CHAPTER – 2 Solar Thermal Energy – A Ray of Hopeshodhganga.inflibnet.ac.in/bitstream/10603/12383/8/08_chapter 2.pdf · Chapter-2 Solar Thermal Energy - A Ray of Hope 13 ... A

Chapter-2 Solar Thermal Energy - A Ray of Hope 13

Thesis Submitted to Jawaharlal Nehru Technological University, Anantapur

CHAPTER – 2

Solar Thermal Energy – A Ray of Hope



2.1 INTRODUCTION

A solar thermal system has wide applications such as hot water

generation, operating house-hold electrical appliances, irrigation,

drying of fruits and vegetables, timber, coconut etc. A solar thermal

system can heat water or air. Usually, solar panels are installed on the

roof or on a frame at the ground level and a hot water cylinder is

installed near the panels.

Fig. 2.1 80 – 20 Principle of solar energy

2.2 PRINCIPLE

The solar panels (collectors) heat up when day light (the Sun's

radiation) falls onto them. This radiation heats up a liquid inside the

panel, usually anti-freeze. This heat is then transferred by the heat

transfer medium to the cylinder or heat exchanger to heat the water.

When cold water is pumped through the solar panel it will be heated

by solar energy [3]. This hot water can be used directly for industrial

purposes or can be supplied to the boiler to generate steam.

80 % AS HEATENERGY20 % AS LIGHT

ENERGY



In fact, a solar thermal system needs daylight to work, not

direct sunlight. Any solar collector works on the amount of Sun's

radiation or light received on Earth. The energy can be collected on

clear summer days as well as on cloudy winter days. Current thermal

systems are much more efficient than ever before. In summer the

water in the cylinder can reach up to 800C within half a day and the

insulation on the cylinder will keep the water warm for the following

day [3].

Typically, the solar hot water system will reduce the firewood

consumption, deforestation and pollution.

2.3 SOLAR WATER HEATING SYSTEM [4]

A solar water heating system (SWHS) is made of several

important elements: one or more solar collectors, a pump, a heat

exchanger, a storage tank (or multiple tanks) and a back-up storage

tank. The Solar heating system can be classified as passive or

active.

For water heating purposes, the general practice is to use flat-

plate solar-energy collectors (FPC). However, although the Evacuated

Tube Collectors (ETC) and Evacuated Tube Heat Pipe Collectors

(ETHP) are more efficient, even the initial cost is comparatively

higher.

2.3.1 Solar Collectors [5]

Every installation is different and every collector brand is made

slightly different, hence, the annual energy output may vary from one



to other. The output also depends on the aperture area of the

collector, which is the opening that collects the sun’s radiation, but

not on the gross surface area of the solar collector [3].

A solar collector is very efficient at turning sun light into heat.

There is a special coating called an “Absorber Surface Coating” that is

spluttered or fused at a very high temperature, with the metal sheet

inside the solar collector. This surface makes the collector efficient

and effective. It is all about the "aperture area or absorber surface"

which is part of the collector that collects light and transforms into

heat. All efficient panels are made of a strong aluminum body that is

non-corrosive.

The heat absorbed by the solar collector is protected by a

toughened solar glass that covers the entire solar panel. This

transparent glass cover prevents wind and breezes from carrying the

collected heat away (convection). Together with the frame, the glass

protects the absorber from adverse weather conditions. Typical frame

materials include aluminum and galvanized steel; sometimes

fiberglass-reinforced plastic is used.

As far as the water heating system is concerned, the panels may

be either Flat-Plate type or Vacuum Tube type. Both flat-plate and

vacuum tube collectors can work on cloudy days. If we compare flat-

plates and evacuated tubes by aperture area, vacuum tubes are more

efficient than the flat plates.



Vacuum Tubes are more suitable for water heating systems,

where high temperatures are required even in cold climates. For a

similar output, a 3 m² vacuum tube system is sufficient in place of a 5

m² flat plate system. The average lifetime of a well-designed and built

solar thermal collector is over 25 years, and the maintenance on solar

thermal system is very little. Once the installation is completed, there

are no further fuel costs. Also, it will save tons of CO2 being released

through conventional energy sources, into the atmosphere.

The systems from well experienced and reputed companies can

provide hot water for 25 years and are fully automated with no user

intervention. These collectors are also free from scales and frost

damage.

