Solar Radiation Geometry, Solar Thermal Conversion and Applications

Dr. Ramesh B T
Assistant Professor
Mechanical Engg. Dept.
JIT-Davanagere
Email Id: rameshbt049@gmail.com
Solar Radiation Geometry
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Dr. Ramesh B T

Let us first define below angles,
1. ɸl=Latitude of location,
2. δ=Declination,
δ = 23.45 sin [
360
365
(284+n)]
3. ω=Hour angle, S=slope,
4. γs=Solar Azimuth angle,
5. α=Altitude angle,
6. θz= Zenith angle
Θz=
𝜋
2
- α
7. Surface Azimuth angle (γ)
8. Solar Incident angle (θ)
9. Day Length (td)
10. Local Solar time (Local Apparent time) LAT
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Solar altitude angle(α):
Altitude Angle is the angle between the Sun‘s rays and projection of the Sun’s rays on the horizontal plane
Zenith angle(θz):
It is Complementary angle of Sun‘s Altitude angle. It is a vertical angle between Sun‘s rays and line perpendicular to the
horizontal plane through the point i.e. angle between the beam and the vertical
Θz=π/2-α
Solar Azimuth Angle(γs):
It is the solar angle in degrees along the horizon east or west of north
or
It is the horizontal angle measured from north to the horizontal projection of sun‘s rays.
Declination(δ):
It is the angle between a line extending from the centre of the Sun and center of the earth and projection of this on earth‘s
equatorial plane.
Declination is the direct consequence of earth‘s tilt and It would vary between 23.5o on June 22 to – 23.5o on December
22. On equinoxes of March21 & Sept22 declination is zero.
The declination is given by the formula
Where n is the day of the year
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Meridian:
Meridian is the immaginery line passing through a point or place on
earth and north and south poles of the earth‘.
hour angle(ω):
Hour angle is the angle through which the earth must turn to bring meridian of
the point directly in line with the sun‘s rays.
Hour angle is equal to 15o per hour.
slope(β):
Angle between the collector surface with the horizantal plane is called slope(β).
surface azimuth angle(γ):
Angle between the normal to the collector and south direction is called surface
azimuth angle(γ)
Solar Incident angle(θ):
It is the angle between an incident beam radiation falling on the collector and
normal to the plane surface
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Day Length:
At the time of sunset or sunrise the zenith angle θz=90o , we
obtain sunrise hour angle as
Local Solar Time(Local Apparent Time (LAT):
Local Solar Time can be calculated from standard time by applying two corrections. The first correction arises
due to the difference in longitude of the location and meridian on which standard time is based. The
correction has a magnitude of 4minutes for every degree difference in longitude. Second correction called the
equation of time correction is due to the fact that earth‘s orbit and the rate of rotation are subject to small
perturbations. This is based on the experimental observations.
Thus,
Local Solar Time=Standard time± 4(Standard time Longitude-Longitude of the location)+(Equation of time
correction)
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Determine the Local solar time and declination at a location latitude 23° 15’N, longitude
77° 30’ E at 12.30 IST on June 19. Equation of time correction is given from standard table
or chart=-(1’ 01”).
Soln: WKT The local solar time=IST-4(Standard time longitude-longitude of
location)+Equation of time correction
=12ʰ 30’-4(82° 30’-77° 30’)-1’ 01’’
Note: Indian Standard Time(IST) is the local civil time corresponding to 82.5° E (82° 30’)
longitude
= 12ʰ 30’-4 x 5- 1’ 01’’
L S T= 12ʰ 8’ 59’’
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Declination ‘δ’ can be obtained by Cooper’s equation i.e.,
δ = 23.45 sin [
360
365
(284+n)]
= 23.45 sin [
360
365
(284+170)]
Where n is the days up to June 19 = 170 days
= 23.45 sin 447.78
= 23.45 x 0.999
δ = 23.43°
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Solar Radiation on Tilted surfaces
The rate of receipt of solar energy on given surface on ground depends on orientation of surface
with reference to the sun. A fully sun-tracking surface that always faces the sun receives the
maximum possible solar energy at particular location. A surface of same area oriented in any other
direction will receive a smaller amount of solar radiation.
