PRINCIPLES OF SOLAR ENERGY

SOLAR ENERGY• Solar energy is radiant light and heat from the Sun that is harnessed using a range

of ever-evolving technologies(electro magnetic radiation).• It is an important source of renewable energy and its technologies are broadly

characterized as either passive solar or active solar depending on how they capture and distribute solar energy or convert it into solar power.

• Energy used for cooling/heating/drying/distillation/power generation ,etc.,• The Earth receives 174,000 terawatts (TW) of incoming solar radiation

(insolation) at the upper atmosphere.• Most of the world's population live in areas with insolation levels of 150-300

watts/m², or 3.5-7.0 kWh/m² per day.

The energy radiated from the sun is electromagnetic waves reaching the planet earth in three spectral regions;(i) Ultraviolet 6.4 % (ƛ ≤ 0.38 µm), (ii) Visible 48.0 % (0.38 µm < ƛ < 0.78 µm), and(iii) Infrared 45.6 % (ƛ ≥ 0.78 µm) of total energy. Due to the large distance between the sun and the earth (1.495 × 108 km) the beam radiation received from the sun on the earth is almost parallel.

Direct Radiation: Solar radiation that reaches to the surface of earth without being diffused is called direct beam radiation.

Diffused Radiation: As sunlight passes through the atmosphere, some of it is absorbed, scattered and reflected by air molecules, water vapour, cloud, dust, and pollutants from power plants, forest fires, and volcanoes. This is called diffused radiation.

Global Solar Radiation: The sum of diffuse and direct solar radiation is called global solar radiation.

6

• The potential solar energy that could be used by humans differs from the amount of solar energy present near the surface of the planet because factors such as geography, time variation, cloud cover, and the land available to humans limit the amount of solar energy that we can acquire.

• However, the use of photovoltaics that can follow the position of the sun can significantly increase the solar energy potential in areas that are farther from the equator.

• Solar hot water systems use sunlight to heat water.

ENVIRONMENTAL IMPACT OF SOLAR POWER

• Every type of energy utilization for electricity generation has environmental consequences, including renewable energies.

• Such as follows:• manufacture processes• aesthetic impact • use of large areas of land • impact on the eco-system

BY MANUFACTURE PROCESSES

• Due to the large size of the systems involved, manufacture, installation, maintenance and ultimately disposition of all the system components are to be optimised and subjected to an LCA(life cycle assessment) analysis[Cradle to Grave].

• Should photovoltaic cells be considered, the hazardous materials contained in them (arsenic and cadmium) can pose a serious problem in areas subject to dust abrasion, such as deserts. Even silicon dust might pose a health problem.

ACTIONS REQUIRED: 1.Rigorous and quantitative LCA analysis.2. Study of the rates of removal of hazardous materials from atmospheric agents .

BY AESTHETIC IMPACT

• The construction of overhead transmission lines and other facilities of a HVDC grid (pylons and transmission towers) in scenic areas.

ACTIONS REQUIRED:1.Contingent analysis to identify the locations suitable for the construction of wind turbine towers.2.Consider tunneling and micro tunneling, using the technology borrowed from oil field exploration

BY USE OF LAND

• While wind power does not pose any significant problem, solar energy does, unless on worthless soil (deserts).

• The use of energy crops sent prices soaring and created the 3F-conflict (Food - Feed - Fuel).

ACTIONS REQUIRED:1. Use wastes, refuses and lingo-cellulosic products or energy crops harvested in

off-years2. Optimise the production of electricity, fuels and chemicals in integrated

biorefineries

BY IMPACT OF ECO-SYSTEMS

• The major impact reported for solar is bird deaths from electrocution or collisions with spinning rotors.

• Large extensions of concentrating solar systems might disturb migratory birds.• ACTIONS REQUIRED:1. Identify areas which are not included in migratory paths

LIFE-CYCLE GLOBAL WARMING EMISSIONS

PHYSICS OF THE SUN

• The phenomena of the sun is determined by solar magnetic field it was done by the astronomical methods.

• It intersects with many disciplines of pure physics, astrophysics, and computer science, including fluid dynamics, plasma physics including magneto-hydrodynamics(MHD), seismology, particle physics, atomic physics, nuclear physics, stellar evolution, space physics, spectroscopy, radiative transfer, applied optics, signal processing, computer vision, computational physics, stellar physics and solar astronomy.

CHARACTERISTICS OF SUN

PLANETS OF EARTH

DISTANCE OF PLANETS FROM EARTH INMILES

SOLAR CONSTANT

The rate at which energy reaches the earth's surface from the sun, usually taken to be 1,388 watts per square metre.• The formula for calculating the solar constant is written as•  So = E(Sun) x (R(Sun) / r)2,• So-solar constant,• E- irradiance of the sun• R-Radius of the sun• r-distance between the Earth and the sun

ASTRONOMICAL UNIT-A unit of length used for distances within the solar system; equal to the mean distance between the Earth and the Sun (approximately 93 million miles or 150 million kilometers)

EXTRA TERRESTRIAL SOLAR RADIATION

• solar radiation incident outside the earth's atmosphere is called extraterrestrial radiation. On average the extraterrestrial irradiance is 1367 Watts/meter2 (W/m2).

