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Sola Photovoltaics Solar Photovoltaics Phenomenal Price Reduction of Solar Photovoltaics Phenomenal growth of installation of Solar Photovoltaics Mainly Due to massive production of SPV in China Basic Features of Solar pV pV systems have no fuel requirement in remote areas diesel or kerosene fuel supplies are erratic and often very expensive. The recurrent costs of operating and maintaining pV systems are small. pV systems are modular – A solar array is composed of individual pV moduels so each system can be sized to meet the particular demand. pV systems can be used to improve quality of life - for example the provision of lighting in a rural school allows evening educational or community activities. Refrigeration at a health centre improves effectiveness of immunization programmes. pV Systems are highly reliable – the reliability of pV systems are significantly higher that of diesel or any similar generators pV Systems are easy to maintain – Operation and routing maintenance requirements are simple. pV modules have long life – There is little degradation in performance of over 15 yrs. pV systems provide national economic benefits – Reliance on imported fuel such as coal and oil is reduced. pV systems are environmentally begin – There is no harmful pollution through the use of a pV system. Pv systems are economically viable – On a life cycle cost basis and taking into consideration the higher reliability of PV many small scale applications can be more economically powered by PV than with diesel systems or some other small systems. Applications of Photovoltaics RURAL ELECTRIFICATION(EITHER GRID CONNECTED OR OFF GRID) SOLAR HOME SYSTEMS (SHS) WATER PUMPING AND TREATMENT SYSTEMS HEALTH CARE SYSTEMS COMMUNICATIONS MID SEA BUOYS CATHODIC PROTECTION Stationary power station (Off grid or mini grid) • grid ) Solar cell capacity: 3.4kW Wind Power capacity: 1.8kW Inverter capacity: 5kVA 11 • Stationary power station (Grid connected ) Site: Installation: Capacity: Purpose: 12 Funafuti Tuvalu Feb. in 2008 40kW Grid connected power supply for fuel conservation and CO2 reduction. Solar array Solar array Solar array Controller Light Solar array Storage battery • Roof top of school ,community-center building. (For education and emergency power) 14 Roof top of residence ( Grid connected ) Owner can sell excess power to power utility. Most popular installation style in Japan. (Almost 85% PV in Japan ) 15 Distant and independent power supply ( Off grid ) Advertising sign beside highway Relay station on top of mountain 16 Solar Home Systems in remote locations • Mountain lodge ( Off grid ) Inverter and controller 1.2kW system 17 Technical Comparison of off grid energy System Off Grid Systems – Diesel Generators Advantages Widespread Operating and maintenance experience Moderate capital cost Easy to install Can be a combined power supply for additional uses Disadvantages Creates noise and fume pollution Requires a reliable fuel supply High running costs High maint. Costs Low operating efficiency Automotive Battery Recharging Advantages Low capital cost Easy to install Batteries locally available Disadvantages Relies on transportation to charging centres High charging fees often apply Short battery life times Photo – Voltaics High reliability Low maintenance requirements Low running costs Suited to most locations Long life expectancy for main components Involves the introduction of a new and poorly understood technology High capital cost Not physically robust so vulnerable to damage Specialized batteries not widely available Micro Hydro Systems Uses simple engineering principles hence widely accepted technology Locally available skills only required for most applications Robust machinery used Most village level and local technicians can do maintenance Relatively high capital cost Generation depends on availability of water Control gear may require sophisticated components Conflicting water users may hinder total potential unlisation Solar PV is a very good substitute for Kerosene lighting ! Solar Phtovoltaic Technology Semi-conductor Physics • In an intrinsic semi-conductor valance band has four electrons and hence only very few electrons can escape to conduction band. EG = Energy gap energy required for an electron to jump from the valance band to conduction band ~ 0.5 eV to 2.5 eV. Solar light wave length~ 0.3 μmto2.5μm This corresponds to photon energy range of 0.5 eV to 4.0 eV 1 eV= 1.6x10-19 J E= hν Where ν=c/λ h= 6.626x10-34 J-s Plank’s Constant Fermi Level • Fermi Level Ef is the energy level at which an electron has an equal probability of being either in the valance band or the conduction band • Hence in an intrinsic semiconductor Fermi level lies exactly at the mid point of the forbidden zone or the energy gap. Fermi Level in a n type semi conductor • Fermi level lies close to conduction band Fermi Level in a p type semi conductor • Fermi Level lies close to valance band When a n type and p type junction is created in a semiconductor • The energy level at each end of the semiconductor and at the junction appears like this: Initially electrons diffuse to p type and holes diffuse to n type at the junction This diffusion creates an electric field that leads to a drift current Ie while the movement of holes from p type and electrons from n type creates a current known as the diffusion current Id Due to the electric field at thermal equilibrium Ie = Id Behavior under forward bias of a Diode • When a diode if forward biased , an electric current flows in the forward direction of the diode i.e. a current pass through the diode from p type to n type in the semiconductor When a Diode if forward biased E decreases Hence Ie decreases Vb increases Id increases When a Diode if forward biased • Vb Increases causing Id to increase and E decreases causing Ie to decrease hence when a diode is forward biased a current passes through the diode Characteristic curve of a Diode • I increases rapidly when a diode is forward biased caused by excitation of electrons across the n-p junction to gain enough energy from the battery to jump to the valance band n-p junction under solar Insolation • With the absorption of photon energy from the light more electron – hole pairs are created in the solar cell (n-p junction) What happens when a solar cell exposed to light is connected externally With the solar insolation a current flows from the solar cell depicting I = IL-Id where IL is the current created by excitation of electrons in the junction to flow out of the n side in the external circuit to combine with holes created in the p type thus a current flows in the external circuit from the p side to the n side. Due to this current , a voltage is built up in the external circuit forward biasing the diode hence the ‘drift current flows in the opposite direction of the current created by solar light What Happens When the Solar Cell is Short Circuited Under Short Circuit conditions V=0 hence diffusion current Id becomes zero. Hence the current flowing in the external circuit is the same current produced in the solar cell due to solar light equal to the drift current Characteristic Curve of a solar cell • At Short circuit V = 0 hence I = IL • At Open Circuit No external current flows hence Ie= Id The Equivalent circuit of a solar cell • This is the simplified equivalent circuit of a solar cell however the real solar cell should comprise of a series resistance depicting the internal resistance of the cell and the contact resistance and also a parallel resistance depicting the reverse saturation current of the diode.