24-12-2012, 02:12 PM
ANALYSIS OF SOLAR POWER PLANT
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INTRODUCTION:
When the world was at the point of power crisis there came the idea of generating power from the renewable sources or natural sources like sun, water, wind etc… At that point of time the rural electrification was the major problem. To this problem the best solution came up to be solar power. There are so many advantages with solar power like it is noise free, robust, long lasting, pollution free,& reliable.
The earth receives more energy from the Sun in just one hour than the world's population uses in a whole year. The total solar energy flux intercepted by the earth on any particular day is 4.2 X 1018 Watt-hours or 1.5 X 1022 Joules (or 6.26 X 1020 Joules per hour). This is equivalent to burning 360 billion tons of oil ( toe ) per day or 15 Billion toe per hour.
In fact the world's total energy consumption of all forms in the year 2000 was only 4.24 X 1020 Joules. In year 2005 it was 10,537 M toe (Source BP Statistical Review of World Energy 2006)
Solar Radiation
Sunlight comes in many colors, combining low-energy infrared photons (1.1 eV) with high-energy ultraviolet photons (3.5 eV) and all the visible-light photons between.
The graph where the spectrum of the solar energy impinging on a plane, directly facing the sun, outside the Earth's atmosphere at the Earth's mean distance from the Sun. The area under the curve represents the total energy in the spectrum. Known as the "Solar Constant" G0, it is equal to 1367 Watts per square meter (W/m2).The radiant energy falling within the visible spectrum is about 43% of the total with about 52% in the infra red region and 5% in the ultra violet region.
Direct energy is the energy received directly from the sun.
Global energy includes energy diffused, scattered or reflected from clouds and energy re-radiated by the earth itself. Energy received at sea level is about 1kW/m2 at noon near the equator
Irradiance and Insolation
Total solar irradiance is defined as the amount of radiant energy emitted by the Sun over all wavelengths, not just visible light, falling each second on a 1 square meter perpendicular plane outside Earth's atmosphere at a given distance from the Sun. It is roughly constant, fluctuating by only a few parts per thousand from day to day.
On the outer surface of the Earth's atmosphere the irradiance is known as the solar constant and is equal to about 1367 Watts per square meter.
The amount of solar energy that actually passes through the atmosphere and strikes a given area on the Earth over a specific time varies with latitude and with the seasons as well as the weather and is known as the insolation (incident solar radiation).
When he Sun is directly overhead the insolation, that is the incident energy arriving on a surface on the ground perpendicular to the Sun's rays, is typically 1000 Watts per square meter. This is due to the absorption of the Sun's energy by the Earth's atmosphere which dissipates about 25% to 30% of the radiant energy.
Available Solar Energy
Since the Earth's cross sectional area is 127,400,000 km², the total Sun's power it intercepted by the Earth is 1.740×1017 Watts but as it rotates, no energy is received during the night and the Sun's energy is distributed across the Earth's entire surface area so that the average insolation is only one quarter of the solar constant or about 342 Watts per square meter. Taking into account the seasonal and climatic conditions the actual power reaching the ground generally averages less than 200 Watts per square meter. Thus the average power intercepted at any time by the earth's surface is around 127.4 X 106 X 106 X 200 = 25.4 X 1015 Watts or 25,400 Terawatts.
PROCESS OF GENERATION:
Solar voltaic power generation is the direct conversion of solar energy into electricity.
Sunlight comes in many colors, combining low-energy (1.1 electron Volts (eV)) infrared photons with high-energy (3.5 eV) ultraviolet photons and all the rainbow of visible-light photons in between. Solar cells, also called photovoltaic or PV cells, are semiconductor devices designed to capture these photons and convert their energy directly into electrical energy. The main process involved in the generation is the tracking of the solar light. This is discussed below.
Solar Tracking:
As indicated above the amount of energy captured by a solar system can be maximized if the collector can follow the ecliptic path of the Sun so that the plane of the collector or array is always perpendicular to the direction of the Sun.
Automatic mechanical tracking systems make it possible to track both the azimuth and the elevation of the Sun's position to maximize energy capture. Note the lower zenith and the reduced azimuth range of the winter Sun.
• Azimuth Tracking
Azimuth tracking keeps the collector pointing at the Sun as the Earth rotates.
The insolation varies between zero and its maximum value during the course of every day and remains around its maximum value for a relatively short period of time. Azimuth tracking enables the collector to follow the Sun from East to West throughout the day and brings the most benefits.
Passive systems provide the simplest form of azimuth tracking. They have no motors, controllers or gears and they don't use up any of the energy captured by the collector. They depend on the differential heating of two interconnected tubes of gaseous refrigerants, one on either side of the collector. If the collector is not pointing towards the Sun, one side heats up more than the other and vaporizes its refrigerant. The resulting change in weight is used in a mechanical drive mechanism to turn the collector towards the Sun where it will remain when the temperature and weight of the two tubes will be balanced.
• Altitude/Elevation Tracking
Elevation tracking enables the collector to follow the seasonal variations in the Sun's altitude but the economic benefits are less than for azimuth tracking.
Compared with the daily variations in insolation, the seasonal variations are very slow and the range of the variation, due to the solar declination is much more restricted. Because of this, reasonable efficiency gains can be obtained simply by manually adjusting the elevation of the collectors every two months. To avoid the cost and complexity of elevation tracking, it may be more cost effective just to specify larger collectors.
• Dual Axis Tracking
Combining azimuth and elevation tracking enables the installation to capture the maximum energy using the smallest possible collectors but the systems are complex and many installations get by with just azimuth tracking.