SOLAR ENERGY: production of electricity
Heba Khalid Alzawai 12J161690046
Bashayar Talib Al Wahaibi PT12S168281
Rima said altobi. 22S14179
Sharouq Anatar Al-Abri 22s14144
I hereby declare that the thesis entitled “Solar Energy: production of Electricity” submitted by me, for the award of the degree of diploma in chemical engineering to the Higher College of Technology is a record of work carried out by me under the supervision of Mr. Rajeev Gupta.
I further declare that the work reported in this thesis has not been submitted and will not be submitted, either in part or full, for the award of any other degree or diploma in this institute nor any other institute.
The world is under huge demand for alternative sources of energy as we are becoming more aware of the repercussions of relying solely on fossil fuels as well as how non-renewable sources of energy impact our environment as its pollutant gases are threatening our ozone layer and causing drastic changes to global climate. Thus, it is substantial to ensure that we have developed and established technologies which help us exploit renewable sources of energy. Most importantly, solar energy as it is a hugely abundant and available source of energy.
The aim of our project is to make use of the abundant energy given from the sun and capturing that energy into useful electric power. There are various ways, techniques and devices into which we can convert the solar energy into useful electricity. However we have decided to focus our thesis on Solar Power Tower and how it utilizes the suns energy and process it and produce electricity.
First of all we would like to thank Allah for all the blessings he has bestowed upon us. We would also like to utter our sincere gratitude to Mr. Samir Al-Azri, Head of the Engineering Department and Mr. Ashraf Pasha, Head of Section, Mechanical and Industrial Engineering, for permitting us to do this project.
We would like to express our heartfelt gratitude to our Supervisor Mr. Rajeev Gupta for his patience, enthusiasm, encouragement and useful feedbacks. Lastly, we would like to thank our parents and friends who have supported us along the way and motivated us.
Date: Signature of the candidate:
LIST OF FIGURES
LIST OF TABLES
1.1 First Utilization of the Sun’s Energy
1.2 Further Development of Solar energy
2.1 Importance of Solar Energy
2.2 Harnessing the Suns Energy
2.3Modern Technology and development of solar devices
3. Applications of Solar energy
3.1 Solar Water Heating
3.2 Solar Heating of Buildings
3.3 Solar Distillation
3.4 Solar Pumping
3.5 Solar Drying of Agricultural and Animal products
3.6 Solar Furnaces
3.7 Solar Cooking
3.8 Solar Electrical Power Generation
3.9 Solar Thermal Power Production
3.10 Solar Green House
4. Pros and Cons of Solar Energy
4.1 Advantages of Solar Energy
4.2 Disadvantages of Solar Energy
5. Solar Collectors
5.1 Flat Plate Collectors
5.2 Batch Collectors
5.2.1 Evacuated Tube Solar Collector
5.2.2 The Vacuum Collector
126.96.36.199 Heat Pipe Collector
188.8.131.52 U-Pipe Collector
6. Solar Power Tower
6.3 The process of Solar Power Tower
6.4 Solar One: The First Generation of Solar Power Tower Plant
6.5 Solar Two: The Next Generation of Solar Power Tower Plant
6.6 The Design and Construction of Solar Two Power Plant
6.7 Advantages of Using Molten Salt
6.8 Metal Corrosion in the Molten Salt Environment
7. Conclusions and Recommendations for Future Work
7.2 Recommendations for Future Work
List of Figures
Figure Title Page.no
3.1 Solar Water Heating 14
3.2 Solar Heating of Buildings 15
3.3 Solar Distillation 16
3.4 Solar Pumping 17
3.5 Solar Drying of Agricultural Products 18
3.6 Solar Furnace 19
3.7 Solar Cooking Box 20
3.8 Solar Electric Power Generation Plant 22
3.9 Solar Thermal Power Production Plant. 23
3.10 Green House 24
5.2.1 Heat Pipe 29
5.2.2 U-Pipe 30
6.2 Solar Power Tower Plant 32
6.4 Solar One 34
6.5 Solar Two 35
1.1The first Utilization of Solar Energy:
The first time the sun has been utilized for energy and heat was in 400 BC. The Greeks buildings and houses were designed and orientated in a way to obscure the hot rays during the summer and utilize their heat during winter. Then the Romans continued on with making use of the sun’s energy by creating window glass through which the sun’s radiation enters, trapping solar heat. in order to ensure that every house had so much access to the sun the Romans put the sun in their legal system.