2.3.2 Advantages of Solar Water Heating System

Solar Water Heating System (SWHS) is more economical

compared to any other hot water generating systems that run on

conventional fuels. Generation of hot water is completed in a most

hygienic and eco-friendly way. SWHS has very low operation and

maintenance cost and last longer, typically 20 years to 30 years, with

minimum maintenance. The price for production of hot water does not

fluctuate. There will never be a shortage that will cause hot water to

become unaffordable. There are no expensive fuel transportation costs

for producing hot water as the sun shines everywhere.



2.4 AVERAGE SOLAR RADIATION [6]

The average solar radiation in A.P. zone is 4.5 - 6 kWh/m²/day,

with an average of 300 clear days in a year. There is immense

potential solar radiation available to meet domestic and industrial

thermal energy demands. As per Ministry of Non-conventional Energy

Sources (MNES), the potential of solar water heating systems in the

country is around 30 million m² of collector area.

As a result of various promotional efforts, there has been a

steady growth in the cumulative collector area installed. The

cumulative collector area installed has increased from 119000 m² in

1989 to 525000 m² as of March 2001. As of 31 March 2005, in India,

the cumulative installed capacity of solar water heating systems was 1

million m² of collector area.

2.5 ENERGY CALCULATIONS

Thermal systems now are much more efficient than they were

years ago. For example, the maximum output from a domestic solar

hot water system (on a clear summer day) is approximately 700 W/m²

aperture areas [6].

A Flat-Plate (FP) system for 3 to 5 people, for example has an

aperture area of 4.4 m², then 4.4 m² x 700 W/m² = 3.08 kW is the

system output. So, a system of this size would have the same output

as a 3 kW immersion heater typically found in hot water cylinders.

The average ambient temperature in Andhra Pradesh would be around



35°C. At maximum output of 3 kW, FPC based SWHS would take just

over 5 hours to heat 250 liters of water from 35°C to 65°C.

2.6 SWHS FOR SILK INDUSTRY [5]

The Solar Water Heating System (SWHS) is broadly of two types:

1) Flat-Plate Collector based SWHS (FPC-SWHS) 2) Evacuated Tube

Collector based SWHS (ETC-SWHS).

For water heating purposes, the general practice is to use Flat-

Plate Solar Collectors (FPC). But the Evacuated Tube Heat Pipe

Collectors or Evacuated Tube Collectors (ETHP or ETC) are more

efficient, even the initial cost is comparatively high.

2.6.1 Flat-Plate Collector based SWHS [5]

Fig. 2.2 Flat-plate collectors [7]

The FPC-SWHS, which is of older technology, can generate hot

water between 60°C and 70°C, depending on the size and quality of

the collectors. A flat-plate collector consists of an absorber, a

transparent cover, a frame, and insulation. Usually, a solar safety



glass is used as a transparent cover, as it transmits a great amount

of short-wave light spectrum. Absorbers are usually black, as dark

surfaces will have high degree of light absorption.

As the absorber warms up to a temperature higher than the

ambient temperature, it gives off a great part of the accumulated solar

energy in the form of long-wave heat rays. The ratio of absorbed

energy to emitted heat is indicated by the degree of emission. The

most efficient absorbers have a selective surface coating, which

enables the conversion of a high proportion of solar radiation into

heat, simultaneously reducing the emission of heat.

The usual coatings provide a degree of absorption of over 90%.

Solar paints, which are painted or sprayed manually on the absorbers,

are not very selective, as they have a high level of emission. Some

selective coatings that include black chrome, black nickel and

aluminum oxide with nickel will absorb the heat more efficiently.

Relatively new is a titanium-nitride-oxide layer, which is applied via

steam in a vacuum process. This type of coating stands out because of

its low emission rates and efficiency.

2.6.1.i Cost of FP-SWHS

Assumptions: 1) Boiler consumes 2000 liters of water per day

2) Ambient temperature of cold water 300C – 350C 3) Sunshine days

as 300 per year 4) Cost of firewood Rs.2.00 per kg. (500 to 1000 liters

of water per day/boiler is the actual consumption by the reeling and

dyeing units.)



FPC-SWHS of 2000 liters capacity, from a reputed company,

with 16 panels with 9 copper fins in each collector, to produce 65°C,

costs around Rs.3,50,000.00 to Rs.3,75,000.00, @ Rs.175.00 to

Rs.187.50 per liter (includes tank, freight and taxes). Nonetheless, the

plumbing charges are extra, which may be between 4% and 6% of the

total cost.

