By,N Venkata Srinath,MS Power Systems.

IntroductionSolar energy is a very large, inexhaustible source of

energy. The power from the sun intercepted by the earth is approximately 1.8 X 1011 MW which is many thousands of times larger than the present consumption rate.

Thus, in principle, solar energy could supply all present and future energy needs of the world on a continuing basis.

However, there are many problems associated with its use. The main problem is that it is dilute source of energy.

The second problem is that its availability varies widely with time. The variation in availability occurs daily because of the day-night cycle and also seasonally because of the earth’s orbit around the sun. (requirement of storage)

RadiationEnergy radiated by the sun as electromagnetic waves of which 99

percent have wave lengths in the range of 0.2 to 4.0 micrometers. Solar energy reaching the top of earth’s atmosphere consists of

about 8 percent ultraviolet radiation (short wavelength, less than 0.39 micrometer), 46 percent of visible light (0.39 to 0.78 micrometer), and 46 percent of infrared radiation (long wave length more than 0.78 micrometer).

The rate at which solar energy arrives at the top of the atmosphere is called the “solar constant”. This is the amount of energy received in unit time on a unit area perpendicular to the sun’s direction.

The NASA standard value for the solar constant is: 1.353 kilowatts per meter square of 1353 watts per meter

square.

Wavelength(μ) 0-0.38 0.38-0.78 0.78-4.0

Approx. energy(W/sq.m

)

95 640 618

Approx.% of total energy.

7 47.3 45.7

Radiation received at the earth surface is entirely different due to the various reasons.

Solar radiation that has not been absorbed or scattered and reaches the ground directly from the sun is called “direct radiation” or “beam radiation”.

Diffuse radiation is that solar radiation received from the sun after its direction has been changed by reflection and scattering by the atmosphere. Because this scattering takes place in all directions, diffuse radiation comes from all parts of the sky.

Ultra violet radiation is absorbed by oxygen and ozone, some energy in the infrared region is absorbed by carbon dioxide and water vapour.

Insolation:- the total solar radiation received at any point on the earth’s surface is the sum of direct radiation and diffuse radiation.

Solar Energy CollectorsUtilization of solar energy requires solar collectors.

Solar collector is a device which collects solar radiation and transfer the energy to a working fluid passing in contact with it.

These are of two types:1. Non concentrating or flat plat type solar

collectors.2. concentrating(focusing) type solar collectors.

Non Concentrating or Flat-Plate CollectorsThese are used, where temperatures upto 90 deg C are

adequate.

They are generally used for space and water heating.

They are made in rectangular panels of about 1.7 to 2.9 sq.m in area and are relatively simple to construct and erect.

Flat plates can collect and absorb both direct and diffuse solar radiation, they are consequently partially effective even on cloudy days.

These are of two types:Liquid heating collectors are used for heating water and non freezing solutions(Eg: ethylene glycol).Air or gas heating collectors are employed as solar air heaters.

The majority of the flat plate collectors have five main components and are as fallows:

A transparent cover which may be one or more sheets of glass or radiation transmitting plastic film or sheet.

Tubes, fins, passages or channels are integral with the collector absorber plate or connected to it, which carry the water, air or other fluid.

The absorber plate, normally metallic or with a black surface materials can be used.

Insulation, which should be provided at the back and side to minimize the heat losses.

The casting or container which enclose the other components and protects them from weather.

Concentrating or focusing collectors

Focusing collectors is a device to collect solar energy with high intensity of solar radiation.

Focusing collectors generally use optical system in the form of reflectors.

As a result of the energy concentration, working fluids can be heated to temperature of 500 deg C or more.

Types of concentrating collectors:Parabolic trough collector.Dish type collector.Power tower.

Parabolic trough collector

Dish type collector

Power tower

Application of solar energySolar water heatingSpace heatingSolar distillationSolar pumping Industrial processSolar furnaceSolar cookingSolar LED lightsSolar energy: Thermal Electric Conversion

Solar energy: Photovoltaic Electric Conversion.