1.2The Further Development of Solar energy devices:
The Satellite industry has contributed massively to the further development of the solar energy . Solar cells were expensive and pretty much useless until satellites came. Because it is impractical to tether satellites it became necessary to develop solar energy at any cost that would power these satellites. This created a sustainable market for solar power, the first of its kind.
2.1 Importance of Solar Energy
Today, in the modern fast paced world we live in relying wholly on dwindling fossil fuels became a more threatening way to generate electricity. As we are now more conscious and aware of its negative effects on our environment and atmosphere. Therefore, our need for alternative clean and safe energy sources has amplified.
utilization of solar energy is not a new thing. solar energy has been utilized in so many different ways in the past. However, it has been made easier and more efficient by today’s modern technology. The industry has shown an exponential and continuous development of solar devices and cells. The significance of solar energy lies in its non-pollutant nature and inexhaustibility as it contains neither carbon nor bad chemicals that could potentially affect the environment . In addition, solar energy can be harnessed domestically as it is a safe and clean source of energy. As if that weren’t enough utilization of solar energy is more economical than fossil fuels knowing that after installing the solar panels once, they will be working for many years as its lifespan is as long as 25 years. Besides this, they would need less money than fossil fuels as they do not requires many transformations before use.
Sunlight is free, and is constant. Energy independence has become a national goal it is important to tap our other energy resources rather than rely on the fuel supplies and political alliances that are very uncertain and unpredictable. From the history of solar energy, and the present developments, having your own solar power is very attainable for everyday life. Furthermore, solar energy could be used to a much larger scale; to supply public buildings or even common objects used daily.
2.2 Harnessing Solar Energy
More people are working on improving and developing the utilization of active solar power. Although most may not realize, solar energy has already woven itself pretty deep into human life. Solar energy is applied in calculators, flashlights, and other small items used daily by almost everyone. Now, the main problem is to find a way to collect enough solar energy to help power whole cities and towns. There have been many suggested solutions , although they may not be the best.
2.3 Modern Technology In solar Energy Production
Therefore, to expand the popularity of utilizing solar energy and make the use of solar power easier for all, mirrors should be placed around solar collecting objects . In order to improve and develop solar energy first we will have to develop the technology used to harness that energy and also look for alternative materials in which the solar panels are made of . To achieve that, every country should assign a large budget to this field of research to allow the creation of research laboratories and involve a large number of scientists in this project.
This way, the performance of solar cells could be improved and their life expectancy could be increased . Besides photovoltaic cells and solar panels, they might even find new ways of converting sun’s radiation into useful electricity. Additionally, the solar panels elevated price being largely due to a need of high quality material to construct them, another major objective of these studies should be to find other materials from which those panels may be made. Thereby, it should make these solar panels less costly and affordable for most people.
Applications of Solar Energy
Solar energy can utilized in a numeral ways to produce electricity, heat water, heat buildings or even to distill water. Its uses branch from domestic to higher scale utilization in factories and industrial sites.
These are the types of uses that can be applied to solar energy:
3.1 Solar heating of :
A solar water heating unit consists of a dark flat plate metal collector with an associated metal tubing facing the direction of the sun. The plate collector has a transparent glass cover above and a layer of thermal insulation beneath it.
3.2 Solar heating (building)
-solar energy can be used for space heating of buildings in many ways including:
(a) Solar radiation is collected by some element in the building itself.
(b) To heat water or air separate solar collectors can be used. Storage devices help to accumulate the collected energy for use at night and during inclement days.
Solar distillation uses abundant sunlight to convert saline water into potable distilled water. In this method, solar radiation is admitted through a transparent air tight glass cover into a shallow blackened basin containing saline water.
Solar radiation passes through the covers and is absorbed and converted into heat in the blackened surface which then causes the water to evaporate from the brine (impure saline water). As a result of the condensed vapors purified water is formed in the cool interior of the roof.
The condensed water flows down the sloping roof and is collected in the troughs placed at the bottom and from there into a water storage tank to supply potable distilled water.
