SOLAR HYBRID CHIMNEY A MAJOR PROJECT REPORT Submitted By Hitender Singh Pawan Kumar Ashutosh Sharna Inderjeet Singh In partial fulfillment fulfillment for the award award of the degree Of
Bachelors In Mechanical Engg. M. I. E. T. Kurukshetra
KURUKSHETRA UNIVERSITY: KURUKSHETRA
Session: May/ June- 2012
ACKNOWLEDGEMENT It gives us a great pleasure to express our deep sense of gratitude and indebtedness to our guide Mr. Jashandeep Singh (Lect M.E. Deptt.) for his valuable support and encouraging mentality
throughout the project. We are highly obliged to him for providing us this opportunity to carry out his ideas and work during our project period and helping us to gain the successful completion of our Project. Our special thanks is going to our Parents; to Head of the Department of Mechanical Engineering of our college, Prof. Manoj Tiwari and to all of the faculties for allowing us to come here and encouraging us constantly to work hard in this project. We are immeasurably thankful to our friends which are student of M.E. For their kind, friendly behavior and support throughout our project. We express our deep gratitude to all.......... Hitender Singh Pawan Kumar Ashutosh Sharma Inderjeet Singh
MODERN INSTITUTE OF ENGG. AND TECHNOLOGY KURUKSHETRA
CERTIFICATE Certified that this project report “Solar Hybrid Chimney” is bonafide work of “Hitender Singh (3908607), Pawan Kumar (3908628), Ashutosh Sharma (3908630) & Inderjeet Singh (3908632)” , who carried out project work under my supervision. During this project they had undergone the requisite work as prescribed by KUK University, Kurukshetra.
Signature:
Signature:
Prof. Manoj Tiwari, Head Of Deptt. Mechanical Engg. M. I. E. T. Kurukshetra.
Er. Jashandeep Singh, Project Guide, Lect. Mech. Engg. M. I. E. T. Kurukshetra.
Signature: External Examiner.
ABSTRACT Solar thermal hybrid chimney is a new method for producing electric power from a solar-wind hybrid system. It combines three old and proven technologies: the chimney effect, the greenhouse effect, and the wind turbine. Energy from sunlight is converted to heat by a large solar collector. The collector is a transparent membrane suspended several meters off the ground, which can be made of glass or a strong transparent polymer. Sunlight penetrates this membrane, and the solar radiation is converted to heat upon hitting the ground. The air underneath the membrane quickly increases in temperature due to the greenhouse effect and flows towards the chimney, which, through the stack effect, becomes the lowest point of pressure in the system. This continuous airflow spins a turbine located at the base of the chimney. Inside the chimney wind turbines convert the wind’s energy into electricity. This method can also be useful during
night time. The project work requires a significant area of land. A small-scale solar updraft tower may be an attractive option for remote regions in developing countries.
CONTENTS CHAPTER 1……………………………………………………………………………1
1.1.Need Of Solar Thermal Power……………………………………………………...2 Po wer Scenario……………………………… Scenario………………………………………………………… ……………………………..3 …..3 1.2. India’s Power 1.3. Solar Energy Potential……………………………………………………………...4 1.4. Solar thermal power generation technologies……………………………………...5 1.5.Solar thermal power generation program of India………………………………….6 1.6.Opportunities For Solar Thermal Power Generation In India……………………...7 Chapter 2……………………………………………………………………………… 2……………………………………………………………………………… 8
2.1.
Introduction To Solar Hybrid Chimney………………………………………...9
2.2.
History Of Solar Hybrid Chimney…………………………………………….11
2.3.
Modern Development In Solar Hybrid Chimney……………………………..14
Chapter 3……………………………… 3…………………………………………………………… ……………………………………………...16 ………………...16
3.1. Working Principle Of Solar Hybrid Chimney……………………………………17 3.2. Main Parts Of solar Hybrid Chimney…………………………………………….19 3.2.1
The collector…………………………………………………………………..19
3.2.2. Turbines……………………………………………………………………….20 3.2.3
Chimney………………………………………………………………………21
Chapter 4. …………………………… ………………………………………………………… ……………………………………………...22 ………………...22 4.1.
Design Of Solar Hybrid Chimney……………………………………………23
4.2.
Material Used For Making Solar Hybrid Chimney………………………….26
4.2.1. Concrete……………………………………………………………………...26 4.2.2. Glass………………………………………………………………………….26 4.2.3. Stainless Steel………………………………………………………………..27 4.2.4. Black Ceramic Gravel……………………………………………………….27 Chapter 5……………………………………………………………………………28 5……………………………………………………………………………28
5.1.
The Energy Storage Inside A Solar Hybrid Chimney……………………….29
5.2.
Efficiency Of Solar Hybrid Chimney……………………………………….30
5.3.
Energy Production Costs Of A Solar Hybrid Power Plant …………………..31
Chapter 6…………………………………………………………………………....34
6.1.
Advantages Of Solar Hybrid Chimney Power Plant………………………...35
6.2.
Disadvantages Of Solar Hybrid Chimney Power Plant…………………… ..37
Chapter 7…………………………………………………………………………...38
7.1.