Table: 2.1 Returns-on-investment (Source: M/s Tata BP Solar India

Limited, Bangalore)

Customer: Silk Reeling and Dyeing Sectors

FP-SWHS Capacity 2000 Liters / day

FP-SWHS output temperature 65 Degree Celsius

Energy Calculations

Avg. Ambient temperature 30 Degree Celsius

Heat gained by SWHS

(2000 liters * (65-30))

70000 K.cals/day

Heat gained/year 21000000 K.cals/300 days

Energy Savings

Calorific Value of firewood 2800 K.cals/kg

Combustion Efficiency of fuel 55% (45% emission ofCO2, N2 and other gases)

Conversion efficiency 90% (10% for evaporation)

Equivalent fuel energy saved

through SWHS kg

15,152.00 21000000/(2800*0.55*0.9)

Cost saved / year through fuelRs.

30303.00 15,152.00 * Rs.2.00

Cost saved in fuel Inflation /year say @ 10% Rs.

3030.00

Cost saved in maintenancefuel cost inflation/ year say@ 10% Rs.

0.00

Total savings / year Rs. 33,333.00



Table: 2.2 Payback calculations with FP-SWHS (Source: M/s Tata

BP Solar India Limited, Bangalore)

Estimated project cost (for 2000 liters FP-SWHS) - Rs.3,75,000.00

(@ Rs.187.5/- per liter )

Initial Investment

(Rs.)

Savings

(Rs.)

Balance at

year end (Rs.)

Yr.

No.

3,75,000.00 33,333.00 3,41,667.00 1

3,41,667.00 36,666.00 3,05,000.00 2

3,05,000.00 40,332.00 2,64,667.00 3

2,64,667.00 44,365.00 2,20,302.00 4

2,20,302.00 48,801.00 1,71,496.00 5

1,71,496.00 53,681.00 1,17,815.00 6

1,17,815.00 59,049.00 58,766.00 7

58,766.00 64,957.00 -(6,191.00) 8

The first common term is simple payback, which expresses the

number of years the investor has to wait before investment is paid

back out of fuel savings.

Here, the pay back period of FPC system is 7 years to 8 years.

2.6.1.ii Disadvantages

We are familiar with the flat-plate solar hot water systems seen

on roofs, collecting the radiant heat from the sun to heat the water. As

collection plates are flat, they have some limitations. They can only

operate at maximum efficiency when the sun is directly overhead at

midday. At other times, the sun rays that are striking the collector at

varying angles reduce efficiency.



No sun tracking is possible due to flat surface collectors and the

maximum heat absorption is possible only at 12 noon. Further, each

FP panel weighs around 50 kg. Therefore, a 16 panel flat plate solar

water heating system alone weighs over 800 kg and weighs 2000-plus

kg load on a roof with water tank, which requires expensive

modification to bear around 3 tons weight. The hardness of water

should also be very less. If the hardness of water is more, then the

copper tubes will be choked due to scales that are very difficult to

remove.

These problems can be overcome through Evacuated Tube Solar

Hot Water Systems, as the collector consists of a series of tubes and

the sun rays are perpendicular to the tubes for most of the day,

allowing the system to operate at high efficiency for much longer than

flat-plate units.

Another advantage of the evacuated tube technology is that the

weight problems caused by standard flat plate systems are eliminated.

And the evacuated borosilicate tubes can work efficiently up to 600

ppm of water hardness [8].

The scales formed in the tubes can easily be removed due to

comparatively larger inner diameter of the tube. In ETC, circular glass

tubes allow auto sun tracking and ensure maximum heat absorption

through out the day.



2.6.2 Evacuated Tube Collector based SWHS [9]

In order to reduce heat loss within the frame by convection, the

air can be pumped out of the collector tubes. Such collectors then can

be called as evacuated-tube collectors. They must be re-evacuated

once every one to three years.

Evacuated tube solar collectors are very efficient and can

achieve very high temperatures. They are well-suited to commercial

and industrial heating applications and can be an effective alternative

to flat-plate collectors for industrial purposes; especially in areas

where it is often cloudy. An evacuated-tube collector contains several

rows of glass tubes connected to a header pipe. Each tube has the air

removed from it to eliminate heat loss through convection and

radiation.

Fig. 2.3 Evacuated Tube Solar Collector (ETC)

Fig. 2.3 is a snapshot taken during demonstration of ETC

during Technology Up-gradation Programme organized at Silk



Conditioning and Testing House (SCTH), Central Silk Technological

Research Institute (CSTRI), Central Silk Board (CSB), Dharmavaram.