TERRESTRIAL SOLAR RADIATION

• Terrestrial radiation is the energy released by the Earth itself as opposed to solar radiation that it receives from the Sun.

• Apart from the energy generated by the decay of radioactive minerals in rock, the energy that drives terrestrial radiation ultimately comes from the Sun, and it is a major factor in the study of global warming

TERRESTRIAL REGION OF EARTH

SOLAR RADIATION ON TITLED SURFACE

IRRADIANCE VARIABLES:1. Latitude at the point of observation

2. Orientation of the surface in relation to the sun3. Day of the year4. Hour of the day5. Atmospheric conditions

24

Rb,t = Ratio of Beam Irradiance normal to the earth’s surface to Beam Irradiance normal to normal to a tilted surface

, ,,

,

cos coscos cos

b t b nb t

b b n z z

G GR

G G

SOLAR RADIANCE ON A TILTED SURFACE

,b nG,b tG

bG

,b nG

25

B 1 . 3 N a t u r e o f t h e s o l a r r e s o u r c eS o l a r g e o m e t r y : C o l l e c t o r a n g l e s

c o s c o s s i n s i n s i nc o s c o s s i n c o ss i n c o s

s s

s s

s

c o s s i n s i n c o s c o s s i n c o s

c o s c o s c o s c o s s i n s i n c o s

c o s s i n s i n s i n

= A n g l e o f i n c i d e n c e

s = S o l a r a t t i t u d e a n g l e

= S u r f a c e a z i m u t h a n g l e

s = S o l a r a z i m u t h a n g l e

= C o l l e c t o r s l o p e = D e c l i n a t i o n = L a t i t u d e = H o u r a n g l e

S u n a n g l e s

E a r t h a n g l e s

26

INSTRUMENTS FOR MEASURING SOLAR RADIATION

• The global solar radiation has two components namely direct and diffuse radiation.

• The global radiation is measured with the pyranometers, and the direct radiation with pyrheliometer.

• The devices use two types of sensors: thermal and photovoltaic.

27

• A pyranometer shaded from direct solar radiation can be used to measure diffuse radiation. One implementation uses a band stretching from the eastern to the western horizon that is oriented according to the solar declination to shade the pyranometer with the plane of the band parallel to the celestial equator. Since the solar declination changes, this band must be adjusted with a frequency that depends on accuracy requirements and time of year.

PYRANOMETER

PYRHELIOMETER

It measure the direct component of solar irradiance which is important when installing concentrating collectors.

WORKING PRINCIPLE OF PYRHELIOMETER

31

The pyranometer with solar cell sensor The pyranometer with thermal sensor

advantages

The time of the response is very good 10 μscheap;stability;ruggedness;tolerance to soiling.

nearly constant spectral response on the whole solar spectral range;highly used.

disadvantages

the limited spectral response;the nonuniform spectral response;the temperature influence upon the response.

The response time is a disadvantage, in the order of seconds;Introduces significant errors for instantaneous measurements (clear-cloudy);are expensive.

The advantages and disadvantages of the two types pyranometers

SUN SHINE (SUN SET)

SUN SHINE RECORDERS

SUN SHINE METHOD•Calibrated pyrheliometer and solar tracker•Clear sky periods•Alternate shade and unshade of pyranometerAdvantages•Can automated•Provides unbiased estimate of cosine response•No zero irradiance biasDisadvantages•Which value of K?•Transitions of bright sun to sky

Most ideal for daily exposure calibrations

SUN SHINE

• The duration and the intensity of sunlight is measured using a Campbell-Stokes sunshine recorder.

• • These focus light from the sun onto a

piece of card where it leaves a burnt trace. The more sunshine there is, the longer the line.

SOLAR RADIATION DATA

• Solar radiation is the electromagnetic energy emitted by the sun, can be captured and converted into useful forms of energy.(nasa)[National Solar Radiation Database]

SOLAR ENERGY COLLECTION

• A solar thermal collector collects heat by absorbing sunlight.• It is possible to harness the energy from the sun and convert it into either

electricity or heat using PV (photo-voltaic) or ST (solar thermal) technologies respectively.

• An evacuated solar system is the most efficient and a common means of solar thermal energy generation with a rate of efficiency of 70 per cent.