Alternative Concepts and Applications……………………………………..39
Conclusion………………………………………………………………………….40 References…………………………………………………………………………..41 Appendix……………………………………………………………………………42
List Of Figures Fig. No.
Name Of Figure
Page No.
1.1
Solar Radiation On India.
4
2.1
A Solar Hybrid Chimney.
10
2.2
Solar Hybrid Chimney Proposed By Cabanyes.
11
2.3
Solar Chimney Proposal Presented By Gunther.
12
2.4
Solar Chimney Futurist Representation presented By Gunther.
13
2.5
Solar Hybrid Chimney Power Plant At Manzanares.
14
3.1
Working Principle Of Solar Hybrid Chimney.
17
3.2
The Glazed Solar Collector Of Solar Hybrid Chimney.
19
3.3
Turbines For Solar Hybrid Chimney.
20
3.4
Mildura Solar Chimney.
21
4.1
Wall Thickness Of A Chimney Tube.
24
5.1
Principle Of Heat Storage.
29
5.2
Comparison Between Energy Production Costs.
31
5.3
Energy Production on Solar Chimney.
33
LIST OF SYMBOLS AND ABBREVIATIONS Abbreviations:
a) b) c) d) e) f)
STE………………………… Solar Thermal Electricity. MNRE……………………… Ministry Of New And Renewable Energy. GEF………………………… Global Environment Facility. BHEL………………………. Bharat Heavy Electricals Limited. US…………………………... United States. SCPP……………………….. Solar Chimney Power Plant.
Symbols:
a) b) c) d) e) f) g) h) i) j)
ηt ……………………….. … Thermal Efficiency. ηtur……………………………. Turbine Efficiency. ηc ……………………………... Collector Efficiency. ηtot……………………………. Total Efficiency. cp……………………… Air Heat Capacity. Hc………………………Chimney Height. g……………………….. Acceleration Due To Gravity. K……………………….. Kelvin. %............................... Percent. Dc…………………. Chimney Diameter
CHAPTER-1
1.1.
Need Of Solar Thermal Power:
The future of this earth and mankind substantially depends on our ability to slow down the population increase in the “Third World” by civilized means. The key is to increase the standard
of living, to overcome the inhumane poverty and deprivation. To achieve this traditional means will not suffice any longer as exemplified by a "paradox on”.
Those countries where agriculture provides more than 20 % of the gross national product are those also stricken by starvation! Development requires mechanization and energy. Energy consumption increases proportionally to the gross national product or prosperity while simultaneously the population growth will decrease exponentially. Many developing countries possess hardly any energy sources and their population doubles every 15 to 30 years! The results are commonly known: Civil wars and fundamentalism. If these developing countries are provided with only a humane and viable minimum of energy the global energy consumption will drastically increase! Who could supply such an enormous amount of energy without an ecological breakdown (because poor countries cannot afford environmental protection) and without Safety hazards (because they are not acquainted with the safety requirements for nuclear power plants and without a rapid depletion of natural resources at the expense of future generations? The sun! Many of these countries are lavishly provided with solar radiation in their desert areas. Energy is considered a prime agent in the generation of wealth and a significant factor
in
economic development. Limited fossil resources and environmental problems associated with them have emphasized the need for new sustainable energy supply options that use renewable energies. Solar thermal power generation systems also known as Solar Thermal Electricity (STE) generating systems are emerging renewable energy technologies and can be developed as viable option for electricity generation in future. This paper discusses the technology options, their current status and opportunities and challenges in developing solar thermal power plants in the context of India.
1.2.
India’s Power Scenario:
India’s current electricity installed capacity is 135 401.63MW. Currently there is peak power
shortage of about 10 % and overall power shortage of 7.5 %. th
The 11 plan target is to add 1,00,000 MW by 2012 and MNRE has set up target to add 14,500 MW by 2012 from new and renewable energy resources out of which 50 MW would be from solar energy. The Integrated Energy Policy of India envisages electricity generation installed capacity of 800 000 MW by 2030 and a substantial contribution would be from renewable energy. This indicates that India’s future energy requirements are going to be very high and solar
energy can be one of the efficient and eco-friendly ways to meet the same.
1.3.
Solar Energy potential:
India is located in the equatorial sun belt of the earth, thereby receiving abundant radiant energy from the sun. The India Meteorological Department maintains a nationwide network of radiation stations, which measure solar radiation, and also the daily duration of sunshine. In most parts of India, clear sunny weather is experienced 250 to 300 days a year. The annual global radiation 2
varies from 1600 to 2200 kWh/m , which is comparable with radiation received in the tropical and sub-tropical regions. The equivalent energy potential is about 6,000 million GWh of energy per year. Figure 1 shows map of India with solar radiation levels in different parts of the country. It can be observed that although the highest annual global radiation is received in Rajasthan, northern Gujarat and parts of Ladakh region, the parts of Andhra Pradesh, Maharashtra, Madhya Pradesh also receive fairly large amount of radiation as compared to many parts of the world especially Japan, Europe and the US where development and deployment of solar technologies is maximum.
Fig. 1.1. Solar Radiation On India
1.4.