2.6.2.i Types of Evacuated Tube Collectors [9]

There are two main types of evacuated tube collectors: i) Direct

Flow Evacuated Tube Collectors (ETC) and ii) Evacuated Tube Heat

Pipe (ETHP) collectors.

2.6.2.i.1 Direct-flow evacuated-tube collectors [9]

A direct flow evacuated tube collector consists of a glass tube,

with a flat or curved aluminum fin attached to a metal or glass pipe.

The fin is covered with a selective coating that transfers heat to the

fluid that is circulating through the pipes, one for inlet fluid and the

other for outlet fluid. In this type of vacuum collector, the absorber

strip is located in an evacuated and pressure proof glass tube. The

heat transfer fluid flows through the absorber directly in a U-tube or

in countercurrent in a tube-in-tube system. Several single tubes,

serially interconnected, or tubes connected to each other via manifold,

make up the solar collector.

2.6.2.i.1.a Cost of ETC-SWHS

ETC-SWHS of 2000 liters capacity, with 4 set collectors (1 set =

60 to 76 tubes) of 3-layer tubes, to produce 60°C to 80°C, from

reputed companies costs around Rs.3,00,000.00 to Rs.4,40,000.00

@ Rs.150.00 to Rs.220.00 per liter (which includes tank cost, freight,



installation and taxes). Nevertheless, the plumbing charges are extra

that may vary 4% to 6% of the total cost.

The pay back period with ETC system could be 6 to 7 years.

2.6.2.i.1.b Requirement of Roof Area and Tank Height

For every 500 liters of ETC–SWHS, 3.5 m X 3.5 m shadow free

area is required. The system height from the roof top is 2.5 m and

minimum height of the over head tank from roof top should be 3 m.

2.6.2.ii.1 Evacuated Tube Heat Pipe Collectors

The ETHP based collectors do not heat the water directly within

the vacuum tubes. Instead, a sealed copper ‘heat pipe’ transfers the

heat via convection of its internal heat transfer fluid to a ‘hot bulb’

that indirectly heats a copper manifold within the header. The heat

pipes are inserted into curved absorbers forming an assembly which

in inserted into the glass tubes (Fig. 2.4). The tubes are made of

borosilicate glass, which is strong and has a high transmittance for

solar irradiation [10].

Heat pipes in the collector are inorganic, nontoxic heat transfer

compound and have continuous operating life of more than 1, 10,000

hours [10]. The heat pipe is hollow and the space inside is also

evacuated. The heat pipe contains a small quantity of liquid, such as

alcohol or purified water plus special additives. When sunlight falls on

the surface of the absorber, the liquid in the heat tube quickly turns

to hot vapor and rises to the top of the pipe [9].



Fig. 2.4 Header pipe inserted in glass tube [10]

Glass evacuated tubes are the key component of the Evacuated

Tube Heat Pipe (ETHP) solar collectors. Each evacuated tube consists

of two glass tubes (Fig. 2.5). The outer tube is made of extremely

strong transparent borosilicate glass that is able to resist impact from

hail up to 38 mm in diameter [11].

Fig. 2.5 ETHP Glass Tube [12] Fig. 2.6 Array of ETHP solarcollectors [12]

Interestingly, the total weight of 20 Vacuum Tube Collectors

(say 1 set) would be 55 kg to 61 kg. Generally, the diameter of each

vacuum tube is 47 mm. The panel area of a 20 tube collectors would

be 2.25 m2 with an absorber or aperture area of 2.20 m2. Normally,

the angle of inclination is 150 to 900 [10].



In good conditions it will take less than 5 minutes for the tip of

the heat pipe to get too hot to hold. The tube will continue to provide

heat even after the sun has set [10]. Evacuated tubes offer the

advantage that they work efficiently with high absorber temperatures

and with low radiation. Higher temperatures also may be obtained for

applications such as hot water heating, steam production, and air

conditioning [13].

The ETHP – SWHS can generate hot water even up to 95°C.

For example, if the entrepreneur desires to have hot water at

95°C, it may be very difficult to attain it with FP-SWHS, but it can be

attained through evacuated tube heat pipe collectors (ETHP).

Fig. 2.7 ETHP Vs Flat-plate collector efficiency diagram [12]

The efficiency diagram (Fig.2.7) depicted above illustrates the

effectiveness of both flat-plate and evacuated tube hot plate collectors.

