Renewable Energy 23 (2001) 685694www.elsevier.nl/locate/renene
Potential of solar energy utilization in thetextile industry a case study
Adel M. Abdel-Dayem a, M.A. Mohamad b,*a Mubarak City for Scientific Research, Informatics Research Institute, El-Dekheela, Alexandria, Egypt
b NRC, Solar Energy Department, Tahrir Street, Dokki, Cairo, Egypt
There is high energy consumption in the industrial sector at low-temperature levels, andsolar energy could save a considerable part of this energy. A feasibility study to obtain thepotential of solar energy utilization in the textile industry is presented. Two categories wereconsidered in this study. The first category is a preheat solar system that can feed the boilerwith hot water. This system can be efficiently utilized in this case because it can operate underdifferent conditions of flow rate and output temperature. The second category is to feed theprocess of textile dyeing that needs low temperatures (up to 85 C) directly with hot water. Inthis case, the collector area is limited by the available area in the factory. Economic comparisonbetween the two categories was provided to determine the optimal system that can be usedefficiently. The optimum design of the two systems was studied depending on the optimumcollector area and flow rate. It was found that the second system is more economic and efficientthan the first. The environmental impact of using such a system was studied for different airand water pollutants. Reduction of carbon dioxide emission was found to be the main advan-tage of using solar energy as a clean energy source. 2001 Elsevier Science Ltd. Allrights reserved.
The textile industry is a case study in which solar energy can be practically util-ized. Where lower temperatures are needed for the textile process-heat, solar energycan be efficiently used at this level. In this case a simple cheap control system isrequired to control the system operation. In addition, using the solar energy as anenergy source can save a large amount of the energy consumed in this industry.
A feasibility study was carried out for a textile factory (El-Shourbagy Textile
* Corresponding author.
0960-1481/01/$ - see front matter 2001 Elsevier Science Ltd. All rights reserved.PII: S 09 60 -1481( 00 )0 0154-3
686 A.M. Abdel-Dayem, M.A. Mohamad / Renewable Energy 23 (2001) 685694
A collector area, m2cA collector pricecf fuel price, (12 E/GJ was considered)CM price of the storage tank, E/kgc0 fixed cost of collector system, EL life-cycle savings (payback), EM mass of the storage tank, kgN lifetime of the collector, yr. (20 years was expected)OM annual charge for operation and maintenance of collector expressed
as a fraction of capital cost (=2% was assumed)qcol output energy of the collector, Jr real rate of return on alternative investments of comparable riskrf real fuel escalation ratehbackup boiler backup efficiency (75% was normally considered)
Factory, Cairo 30 N) to obtain the potential of solar energy in this field. The dyeingand drying of the textiles are the two processes that need a large amount of energyfor heating in this industry. Where the hot water at 80 C is required for the dyeingprocess, the drying process needs steam to dry the wet textile. In this process, thetextile is passed over a hot surface of a cylinder and the steam from a boiler heatsthe inside of the cylinder.
Two solar systems were considered in this study. The first is a system that canfeed the dyeing process directly with hot water and the other is a part-load systemthat can supply the boiler with hot water as a pre-heater. An economic comparisonbetween the two systems was carried out based on the solar fraction (i.e. ratio ofthe solar system output to the load) and the system efficiency.
The proposed two systems are shown in Fig. 1 and Fig. 2. The solar system in
Fig. 1. Schematic diagram of the dyeing solar system.
687A.M. Abdel-Dayem, M.A. Mohamad / Renewable Energy 23 (2001) 685694
Fig. 2. Schematic diagram of the pre-heat (part-load) solar system.
general consists of collector, storage tank, control, pipes and pump. In Fig. 2 theused steam in the drying process, which is about 50% of the total steam generated,is returned to the boiler while the total steam generated is about 20 ton/hr during10 hours a day. On the other side the contaminated water that is used in the dyeingprocesses cannot be reused.
The TRNSYS Program was used to design the two systems considered. Themeteorological data such as the solar radiation and the ambient temperature, as wellas the wind speed, were fitted from the monthly average values. The payback (life-cycle savings) and the solar fraction as well as the system efficiency were integratedalong the year. Hence, the yearly average outputs were provided for each system.