Solar thermal power generation technologies:
Solar Thermal Power systems, also known as Concentrating Solar Power systems, use concentrated solar radiation as a high temperature energy source to produce electricity using thermal route. Since the average operating temperature of stationary non-concentrating collectors 0
is low (max up to 120 C) as compared to the desirable input temperatures of heat engines (above 0
300 C), the concentrating collectors are used for such applications. These technologies are appropriate for applications where direct solar radiation is high. The mechanism of conversion of solar to electricity is fundamentally similar to the traditional thermal power plants except use of solar energy as source of heat. In the basic process of conversion of solar into heat energy, an incident solar irradiance is collected and concentrated by concentrating solar collectors or mirrors, and generated heat is used to heat the thermic fluids such as heat transfer oils, air or water/steam, depending on the plant design, acts as heat carrier and/or as storage media. The hot thermic fluid is used to generated steam or hot gases, which are then used to operate a heat engine. In these systems, the efficiency of the collector reduces marginally as its operating temperature increases, whereas the efficiency of the heat engine increases with the increase in its operating temperature. Some of these technologies are as following:
Concentrating solar collectors.
Power tower system.
Parabolic dish system.
Solar hybrid chimney.
1.5.
Solar thermal power generation program of India:
In India the first Solar Thermal Power Plant of 50kW capacity has been installed by MNES following the parabolic trough collector technology (line focusing) at Gwalpahari, Gurgaon, which was commissioned in 1989 and operated till 1990, after which the plant was shut down due to lack of spares. The plant is being revived with development of components such as mirrors, tracking system etc. A Solar Thermal Power Plant of 140MW at Mathania in Rajasthan has been proposed and sanctioned by the Government in Rajasthan. The project configuration of 140MW Integrated Solar Combined Cycle Power Plant involves a 35MW solar power generating system and a 105MW conventional power component and the GEF has approved a grant of US$ 40 million for the project. The Government of Germany has agreed to provide a soft loan of DM 116.8 million and a commercial loan of DM 133.2 million for the project. In addition a commercial power plant based on Solar Chimney technology was also studied in North-Western part of Rajasthan. The project was to be implemented in five stages. st
In the 1 stage the power output shall be 1.75MW, which shall be enhanced to 35MW, 70MW, 126.3MW and 200MW in subsequent stages. The height of the solar chimney, which would initially be 300m, shall be increased gradually to 1000m. Cost of electricity through this plant is expected to be Rs. 2.25 / kWh. However, due to security and other reasons the project was dropped. BHEL limited, an Indian company in power equipments manufacturing, had built a solar dish based power plant in 1990’s as a part of research and development program of then the Ministry of Non-conventional Energy Sources. The project was partly funded by the US Government. Six dishes were used in this plant. Few states like Andhra Pradesh, Gujarat had prepared feasibility studies for solar thermal power plants in 1990’s. However, not much work was carried out later on.
1.6.
Opportunities For Solar Thermal Power Generation In India:
Solar thermal power generation can play a significant important role in meeting the demand supply gap for electricity. Three types of applications are possible 1. Rural electrification using solar dish collector te chnology. 2. Typically these dishes care of 10 to 25 kW capacity each and use striling engine for power generation. These can be developed for village level distributed generation by hybridizing them with biomass gasified for hot air generation. 3. Integration of solar thermal power plants with existing industries such as paper, dairy or sugar industry, which has cogeneration units. Many industries have steam turbine sets for cogeneration. These can be coupled with solar thermal power plants. Typically these units are of 5 to 250 MW capacities and can be coupled with solar thermal power plants. This approach will reduce the capital investment on steam turbines and associated power-house infrastructure thus reducing the cost of generation of solar electricity. 4. Integration of solar thermal power generation unit with existing coal thermal power plants. The study shows that savings of up to 24% is possible during periods of high isolation for feed 0
water heating to 241 C (4).
CHAPTER-2
2.1.
Introduction To Solar Hybrid Chimney:
A wide range of existing power technologies can make use of the solar energy reaching Earth. Basically, all those ways can be divided into two basic categories: transformed for use elsewhere or utilized directly – direct – and involving more than one transformation to reach a usable form – indirect. The Solar Chimney Power Plant (SCPP) is part of the solar thermal group of indirect
solar conversion technologies. More specifically, a natural phenomenon concerning the utilization of the thermal solar energy involves the earth surface heating and consequently the adjacent air heating by the sun light. This warm air expands causing an upward buoyancy force promoting the flow of air that composes the earth atmosphere. The amount of energy available due to the upward buoyancy force associated with the planet revolution is so vast that can generate catastrophic tropical cyclones with disastrous consequences. From another standpoint, such phenomenon can be enhanced and used in benefit of the human well-being. In this way, the SCPP is a device developed with the purpose to take advantage of such buoyancy streams converting them into electricity. For that, a greenhouse (the collector) is used to improve the air heating process, a tall tube (the chimney) promotes the connection between the warm air nearby the surface and the fresh air present in higher atmosphere layers and a system to convert the kinetic energy into electricity ( the generator-turbine system). This is a fairly simple concept. The solar chimney has a tall chimney at the center of the field, which is covered with glass. The solar heat generates hot air in the gap between the ground and the gall cover which is then passed through the central tower to its upper end due to density difference between relatively cooler air outside the upper end of the tower and hotter air inside tower. While traveling up this air drives wind turbines located inside the tower. These systems need relatively less components and were supposed to be cheaper. However, low operating efficiency, and need for a tall tower of height of the order of 1000m made this technology a challenging one. A pilot solar chimney project was installed in Spain to test the concept. This 50kW capacity plant was successfully operated between 1982 to 1989. Figure shows the picture of this plant. Recently, EnviroMission Limited, an Australian company, has started work on setting up first of its five projects based on solar chimney concept in Australia.