Because solar radiation is such a ‘dilute’ form of energy, it is desirable to capture as much as
possible on a given area.
It is seen in the preceding sections that the measuring instruments give the values of solar radiation
falling on horizontal surface.
The expression for flux on tilted surface is given by
cos θᴛ = sin δ sin(ɸ-s) + cosδ cosω cos(ɸ-s)
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Beam radiation
In most cases; the tilted surface faces due to south i.e., γ=0, for this case,
cos θ = sin δ sin (ɸ-s)+ cos δ cos ω cos (ɸ-s)
For horizontal surface (θ= θz)
cos θz = sinɸ sinδ+ cosɸ cosδ cosω
It follows that, the ratio of beam radiation flux falling on tilted surface to that of
horizontal surface is called the Tilt factor for beam radiation, it is given by
Rb=
𝐻𝑇
𝐻
=
cos θ𝑇
𝑐𝑜𝑠θ𝑧
Rb =
sin ɸ−s 𝑠𝑖𝑛δ+cos ɸ−s 𝑐𝑜𝑠δ 𝑐𝑜𝑠ω
𝑠𝑖𝑛ɸ 𝑠𝑖𝑛δ+𝑐𝑜𝑠ɸ 𝑐𝑜𝑠δ 𝑐𝑜𝑠ω
this ratio is called the tilt
factor for beam radiation.
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Diffuse Radiation
The ratio of diffuse radiation flux falling on tilted surface to that of horizontal surface is
called the Tilt factor for diffuse radiation.
Its value depends on distribution of diffuse radiation over the sky and portion of sky dome
seen by the tilted surface.
Assuming that the sky is an isotropic source of diffuse radiation, for a tilted surface with
slope s,
We have, Rd =
𝟏+𝒄𝒐𝒔 𝒔
𝟐
is the shape factor for a tilted surface w. r. t. sky.
Reflected Radiation and Total Radiation
It is the portion of total radiation which has been reflected from earth surface and received on flat
faced thermopile surface. For total radiation, let Hb= Hourly beam radiation and Hd = Hourly diffuse
radiation.
Thus the total radiation such as beam, diffuse and reflected radiations incident on a tilted surface is
given as,
HT = Hb Rb =
𝐻𝑑(1+cos 𝑠)
2
+
𝐻𝑏+𝐻𝑑 (1−cos 𝑠)
2
ρ 21-06-2021
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Soln: γ=0 since collector is pointing due south. For this case we have an equation,
cos θᴛ = cos(ɸ-s) cosδ cosω + sin (ɸ-s) sinδ
Declination δ can be obtained with the help of Cooper equation on December 1, then
No. of Days n=335.
δ = 23.45 sin [
360
365
(284+n)]
δ = 23.45 sin [
360
365
(284+335)] = 23.45 sin (610.52)
δ = -22.10°
Problem on tilted surface
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Hence,
cos θᴛ = cos(28.58°-38.58°) cos(-22.11°) cos45° + sin (28.58°-
38.58°) sin(-22.11°)
= cos(10°) cos(22.11°) cos45° + sin (10°) sin(22.11°)
= 0.6451+ 0.0653
cos θᴛ = 0.7104
(or) θᴛ = 44.72°
Hour angle ω corresponding to 9.00 hour = 45
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Solar Thermal Conversion
Solar Energy Collectors and Storages
A solar Collector is a device for collecting solar radiation and transfer the energy to
a fluid passing in contact with it. There are two types of collectors are,
i) Non concentrating or Flat plate type solar collector: In this the collector area
is same as the absorber area. The maximum temperature achieved in this type is
about 100°c.
ii) Concentrating (focusing) type solar collector: Here the area intercepting the
solar radiation is greater(100 times) than the absorber area. In this much higher
temperature can be obtained and shows better efficiency than flat plate type.
The maximum temperature achieved in this type is about 350°c.
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Principle of solar energy conversion to heat
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The principle on which the solar energy is converted in to heat is the greenhouse effect. The name is
derived from the first application of green houses in which it is possible to grow vegetation in cold
climate through the better utilization of available sunlight.
The solar radiation incident on earth surface at a particular wavelength increases the surface
temperature of earth. As a result of difference in temperature between the earth surface and
surroundings, the absorbed radiation is reradiated back to the atmosphere with its wavelength
increased.
The Co2 gas in the atmosphere is transparent to the incoming shorter wavelength solar radiation,
while it is opaque to the long wavelength reradiated radiation. As a result of this the long wavelength
radiation gets reflected repeatedly between earth atmosphere and earth surface resulting in increase
in temperature of earth surface.
Dr. Ramesh B T

