The document discusses the various methods of utilizing solar energy, including direct and indirect uses. Direct uses include thermal conversion through solar water heating, space heating/cooling, power generation, distillation, drying, and cooking. Indirect uses involve utilizing solar energy to create wind, biomass, ocean/hydro energy. A typical solar energy plant consists of six subsystems: solar collectors to concentrate diffuse sunlight, energy transportation mechanisms, storage systems for intermittent sunlight, conversion to electricity or steam, power conditioning, and alternative backup supplies.

1. 2.4.SOLAR ENERGY UTILIZATION:
There are different methods of solar energy utilization as
shown in following Fig.2.5
Fig. 2.5 Utilization Of Solar Energy
The energy from sun is used directly or indirectly. The direct
use includes thermal and photovoltaic conversion, whereas
indirect use includes water power, wind, biomass and ocean
energy. The ocean energy is further utilised as ocean wave,
ocean tide, marine current and ocean temperature difference.
2.4.1 Thermal Route:The utilization of solar energy via
thermal route includes number of ways. These are as follows :
1.Water heating :
Solar water heater is the most attractive and common thermal
applicationofsolarenergy.Itismosteconomicandworksonflat-
plate collector. There are two types of solar water heating
systems namely (i) natural circulation (thermosyphon) system
and (ii) forced circulation system. The natural circulation system
is simple, has small capacity and is useful for domestic use.
However, the forced circulation system is used when large
amount of water is required and is useful for industrial and
commercial purposes such as factories, hotels, hospitals, offices

2. etc. The hot water per liter per day is less for the forced
circulation system than the natural circulation system.
2.Space heating :
This application of solar energy is prominently used in
western countries where a significant amount of energy is
required for heating the space in buildings, especially houses
and offices in winter. This space heating can be done by active
method or passive method. In active method the air or fluid
heated by solar energy is blown or circulated with the help of air
blower or circulator respectively. In passive method of space
heating the thermal energy flows through a living space by
natural means without the use of mechanical devices such as
pump or blower. there are different types of designs available
for both the methods of heating.
3.Space cooling and Refrigeration :
Here, solar energy is used to cool the space to provide
comfortable living conditions (air conditioning) or to keep the
food products cold (refrigeration). This application is mostly
required in summer and solar energy received as heat is used as
absorption refrigeration cycle. Due to high cost of solar
absorption refrigeration system, it is not commercialized.
4.Power generation :The generation of electrical power from
solar energy is possible by direct or indirect way. In direct
conversion, solar energy is converted into
electrical energy by photovoltaic cell or solar cell. However,
in indirect method, solar energy is converted into thermal
energy which in turn is converted into electrical energy. There
are different solar thermal power cycles such as low, medium
and high temperature cycles.

3. The low temperature cycle works at maximum temperature
of about 100°C and uses flat-plate collectors or solar ponds
for collecting solar energy. The medium temperature cycle
works at maximum temperature upto 400°C and uses line
focussing parabolic collectors.
The high temperature cycle works at temperatures above
400°C and uses either paraboloid dish collectors or central
receivers located at the top of towers.
5.Distillation :
Solar energy can be used for distillation of water. Solar
distillation is a process in which saline brackish water is
converted into potable water by using solar energy. In this
method, in principle, the saline water is heated up by about
10°C to 20°C and causes it to evaporate. The resulting
vapour rises and condenses as pure water which is properly
collected.
6.Drying :
This is the most traditional use of solar energy by thermal
route. The solar energy is used for drying clothes and
agricultural products. The solar drying removes moisture
and helps in preservation of product. Traditional drying is
done on open ground which is slow and causes insects and
dust mixing. Therefore, there are some specially designed
dryers which remove above disadvantages and drying
becomes faster and of better quality. The different types of
solar dryers are cabinet dryer, forced circulation dryer, etc.
7.Cooking :
This is an important domestic thermal application of solar
energy. In last few years, a number of designs of solar cookers
have been developed which include box type cooker, scheffler
cooker, etc. These cookers have varied features, but the same

4. principle. In box type cooker, the cooking of food is slow and
it is useful for domestic purpose. The solar radiations enter
through one or two glass covers on the top of the box and
reach the box of typical size and shape where cooking takes
place. The time taken for cooking depends upon the solar
radiation received and varies generally from half an hour to
three hours.
Scheffler cooker uses paraboloid type collector giving
concentrated thermal energy and it also uses mirror reflector
for more concentration of solar energy. Further, this cooker
requires tracking. Hence, the temperature as high as 400°C
can be obtained (more than box type cooker) and all types
of cooking/frying are possible. This cooker can be used for
commercial applications.
2.4.2 Photovoltaic Route
It is the method in which solar energy is directly converted
into electrical energy. This is discussed in latter sections of
this chapter (section 2.8).
2.5 ESSENTIAL SUBSYSTEMS IN SOLAR ENERGY PLANT
The essential subsystems in solar energy plant, which aim
at constant and continuous energy supply for different
applications, depend upon the peculiar characteristics of
solar energy and the application for which solar energy is
used. The characteristics of solar energy available include Its
dilute nature (about 0 to 1 kW/m2
), discontinuous
(intermittent) source of energy, sensitive to atmospheric
conditions, clouds, storms, location of place and inclination of
the sun. Taking into account all these facts it is required to
construct the solar energy plant. A typical solar energy plant
has following six subsystems.
1. Solar collectors :