Fig. 2.1. A Solar Hybrid Chimney
The Luz Company which developed parabolic trough collector based solar thermal power technology went out of business in 1990’s which was a major setback for the development of solar thermal power technology.
2.2.
History Of Solar Hybrid Chimney:
One of the earliest descriptions of a solar chimney power station was written in 1903 by Isidoro Cabanyes, a Spanish artillery colonel. He made public the proposition “Proyecto de motor solar”
(solar engine project) introducing an apparatus consisting of an air heater attached to a house with a chimney. In the house interior, a kind of wind propeller was placed with the purpose of electricity production. In 1926 Prof Engineer Bernard Dubos proposed to the French Academy of Sciences the construction of a Solar Aero-Electric Power Plant in North Africa with its solar chimney on the slope of the high height mountain. The author claims that an ascending air speed of 50 m/s can be reached in the chimney, whose enormous amount of energy can be extracted by wind turbines.
Fig. 2.2. Solar Hybrid Chimney Proposed By Cabanyes.
Fig. 2.3. Solar chimney proposal presented by Gunther, 1931.
Fig. 2.4. Solar chimney futurist representation presented by Gunther, 1931.
2.3.
Modern Development In Solar Hybrid Chimney:
Detailed theoretical preliminary research and a wide range of wind tunnel experiments led to the establishment of an experimental plant with a peak output of 50 kW on a site made available by the Spanish utility Union Electrica Fenosa in Manzanares (about 150 km south of Madrid) in 1981/82, with funds provided by the German Ministry of Research and Technology (BMFT). The aim of this research project was to verify, through field measurements, the performance projected from calculations based on theory, and to examine the influence of individual components on the plant's output and efficiency under realistic engineering and meteorological conditions.
Fig. 2.5. Solar Hybrid Chimney Power Plant At Manzanares
To this end a chimney 195 m high and 10 m in diameter was built, surrounded by a collector 240m in diameter. The plant was equipped with extensive measurement data acquisition facilities. The performance of the plant was registered second by second by 180 sensors. Since the type of collector roof primarily determines a solar chimney's performance costs, different building methods and materials for the collector roof were also to be tested in Manzanares. A realistic collector roof for large-scale plants has to be built 2 to 6 meters above
ground level. For this reason the lowest realistic height for a collector roof for large-scale technical use, 2 meters, was selected for the small Manzanares plant. (For output, a roof height of 50 cm only would in fact have been ideal.) Thus only 50 kW could be achieved in Manzanares, but this realistic roof height also permitted convenient access to the turbine at the base of the chimney. This also meant that experimental planting could be carried out under the roof to investigate additional use of the collector as a greenhouse. The experimental plant in Manzanares operated for about 15,000 hours from 1982 onwards. The following tests were run in the course of the project: In 1986 the structural improvement work that made occasional operational interruptions necessary was completed. After that, from mid 1986 to early 1989 it was possible to run the plant on a regular daily basis, except for a period of four months which was set aside for special measurements and specific modifications. During this 32 month period, the plant ran, fully automatically, an average of 8.9 hours per day for a total of 8611 operating hours. One person at the most was needed for supervision. Thus there is no doubt that solar chimneys can be built, run in the long term and reliably maintained even in countries that are technologically less developed. During the 32 month period, plant reliability was over 95 %. Sporadic storm damage to the old plastic film area of the collector was repaired without switching off the plant. The 5 per cent nonoperational period was due to automatic plant switch-off at the weekend when the Spanish grid occasionally failed.
CHAPTER-3
3.1.
Working Principle Of Solar Hybrid Chimney:
Man learned to make active use of solar energy at a very early stage: greenhouses helped to grow food, chimney suction ventilated and cooled buildings and windmills ground corn and pumped water. The solar chimney's three essential elements - glass roof collector, chimney, and wind turbines have thus been familiar from time immemorial.
Fig. 3.1. Working Principle Of Solar Hybrid Chimney.
Air is heated by solar radiation under a low circular glass roof open at the periphery; this and the natural ground below it form a hot air collector. Continuous 24 hours-operations is guaranteed by placing tight water-filled tubes under the roof. The water heats up during the daytime and emits its heat at night. These tubes are filled only once, no further water is needed. In the middle of the roof is a vertical chimney with large air inlets at its base. The joint between the roof and the
chimney base is airtight. As hot air is lighter then cold air it rises up the chimney. Suction from the chimney then draws in more hot air from the collector, and cold air comes in from the outer perimeter. Thus solar radiation causes a constant up draught in the chimney. The energy this contains is converted into mechanical energy by pressure-staged wind turbines at the base of the chimney, and into electrical energy by conventional generators.