The figure illustrates that at lower temperatures (40°C), the efficiency

of both flat-plate collectors and Evacuated Tube Heat Pipe collectors is

same; whereas at high temperatures (above 90°C) ETHP collectors

perform effectively.

ETHP v/s Flat Plate Collector

00.10.20.30.40.50.60.70.8

40 50 60 70 80 90 100 110 120 130

Heating Fluid Temperature

Colle

ctor

Effi

cienc

y

Flat Plate CollectorETHP Collector



2.6.2.ii.1.a Cost of ETHP-SWHS

Assumptions: While solar energy is available for 10 hours a day, 300

days a year and 65 days in a year are considered as cloudy days.

We can expect shorter paybacks in areas with higher energy

costs. After the payback period, we accrue the savings over the life of

the system, which ranges from 15 years to 25 years or even more,

depending on the system and how well it is maintained.

ETHP based SWHS of 2000 liters capacity having 13 sets (1 set

=20 ETHP tubes), which produces 90°C hot water costs approximately

Rs.11,00,000.00 @ Rs.550.00 per liter. Tank (to store hot water) and

pump (to pump the hot water from solar tank to the boiler) costs

would be extra. The tank of 2000 liters capacity costs approximately

Rs.1,20,000.00 and the hot water pump of 0.5 HP costs around

Rs.10,000.00. The freight and taxes may be around 4% and plumbing

charges vary from 4% to 6% of the total cost.

The payback period with ETHP system would be 4 to 5 years.

(Courtesy: M/s Mamata Energy Private Limited, Ahmadabad, Gujarat).

2.6.2.ii.1.b Advantages of ETHP System [14]

Solar collectors can often be used in subzero temperatures

without the system sustaining damage. Flat plate systems often

require expensive and complicated "antifreeze" systems to be installed.

Evacuated tubes are strong, long lasting, inexpensive and easy to

replace. Their maintenance cost is quite negligible.



If a flat plate collector panel is damaged the whole panel must

be replaced. Due to the high efficiency absorption of solar radiation

even during overcast conditions, combined with excellent insulation

properties of the solar tube, solar tube collectors can heat water all

year round.

Due to various advantages of evacuated tube collector over flat

plate collectors, a smaller collector can be used to provide the same

heating performance. When averaged over an entire year, evacuated

tube collector heat output per net m2 of absorber area, is much

greater than a flat plate collector. It is also very easy to install.

As per the list of Ministry of New and Renewable Energy, there

are two - ETHP-SWHS, seventy seven - ETC-SWHS and sixty three -

FP-SWHS manufacturers available in India, as approved by Bureau of

Indian Standards (BIS) [6].

2.7 SOLAR HOT AIR GENERATING SYSTEM

Apart from hot water requirement, it is also very much

essential to generate hot air for various applications like silk cocoon

stifling, silk yarn drying on reeling/re-reeling machines etc., which

are discussed in detail in Chapter 3. The conventional hot air drying

methods burden the entrepreneurs. This recurring financial burden

can be significantly minimized through free solar energy.

We can achieve the hot air of ~85°C temperature, through

Evacuated Tube Heat Pipe based Solar Hot Air Generating System

(ETHP-SHAGS). This is 74% of the maximum temperature i.e. 115°C



that is required in conventional method of electrical hot air stifling.

Therefore, the silk industry can make use of the common solar energy

systems with electronic temperature controllers to minimize the

recurring expenditures on electricity and firewood. As SHAGS can

generate ~85°C hot air, it is easy to raise another ~30°C through

electrical heaters, which is discussed in Chapter 3.

Generating hot air from the sun's energy is the most efficient,

cost-effective way of transforming solar energy to domestic and

industrial energy use. The collectors which are used for generating

hot air are called “Solar Forced Air Heaters” because cool air is forced

by a fan through a specially designed solar heating panel that

absorbs heat energy generated by the sun. The solar energy for heat

conversion is instant and incessant as long as the sun shines,

including light cloudy days [15].

Drying is the removal of moisture from a product until its

moisture content is low for safe storage. The method of renewable

energy based drying is not a new concept, but the place of application

may be new. The process involves vaporization of water in the product

and carrying away the water vapor mixed with drying air. The factors

that affect the rate of removal of moisture from the product are

temperature, humidity and flow rate of air. Solar dryers are classified

as direct solar dryers, indirect solar dryers and mixed mode solar

dryers [16].

