Software Desgn for Lfe Cycle Analyss of a Stand-Alone PV System n Turkey İRFAN GÜNEY, NEVZAT ONAT, GÖKHAN KOÇYİĞİT* *Techncal Educaton Faculty, Department of Electrcal Educaton Marmara Unversty Göztepe Kampüsü, Kadıköy 34722 İstanbul TURKEY rfan.guney@acbadem.edu.tr, nonat@marmara.edu.tr, gokhankocygt@marmara.edu.tr Abstract: - Lfe Cycle Cost Analyss (LCCA) s an economc method of project evaluaton n whch all costs arsng from ownng, operatng, mantanng and ultmately dsposng of a project are consdered to be potentally mportant to that decson. LCCA s partcularly sutable for the evaluaton of buldng desgn alternatves that satsfy a requred level of buldng performance, but that may have dfferent ntal nvestment costs; dfferent operatng, mantenance and repar (OM&R) costs; and possbly dfferent lves. In ths study, a software computer program for educatonal purposes s desgned to determne ntal, lfe cycle and unt energy costs of a stand-alone photovoltac system n Turkey. Dependng on the selected locaton, materal and crtera, the proposed software mplements the lfe cycle analyss of the system. Key-Words: - Photovoltac cell, Lfe Cycle Cost, Present Worth, PV System Desgn. 1 Introducton Photovoltacs are the technology that generates drect current (DC) electrcal power measured n watts or klowatts from semconductors when they are llumnated by photons. As long as lght s shnng on the solar cell (the name for the ndvdual PV element), t generates electrcal power. When the lght stops, the electrcty stops. Solar cells never need rechargng lke a battery. Some have been n contnuous outdoor operaton on Earth or n space for over 3 years [1]. Many photovoltac systems operate n a standalone mode. Such systems consst of a PV generator, energy storage (for example a battery), AC and DC consumers and elements for power condtonng as shown n Fgure 1. Fgure 1 Major components of a stand-alone PV system Table 1 lsts some of the advantages and dsadvantages of photovoltacs. Note, that they nclude both techncal and nontechncal ssues. Often, the advantages and dsadvantages of photovoltacs are almost completely opposte of conventonal fossl-fuel power plants. Notce that several of the dsadvantages are nontechncal but relate to economcs and nfrastructure. They are partally compensated for by a very hgh publc acceptance and awareness of the envronmental benefts. Durng the late 199s, the average growth rate of PV producton was over 33% per year [2, 3]. Table 1 Advantages and Dsadvantages of PV Systems Advantages of photovoltacs Fuel source s vast and essentally nfnte No emssons, no combuston or radoactve fuel for dsposal (does not contrbute perceptbly to global clmate change or polluton) Low operatng costs (no fuel) No movng parts Ambent temperature operaton Hgh relablty n modules (>2 years) Modular (small or large ncrements) Quck nstallaton Can be ntegrated nto new or exstng buldng structures Can be nstalled at nearly any pont of use Daly output peak may match local demand Hgh publc acceptance Excellent safety record Dsadvantages of photovoltacs Fuel source s dffuse (sunlght s a relatvely low densty energy) Hgh nstallaton costs Poorer relablty of auxlary (BOS) elements ncludng storage Lack of wdespread commercally avalable system ntegraton and nstallaton so far Lack of economcal effcent energy storage ISSN: 179-595 347 ISBN: 978-96-474-93-2
2 Lfe Cycle Cost Analyss of a PV System Lfe Cycle Cost Analyss (LCCA) s an economc method of project evaluaton n whch all costs arsng from ownng, operatng, mantanng and ultmately dsposng of a project are consdered to be potentally mportant to that decson. LCCA s partcularly sutable for the evaluaton of buldng desgn alternatves that satsfy a requred level of buldng performance, but that may have dfferent ntal nvestment costs; dfferent operatng, mantenance and repar (OM&R) costs; and possbly dfferent lves [4]. Dong a LCCA gves the total cost of a PV system -ncludng all expenses ncurred over the lfe of the system. There are two reasons to do an LCC analyss: 1) to compare dfferent power optons and 2) to determne the most cost-effectve system desgns. For some applcatons there are no optons to small PV systems so comparson of other power supples s not an ssue. The PV system produces power where there was no power before. For these applcatons the ntal cost of the system s the man concern. However, even f PV power s the only opton, a LCCA can be helpful for comparng costs of dfferent desgns and/or determnng whether a hybrd system would be a cost-effectve