A single solar chimney with a suitably large glazed roof area and a high chimney can be designed to generate 100 to 200 MW continuously 24 h a day. Thus even a small number of solar chimneys can replace a large nuclear power station. Solar chimneys can be built now, even in less industrially developed countries. The industry already available in most countries is entirely adequate for their requirements. No investment in high-tech manufacturing plant is needed. Even in poor countries it is possible to build a large plant without high foreign currency expenditure by using their own resources and work-force; this creates large numbers of jobs and dramatically reduces the capital investment requirement and the cost of generating electricity. Solar chimneys can convert only a small proportion of the solar heat collected into electricity, and thus have a "poor efficiency level". But they make up for this disadvantage by their cheap, robust construction and low maintenance costs. Solar chimneys need large collector areas. As economically viable operation of solar electricity production plants is confined to regions with high solar radiation, this is not a fundamental disadvantage; as such regions usually have enormous deserts and unutilized areas. And so "land use" is not a particularly significant factor, although of course deserts are also complex biotopes that have to be protected.
3.2.
Main Parts Of solar Hybrid Chimney:
3.2.1. The collector:
Hot air for the solar chimney is produced by the greenhouse effect in a simple air collector consisting only of a glass or plastic film covering stretched horizontally two to six meters above the ground. The height of the covering increases adjacent to the chimney base, so that the air is diverted to vertical movement with minimum friction loss. This covering admits the short-wave solar radiation component and retains long-wave radiation from the heated ground. Thus the ground under the roof heats up and transfers its heat to the air flowing radially.
Fig. 3.2. The Glazed Collector Of Solar Hybrid Chimney.
The following points should be taken into account while making a collector:
There is no limitation for the surface area. The larger the area, the more energy generated from the chimney.
There should be slightly increasing height towards to the chimney in order to obtain minimum friction loss.
Covering materials may be different, such as; glass, plastic film or glazed collector. The most efficient one is glazed collector.
It can convert up to 70% of irratiated solar energy into heat a typical annual average is 50%.
3.2.2. Turbines:
Using turbines, mechanical output in the form of rotational energy can be derived from the air current in the chimney. Turbines in a solar chimney do not work with staged velocity like a freerunning wind energy converter, but as a cased pressure-staged wind turbo generator, in which, similarly to a hydroelectric power station, static pressure is converted to rotational energy using a cased turbine - in this application installed in a pipe. The power output of a cased pressure-staged turbine of this kind is about eight times greater than that of a speed-stepped open-air turbine of the same diameter. Air speed before and after the turbine is about same. The output achieved is proportional to the product of volume flow and the fall in pressure at the turbine. With a view to maximum energy yield the aim of the turbine regulation system is to maximize this product under all operating conditions. Blade pitch is adjusted during operation to regulate power output according to the altering airspeed and airflow. If the flat sides of the blades are perpendicular to the airflow, the turbine does not turn. If the blades are parallel to the air flow and allow the air to flow through undisturbed there is no drop in pressure at the turbine and no electricity is generated. Between these two extremes there is an optimum blade setting: the output is maximized if the pressure drop at the turbine is about two thirds of the total pressure differential available.
Fig. 3.3. Turbine For Solar Hybrid Chimney
3.2.3. Chimney:
The chimney itself is the plant's actual thermal engine. It is a pressure tube with low friction loss (like a hydroelectric pressure tube or penstock) because of its optimal surface volume ratio. The up thrust of the air heated in the collector is approximately proportional to the air temperature rise Toll in the collector and the volume, (i.e. the height (Hc) multiplied by the diameter (Dc)) of the chimney. In a large solar chimney the collector raises the temperature of the air by about 35 K. This produces an up draught velocity in the chimney of about 15m/s. It is thus possible to enter into an operating solar chimney plant for maintenance without difficulty. Chimneys 1,000 m high can be built without difficulty. The television tower in Toronto, Canada is almost 600 m high and serious plans are being made for 2,000 meter skyscrapers in earthquake-ridden Japan. But all that is needed for a solar chimney is a simple, large diameter hollow cylinder, not particularly slender, and subject to very few demands in comparison with inhabited buildings. There are many different ways of building this kind of chimney. They are best built freestanding, in reinforced concrete. But guyed tubes, their skin made of corrugated metal sheet, as well as cable-net designs with cladding or membranes are also possible. All the structural approaches are well known and have been used in cooling towers. No special development is needed.
Fig. 3.4. Mildura Solar Chimney
CHAPTER- 4
4.1.
Design Of Solar Hybrid Chimney:
Measurements taken from the experimental plant in Manzanares and solar chimney thermodynamic behavior simulation programs were used to design large plants with outputs of 200 MW and more. Detailed investigations, supported by extensive wind tunnel experiments, showed that thermodynamic calculations for collector, tower and turbine were very reliable for large plants as well. Despite considerable area and volume differences between the Manzanares pilot plant and a projected 100 MW facility, the key thermodynamic factors are of similar size in both cases. Using the temperature rise and wind speed in the collector as examples, the measured temperature rise at Manzanares was up to 17 K and the wind speed up to 12 meters per second, while the corresponding calculated figures for a 100 MW facility are 35 K and 16 meters per second. In this way the overall performance of the plant, by day and by season, given the prescribed climate and plant geometry, considering all physical phenomena including single and double glazing of the collector, ground storage, condensation effects and losses in collector, tower and turbine, can be calculated to an accuracy of ± 5%. Structural design of large plants showed that the glazed collector can be used for large plants without major modifications. This was successfully demonstrated in the Manzanares experimental plant, and thus represents a proven, robust and reasonably priced solution. The Manzanares experience also provided cost calculation data for the collector.