Direct solar dryers consist of an insulated chamber with a

transparent cover, and appropriately placed openings to facilitate



airflow. Products to be dried are spread in a thin layer on wire mesh

trays and placed inside the chamber. In indirect solar dryers,

products are not exposed to direct sun, but hot air from a solar air

heater is passed through the drying chamber containing the products.

Airflow can be due to natural convection or forced circulation using

fans or blowers [17].

Indirect solar dryers are particularly useful in drying certain

high value products that are sensitive (like cocoons) to direct solar

radiation. In mixed mode dryers, where the features of both direct and

indirect solar dryers are combined, hot air from solar collectors is

passed through the product in a chamber with transparent cover and

absorber walls. There are many variations among the dryer designs.

Some solar dryers have heat storage elements to extend the drying

time into night periods [17].

In hybrid dryers, solar air heaters are supplemented with air

heated by a furnace operated with kerosene, Liquefied Petroleum Gas

(LPG), or biomass; therefore, drying can be continued over night or in

rainy seasons, resulting in considerably shorter drying times.

Successful drying depends on enough heat to draw out

moisture, dry air to absorb the released moisture; and adequate air

circulation to carry off the moisture. When drying cocoons, the key is

to remove moisture as quickly as possible at a temperature that does

not seriously affect the texture and color of them.



Fig. 2.8 Solar hot air generating system with air storage tank [12]

Fig. 2.8 shows a solar hot air generating system with ETHP

solar panels and a storage tank, for storing the hot air that is

generated. Ambient air is heated by the solar collector, and the hot

air is passed through the drying chamber where products to be dried

are loaded. Airflow can be due to natural convection or forced

circulation using fans or blowers (Fig. 2.9).

Fig. 2.9 Schematic diagram of SHAGS [12]



Effective drying is accomplished with a combination of heat and

air movement. Too much heat especially early in the process will

prevent complete drying. The hot air generated through the solar-

forced air heaters can be sent directly to the product to be dried or

can be stored in a puffed storage tank for later use.

The products are spread into thin layers in several trays inside

the drying cabinet to facilitate better contact of drying air with the

product. Warm moist air from inside the drying chamber exits through

the chimney at the top, assisted by draft created in the chimney.

There are many variations among the dryer designs. Some solar

dryers have heat storage elements to extend the drying time overnight.

The hot air dryers provide hot air continuously, which can be used for

stifling the cocoons in the present 5 kW to 7 kW, 3-Phase, 440 V

electric hot air dryers, available with the reelers, so that the electrical

charges can be slashed.

Also, with the same hot air, the yarn on reeling and re-reeling

machines too can be dried effectively, so that 30% to 40% of steam

consumption can be reduced.

2.7.1 Benefits of Solar Hot Air Drying System

The use of solar hot air drying system to dry the cocoons and

yarn is viable and economical. Solar dryer system improves the quality

of the product, while reducing waste and traditional fuels. SHAGS has

very low payback and optimal performance even at low ambient

temperatures. Another advantage is, seamless integration with



existing systems i.e. it is easily attachable with present conventional

drying systems [12].

It is most suitable for hot air requirements ranging start from

30°C to 85°C. It has a long life, low maintenance. Solar dried products

reduce fuel transportation and storage costs as well as associated

problems from climatic effects. Solar dryers are a cost-effective

solution. Implementing the use of solar drying systems will result in

significant savings to the reeling entrepreneurs.

Solar hot air is ideal for drying purposes in silk and other textile

industries.

2.8 CONCLUSION

Current thermal systems are much more efficient than ever

before. Depending upon the type of the SWHS installed the output hot

water temperatures can vary from 60°C to 95°C. Though the initial

cost for procuring the SWHS is high, the returns on investment can be

achieved with in a short period by means of saving the firewood. The

pay back period depends on the SWHS system that adopted for silk

industry. We can expect shorter paybacks in areas with higher energy

costs.

Similarly, SHAGS can solve several obstacles that involved in

the silk industry. Hot air that generated through it can slash the

electrical bill and saves 30% to 40% of steam. Typically, the solar

thermal systems will reduce the firewood consumption, deforestation

and pollution.

Documents

CHAPTER – 2 Solar Thermal Energy – A Ray of Hopeshodhganga.inflibnet.ac.in/bitstream/10603/12383/8/08_chapter 2.pdf · Chapter-2 Solar Thermal Energy - A Ray of Hope 13 ... A