I.
Where temperatures below about 90°C are adequate, as they are for space and service water
heating flat plate collectors, which are of non-concentrating type, are particularly convenient.
Flat plate can collect and absorb both direct and diffuse solar radiation, they are consequently
partially effective even on cloudy days when there is no direct radiation.
Flat-plate solar collectors may be divided in to two main types based on type of heat transfer
fluid based. They are
1) Liquid heating collectors or Typical liquid collector
2) Solar air heater or Typical air collector
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Five main components of Flat-plate collector
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1) Liquid heating collectors or Typical liquid collector
It is the plate and tube type collector. It is used for heating water and non-
freezing aqueous solutions and occasionally for non-aqueous heat transfer fluids.
Fig: Selection through typical flat-plate
collector
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Dr. Ramesh B T

1) Heating buildings
2) Drying agricultural produce and lumber
3) Heating green houses
4) Air conditioning buildings utilizing desiccant beds or a absorption refrigeration process
5) Using air heaters as the heat sources for heat engine such as Brayton or Stirling cycle.
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II. Concentrating or Focusing type solar collector
Focusing collector is a device to collect solar energy with high intensity of solar radiation
on the energy absorbing surface. Such collectors generally use optical system in the form of
reflectors or refractors.
A focusing collector is a special form of flat-plate collector modified by introducing a
reflecting surface between solar radiations and absorber.
Since the radiation is focused, the efficiency of concentrating collector is always greater
than that of non-focusing or FPC.
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It has generally two categories:
I. Focusing Type
a) Line focusing b) Point focusing type
1) Parabolic trough collector 1) Paraboloidal collector
2) Cylindrical Parabolic 2) Central Tower concept
3) Mirror strip reflector
4) Fresnel lens collector
II. Non-Focusing Type
1) Flat-plate collector with adjustable mirrors
2) Compound parabolic concentrator (C.P.C) 21-06-2021
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Fig. Cross-section of Parabolic-trough
collector 21-06-2021
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https://youtu.be/lrRTCbXE0Jc

Fig: A typical cylindrical parabolic collector
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https://www.youtube.com/watch?v=S2hN_p1oZQI

Fig: Point focus solar collector (Paraboloidal type)
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https://www.youtube.com/watch?v=EfMDiv6mV9s

1) Reflecting surfaces required less material and are structurally simpler than flat-plate
collector.
2) The absorber area of concentrator system is smaller than that of flat-plate system.
3) The working fluid can attain higher temperature in concentrating system than in flat-
plate collector of same solar energy collecting surface.
4) Focusing system can be used for electric power generation when not used for heating
or cooling.
5) Higher temperature of working fluid attainable, which results to attain higher
efficiency.
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1) Out of beam and diffuse solar radiation components, only beam component is collected
in case of focusing collectors.
2) Additional requirements of maintenance particular to retain the quality of reflecting
surface against dirt, weather, oxidation etc.
3) Non-uniform flux on the absorber whereas flux in flat-plate collectors is uniform.
4) Additional optical losses such as reflectance loss and intercept loss, so they introduce
additional factors in energy balances.
5) High initial cost.
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Solar Energy Storage
Solar energy is a time dependent and intermittent energy resource. In general energy needs
or demands for a very wide variety of applications are also time dependent, but in an
entirely different manner from the solar energy supply.
Classification of solar energy storage systems are:
1. Thermal energy storage a) Sensible Heat Storage
b) Latent heat storage
2. Electrical storage
3. Chemical storage
4. Electro-magnetic energy storage
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It is a type of thermal energy storage which involves a material that undergoes no change in
phase over the temperature domain encountered in storage process. The basic equation for
energy storage unit, operating over a finite temperature difference is,
Qs = (m Cp)s (T1-T2)
The ability of store thermal energy in a given container of volume V is,
Qs
𝑉
= ρ Cp ΔT where, ρ = Density of storage medium
Materials which are generally used for sensible heat storage are i) Water, ii) Rock, gravel or
crushed stone iii) Iron shot iv) Iron or iron ore v) Concrete, vi) Refractory materials like
MgO, Al2O3, SiO2.
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Fig: Schematic of Packed bed storage
unit
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It is also type of thermal energy storage in which, heat is stored in a material when it melts
and extracted from the material when it freezes. Material that undergo a change of phase in
a suitable temperature range may be useful for energy storage.
Fig: A typical latent heat storage
arrangement
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Applications of Solar energy
The actual and proposed applications of solar energy may be considered in three general categories:
a) Direct Thermal Applications
b) Solar Electric applications
c) Energy from Biomass and Bio-gas
Base on above classification, Solar electric applications are as follows
* Solar water heating, Space heating
* Space cooling, Thermal electric conversion
* Photovoltaic electric conversion
* Solar Distillation, Solar Pond
* Solar pumping
* Agriculture & Industrial process unit
* Solar furnace
* Solar cooking
* Solar production of hydrogen and
* Solar green houses 21-06-2021
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Solar Pond
A natural or artificial body of water for collecting and absorbing solar radiation energy and storing it
as heat. Thus a solar pond combines solar energy collection and sensible heat storage.
Solar ponds promise an economical way over flat-plate collectors and energy storage by employing a
mass of water for both collection and storage of solar energy.
The energy is stored in low grade (60 to 100°c) thermal form which, in self, might be suitable for
variety of applications such as space heating, industrial process heat and to obtain mechanical and
electrical energy.
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Principle of Operation and Description of non-
convective solar pond
A solar pond is a mass of shallow water about 1 or 2 metres deep with a large collection
area, which acts as a heat trap. It contains dissolved salts to generate a stable density
gradient.
Part of incident solar radiation entering the pond surface is absorbed throughout the depth
and remainder which penetrates the pond is absorbed at the black bottom.
If the pond were initially filled with fresh water, the lower layers would heat up, expand and
rise to surface.
At the bottom of the pond, a thick durable plastic liner is laid. Materials used for liner
include butyl rubber, black polyethylene and hypalon reinforced with nylon mesh.
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Solar Pond has three zones with following salinity with depth:
i) Surface convective zone or upper convective zone (0.3-0.5m), salinity<5%.
ii) Non-convective zone 1 to 1.5m, salinity increases with depth.
iii) Storage zone or lower convective zone (1.5-2m), salinity(salt conc )=20%
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Extraction of thermal energy stored in lower layers of pond can be easily accomplished
without disturbing the non-convecting salt gradient zone.
Hot water can be extracted from solar pond without disturbing the concentration gradient.
This is achieved by installing the water outlet at same height as water inlet.
Hot brine can be withdrawn and cool brine returned in a laminar flow pattern because of
presence of density gradient.
For small ponds, heat exchangers consisting of pipes can be placed in hot lower layers, but
this entails not only the initial installation cost but the continued pumping losses associated
with heat transfer fluid.
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Dr. Ramesh B T
https://youtu.be/qn5DZ2CQQEs