In solar pumping, solar radiation is used to generate energy which is utilized for pumping water for irrigation purposes.
3.5 Solar Drying of Agricultural and Animal Products:
Agricultural products are dried in a simple cabinet dryer which consists of a box insulated at the base, painted black on the inner side and covered with an inclined transparent sheet of glass.
At the base and top of the sides ventilation holes are provided to ease the flow of air over the drying material which is placed on perforated trays inside the cabinet. These perforated trays are carefully designed to provide controlled exposure to solar radiations.
3.6 Solar Furnaces:
A High temperature in solar furnaces is achieved by concentrating the solar radiations onto a specimen using heliostats arranged on a sloping surface.
Heating can be accomplished without any contamination and temperature can be easily controlled by changing the position of the material in focus. The Solar furnace can also be used for the production of nitric acid and fertilizers from the air.
3.7 Solar Cooking:
A simple solar cooker is the flat plate box type solar cooker.
It consists of a well-insulated metal or wooden box which is blackened from the inner side. The solar radiations entering the box are of short wavelength. Heat loss is minimized by the re radiation from the blackened interior to outside of higher wavelength radiations which cannot pass through the glass covers. This is a result of the minimization of the box through the two glass covers.
The heat loss due to convection is minimized by making the box airtight. When placed in sunlight, the solar rays penetrate the glass covers and are absorbed by the blackened surface thereby resulting in an increase in temperature inside the box. Cooking pots blackened from outside are placed in the solar box.
The solar cooker requires neither fuel nor attention while cooking food and there is no pollution, no charring or overflowing of food and the most important advantage is that nutritional value of the cooked food is very high as the vitamins and natural tastes of the food are not destroyed.
Maintenance cost of the solar cooker is negligible. The main disadvantage of the solar cooker is that the food cannot be cooked at night, during cloudy days or at short notice. Cooking takes relatively more time.
3.8 Solar Electric Power Generation:
Electric energy or electricity can be produced directly from solar energy by means of photovoltaic cells. The photovoltaic cell is an energy conversion device which is used to convert photons of sunlight directly into electricity.
It is made of semiconductors which absorb the photons received from the sun, creating free electrons with high energies.
These high energy free electrons are induced by an electric field, to flow out of the semiconductor to do useful work.
3.9 Solar Thermal Power Production:
Solar thermal power production involves the conversion of solar energy into electricity through thermal energy. In this procedure, solar energy is utilized to heat up a working fluid, gas, water or any other volatile liquid. This heat energy is then converted into mechanical energy turbine. Then, electrical energy is generated by converting the mechanical energy to electrical energy through the conventional generator coupled to a turbine.
3.10 Solar Green Houses:
A green house is a structure covered with transparent material (glass or plastic) that acts as a solar collector and utilizes solar radiant energy to grow plants.
Solar radiations can pass through the green house glazing but the thermal radiations emitted by the objects within the green house cannot escape through the glazed surface. As a result, the radiations get trapped within the green house and result in an increase in temperature.
4.1 Advantages of Solar Energy
1 Solar power is pollution free and its installation doesn’t emit any greenhouse gases.
2 Reduced dependence on fossil fuels.
3 Availability of the solar energy allows to utilize it at any time we want. It is also a renewable clean source of energy.
4 Return on investment unlike paying for utility bills
5 Virtually no maintenance as solar panels last over 30 years
6 Creates jobs by employing solar panel manufacturers, solar installers, etc. and in turn helps the economy
7 Excess power can be sold back to the power company
8 Ability to live grid free if all power generated provides enough for the home / building
9 Can be installed virtually anywhere; in a field to on a building
10 Use batteries to store extra power for use at night
11 Solar can be used to heat water, power homes and building, even power cars
12 safe energy source. Safer than traditional electric current
13 Efficiency is always improving so the same size solar that is available today will become more efficient tomorrow
14 Federal grants and tax incentives are available to help with initial costs
4.2 Disadvantages of Solar Energy
1 High initial costs for material and installation
2 Requires lots of space as efficiency is not 100% yet
3 Solar power is not available at night creating a need for a large battery bank
4 Devices that run on DC power directly are more expensive
5 Depending on geographical location the size of the solar panels vary for the same power generation
6 Cloudy days do not produce much energy
7 Solar panels are not being massed produced due to lack of material and technology to lower the cost enough to be more affordable
8 Solar powered cars do not have the same speeds and power as typical gas powered cars
9 Lower production in the winter months
A box, frame, or room that traps the sun’s rays to produce heat
Type of collectors
5.1 Flat-plate collectors:
In a flat plate collector the absorber plate absorbs solar radiation and then it is transferred to a fluid which circulates through the collector in tubes that are connected directly to the absorber plate.
