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  1. 1. Siddharth Wadhawan, Harshal Arekar / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 Vol. 2, Issue 5, September- October 2012, pp.2185-2190 Captive Energy Methods For Electrical Power System Siddharth Wadhawan, Harshal Arekar *Fr.Conceicao Rodrigues Institute of Technology Navi Mumbai **Fr.Conceicao Rodrigues Institute of Technology Navi MumbaiAbstract In Electric Power systems, power quality been proportional. The power sector has not seenand reliability has become one of the issues of tremendous increase as it should have seen in termsprime importance. Some of the major of its capacity. Also for the past many years there hasdisadvantages in electric power supply system are been a shortfall in the peak load demand and thethe deviations in power supply which make some demand that is met by the power sector utilities. Thisof the electronic equipment’s and domestic is shown by the figure below. All these havedevices highly sensitive to it. To avoid such eventually lead to voltage fluctuations and deviationsproblems we need to find out devices that can and other issues related to power quality.provide a backup during the time of voltage sagsand such deviations. Energy storage technologieshelp to avert such conditions.The energy storagedevices does not represent energy sources, theyprovide valuable added benefits to improvestability, power quality, and reliability of supply.Over the past few decades many new andinnovative ideas have been explored in the broadarea of energy storage.Battery technologies haveimproved significantly in order to meet thechallenges of practical electric utilities. Flywheeltechnologies are being used as an advancednonpolluting uninterruptible power supplytechnique. Superconducting energy storagesystems are still in their prototype stages butreceiving attention for utility applications.Compressed Air Energy Storage and Thermalheat storage are a few recent methods developedfor providing peak load supplies. Also there arehydrogen fuel and pump storagehydroelectricity technologies for storing energy.These technologies can also be incorporated into Figure 1. India’s peak demand gaptraditional power generating stations to increasethe overall efficiency. These energy storage Talking in terms of the future, according todevices and technologies help to store and the Five-year plans established by the government’sharness the renewable source of energy which is Planning Commission has laid out specific targets forvery essential. This paper focuses on these new generation capacity. For the 12th five-year planadvancements made and provides a composite (2012–2017), 83,000 MW of new capacity has beenpicture of costs and trends in storage targeted [ 8]. In order to achieve this target wetechnologies. require better captive energy storage systems to increase the overall generation capacity and theI. INTRODUCTION power quality. The generation of electric power is the basic These storage elements will also help to pillar for normal functioning of every modern meet the consumer’s demand for electric power society. India has experienced impressive gross which varies cyclically during day and night, as well domestic product (GDP) growth rates exceeding 7% as within the week and the seasons. Moreover the over the past few years. Although recent trends quality of an electric power supply is determined by appear to indicate an economic slowdown, long-term the available reserve capacity at the energy utility. In 7%+ GDP growth is expected to continue through at general an electrical power generating system should least 2020. To support India’s expanding economy, have 15-20% of reserve power available to meet any large-scale power capacity additions in the range of consumer demand. In case the demand is not met or 150 GW to 175 GW are projected over the next 10 there is insufficient reserve capacity to meet that years. However the rate of growth of the economy demand, a decline in voltage at the consumer side and the powetgeneration capacity of India has not will appear which would upset the normal operation 2185 | P a g e
  2. 2. Siddharth Wadhawan, Harshal Arekar / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 Vol. 2, Issue 5, September- October 2012, pp.2185-2190at the user’s end and would eventually lead to a high energy capability, roundtrip efficiency, cyclingfailure. For this reason it is essential for the normal capability, life span, and initial cost.There are afunctioning and development of each nation to have number of battery technologies underreliable national and local electric power systems considerationfor large-scale energy storage. Lead-with capacities exceeding the actual energy demand acid batteriesrepresent an established, matureby at least 15%. However, in most of the developing technology. Lead-acidbatteries can be designed fornations like India have capacities that can only just bulk energy storage or for rapid charge ormeet their energy demands, and in some cases are discharge.Lead-acid batteries still represent a low-simply inadequate as shown in fig1. This shortfall of cost option for most applications requiring largeelectrical energy often hinders the social and storage capabilities, with the low energy density andeconomic progress of a nation. limited cycle life as the chief disadvantages. Mobile Now with