘holes’ • The p-n junction generates an electric field that acts as a diode, pushing electrons to flow from the P side to the N side
- 6. When Light Hits the Cell • Light energy (photons) ionizes the atoms in the silicon and the internal field produced by the junction separates some of the positive charges (holes) from the negative charges (electrons) • The holes are swept into the p-layer and the electrons are swept into the n-layer • The charges can only recombine by passing through an external circuit outside the material • Power is produced since the free electrons have to pass through the load to recombine with the positive holes
- 7. Efficiency of Solar Cells • The amount of power available from a PV device is determined by • Type and area of the material • The intensity of the sunlight • The wavelength of the sunlight • Single crystalline solar cells 25% efficency • Polycrystalline silicon solar cells less than 20% • Amorphous silicon solar cells less than 10% • Cells are connected in series to form a panel to provide larger voltages and an increased current
- 8. Arrays and Systems • Panels of solar cells can be linked together to form a larger system – an array (a) a PV panel array, ranging from two to many hundreds of panels; (b) a control panel, to regulate the power from the panels; (c) a power storage system, generally comprising of a number of specially designed batteries; (d) an inverter, for converting the DC to AC power (eg 240 V AC) (e) backup power supplies such as diesel startup generators (optional) (f) framework and housing for the system (g) trackers and sensors (optional);
- 9. Solar Cells are used in a wide variety of applications • Toys, watches, calculators • Electric fences • Remote lighting systems • Water pumping • Water treatment • Emergency power • Portable power supplies • Satellites
- 10. Future Applications • Looks like denim • Can be draped over any shape • No rigid, silicon base • Made of thousands of flexible, inexpensive solar beads between two layers of aluminum foil • Each bead functions as a tiny solar cell The Flexible Solar Cell
- 11. Future Applications • Based on photosynthesis in plants • Use of light-sensitive dyes • Cost of manufacture is decreased by 60% Organic Solar Cells New Alloys • Indium, gallium, and Nitrogen • Converts full spectrum of sunlight from near-infrared to far-ultraviolet
- 12. Future Applications • Tiny rods are embedded in a semi-conducting plastic layer sandwiched between two electrodes • Rods act like wires, absorbing light to create an electric current Nano Solar Cells Tetrapod Nanocrystals • May double the efficiency of plastic solar cells • Made of cadmium, tellurium