5. These are also called as solar concentrators. As already
mentioned, because of very dilute nature of solar energy, it is
required to make the energy source strong. The purpose of
solar energy collector or concentrator is to transform very
dilute solar energy source into concentrated source of solar
energy. There are different types of solar collectors as
discussed below.
(a)Flat plate collectors : These are the collectors which have no
focussing. Most widely used form is liquid flat plate collector,
because it is simple in design, has no moving parts and requires
little maintenance. Besides this conventional collector a
number of novel designs of this collector are developed in
recent years. This includes Evacuated Tube Collectors (ETC),
the polymer solar collector, the Brookhaven National
laboratory (BNL) collectors and the concrete collectors.
(b) Parabolic collectors : There are two types of parabolic
collectors. One is parabolic through type collector in which solar
energy is concentrated along a line. The other is parabolic dish
type collector where all the solar radiations falling on the dish
are collected at a point which is the focus of parabolic dish.
(c) Fresnel lens : It is special type of lens in which solar energy
is condensed at the focus of the lens.
(d) Heliostatic central receiver : It is formed by array of arcs
(mirrors) around the central tower. They intercept, reflect and
concentrate the solar radiation on to the receiver. The array
has tracking control system. It gives most concentrated
source of solar energy and can be used to construct solar-
thermal-electric plant of the order of MW.
(f) Concentrating collectors : Formed by using mirrors and
lenses.
2.Energy transportation :

6. The solar energy (generally thermal) concentrated by
collectors needs to be transported from collectors to the place
of application. This can be done by using medium such as
water or steam, liquid, metal, gas etc. In solar PV system, solar
energy is directly converted into electrical energy which is
then transported by electrical means.
3.Energy storage :
The storage system is needed because there is some
mismatch between energy needed and energy available. As
already discussed, the solar energy is not continuously
available. Hence, significant amount of energy storage is
required to supply power to the load during night and cloudy
hours. The commonly used energy storages in solar energy
plant are (i) thermal energy storage, (ii) energy stored in
electrical form by means of batteries, (iii) energy stored by
pumped storage in hydroelectric plant. In general, storage
system stores energy when collected amount of energy is in
excess of requirements of the application. This stored energy
is discharged when the collected amount is inadequate.
There are three basic methods of thermal energy storage.
(a)Heating of liquid or solid without changing its phase :
This is called sensible heat storage. If mass m of solid or
liquid is having specific heat C. and when its temperature
is increased from T1 to T2, then amount of energy stored
is
𝐸 = m ∫ Cp
T2
T1
d𝑡
where dt = T2 - T1 = temperature swing.
(b)Heating of material which undergoes phase change :
It is generally melting. This is called latent heat storage. If

7. material has latent heat L and it mass is m, then amount
of energy stored is
E = mL
(c)Heating of material causing chemical change : Here,
certain chemical reactions are induced by absorbing
solar energy and then storing it in the products. The heat
is released when reverse reaction is made to occur.
Thus it is seen that this subsystem of energy storage in
solar energy plant is vital and most decisive economic
factor. Further, thermal energy storage has different types
namely buffer storage, Diuranal storage and annual
storage.
4.Energy conversion plant :
The solar energy in thermal form collected from the collectors
can be used for producing steam or hot water. Further, the
thermal energy can be used as an input to steam-thermal or
gas-thermal power plant. The direct conversion of solar
energy into electrical one is possible with solar PV cell.
5.Power conditioning :
Due to intermittent, variable and unpredictable nature of
solar radiation, there is mismatch in demand and supply of
energy. Further, requirement of energy in different forms such
as heat, process steam or electrical energy is sensitive to time.
This asks for energy supply with certain specifications and
quality requirement. It includes
(i) temperature and pressure of steam
(ii) voltage, current, frequency and power of electrical
energy, etc.
This power conditioning unit also performs the operation of
power control and also protection of the system by manual
or automation technique.

8. Thus, this subsystem is responsible for providing solar
energy in required form and required characteristics.
6. Alternative supply :
It is the standby arrangement of power supply. When
regular solar energy supply and so also the storage system
fails or inadequate to supply the load requirement, then the
standby or alternative power supply is used. This occurs
mainly during night hours, cloudy hours, monsoon and
winter etc. when solar energy has very low power density (0
to 0.2 kW/m2
). The alternative power can be obtained
from conventional electrical power network or from
independent standby diesel generator.