1) Heating and Cooling of buildings
2) Production of power
3) Industrial process heat
4) Desalination
5) Heating animal housing and
drying crops on farms
6) Heat for biomass conversion
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1) Solar water heating (Hot water Supply System)
The basic elements of a solar water heater are:
i) Flat plate collector
ii) Storage tank
iii) Circulation system and auxiliary heating system
iv) Control of system
The use of solar energy for heating water in many respects quite similar to its use for
heating buildings. There are however, several aspects of solar water heating, that make it
potentially better investment of energy, money and effort than solar building heating.
The solar building heating system, on other hand, fully operational only during the coldest
months of heating season.
The simplest type of solar water heater is the thermo siphon system.
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*
i) Natural circulation solar water heater (pressurized)
ii) Natural circulation solar water heater (non-pressurized)
iii) Forced circulation solar water heater
i) Natural circulation solar water heater (pressurized)
Fig: Schematic of natural circulation Solar water heater
(Pressurized)
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*
Fig: Non-Pressurized solar water
heater
Fig: Typical solar water heater
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*
Fig: Solar water heating system with
antifreeze
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Space Heating (Solar heating of building)
Many different concepts have been proposed and tested for using solar energy in space
heating of buildings. There are two primary categories into which virtually all solar heating
systems may be divided.
The first is Passive systems, in which solar radiation is collected by some element of
structure itself, or admitted directly in to building through large, south facing windows.
The second is the Active systems which generally consists of
a) Separate solar collectors, which may heat either water or air
b) Storage devices which can accumulate the collected energy for use at nights and during
inclement days, and
c) A back up system to provide heat for protected periods of bad weather.
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A) Passive Heating Systems
Passive heating systems operate without pumps, blowers or other mechanical devices; the
air is circulated past a solar heated surface and through the building by convection.
Fig: Passive solar heating
system
The basic design principles are:
i) Direct gain
ii) Thermal storage wall
iii) Attached sun space
iv) Roof storage
v) Convective loop
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Fig: Convective loop passive solar
heating
Fig: Roof storage of solar
heat
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B) Active space–Heating systems
It is a type of heating system in which, separate collectors are used together the solar
radiation, transfer it to water or air, and store it in tanks of water or rock piles or both. The
water and air are circulated by pumps or fans and conventional means are used to distribute
the heat to interior of residencies.
General principles: The solar space heating and hot water supply system utilize three main
components in addition to pumps and blowers:
1) A solar radiation collector with its associated heat transport fluid,
2) A heat storage medium, and
3) A distribution systems
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Fig: Schematic of basic hot water active
system
Fig: Solar space heating and hot water
system
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1. In case of water heating, a common heat transfer and storage medium, water is used, this
avoids temperature drop during transfer of energy into and out of storage.
2. It requires relatively smaller storage volume.
3. It can be easily adopted to supply of energy to absorption air conditioners, and
4. Relatively low energy requirements for pumping of heat transfer fluid.
Disadvantages
1. Solar water heating system will probably operate at lower water temperature than
conventional water system.
2. Water heaters may also operate at excessively high temperature and means must be
provided to remove energy and avoid boiling and pressure buildup.
3. Collector storage has to be designed for overheating during the period of no energy
level.
4. Care has to be taken to avoid corrosion problems.
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Fig: Schematic diagram of basic hot air heating
system
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i) There is no problem with freezing in the collectors.
ii) Corrosion problems are minimised.
iii) Conventional control equipment for air heating is already available and can be
readily used.
iv) Problems of designing for over heating during periods of no energy removal are
minimized.
v) The working fluid is air and warm air heating system are in common use.
Disadvantages
i) Relatively higher power cost for pumping air through the storage medium.
ii) Relatively large volumes of storage units.
iii)Difficulty of adding absorption air conditioners to the system.
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Space Cooling ( Solar Cooling of Buildings)
The major current interest is in mechanical cooling (or air-conditioning) systems that
depend on solar heat for their operation and are unaffected by atmospheric humidity. The
two most common refrigeration techniques are vapour compression and absorption.
1) Absorption air conditioning
Two approaches have been to solar operation of absorption coolers. The first is continuous
cooler which is in construction and operation, is similar to conventional vapour absorption
refrigeration system. The solar collector storage supplies the energy to generator, where
solar energy is available, otherwise it is supplied with auxiliary energy source.
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*
Classification of Absorption air conditioning
The two types of absorption air conditioners available in the market are,
(A)Lithium-bromide water (LiBr-H2O) system and
(B)Ammonia-water (NH3-H2O) system.
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*
LiBr-H2O system consists of two parts:
(i) The solar collector and storage, and
(ii) The absorption air conditioner and auxiliary heating.
Fig: Schematic of solar operated absorption air
conditioner
The essential components of cooler are,
i) Generator (G)
ii) Condenser (C)
iii) Evaporator (E)
iv) Absorber (A)
v) Heat-exchanger (HE)
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*
The schematic diagram of an ammonia water cooler is similar to that of lithium bromide
water. Except that a rectifying section must be added to the top of generator to reduce the
water vapour content of vapour stream going to the condenser.
The basic solution processes are similar to those of LiBr-H2O system, except that pressure
and pressure difference are much higher. Mechanical pumps are required to return solutions
from absorber to generator.
In many applications the condenser and absorber are air cooled, with generator temperatures
in the range of 125 to 175ᵒC. In applications where water cooling is used , generator
temperature may be in the range of 95 to 120ᵒC.
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*
Fig: Intermittent absorption
refrigeration
This system consists of two vessels which function in two alternative modes
a) Regeneration mode and b) Refrigeration mode 21-06-2021
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Dr. Ramesh B T