• Solar Thermal Energy Collector: Solar thermal energy collector is an equipment in which solar energy is collected by absorbing the radiation in an absorber and then transferring to a fluid. There are two type of collectors

TYPES OF SOLAR COLLECTORS

• Back-pass solar collectors• Used to heat air• Glazed surface• May be integrated with thermal mass

• Concentrating solar collectors• Best suited for clear skies• Steam production• Concentrates light at absorber which can increase efficiency at high temperature• Four forms: parabolic trough, parabolic dish, power tower, stationary solar collectors

• Trombe Wall• Thermal mass designed to radiate heat during the night• Glass to allow sunlight through• With added salt fillers stored energy changes from 200 cal/day to 80,000 cal/day

• Batch Solar Collectors• Water heating• Glazed water collectors

• Solar cookers• Liquid Solar Collectors

• Vacuum tubing

FLAT PLATE COLLECTORS

• It has no optical concentrator. Here the collector area and the absorber area are numerically same. The efficiency of flat plate collector is low and temperature of working fluid can be raised only up to 100 0C.

SCHEMATIC CROSS SECTION OF A FLAT PLATE COLLECTOR

The flat plate collector consists of five major parts as given below:

1: A metallic flat absorber plate: It is made of copper, steel or aluminium (having high thermal conductivity) and having black surface. The thickness of the metal sheet ranges from 0.5 to 1.0 mm.

2: Tubes or channels: they are soldered to the absorber plate. Water flowing through these tubes takes away the heat from the absorber plate. The diameter of tubes is around 1.25 cm, while that of the header pipe which leads water in and out of the collector and distributes it to absorber tubes is 2.5 cm.

3: A transparent toughened glass sheet: of 5 mm thickness is provided as the cover plate. It reduces convection heat losses through a stagnant air layer between the absorber plate and the glass. Radiation loss are also reduced as the spectral transmissivity of glass is such that it transparent to short wave radiation and nearly opaque to long wave thermal radiation emitted by interior collector walls and absorbing plate.

4: Fibre glass insulation: of 2.5 to 8.0 cm thickness is provided at the bottom and on the sides in order to minimize the heat loss.

5: A container encloses the whole assembly in a box made of metallic sheet or fibre glass.

The commercially available collector have a face area of 2 m2. The whole assembly is fixed on a supporting structure that is installed on a tilted position at a suitable angle facing south in northern hemisphere. For the whole year, the optimum tilt angle of collector is equal to the latitude of its location. During winter the tilt angle is kept 10-150 more than the latitude of the location, while in summer it should be 10-150 less than the latitude.

CONCENTRATING TYPE SOLAR COLLECTOR

Here the receiving area of solar radiation is several times greater than the absorber area and the efficiency is high. Mirrors and lenses are used to concentrate sun rays on the absorber. The temperature of working fluid can be raised only up to 500 0C.

For better performance, the collector is mounted on a tracking equipment to always face the sun with its changing position

Types of concentrating collectors

• Parabolic trough system• Parabolic dish • Power tower• Stationary concentrating collectors 

PARABOLİC TROUGH SYSTEM 

Parabolic troughs are devices that are shaped like the letter “u”. The troughs concentrate sunlight onto a receiver tube that is positioned along the focal line of the trough. Sometimes a transparent glass tube envelops the receiver tube to reduce heat loss [3].

Figure 3.1.2 Parabolic trough system [3]. Figure 3.1.1 Crossection of parabolic trough [4].

The parabolic trough sytem is shown in the figure 3.1.2 below.

Their shapes are like letter “u” as shown figure 3.1.1 below.

PARABOLİC DİSH SYSTEMS 

A parabolic dish collector is similar in appearance to a large satellite dish, but has mirror-like reflectors and an absorber at the focal point. It uses a dual axis sun tracker .

Figure 3.2.2 Parabolic dish collector with a mirror-like reflectors and an absorber at the focal point [Courtesy of SunLabs - Department of Energy] [3].

Figure 3.2.1 Crossection of parabolic dish [4].

The below figure 3.2.1 shows crossection of parabolic dish.

The Parabolic dish collector is shown in the below figure 3.2.2.

POWER TOWER SYSTEM A heliostat uses a field of dual axis sun trackers that direct solar energy to a large absorber located on a tower. To date the only application for the heliostat collector is power generation in a system called the power tower .

Figure 3.3.2 Heliostats [4].Figure 3.3.1 Power tower system [4].

Heliostats are shown in the figure 3.3.2 below.

The Power tower system is shown in the figure 3.3.1 below.

STATİONARY CONCENTRATİNG SOLAR COLLECTORS

Stationary concentrating collectors use compound parabolic reflectors and flat reflectors for directing solar energy to an accompanying absorber or aperture through a wide acceptance angle. The wide acceptance angle for these reflectors eliminates the need for a sun tracker.

This class of collector includes parabolic trough flat plate collectors, flat plate collectors with parabolic boosting reflectors, and solar cooker. Development of the first two collectors has been done in Sweden. Solar cookers are used throughout the world, especially in the developing countries .

Thank

You