The optimal system that was considered in this study has the maximum paybackpayment during the lifetime (20 years was assumed). That means this system is moreefficient with relatively low principal cost. Some authors, as in  and , expectedthis method of optimization that is based on the life-cycle savings (paybackinvestment) of the system.
The life-cycle savings (L) are the difference between fuel savings and the cost ofthe capital, operation and maintenance (),
hbackup(r- rf)F12F1+rf1+rGNG (2)
[12(11r) - N] (3)
The second factor is the solar fraction that is defined as the ratio between
688 A.M. Abdel-Dayem, M.A. Mohamad / Renewable Energy 23 (2001) 685694
Solar fraction5System output energy
the useful output energy of the solar system, and the required load energy. The thirdeffective factor in the comparison is the system efficiency that
System efficiency5System output energy
Input solar energy ,
the ratio between the output energy of the solar system to the input solar energy tothe system.
3. Results and discussion
Both optimum collector area and flow rate of the collector was deduced for eachsystem to obtain the optimal system design. This optimization was decided basedon the life-cycle savings of the system. The optimal design for each system wasdeveloped as follows:
3.1. Dyeing solar system
The dyeing heat process in the factory needs hot water at only 80 C, but the steamis really used to heat the water to the required temperature. So, a solar system shownin Fig. 1 that can feed this process directly by hot water, with the boiler used onlyas an auxiliary of this system, was considered.
According to the system performance improvement, the collector area is the mostimportant factor that must be optimized. Moreover, the principal cost of the solarsystem is mainly dependent on the collector price. Therefore, the payback (life-cyclesavings) of the system was calculated over the lifetime (i.e. 20 years was assumedas practical) as shown in Fig. 3 for different collector areas. The optimum collectorarea at which the system has the maximum life-cycle savings was obtained fromFig. 3 and equals 2300 m2. Fortunately, the roof area required for installing thiscollector area is available in the textile factory.
Although this size area of collectors has a large initial cost (about 690,000 E) ithas maximum payback investment. At a collector area greater than the optimum one,the system output investment cannot pay back the extra in principal system cost.
The solar fraction of this system was also calculated in Fig. 3 against differentcollector areas. As expected, the solar fraction is improved with a large collectorarea, i.e. the output energy of the solar system is increased. In Fig. 3 the systemefficiency was also estimated to show the system performance according to the col-lector area. The maximum system efficiency is obtained at the collector area equalto 1600 m2, not at the optimal area (2300 m2) where the ratio between the cost ofthe useful energy to the principal cost of the system is maximized.
Furthermore, the collector flow rate is the other factor that greatly affects thecollector efficiency as well as the system efficiency. Furbo and Shah , Tolonen
689A.M. Abdel-Dayem, M.A. Mohamad / Renewable Energy 23 (2001) 685694
Fig. 3. Optimum collector area for the dyeing solar system.
and Lund , and Wuestling et al.  studied this point. They found that the opti-mum collector flow rate for the large solar systems is in between 0.0025 to 0.005kg/m2 s. In fact, the load temperature affects the collector flow rate, so this pointwas considered in this study to determine the precise optimal collector flow rate.
In Fig. 4, the life-cycle savings, solar fraction and the system efficiency were
Fig. 4. Optimum collector flow rate for the dyeing processes.
690 A.M. Abdel-Dayem, M.A. Mohamad / Renewable Energy 23 (2001) 685694
calculated against the collector flow rate at the optimal collector area (i.e. 2300 m2).The optimal collector flow rate was estimated based on the payback of the systemas before, and it was found to equal 0.004 kg/m2 s. This value is in the range thatwas indicated before by many authors . The solar fraction and the systemefficiency are also maximized at the similar point in which the system output energyis maximized.
After estimating of the collector area and flow rate, the optimal system designwas obtained because there are no other factors that can be optimized in this design.In the next section, the optimal design of the other system, the part-load system(preheat system) was studied to compare the two systems.
Referring to Fig. 4, the system efficiency and the solar fraction are not affectedgreatly by collector flow rate. This is due to the small improvement in the usefulenergy output from the solar system with variable collector flow rate. However, thelife-cycle savings are dependent only on the output energy in this case (the principalsystem cost is not changed), the optimum collector flow rate is located where themaximum system efficiency is obtained.