this growth of different industries applications are favoring sealed lead-acid batterythe mechanical and electronic loads have increased technologies for safety and ease of maintenance.tremendously. Thus the issue of quality of power Valve regulated lead-acid (VRLA) batteries havesupply has become a critical issue and has gained better cost and performance characteristics forimportance. Power system engineers facing these stationary applications. Several other batterychallenges seek solutions to allow them to operate the technologies also show promise for stationary energysystem in a more flexible, controllable manner. storage applications. All have higher energy densityGenerally when power system disturbances occur, capabilities than lead-acid batteries, but at present,synchronous capacitors which are mostly used are they are not yet cost effective for higher powernot always able to respond rapidly enough to keep applications. Leading technologies include nickel–the system stable. This is where energy storage metal hydride batteries, nickel–cadmium batteries,technology can play a very important role in and lithium-ion batteries. The last two technologiesmaintaining system reliability and power quality. The are both being pushed for electric vehicleideal solution is to have means to rapidly damp applications where high energy density can offsetoscillations, respond to sudden changes in load, higher cost to some load during transmission or distribution Due to the chemical kinetics involved,interruptions, correct load voltage profiles with rapid batteries cannot operateat high power levels for longreactive power control, and still allow the generators time periods. In addition,rapid, deep discharges mayto balance with the system load at their normal speed. lead to early replacementof the battery, since heatingThus with this paper we provide an insight into the resulting in this kind of operationreduces batterynew methods of captive energy storing. lifetime. There are also environmentalconcerns related to battery storage due to toxic gasII. EXSISTING METHODS OF ENERGY generationduring battery charge/discharge. The STORAGE disposal of hazardousmaterials presents some battery Electrical energy in a system cannot be disposal problems. The disposal problem varies withstored electrically. However, energy can be stored battery converting the ac electricityand storing itelectromagnetically, electrochemically, kinetically, B. FLYWHEEL ENERGY STORAGEor as potential energy. Each energy storage SYSTEM(FESS)technology usuallyincludes a power conversion unit A flywheel stores energy in a rotating convert the energy from one form to another. Depending on the inertia and speed of the rotating The existing methods for energy storage include mass, a given amount of kinetic energy is stored asbatteries and flywheel while, the latest technology in rotational energy. The flywheel is placed inside aincludes compressed air energy storage, super vacuum containment to eliminate friction-loss fromcapacitor energy storage and superconducting the air and suspended by bearings for a stabilemagnetic energy storage. operation. Kinetic energy is transferred in and out of the flywheel with an electrical machine that canA. BATTERY STORAGE SYSTEMS. function either as a motor or generator depending on Batteries are one of the most cost-effective the load angle (phase angle). When acting as motor,energy storagetechnologies available, with energy electric energy supplied to the stator winding isstored electrochemically.A battery system is made up converted to torque and applied to the rotor, causingof a set of low-voltage/powerbattery modules it to spin faster and gain kinetic energy. In generatorconnected in parallel and series to achievea desired mode kinetic energy stored in the rotor applies aelectrical characteristic. Batteries are “charged”when torque, which is converted to electric energy. Thusthey undergo an internal chemical reaction under flywheel is basically an electromechanical device thatapotential applied to the terminals. They deliver the couples a motor generator with a rotating mass toabsorbedenergy, or “discharge,” when they reverse store energy for shortdurations.The kinetic energythe chemicalreaction. Key factors of batteries for stored. The kinetic energy stored in a flywheel isstorage applicationsinclude: high energy density, 2186 | P a g e
  3. 3. Siddharth Wadhawan, Harshal Arekar / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 Vol. 2, Issue 5, September- October 2012, pp.2185-2190proportional to the mass and to the square of its orreformed from other fossil fuels. The technology isrotational speed. developing with a few commercial uses today, but with a promise toemerge as a significant source of 1 2 electricity in the near future. This process is much 𝑇= 𝐽𝜔 more efficient than traditional thermal power plants, 2 theoretically converting up to 80% of the chemical Where J is polar moment of inertia about energy in the fuel into electricity (compared to theaxis of rotation and ω is the angular velocity. The 60% efficiency of combined cycle power plants).Theenergy storage capability of flywheels can be overall efficiency of hydrogen storage dependsimproved either by increasing the moment of inertia greatly on the technique used and the scale of theof flywheel or by turning it at higher rotational operation, but