Reliable statically and dynamic calculation and construction for a chimney about 1,000 meters high (slenderness ratio = height: diameter < 10) is possible without difficulty today. With the support of a German and an Indian contractor especially experienced in building cooling towers and chimneys, manufacturing and erection procedures were developed for various types in concrete and steel and their costs compared. The type selected is dependent on the site. If sufficient concrete aggregate materials are available in the area and if anticipated seismic acceleration is less than g/3, then reinforced concrete tubes are the most suitable. Both conditions are fulfilled world-wide in most arid areas suitable for solar chimneys. Detailed statically/structural research showed that it is appropriate to stiffen the chimney at about four levels with cables arranged like spokes within the chimney, so that thinner walls can be used. Detailed research by the Indian contractor showed that it is possible to build such tall concrete chimneys in India, and that construction would be particularly reasonable in terms of cost.
Fig. 4.1. Wall thickness of a chimney tube 1.000 m high and 170 m in diameter and a 1.000m chimney tube under construction.
For mechanical design, it was possible to use a great deal of experience with wind power stations, cooling tower ventilation technology and the Manzanares solar chimney's years of operation. Although for plants up to approx. 100 MW one vertical axis turbine at the base of the tower is seen as the correct solution, the cost estimate was based on horizontal axis turbines arranged concentrically at the periphery of the tower, in order to be able to utilize turbines of existing sizes - particularly with regard to rotor diameter. Aerodynamic design for entrance area and turbines was achieved by means of wind tunnel airflow experiments. As already shown, there is no physical optimum for solar chimney cost calculations, even when meteorological and site conditions are precisely known. Tower and collector dimensions for a required electrical energy output can be determined only when their specific manufacturing and erection costs are known for a given site.
4.2.
Material Used For Making Solar Hybrid Chimney:
Solar chimneys are technically very similar to hydroelectric power stations so far the only really successful large scale renewable energy source: the collector roof is the equivalent of the reservoir, and the chimney of the penstock. Both power generation systems work with pressurestaged turbines, and both achieve low power production costs because of their extremely long life-span and low running costs. The collector roof and reservoir areas required are also comparable in size for the same electrical output. But the collector roof can be built in arid deserts and removed without any difficulty, whereas useful (often even populated) land is submerged under reservoirs. Solar chimneys work on dry air and can be operated without the corrosion and cavitations typically caused by water. They will soon be just as successful as hydroelectric power stations. Electricity yielded by a solar chimney is in proportion to the intensity of global solar radiation, collector area and chimney height. As the solar hybrid chimney power plant faces direct environment attacks, so its construction should be robust and stable. The following are the materials which are used for construction of various parts of solar hybrid chimney:
4.2.1. Concrete:
The chimney is basically made of reinforced concrete that can easily absorb heat which can be transformed to usable energy. In fact, the chimney acts as a thermal engine. Due to its favorable surface to volume ratio, the chimney acts like a pressure tube with low friction loss. Solar chimneys made of concrete can be built easily as you have to do is create a hollow cylinder with large diameter. It is quite simple but it is not particularly slim. In some large cities such as Toronto and Tokyo you will be able to find all buildings with solar chimneys.
4.2.2. Glass:
Solar chimneys can also be made of glass which is also known to be good heat absorbing material. Glass is expensively used in building the solar collector area of the solar chimney which is usually situated on top of the chimney or sometimes the entire shaft. There are usually three to five vertical shaft needed for the cooling and ventilation process.
4.2.3. Stainless Steel:
Chimneys made of stainless steel can also absorb heat easily. Moreover this material is perfect for enhancing the air flow inside a building or house because it is low friction material. The solar chimney is made of a minimum of three basic stuffs, one of which is the round exhaust stuff made of stainless steel. The airflow inside the building is improved when the stainless steel chimneys produces “stack ventilation”. This stack effect is necessary for the building specially
during warm days. It facilitates hot air to escape.
4.2.4. Black Ceramic Gravel:
Experts agree that black ceramic gravel is the best material to use as solar collector or a solar chimney. The optimum size of the collector for the solar chimney depends on the amount of ventilation power you would like to produce. Naturally a collector made from black ceramic gravel absorbs little heat if it is small. Keep in mind that the earth materials are good conductor of heat. When the sunlight strikes a dark object, it is turned to heat power. A solar collector made from black ceramic gravel is also used in consumption with wind at sun power plant great types of alternative energy.
CHAPTER- 5
5.1.
The Energy Storage Inside A Solar Hybrid Chimney:
Water filled black tubes are laid down side by side on the soil under the glass roof collector. They are filled with water once and remain closed thereafter, so that no evaporation can take place. The volume of water in the tubes is selected to correspond to a water layer with a depth of 5 to 20 cm depending on the desired power output characteristics.
Day
Night
Fig. 5.1. Principle of heat storage underneath the roof using water-filled black tubes.