Solar Distillation
Fresh water is a necessity for the sustenance of life and also key to man’s prosperity.
It is generally observed that in some arid, semi arid and coastal areas which are
thinly populated and scattered, one or two family members are always busy in
bringing fresh water from a long distance.
In these areas solar energy is plentiful and can be used for converting saline water in
to distilled water. The pure water can be obtained by distillation in simplest solar
still, generally known as the “basin type solar still”.
Fig: Solar water still
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The performance rating and efficiency of solar still is determined by plotting the graph of
amount of fresh water produced per unit of basin area in one day versus the solar radiation
intensity over same period. Such curves for several stills are drawn. Efficiency is defined as
η =
𝑤∆ℎ
𝐻
Where, 𝑤= weight of distillate per square meter per day.
∆ℎ= Enthalpy change from cold water to vapour
𝐻=Solar radiation intensity per square meter per day
Operating efficiency of 35 to 50% for basin type still have been achieved in practical units,
as compared with a theoretical maximum of slightly more than 60%.
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Solar Cooking
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Solar cooking refers to using energy of direct sunlight to cook and heat food. A solar cooker
lets the UV light rays in and then converts them to longer infrared light rays that cannot
escape. Infrared radiation has the right energy to make the water, fat and protein
molecules in food vibrate vigorously and heat up.
There are three main components to most solar cookers, or you could say three main
principles to effective solar cooking; these being:
1. Concentration (reflection, or reflectance)
2. Absorption (ability to attract or hold heat.
3. Retention (means or capacity to retain heat)

Thank YOU
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Dr. Ramesh B T

Solar Radiation Geometry, Solar Thermal Conversion and Applications

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