is typically 50 to 60% which is lowervelocities, or both. than for compressed air systems or batteries. Hence Apart from the flywheel additional power this process is generally avoided for providing theelectronics is required to control the power in- and excess energy demand.output, speed, frequency etc. This forms the flywheelelectrical interface and generally includes the motor III. EMERGING TECHNOLOGIES FORdrive inverter and bus voltage regulator. The figure ENERGY STORAGEbelow shows the flywheel energy storage system The above methods are not very efficient and also prove costly in terms of both feasibility and maintainability. Hence, there have been quite a few emerging techniques which have been developed over a period of years. These techniques help us to provide efficient solutions to all storage related problems. These methods also act as an storage element for renewable sources of energy like solar, wind and geothermal. The major upcoming techniques include compressed air energy storage, super magnetic energy storage. A. COMPRESSED AIR ENERGYFigure 2. Basic layout of flywheel energy storage STORAGE(CAES) The largest share of the energy generated Flywheels can respond to many power by a gas turbine is consumed by itscompressor. Thisquality issues such as frequency deviation, fact combined with the fluctuations in the demandtemporaryinterruptions, voltage sags, and voltage for power and itsconsequent time of use pricingswells. The amount of energy stored in an FES formed the motivation for the development ofdevice mainly depends on the angularvelocity of the theCompressed Air Energy Storage (CAES)rotor. Flywheel energy storage system constitutes technology.short term storage systems, which are generally As the name implies, the compressedsufficient to improve the power qualitycompared to air energy storage (CAES) plant uses electricity toother ways of storing electricity, Flywheel energy compress air which is stored in undergroundstorage systems have long lifetimes. Rapid charging reservoirs.The CAES technology consists ofof a system occurs in less than 15 minutes. FESS has converting excess base load energy intoan overall round trip efficiency includingthe storedpneumatic energy by means of a compressorelectronics, bearings, and flywheel drag of 80-85% . for a later release through a gas turbineas premiumWith the life expectancy of about 20 years, the peaking powerDue to the storage option, a partial-currentflywheel designs are modular and can range in load operation of the CAES plant is also verysize up to 10 plus MW systems. Advanced flywheels flexible. More often, during the period of highconstructed from carbon fibermaterials and magnetic electrical energy demand, the compressed air isbearings can spin in vacuum at speeds up to 40,000 mixed with natural gas and they are burnt together,to 60,000 RPM. in the same fashion as in a conventional turbine plant. This method is actually more efficient as theC. FUEL CELLS compressed air will lose less energy. CAES Fuel cells, electrochemical devices that consumes two third less fuels than otherdirectly convert hydrogen, or hydrogen-rich fuels conventional sources [4]. The basic componentsinto electricity without combustion,are another required in a CAES plant are as shown in fig: 3[7]alternative to reciprocating engines. Although their • During off-peak periods a motor is operated tostructure is somewhat like thatof a battery, the charge drive the compressor train using electricpower fromduration is extended by the ability to use an external the grid, which is usually supplied by coal or nuclearfuel source, mainly hydrogen, stored directly base load plants. 2187 | P a g e
  4. 4. Siddharth Wadhawan, Harshal Arekar / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 Vol. 2, Issue 5, September- October 2012, pp.2185-2190• The air compressor which may require two or more capacitor, basically consists of two electrodes, astages, intercoolers and after coolers to achieve separator and an electrolyte. The electrode made upeconomy ofcompression, and reduce the moisture of a metallic collector, which is the high conductingcontent. part, and an active material, which is the high surface• The recuperator, turbine train, high and low area part. The two electrodes are separated by apressure turbines. membrane, the separator, which allows a mobility of• Equipment control centre for operating the the charged ions but forbids an electroniccombustion turbine, compressor. conductance. The most interesting electrodes• Auxiliaries to regulate and control changeover from materials are: metal oxides, carbons and conductinggeneration mode to storage mode. polymers. The electrolyte may be of the solid state, organic or aqueous type depending on the applicationCapacitors store electric energy by accumulating positive and negative charges separated by an insulating dielectric. The capacitance represents the relationship between the stored charge, and the voltage between the plates. The energy stored on the capacitor depends on the capacitance and on the square of the voltage. It is given as follows 1 𝐸= 𝐶. 