Since the heat transfer between black tubes and water is much larger than that between the ground surface and the deeper soil layers, even at low water flow speed in the tubes, and since the heat capacity of water (4.2 kJ/kg) is much higher than that of soil (0.75 - 0.85 kJ/kg) the water inside the tubes stores a part of the solar heat and releases it during the night, when the air in the collector cools down.
5.2.
Efficiency Of Solar Hybrid Chimney:
Mullett, 1987 started the SCPP operational theoretical models development by deriving overall efficiency and relevant performance data. In his calculation, the overall efficiency is proportional the chimney height, returning about 1% for a height of 1000 m. He concluded that the solar chimney is essentially a power generator of large scale. The chimney efficiency is given by the equation as below:
ηt = gH c T 0
Here, g is the gravity [m/s], H is the chimney height [m], cp is the air heat capacity [J/kg·K] and T 0 is the ambient temperature [K]. For instance, with a chimney height of 1000 m and standard
conditions for temperature and pressure, the chimney efficiency achieves the maximal value of 3%. Considering collector efficiency (ηc) of 60 % and turbine efficiency (ηtur ) of 80 %, the total system efficiency (ηtot ) reaches 1.4%, as shown by equation:
ηtot = ηt. ηc. ηtur = 0.03 * 0.6 * 0.8 = 0.014
Based on the data from the prototype of Manzanares, (Padki & Sherif, 1989) elaborated extrapolated SCPP models for medium-to-large scale power generation. (Yan , et al., 1991) described a more comprehensive analytical model for SCPP by using practical engineering correlations obtaining equations for air velocity, airflow rate, power output, and the thermo fluid efficiency and (Padki & Sherif, 1992) also presented a mathematical model for SCPP. In the end of the 90’s, (Pasumarthi & Sherif, 1998a) built a SCPP small-scale demonstration
prototype to study the effect of various geometric parameters on the air temperature, air velocity, and power output of the solar chimney. Further studies conducted by (Pasumarthi & Sherif, 1998b) exploited the collector performance by extending the collector base and by introducing an intermediate absorber. According to them, both enhancements helped to increase the overall chimney power output.
5.3.
Energy Production Costs Of A Solar Hybrid Power Plant:
With the support of construction companies, the glass industry and turbine manufacturers a rather exact cost estimate for a 200 MW solar chimney could be compiled. We asked a big utility "Energie Baden-Württemberg" (formerly EVS/BW) to determine the energy production costs compared to coal- and combined cycle power plants based on equal and common methods.
Fig. 5.2. Comparison between the energy production costs of a solar chimney (2 solar chimneys with 200 MW each) and 400 MW coal and combined cycle power plants according to the present Business managerial calculations.
Purely under commercial aspects with a gross interest rate of about 11 % and a construction Period of 4 years during which the investment costs increase already by 30 %(!) Electricity from solar chimneys is merely 20 % more expensive than that from coal. In case of the solar chimney
the interest on the fix investment governs the price of electricity, whereas in the case of fossil fuel power plants the variable fuel costs are the deciding factor. By just reducing the interest rate to 8 % electricity from solar chimneys would become competitive today. In low-wage-countries the costs will decrease further especially those of the glass roof collector which alone amounts to 50 % of the overall costs. On the other hand there are a number of advantages: No ecological harm and no consumption of resources, not even for the construction. Solar chimneys predominantly consist of concrete and glass which are made from sand and stone plus self-generated energy. Consequently in desert areas - with inexhaustible sand and stone - solar chimneys can reproduce themselves. A truly sustainable source of energy!
Fig. 5.3. Energy production costs from solar chimneys, coal and combined cycle power plants depending on the interest rate.
The (high) investment costs are almost exclusively due to labour costs. This creates jobs, and a high net product for the country with increased tax income and reduced social costs (= human
dignity, social harmony), and in addition no costly imports of coal, oil, gas which is especially beneficial for the developing countries releasing means for their development. We have no choice but to do something for the energy consent, the environment and above all for the billions of underprivileged people in the Third World. But we should not offer them hand-outs, a multiple of which we deceitfully regain by imposing a high interest rate on their debt. Instead we should opt for global job sharing. If we buy solar energy form Third World countries, they can afford our products. A global energy market with large scale solar energy generation supplementing substantially hydropower, fossil and nuclear fuels is not an utopian dream! Therefore, now it is absolutely essential to build and operate a large solar chimney.
CHAPTER- 6
6.1.
Advantages Of Solar Hybrid Chimney Power Plant:
A single solar chimney with a suitably large glazed roof area and a high chimney can be designed to generate 100 to 200 MW continuously 24 h a day. Thus even a small number of solar chimneys can replace a large nuclear power station. Solar chimneys operate simply and have a number of other advantages:
The collector can use all solar radiation, both direct and diffused. This is crucial for tropical countries where the sky is frequently overcast. The other major large scale solarthermal power plants, parabolic through and central receiver systems, which apply concentrators and therefore can use only direct radiation, are at a disadvantage there.
Due to the heat storage system the solar chimney will operate 24h on pure solar energy. The water tubes lying under the glass roof absorb part of the radiated energy during the day and release it into the collector at night. Thus solar chimneys produce electricity at night as well.
Solar chimneys are particularly reliable and not liable to break down, in comparison with other solar generating plants. Turbines, transmission and generator - subject to a steady flow of air - are the plant's only moving parts. This simple and robust structure guarantees operation that needs little maintenance and of course no combustible fuel.