3.2. Preheat (part-load) system
Similar steps were developed for this system (shown in Fig. 2) to optimize thesystem design. Thus, the optimal collector area was implemented in Fig. 5 and isequal to 1200 m2. The system efficiency is maximized also at this area whereverthe solar fraction is dependent on the system output of energy. Unfortunately, thelife-cycle savings have a negative sign for all collector areas and it means that thesystem investment cannot repay the principal cost of the system during its lifetime.
The collector flow rate was also analyzed based on the life-cycle savings as
Fig. 5. Optimum collector area for the pre-heat solar system.
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presented in Fig. 6. From this figure it was found that the optimal flow rate that hasthe maximum life-cycle savings equals 0.002 kg/m2 s. It also has the maximum solarfraction and system efficiency tending to the maximum output energy of the system.This value is also near the range of the optimum collector flow rate that wasdecided before.
From the above comparison between the two systems, the dyeing system is morepractical than the part-load system as can be expected from the economic point ofview. In addition, the dyeing system is also more efficient and its solar fractionis much more than the part-load system. Therefore, the dyeing system is highlyrecommended to be installed in the textile factory to feed the dyeing processes withhot water.
The principal cost of the dyeing system is about 742,500 E and the cost of theenergy produced by this system is about 0.00031 E/kWh. Whereas the annualenergy produced is 2.719 106 kWh the average annual plant power is 755 kW. Theenvironmental impact of this system was studied in the next section to obtain thepotential of solar energy in this manner.
4. Environmental impact of the dyeing solar system
To investigate the environmental impact of utilizing solar energy the differentemissions from the solar-system manufacturing and the boiler combustion were esti-mated for the lifetime of the solar system. The air emission and the water emissionas well as the wastes were calculated for the solar system and for the boiler operationto compare them from the environmental point of view.
In this study only a limited selection of air and water pollutants, and some waste
Fig. 6. Optimum collector flow rate for the pre-heat solar system.
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categories which are responsible for the most important environmental problems(greenhouse effects, acid rain, summer smog, toxicological effects, pollution of sur-face water and long term risks of land filled waste), are elaborated and discussed.The environmental interventions are expressed in physical units of the emitted sub-stances as, e.g. kg of CO2, CH4, SOx, NOx, etc.
Mazzarella and Menard , and Frischknecht et al.  estimated different emis-sions for each solar system element. The quantity of this emission depends on theelement size of the collector and the storage or depends on the required energy, suchas the pumps and the boiler. Then, the different pollutants mass was calculated forboth the solar system and the boiler, as shown in Figs 710.
As can be seen in Fig. 7 there is a big difference in CO2 emission between the solarsystem and the boiler. The high reduction in CO2 pollution is the main advantage ofusing the solar fuel. This benefit is really approved when it is considered that CO2is the most dangerous pollutant for the destruction of the environment, and thereduction of this emission from the industry costs much money. The oil boiler alsohas more other emissions of air and water than in the case of the solar system, andis presented in Fig. 8 and Fig. 9.
The negative environmental impacts of solar energy systems include land displace-ment, and possible air and water pollution resulting from manufacturing, normalemergency operations, and demolition of the solar system. Land use does not becomea problem where collectors are mounted on the roof.
From the above results, it can be said that the environmental impact is an importantfactor in the decision to use solar energy that is yet more expensive than conventionalfuel. The reality is the potential for solar energy to protect the environment fromdestructive emissions.
Fig. 7. CO2 emissions for the solar system and for the boiler.
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Fig. 8. Other air-emissions for the solar system and for the boiler.
Fig. 9. Water-borne emissions for the solar system and for the boiler.
A feasibility study of using solar energy in the textile industry as a case studywas carried out in this work. The optimal solar system that can feed the dyeing
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Fig. 10. Waste emissions for the solar system and for the boiler.
processes with hot water was obtained from the economic point of view. This systemis more economic than the system that can be used as a preheat system for theboiler. The environmental study explained that the solar system is friendlier to theenvironment than the conventional fuels for different air and water emissions as wellas waste emissions. The reduction of CO2 pollution is the main advantage of utilizingsolar energy.
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