1. Low efficiency
2. Relatively small tolerance for any changes of the Sun rays’ incidence angle (flat absorber works most efficiently with perpendicular sunlight). It is the reason why flat plate solar collector work efficiently only with favorable weather conditions. In less
Favorable circumstances (spring, autumn, winter) collectors’ efficiency drops dramatically.
5.2 Batch collectors:
5.2.1 Evacuated-tube solar collectors
It consists of parallel rows of glass tubes connected to a header pipe. Each pipe has a vacuum in it, those heat pipes help prevent heat loss caused by convention and radiation. A copper pipe is placed inside of every glass tube. They offer much higher temperatures and great efficiency, especially in less favorable weather conditions.
5.2.2 The vacuum collector is an advanced, top product of the solar technique. It is up to 30% more efficient than a flat collector with the same area of absorption, especially in spring, autumn
And winter. They are more efficient than other types of collectors as they are almost perfectly insulated, and heat cannot pass through a vacuum. As the tubes are cylindrical, they are always perpendicular to the sun reducing the amount of energy that is reflected before it hits the absorber. They are capable of achieving much higher temperatures than other solar collectors as the vacuum.
There are two main types of evacuated tube solar collectors:
184.108.40.206 “Heat pipe” collectors. It consists of copper heat pipe, to which is attached aluminum
Absorbing fin. Heat pipe and absorbing fin are placed inside of a vacuum-sealed solar tube.
The heat pipe contains a small quantity of liquid, which circulates inside the pipe. The vacuum allows the liquid to boil (turn from liquid to vapor) at much lower temperature than at normal
220.127.116.11 “U-pipe” collector consists, of a battery which is made of glass vacuum tubes, covered from the inside with an absorbing
Layer designed specially to suit the purpose of the pipe. Inside of each vacuum pipe a U-shaped copper pipe is placed. Inside the u-pipe circulates the solar liquid, transferring heat from the collector to the system.
SOLAR POWER TOWER
The largest power towers ever built are the 30 MW (Solar One and Solar Two plants). The next plants could be assumed to be scaled-up to between 30 and 400 MW.
As non-polluting energy sources become more preferable, molten-salt power towers will have features which include high value as the thermal energy storage gives the plant the benefit of being dispatch able.
A power tower plant can deliver energy during peak load times when it is more valuable which explains why the value of power is worth more.
Unfortunately the negatives of this technology are the high water usage as well as large land usage.
6.2 History of Solar Power Tower
Solar technology has been around since centuries ago. Its history started from the 7th Century B.C. to today. Utilization of solar energy started out by concentrating the sun’s heat with glass and mirrors to light fires. Now, we have far more improved and developed technologies everything from solar-powered buildings to solar powered vehicles. Solar One, which operated from 1982 to 1988, was the world’s largest power tower plant. It proved that large-scale power production with power towers was possible. During the operation of Solar One, research began on the more advanced molten-salt power tower design described. This development culminated in the Solar Two project. Solar Two, which is currently going through its startup phase, will generate (in addition to electric power) information on the design, performance, operation and maintenance of molten-salt power towers.
6.3 The Processing: Solar Power Tower
Solar power towers generate electric power from sunlight by
Focusing concentrated solar radiation on a tower-mounted heat exchanger (receiver).
1) It uses an array of flat, moveable mirrors (called heliostats) to
Focus the sun’s rays on the collector tower.
2) The high energy of concentrated sunlight is transferred to a substance which stores the heat.
3) Liquid sodium is one of the latest heat transfer material that has been successfully demonstrated.
4) Sodium is used as it is a metal with a high heat capacity, which is capable of allowing that energy to be stored and drawn off throughout the evening.
5) Stored energy can be used to boil water for use in steam turbines.