Unlike conventional power stations (and also other solar-thermal power station types), solar chimneys do not need cooling water. This is a key advantage in the many sunny countries that already have major problems with drinking water.
The building materials needed for solar chimneys, mainly concrete and glass, are available everywhere in sufficient quantities. In fact, with the energy taken from the solar chimney itself and the stone and sand available in the desert, they can be reproduced on site.
Solar chimneys can be built now, even in less industrially developed countries. The industry already available in most countries is entirely adequate for their requirements. No investment in high-tech manufacturing plant is needed.
Even in poor countries it is possible to build a large plant without high foreign currency expenditure by using their own resources and work-force; this creates large numbers of
jobs and dramatically reduces the capital investment requirement and the cost of generating electricity.
Solar chimneys can convert only a small proportion of the solar heat collected into electricity, and thus have a "poor efficiency level". But they make up for this disadvantage by their cheap, robust construction and low maintenance costs. Solar chimneys need large collector areas. As economically viable operation of solar electricity production plants is confined to regions with high solar radiation, this is not a fundamental disadvantage; as such regions usually have enormous deserts and unutilized areas. And so "land use" is not a particularly significant factor, although of course deserts are also complex biotopes that have to be protected.
6.2.
Disadvantages Of Solar Hybrid Chimney Power Plant:
Some estimates say that the cost of generating electricity from a solar chimney is 5 times more than from a gas turbine. Although fuel is not required, solar chimneys have a very high capital cost.
The structure itself is massive and requires a lot of engineering expertise and materials to construct
In nights of winter season its efficiency lowers.
CHAPTER- 7
7.1.
Alternative Concepts and Applications:
Probably (Ferreira , et al., 2008) were the first to propose a solar chimney as a device to dry agricultural products. A small scale prototype solar chimney was built, in which the air velocity, temperature and humidity parameters were monitored as a function of the solar incident radiation. Based on theoretical and experimental studies Drying tests revealed the technical feasibility of solar chimneys used as solar dryers for agricultural products. A hot airflow with a yearly average rise in temperature (compared to the ambient air temperature) of 13 ± 1 °C could be achieved allowing a drying capacity of approximately 440 kg. (Zhu , et al., 2008) proposed different heat storage styles for SCPP. The experimental studies showed that the temperature difference in the sealed water system is the largest, while the open water system has the lowest one because of the latent heat consumed by water evaporation. The study also showed that there is the temperature distribution optimization of the system if the heat loss part of the collector to be avoided. The concept for producing energy by integrating a solar collector with a mountain hollow is presented and described by (Zhou , et al. , 2009). As in a conventional SCPP, the hot air is forced by the pressure difference between it and the ambient air to move along the tilted segment and up the vertical segment of the 'chimney', driving the turbine generators to generate electricity. The author claimed that such concept provides safety and reduces a great amount of construction materials in the conventional chimney structure and the energy cost to a level less than that of a clean coal power plant. The hypothesis of combining a salinity gradient solar pond with a chimney to produce power in salt affected areas is examined by (Akbarzadeh , et al., 2009). The salinity in northern Victoria, Australia was analyzed and salinity mitigation schemes were presented. It was shown that a solar pond can be combined with a chimney integrating an air turbine for the production of power. A prototype of a solar pond of area 6 hectares and depth 3 with a 200 m tall chimney of 10 m diameter was investigated.
Conclusion The entire project about SCPP presents an outstanding technological development enlightening considerable advances in its construction, operation, including its technical economical and ecological relevant facets. In contrast with other solar facilities, SCPPs can be used above and beyond power production. Very relevant byproducts are distilled water extracted from ocean water or ground water. Under certain conditions, agribusiness may be appropriate under the solar collector. It can involve fruits and vegetables, medicinal and aromatic essential oils from herbs and flowers, seaweeds and planktons, blue-green algae, ethanol and methane, biodiesel and all manner of vegetable and plant derivatives, etc. Besides, remaining biomass is useful creating additional heat during composting. The insertion of SCPP in the power generation market requires scalability and base, shoulder and peak load electricity generation. Further developments should meet such localized requirements.
References
th
edition, ch.13 Draught
“
http://www.visionengineer.com/env/solar_flue.shtml
www.solartower.org.uk/floating-papageorgiou.php
http://www.sbp.de/de/html/projects/solar/aufwind/pages_auf/enprocos.htm
www.sciencedirect.com/science/article/pii/
www.wikipedia.com
www.howstuffworks.com
Thermal engineering” by R.K.Rajput 6
Appendix A Advantages of solar hybrid chimney, 35 Alternative concepts and applications, 39
B Black ceramic gravel, 27
C Chimney, 21 Collector, 19 Concrete, 26 Conclusion, 40
D Design of solar hybrid chimney, 23 Disadvantages of solar hybrid chimney, 37
E Efficiency, 30 Energy storage, 29 Energy production cost, 31
G Glass, 26
H History of solar hybrid chimney, 11
I India’s power scenario, 2
Introduction to hybrid chimney, 9
M Modern development in solar hybrid chimney, 14 Main parts solar hybrid chimney, 19 Materials, 26