Solar energy: Thermal electric conversion In a solar thermal power production system the energy is first

collected by using a solar pond, a flat plate collector or a focusing collector.

This energy is used to increase the temperature of the working fluid.

Then, turbine generator set is operated by these working fluid.

Thermal electric conversion is of four types Low temperature cycle using flat plate collectors or solar

pond. Concentrating collectors for medium and high temperatures Power tower Distributed collector system

Low temperature cycle

Power tower

Distributed collector system

Solar energy: Photovoltaic Electric Conversion.The direct conversion of solar energy into electrical energy

by means of the photovoltaic effect, that is conversion of light into electricity.

The photovoltaic effect is defined as the generation of an electromotive force as a result of the absorption of ionizing radiation.

Energy conversion devices which are used to convert sunlight to electricity by the use of the photovoltaic effect are called solar cell.

Combination of such cells, designed to increase the electric power output is called solar module or solar array.

PV principleThe base unit of many semiconductor devices is a

semiconductor body, in which two different dopants directly adjoin one another. This is called a p-n junction if a p-doped area merges into an n-doped area within the same lattice.

The interface between these two layers contains an electric field and is called a junction.

Photons with energy greater than Band gap energy are absorbed and excite some of the electrons. (valence to conduction).

When light (photons) hits the solar cell, some of the photons are absorbed in the region of the junction, freeing electrons in the silicon crystal.

If the photons have enough energy, the electrons will be able to overcome the electric field at the junction and are free to move through the silicon and into an external circuit.

Indian scenario India is located in the equatorial sun belt of the earth,

thereby receiving abundant radiant energy from the sun.

In most parts of India, clear sunny weather is experienced 250 to 300 days a year.

India receives solar energy equivalent to over 5,000 trillion kWh per year.

The daily average solar energy incident over India varies from 4 -7 kWh per square meter depending upon the location.

The utilization of solar energy in the country is regularly increasing, however, the high initial cost of the solar energy systems is a barrier in its large-scale utilization.

A total of 33 grid interactive solar photovoltaic power plants have been installed in the country with financial assistance from the Government. These plants, with aggregate capacity of 2.125 Megawatt peak are estimated to generate about 2.5 million units of electricity in a year.

In addition, around 14.5 lakh decentralized off-grid solar photovoltaic systems aggregating to about 125 Megawatt capacity have been installed in the country, which is capable of generating about 150 million units in a year.

Further, a collector area of about 2.15 million square meter has been installed for solar water heating applications.

For projects approved and commissioned by 31st December, 2009, the Ministry will provide generation based incentive up to Rs.12 per kWh for solar photovoltaic power and Rs.10 per kWh for solar thermal power after taking in to account the tariff provided by the State Electricity Regulatory Commissions.

India’s first solar powered village is Rampura village in Jhansi of 8.7KW installed by the help of Scatac solar of Norway with an investment of 31.5lakhs serving to 69 houses of that village.

ManufactureManufacture Place

Ammini Solar Pvt. Ltd. Trivandrum

Bharat Electronics Limited Bangalore

Bharat Heavy Electricals Ltd. Bangalore

EMMVEE Solar Systems Pvt Ltd. Bangalore

Maharishi Solar Technology Pvt. Ltd.

New Delhi

Microsol Power P Ltd. Hyderabad

Moser Baer Photovoltaic Ltd New Delhi

Photon Energy Systems Hyderabad

Rajasthan Electronics Instruments Ltd.

Jaipur

Tata BP Solar India Ltd. Bangalore

Reference

BooksG.D.Rai ‘Non-Conventional energy sources’ Khanna

publishers. John & Tony ‘Renewable energy resources’ Taylor &

Francis group.

WebsitesMinistry of New and Renewable Energy <www.mnre.gov.in

> Ministry of Power Government of India <

www.powermin.nic.in>Solar India online <www.solarindiaonline.com>Trade India <www.tradeindia.com>