𝑣 2 2 The amount of energy a capacitor is capable of storing can be increased by either increasing the capacitance or the voltage stored on the capacitor. Capacitors are used in many ac and dc applications in power systems. DC storage capacitors can be used for energystorage for power applications. At present, ultra capacitors are most applicable for high peak- power, low-energy situations. Capable of floating atFigure 3. Compressed air energy storage system full charge for ten years, an ultra-capacitor can A CAES operates by means of large electric provide extended power availability during voltagemotor driven compressor that store energy in the sags and momentary interruptions [2]. Ultraform of compressed air in cavern. The compression is capacitors can be completely discharged, installeddone outside periods of peak demand. The air is then easily, are compact in size, and can operatepressurized to about 75 bars. To supply electricity to effectively in diverse (hot, cold, and moist)the customers, air is extracted from the cavern. It is environments, no cooling requiredfirst preheated in the recuperator. The recuperator Ultra-capacitors are now availablereuses the energy extracted by the compressor commercially at lower power levels. A disadvantagecoolers. The heated air is then mixed with small is that a SC does not approach the energy density ofquantities of oil or gas, which is burnt in the batteries. Considering the technical maturity, thecombustor. The hot gas from the combustor is chemical inertness ,the environmental impact ,theexpanded in the turbine to generate electricity. The manufacturing process, the expected performanceskey requirement to a CAES system is that the and costs, carbon based supercapacitors are the mostreservoir has to be air tight and very large. interesting and promising devices for industrial The advantages of CAES plants are as it has applications[3].high storage capacity is take less starting time whichmakes it efficient from other conventional storage C. SUPER MAGNETIC ENERGYsystems. It does not involve huge and costly STORAGE(SMES)installation. Also the emission of greenhouse gases is Instead of storing kinetic or chemicalsubstantially lower than in normal gas plants. energy, SMES devices store electrical energy in The only drawback this system has is that magnetic field. An SMES unit is a device that storesthere is actually not a lot of underground cavern energy in the magnetic field generated by the dcaround, which substantially limits the usability of this current flowing through a superconducting coil. Oncestorage method. However, for locations where it is the superconducting coil is charged, the current willsuitable, it can provide a viable option for storing not decay and the magnetic energy can be storedenergy in large quantities and for long times indefinitely. The stored energy can be released back to the network by discharging the coil. It consists of aB. ULTRA CAPACITORS large superconducting coil at the cryogenic An ultra-capacitor, also known as temperature. This cryogenic temperature issupercapacitors or electrochemical double layer 2188 | P a g e
  5. 5. Siddharth Wadhawan, Harshal Arekar / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 Vol. 2, Issue 5, September- October 2012, pp.2185-2190maintained by a cryostat that contains helium or system. The use of high temperature superconductorsnitrogen liquid vessels. should also makeSMES cost effective due to A power conversion/conditioning system reductions in refrigeration needs. There are a number(PCS) connects the SMES unit to an AC power of ongoing SMES projects currently throughout thesystem, and it is used to charge/discharge the coil. world.Two types of power conversion systems arecommonly used. Current source converter (CSC) to IV. ECONOMICS OF ENERGY STORAGEboth interface to the ac system and charge/discharge ELEMENTSthe coil and Voltage source converter (VSC) to Energy storage system costs for ainterface to the ac system and a dc–dc chopper to transmission application are driven by the operationalcharge/discharge the coil. The modes of requirements. The costs of the system can be brokencharge/discharge/standby are obtained by controlling down into three main components: the energy storagethe voltage across the SMES coil. The SMES coil is system, the supporting systems (refrigeration forcharged or discharged by applying a positive or SMES is a big item), and the power conversionnegative voltage across the superconducting coil. The system. The cost of the energy storage system isSMES system enters a standby mode operation when primarily determined by the amount of energy to bethe average VCOIL is zero, resulting in a constant stored. The configuration and the size of the poweraverage coil Current ICOIL shown in figure conversion system may become a dominant The inductively stored energy (E in joules) component for the high-power low energy storageand the rated power ( P in watts) are commonly given applications. Energy storage is economical when thespecifications for SMES devices, and they can be marginal cost of electricity varies more than the costsexpressed as follows: of storing and retrieving the energy plus the price of energy lost in the process. However, the marginal 1 𝑑𝐸 𝐸 = 2 𝐿. 