SOLAR PHOTOVOLTAICS Part 1

Transcription

1 SOLAR PHOTOVOLTAICS Part 1

2 Solar Energy Contents Irradiance, Solar Constant Solar Window & tilt effects Atmospheric effects, air mass Solar spectrum, sensitivity of PV materials to various wavelengths Solar insolation Receiver types Renewable Energy Overview 2

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4 Solar Energy 4 All usable energy forms, apart from nuclear energy and earth s heat, are forms of solar energy Conventional forms of energy are stored solar energy in the form of fossil fuels or biomass Fuels from fossils, produced over a period of many million years from solar energy, cannot last indefinitely Solar energy, which radiates nearly 20,000 times the energy requirement of the world on the surface of the earth, is abundantly available all over India The Sun is a sphere consisting of hot gases. It s diameter is 1.39 million km (109 times that of earth) On an average, the Sun is 150 million km away from the earth The Sun s rays require 9 minutes to cover this distance

5 Irradiance (1/2) The amount of solar power available per unit area is knows as irradiance Represented as H Unit is kw/sqm or watts/sqm or mw/sqcm Measuring Device Pyranometer Peak Value 1kW/sqm Nominal Value 0.8kW/sqm Irradiation fluctuates according to the Sun s location in the sky i.e. changes in both Sun s altitude angle and its azimuth angle For India, the total number of sunshine hours is approximately 4000 in a year The power produced by solar cells is proportional to the intensity of global radiation 5

6 Irradiance (2/2) 6 For optimal use in the northern hemisphere, a solar system is oriented southwards at an inclination from the horizontal The appropriate inclination angle, a, is dependent upon the latitude and on the time of the year In spring and in the beginning of fall, Sun shines exactly overhead at the equator The biggest deviation from this position occurs at the beginning of summer (between degree)and at the beginning of winter( degree) The solar radiations incident on a horizontal surface is comprised of sky radiation and the reflected radiation Wavelength μm Ultraviolet Region ( ) Visible Region ( ) Power (W/sqm) Percentage Power Infrared Region (0.78-)

7 Irradiation 7

8 Solar Constant 8 A Photovoltaic device, outside the earth s atmosphere which maintains normal incidence to the sun s rays receives nearly constant rate of energy. This amount is called the Solar Constant. Solar constant approx. = 1.36 kw/sqm Solar constant and associated solar spectrum are determined solely by nature of the radiating source and distance between earth and sun

9 Solar Window Solar window represents the effective area through which useful levels of sunlight pass throughout the year for a specific location Solar window is used to determine potential shading when designing a photovoltaic system 9

10 Tilt Angle It is the angle, between array and horizontal surface, which gives maximum solar irradiation Solar panels should always face true south if you are in the northern hemisphere, or true north if you are in the southern hemisphere 10

11 Effect of Tilt Angle 11

12 Atmospheric Effects Presence of atmosphere and associated climatic effects both attenuate and change the nature of the solar energy resource 12 Because of cloud cover and scattering of sunlight, the radiation received at a point is both direct and diffuse

13 Diffused Radiations Radiations reaching the Earth's surface after having been scattered from the direct solar beam by molecules or suspensions in the atmosphere 13 Source:

14 Solar Air Mass (1/2) 14 Air mass is defined as (1/cosѲ) (where Ѳ is angle between the Sun and directly overhead) Air mass indicates the relative distance that light must travel through the atmosphere to a given location

15 Solar Air Mass (2/2) 15

16 Solar Spectrum The electromagnetic spectral distribution emitted by the sun or received by a collector or instrument on Earth Sun s total energy is composed of 7% UV radiation 47% Visible radiation 46% Infrared radiation Photovoltaic cells primarily use visible radiation Distribution of colours within the light is important PV cell will produce different amounts of current depending on the various colours shining on it 16

17 Effect of Air Mass 17 Air mass is a measure of how much atmosphere the Sun's rays have to pass through on their way to the surface of the earth Since particles in the atmosphere absorb and scatter light rays the more atmosphere solar radiation passes through on its way to us, the less solar energy we can expect to get

18 Sensitivity of PV Materials to Various Wavelengths (1/2) The spectral distribution of power is important because different photovoltaic cell materials are stimulated by different portions of the solar spectrum 18 Photovoltaic cell research involves developing materials or combinations of materials which better utilize the power within the solar spectrum

19 Sensitivity of PV Materials to Various Wavelengths (2/2) For example- 19 Crystalline silicon responds fairly evenly to most of the visible wavelengths and the near infrared wavelengths up to about 1.1 microns, whereas thin-film silicon favours the blue end of the visible spectrum

20 Solar Insolation (1/2) Solar insolation is radiant energy per unit area Expressed in units of kwh/m 2 /day 20 Average daily solar radiation data for each of the 12 Months Provide average long-term average daily solar radiation data(typically 30 years) Data is useful in predicting long-term performance and in analyzing the economics of solar energy system Peak Sun Hours The number of peak sun hours per day at a given location is the equivalent time at peak sun condition that yields the same total insolation

21 Solar Insolation (2/2) 21 Hourly solar radiation data for each of the 12 Months for a typical year Typical meteorological year consists of 12 months with each month selected so that it best represents the average of that particular month over past years This data is good for photovoltaic system analysis

22 Flat-plate Array Receiver Types (1/4) Flat-plate arrays use both diffuse and direct sunlight and can operate in either a fixed orientation or in a sun-tracking mode In most applications flat-plate arrays are fixed in orientation 22

23 Fixed versus Tracking Array Receiver Types (2/4) 23 For flat-plate arrays Sun-tracking can increase annual energy output by 20% to 40%, depending on location and the type of tracking used Two-axis tracking allows the array to continuously face directly at the sun and provides the maximum energy output The tilt angle is adjusted periodically to increase the output of the array

24 Receiver Types (3/4) 24 Single-axis Tracking Dual-axis Tracking

25 Concentrator Arrays Receiver Types (4/4) These arrays use optical lenses and mirrors to focus sunlight onto high-efficiency cells Major advantage is they use relatively small areas of expensive plastic lenses or other materials 25

26 Renewable Energy - Overview Energy sources that are continually replenished by nature. Eg: Sun, Wind, Water, Earths Heat, Plants. Technology turns these fuels into usable forms of energy. Renewable energy is the most benign and clean. 26

27 Why Renewable Energy? Conventional fuels are limited in supply. Environmental issues of conventional power plants. Safety and waste disposal issues. Continuing rise in demand of energy. Energy security and energy independence. 27

28 RE Technologies 28 Hydro Power Biomass, Bio energy, Biofuels. Geothermal Energy. Solar Energy (Thermal and Electricity) Wind Energy. Ocean Energy. Hydrogen

29 Renewables in India Till Aug Source Capacity ( in Mw) Percentage Wind Small Hydro Biomass Solar Total

30 RE Generation Costs 30 Source Capacity (in Mw) US Cents / Kwh Large Hydro Small Hydro Onshore wind Offshore wind Biomass Geothermal Solar Rooftop 2 5 Kwp Utility Scale solar 200 Kwp 100 Mwp CSP (Conc. Solar Thermal)

31 Contd.