Solar Energy

2003-09-Yan

Energy supply in the world by fuel(sources, IEA, 2002)

Solar Energy

➢Sun is heaviest body of the solar system around which all the planets revolve.

The mass of the sun = 1.98×10 30 kg

Diameter = 1.392×109 ,It is about 109 times the diameter of the earth.

➢The average distance of the sun from the earth =1.496 x 1011m, = oneastronomical unit (AU).

➢The temperature and pressure in the interior of the sun are extremely high, andthe temperature on the surface is 6000K.

➢The light emitted from the sun reaches the earth in 8.3 minutes, and it is themain source of heat and light energy for all the members of solar systemincluding the earth.

➢Solar energy is an important, clean, cheap and abundantly available renewableenergy. It is received on Earth in cyclic, intermittent and dilute form with verylow power density 0 to 1 kW/m2.Solar energy received on the ground level isaffected by atmospheric clarity, degree of latitude, etc

Latitude, Solar declination and Solar hour angle

Hour Angle (ω)

The apparent displacement of the sun away from solar noon. An hour angle ofzero degrees indicates that the sun is directly above, and the sign of the hour angleis determined by occurring either before noon (negative) or after noon (positive).

Angle of Declination (δ)

Declination is the observed angle (due to the polar tilt) between the plane of theEarth’s equator and the plane of the ecliptic (the plane in which the Earth's orbitabout the Sun lies). Declination has a maximum angle of 23.45° at either solstice.In this case of coordinates, the sun observed in the North is positive, and inthe South is negative.

Angle of Latitude (ϕ) and Longitude (λ)

Angle of latitude is angle made by a radial line joining the given location to thecentre of the earth with its projection on equatorial plane. The complement oflongitude (λ) in geospatial coordinates is the latitude. When combined together,we have identified a singular point on the surface of Earth.

Solar Constant

It is defined as the total energy received from the sun per unit of the time, on asurface of unit area, kept perpendicular to the radiation ,in space just outside theearths atmosphere when the earth is at its mean distance from the sun. Value ofsolar constant 1341W/m2

Solar Declination formula and numerical

The advantages of solar energy

(i)Environmentally clean source of energy and

(ii) Freely available in adequate quantities.

(iii)It is renewable source of energy

(iv)Available widely in any part of world

The main problems associated with solar energy are:

(i) Dilute source of energy and

(ii) Availability varies widely with time.

India, being tropical country receives solar insolation in the order of 1650-

2100 kwh/m2/year for nearly 250-300 days.

Applications of solar energy

1.Heating and Cooling of buildings

2. Solar water and air heating

3. Salt production by evaporation of seawater

4. Solar distillation

5. Solar drying of agricultural products

6. Solar cookers

7. Solar water pumping

8. Solar refrigeration

9. Electricity generation through Photo voltaic cells

10. Solar furnaces

11. Industrial process heat

12. Solar thermal power generation

Devices for measuring Solar Energy

Pyranometer

Pyrheliometer

Sunshine Recorder

Pyranometer

Construction

Sunlight enters the instrument through collimator tube and is directed onto a thermopile (sensing element) which converts heat to electrical signal that can be recorded

It collimate the radiation to determine the beam intensity as a function of incidence angle

It is used to measure beam of direct radiation

Sunshine recorder

• Measures the duration in hours of bright sunshine during the course of day

• consist of a glass sphere installed in a section of “spherical metal bowl” having groves for holding a recorder card strip and glass sphere

Solar Energy Generations

There are two main ways of utilization of solar energy:1. Converting sunlight directly into electricity

2. Converting sunlight to heat and temperature

Solar Thermal Energy Technology

❖Solar thermal Energy devices covert radiant energy of the sun intothermal energy for different productive works.

1. Solar collector

❖In any collection device, the principle usually followed is to expose adark surface to solar radiation so that the radiation is absorbed. A part ofthe adsorbed radiation is then transferred to a fluid like air or water.

❖When no optical concentration is done, the device in which thecollection is achieved is called a flat-plate collector. When highertemperatures are required, it becomes necessary to concentrate theradiation. This is achieved using focusing or concentrating collectors.

❖For low temperature applications i.e., below 1000C, flat plate collector isused, while for higher temperatures, concentrating collectors are used.

Various Types of Collector

Solar collector

Flat Plate Collector

Liquid FPC

Air FPC

Concentrating Collector

Flat plate collectorThe flat plate collector mainly consist of a casing, absorber plate, transparentglass covers, insulating material and fluid passage tubes .

Working PrincipleWhen the collector is exposed to sun, the radiation (Beam, diffuse radiation) passthrough transparent glass covers. The radiation is absorbed by absorber plate,which is coated with black absorber paint. The fluid tubes, which are connected toabsorber plate, absorb the heat and transferred to the water passing through thetubes and gets heated. The hot water collected from all the tubes flow into astorage tank.

Insulation (paddy husk, saw dust, glass wool) provided to the absorber plate toavoid loss of heat by conduction. The temperature attained is in the range of 40 –100o C depending upon the intensity of solar radiation. A liquid flat-platecollector is usually held tilted in a fixed position on a supporting structure, facingnorth if located in the northern hemisphere.

Schematic diagram of liquid flat-plate collector/Solar Water heater

Working of Flat plate Collector

Different parts of Flat Plate Collector

• An absorbing plate, essentially flat, made of metal upon which solarradiations fall and are absorbed and charged into heat or thermal energy .

• Tubes, channels or passages are connected to flat-absorbing plate,used forcirculation of fluid into, so that thermal or heat energy of the absorbing platemay be transferred to for application or utilization.

• An insulting material is sufficiently packed at the back and side of theabsorbing plate may be minimized and hence for the maximize efficiency ofthe system

• A transparent cover (one or two sheets) of glass on transparent plastics isfor reducing upward convection and radiation heat losses from the absorberplate. Single - glazing or double - glazing depending on the requirementmay be recommended.

• A weather tight container/enclosure is required which encloses all abovecomponents of the collector and provides good stability agaist weather.

Different components of FPC

Cylindrical Parabolic Concentrating Collector

➢In this type of collector , the radiation coming onconcentrator is diverted to absorber tube, which is coveredwith glass tube to avoid reradiation loss.

➢The heat from the absorber tube is transmitted to the fluidpassing and gets heated up. The hot liquid flows out to astorage tank for further application.

➢ The direction of concentration is changed with the sunmovement by providing single axis tracking.

➢ The temperature attained by the collector is 100-3000C.

Schematic diagram of cylindrical parabolic concentrating collector

Paraboloid Concentrating Collector

This type of collector is provided with two axis tracking and isfree to move both on vertical and horizontal axis. Theradiation received on the collector is reflected towards theconcentrator. The concentrator, which is coated with absorbercoating, is heated up with concentrated radiation. Thetemperature attained with this type of collector is more than300oC.

Air Flat Plate Collector

➢The heat absorbed by the absorber plate is transmitted to theair drawn into the collector .

➢ The hot air leaves the collector to a storage tank for furtheruse. If the size of collector is large, a blower is used to draw airinto the collector and transmit the hot air to dryer.

➢ The most favorable orientation, of a collector, is due south atan inclination angle to the horizontal equal to the latitude plus150 .

Applications of FPC

➢ Heating buildings➢ Drying agricultural produce and lumber➢ Heating green houses ➢ Air Conditioning the buildings ➢ Using air heaters as the heat sources for a heat engine