𝐼2 ,𝑃 = 𝑑𝑡 =V.I cost of electricity varies because of the varying operational and fuel costs of different classes of where L is the inductance of the coil, I is the generators. At one hand, base load power plants suchdc current flowing through the coil, and V is the as coal-fired power plants and nuclear power plantsvoltage across the coil. Since energy is stored as are low marginal cost generators, as they have highcirculating current, energy can be drawn from an capital and maintenance costs but low fuel costs. AtSMES unit with almost instantaneous response with the other hand, peak power plants such as gas turbineenergy stored or delivered over periods ranging from natural gas plants burn expensive fuel but are cheapera fraction of a second to several hours. to build, operate and maintain. To minimize the total operational cost of generating power, base load generators are dispatched most of the time, while peak power generators are dispatched only when necessary, generally when energy demand peaks. However, operators are storing lower-cost energy produced at night, then releasing it to the grid during the peak periods of the day when it is more valuable. This is called economic dispatch.In order to establish a realistic cost estimate, thfollowingsteps are suggested: • Identify the system issue(s) to be addressed; • Select preliminary system characteristics; • Define basic energy storage, power, voltage and current requirementsFigure 4. Components of typical SMES system • Optimize system specification and determine system cost; The dynamic performance of a SMES • Determine utility financial benefits from operation;system is far superior to other storage technologies. • compare system’s cost and utility financial benefitsFaster and more efficient access to the stored energy to Determine adequacy of utility’s return onand a shorter response time are the leading investment;advantages [1]. But there are a few concerns in it • compare different energy storage systemsapplication at large scale. One of the major problems performance and its cost. When compared with other energy storagetechnologies, today’s SMES systems are still costly. V. ANALYSIS OF ENERGY STORAGEThe integration of an SMES coil into existing flexible DEVICESac transmission systems (FACTS) devices eliminates On the basis of different parametersthe cost for the inverter unit, which is typically the different energy storage devices have been analyzedlargest portion of the cost for the entire SMES as shown in the Table 1. 2189 | P a g e
  6. 6. Siddharth Wadhawan, Harshal Arekar / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 Vol. 2, Issue 5, September- October 2012, pp.2185-2190 reduced generation availabilityfor frequency PARAM SMES CA- FES SCES BES stabilization. ETERS ES S S As deregulation takes place, generation and transmissionresources will be utilized at higher TYPICA 1-100 25 Rang 1-250 100- efficiency rates leadingto tighter and moment-by- L MW to ing KW 20 moment control of the spare capacities.Energy RANGE 350 in MW storage devices can facilitate this process,allowing MW KW the utility maximum utilization of utility resources.The new power electronics controller devices will enableincreased utilization of transmission and distribution systems POWER >530 >700 >17500 >(10 with increased reliability. This increased reliance will DENSIT - 0- resultin increased investment in devices that make Y 1800 7000 this asset moreproductive. Energy storage technology (kW/m3) ) fits very well withinthe new environment by enhancing the potential application of custom power, and power quality devices. EMISSI No No No No Very This paper shows that energy storage devices can ONS few be integratedto power electronics and other mechanical devices to provide powersystem stability, enhanced transmission capability, and improvedpower quality. Adding energy storage to ELECTR ~95% ~70 90- <95% 88- power electronicscompensators not only enhances the ICAL % 95% 92% performance ofthe device, but can also provide the EFFICIE possibility of reducingthe MVA ratings requirements NCY of the front-end power electronics conversion system. This is an important cost/benefitconsideration when LIFE ~30 <50 10- 10-20 3-6 considering adding energy storage systems. Also the TIME Years Yea 20 yr Years yrs method is useful in storing energy from non- rs (HS) renewable energy sources. Thus these techniques 20 yr help us to increase the overall efficiency and increase (LS) the net plant output. RESPO Millisec ~1- ~1-2 Millise Few REFERENCES NSE onds 2 Mins conds seco [1] Buckles W., Hassenzahl W. V. May 2000. TIME Min nds Super conducting magnetic energy storage, s IEEE Power Engineering Review. [2] Bullard G. L., Sierra-Alcazar H. B., Lee H. BACKU Seconds Hou Minu Second Hour L., Moms J. L., January 1989. Operating P TIME rs tes s s principles of the Ultracapacitor, IEEETransactions in Magnetics, Vol.25. TABLE I. ANALYSIS OF DIFFERENT [3] Hassenzahl W. V., 1997. Capacitors for ENERGY STORAGE ELEMNTS electric utility energy storage: Electric Power Res. Inst.VI. CONCLUSION [4] Smith S.C., Sen P.K., Benjamin K. 2008. Among the potential performance benefits Advancement of energy storage devices and produced byadvanced energy storage applications are applications in electrical power improved systemreliability, dynamic stability, systems,IEEE PES General enhanced power quality, transmissioncapacity [5] ELNA America Inc.,1988. Comparison of enhancement, and area protection. An energystorage double layer capacitor, batteries and super device can also have a positive cost and magnetic storage device, Technical Paper environmentalimpact by reducing fuel consumption [6] and emissionsthrough reduced line losses and [7] [8] 2190 | P a g e