6.4 Solar One – The First Generation of Power Tower Plant
Solar One was the world’s largest power tower plant, which operated from 1982 to 1988. The Solar One thermal storage system operates by storing heat which is generated from steam by using solar energy in a tank which is filled with rocks and sand and using oil as the heat-transfer fluid.
The Solar One thermal storage system increases the power generation capability of the plant at night and provided heat for generating low-grade steam for keeping parts of the plant warm during off-hours and for morning startup.
The main cons for solar one were that it was complex to operate and thermodynamically inefficient. Solar One also showed the disadvantages of a water/steam system, such as the intermittent operation of the turbine due to cloud transience and lack of effective thermal storage.
6.5 Solar Two – The Next Generation Solar Power Tower
The solar two project was an expansion of the solar one project with added improvements such as increasing the efficiency and reducing the risks technically and economically. These improvements were made by adding nitrate salt receiver, salt storage system, salt steam generator, and a new master control system to the existing Solar One heliostat field, receiver tower, turbine-generator, and balance-of-plant. The risks were reduced as the nitrate salt receiver’s technical characteristics were authenticated along with the technology system. In addition more heliostats were added to the collector field which in turn increased the reflective area making the morning start time shorter and giving more energy to the thermal storage system.
6.6 Design and Construction of the Solar Two Power Tower
The Solar Two power tower is composed of a series of panels, each made of thin walled, stainless steel tubes. Molten salt flows through the stainless steel tubes in a sinuous path. The panels form a shell around the piping, structural supports, and control equipment. For high temperature resistance and high absorbance of the incident light a black paint which is robust, is used to coat the external surfaces of the tubes. The receiver design has been optimized to absorb a maximum amount of solar energy while also reducing the heat losses due to convection and radiation.
To rapidly change the temperature in the receiver without being damaged, the construction has been designed to include non-contact measurement devices laser welding, tube nozzle header connections as well as a tube clip design which makes the tube expansion and contraction easier.
The Salt Mixture
The salt storage medium is primarily made up of a mixture of 60 percent sodium nitrate and 40 percent potassium nitrate. The melting point for this salt is 220ºC and it is maintained in a molten state of 290ºC in the cold storage tank. It then travels through the receiver where it is heated to 565ºC and then on to a hot tank for storage.
Hot salt is then pumped to a steam generating system when power is required from the plant. The Rankin-cycle turbine is generated by the superheated steam which is produced from the hot salts. After coming from the steam generator, the salt is returned to the cold tank where it is stored and eventually reheated in the receiver.
6.7 Advantages of Using Molten Salt
Molten salt is used in solar power tower systems because it is liquid at atmosphere pressure, it provides an efficient, low-cost medium in which to store thermal energy, its operating temperatures are compatible with high-pressure and high-temperature steam turbines, and it is non-flammable and nontoxic. In addition, molten salt is used in the chemical and metals industries as a heat-transport fluid.
6.8 Molten-Salt Environment and Metal corrosion
In order for us to prevent corrosion of metal the pipes, valves and vessels for hot salt were designed and constructed from stainless steel as it has a high resistance to corrosion in the molten salt environment.
The sun’s radiation withholds an immense amount of energy that can be utilized in many ways for a number of applications. The capturing of solar energy into electricity is the most crucial and substantial way of exploiting the suns energy. As there is a growing exponential demand for safer and more environmentally friendly sources of energy.
Throughout the years scientists, engineers and experts have been designing and creating devises that meet our needs and convert solar energy into useful form. The undeniable growth and development of the production of solar plants and devices have noticeably contributed in popularizing the significance of utilizing the sun’s energy, as these devices have become more and more convenient and safer to use for domestic purposes. Thus, expanding the market and diminishing the dependency on fossil fuels.
Solar power tower has stood out amongst the crowd as it proved to be a hugely efficient and easy to operate the plant. Furthermore, it is less costly than most of the major solar plants.
7.2 Recommendations for Future Work
In the constant unstoppable development of solar energy there are also things that we shouldn’t look past. As there will always be ways we can further improve. These improvements should include:
Increasing the power-conversion efficiency
2. Reducing the amount of material needed per cell. Thinner, more flexible films and substrates could reduce cell weight and cost for photovoltaic cells.
3. Reducing the complexity and cost of manufacturing of solar plants.