opton. Some mght want to compare the cost of dfferent power supply optons such as photovoltacs, fueled generators, or extendng utlty power lnes. The ntal costs of these optons wll be dfferent as wll the costs of operaton, mantenance, and repar or replacement. A LCC analyss can help compare the power supply optons. The LCC analyss conssts of fndng the present worth of any expense expected to occur over the reasonable lfe of the system. To be ncluded n the LCC analyss, any tem must be assgned a cost, even though there are consderatons to whch a monetary value s not easly attached. For nstance, the cost of a gallon of desel fuel may be known; the cost of storng the fuel at the ste may be estmated wth reasonable confdence; but, the cost of polluton caused by the generator may requre an educated guess. Also, the competng power systems wll dffer n performance and relablty. To obtan a good comparson, the relablty and performance must be the same. Ths can be done by upgradng the desgn of the least relable system to match the power avalablty of the best. In some cases, you may have to nclude the cost of redundant components to make the relablty of the two systems equal. For nstance, f t takes one month to completely rebuld a desel generator, you should nclude the cost of a replacement unt n the LCC calculaton. A meanngful LCC comparson can only be made f each system can perform the same work wth the same relablty [4, 5]. 2.1 LCC Calculaton The lfe-cycle cost of a project can be calculated usng the formula: LCC = C + M PW + EPW + RPW SP W (1) where the PW subscrpt ndcates the present worth of each factor. Two phonemena affect the value of money over tme. The nflaton rate ( ) s a measure of declne n value of money. The dscount rate ( d ) relates to the amount of nterest that can be earned on prncpal that s saved. If money s nvested n an account ( N ) that has a postve nterest rate,the prncpal wll ncrease from year to year. After n years, the value of the nvestment wll be Nn ( ) = N(1 + d) n (2) However, n terms of thr purchasng power of ths nvestment, for example N( n) dollars wll not purchase the same amount as ths amount of money would have purchased at the tme the nvestment was made. In order to account for nflaton, note that f the cost of an tem at the tme nvestment was made s ( C ), then the cost of the tem after n years wll be Cn ( ) = C(1 + ) n (3) If C = N, the rato of Cn ( ) to Nn ( ) becomes a dmensonless quantty ( Pr), whch represents the present worth factor of an tem that wll be purchased n years later, and s gven by n 1+ Pr = (4) 1 + d The present worth factor of an tem s defned as the amount of money that would need to be nvested at the present tme wth a return of 1d% n order to be able to purchase the tem at a future tme, assumng an nflaton rate of 1%. Hence, for the tem to be purchased n years later, the present worth s gven by ( Pr) C PW = (5) Sometmes t s necessary to determne the present worth of a recurrng expense, such as fuel cost, OM&R costs and replacement costs. For example, f the frst year s supply of fuel s ISSN: 179-595 348 ISBN: 978-96-474-93-2
purchased at the tme the system s put nto operaton, and each successve year s fuel supply s purchased at the begnnng of the year, the present worth of the fuel acqustons wll be 2 3 1+ 1+ 1+ 1+ PW = C + C + C + C +... + C 1+ d 1+ d 1+ d 1+ d Lettng n 1 1+ x =, equaton (6) becomes 1 + d ( 2 1 ) (6) 1... n PW = C + x + x + + x (7) Ths expresson can be smplfedvby observng 1 2 3 that = 1 + x + x + x +... = x The cumulatve 1 x = present worth factor ( Pa) can be defned as PW 1 1 n Pa = = x = x x (8) C 1 x 1 x or, = n = n 1 x Pa = (9) 1 x 2.2 Socal Costs In addton, wth the use of photovoltac cell, envronment polluton and greenhouse gas mpact that called socal cost of conventonal fuels s almost zero. Ths s one of the mportant advantages to encourage the usng of photovoltacs. By the Fraunhofer Insttute n Germany for a detaled study of the electrcal energy produced from fossl sources wll brng total socal cost to be at least.27$/kwh and socal cost of nuclear power plants have been reported n at least.4$/kwh [6]. When we replace the conventonal unts wth ptotovoltac unts, the fuel whch would have been used for power generaton wll be saved due to the use of the PV system. The cost of the conventonal fuel that saved s the part of the socal costs as abovemetoned. The quantty ( M fuel ) and cost of fuel ( C fuel ) saved n ths wse can be calculated by followng equatons: t 1 X Y M fuel = [ ton] (1) LHV = 1 ηü C fuel C t p X Y = [ CU ] (11) LHV = 1 ηü Where, LHV = lower heatng value of fuel used at kj the nput of conventonal unt n kg, X = power n MW whch s replaced by photovoltac unts, η ü = effcency of conventonal generaton unt, Y = percentage of full rated capacty whch s generated by photovoltac unt for a partcular hour, C =cost of fuel n Currency unt/ton [7]. p 3 Photovoltac System Desgn In any photovoltac system desgn, the frst task s normally to determne the load. Once the load has been determned, then the amount of battery backup needs to be determned. Some systems wll not need batteres, some wll have mnmal storage and some wll requre suffcent battery storage to meet crtcal performance requrements. After battery selecton, the sze of the photovoltac array must be determned. Then the electronc components of the system, such as charge controllers, nverters and maxmum power pont trackers are selected. Fnally, the balance of system (BOS) components are selected, ncludng the mountng for the array, the wrng, swtches, fuses, battery compartments, lghtnng protecton and f necessary, montorng nstrumentaton. 3.1 Load Determnaton In photovoltac system desgn, snce battery capacty wll be determned n ampere-hour ( Ah ), t makes sense to determne the load energy requrements n Ah. Most PV systems are used for drect current (DC) electrcal applances because the current produced by a PV cell s bascally of the DC type. However, DC electrcal applances are rarely found n everyday usage, and, moreover, t s not worthwhle convertng exstng alternatng current (AC) electrcal applances for a PV power supply. Instead, an nverter s added to the PV system n order to convert the DC generated by the PV modules nto AC type sutable for AC applances. Daly energy demand ( W ) can be calculated by followng equatons for DC and AC loads.[8] W W AC DC ( kwh year) / 1 1 1 1 = 1 365 V η ηw ηb ( Ah year) / 1 1 = 365 ηw ηb (12) (13) ISSN: 179-595 349 ISBN: 978-96-474-93-2
3.2 Battery Szng The number of days of autonomy requred for crtcal need applcatons depends on the locaton and operatng perod of the system. If the mnmum peak sun hours ( T mn ) over the perod of operaton of the load are known for a locaton, the number of days of autonomy ( D ) can be estmated from the followng equatons: D D crtc noncrtc = 1.9Tmn + 18.3 =.48T + 4.58 mn (14) These equatons are only vald for T mn of about one hour per day. Szng of the batteres must take nto account the loss of capacty under condtons of low temperature, hgh rate of dscharge, or hgh rate of charge. Battery sze B s thus determned from, ( ) D BAh = W D T D ch ( dsch ) ) (15) where DT, Dch and (dsch represent temperature deratng factor, charge/dscharge deratng factor and the depth of dscharge expressed as a fracton respectvely. In ths study, assumed unty value for D D ( dsch).8. T ch 3.3 Array Szng The number of modules for the system s determned by dvdng the array desgn current by the current avalable from a selected module, after correctng for module degradaton from agng or drt accumulaton. The derated desgn current of the array s the desgn current dvded by a degradaton factor, whch s commonly about.9. Addtonal seres modules may be needed f the system voltage hgher than module output voltage (generally 12V). 3.4 Controller, Inverter and/or Converter Selecton The D.C. loads wll requre a battery charge controller as a part of the system and the A.C. loads wll requre both controller and nverter. In the present case, relatvely smple controllers are preferred because complexty sometmes leads to relablty problems. For a motor-drven applance, the desgner must determne whether the motor wll be damaged by D.C. or by harmoncs. 3.5 BOS Components, Wre, Fuse and Swtch Selecton Remanng system parts wll typcally nclude a contaner for the batteres, condut, plugs and receptacles, fuse holders, surge protectors, ground rods, wre nuts, termnal lugs, etc. The cost of BOS components wll typcally be about 1% of the cost of array. Proper wre szng depends on the current to be carred by the wre, but at low voltages prmarly on the length of the wre. To allow for cloud focusng, the rated array current s multpled by 1.25 to obtan the maxmum current from array to controller. Fuse szes are then chosen to be next hgher value above the maxmum current from array to controller. 4 Lfe Cycle Cost Calculaton Software for Stand-Alone PV Systems In ths study, computer software for educatonal purposes s desgned to determne ntal, lfe cycle and unt energy costs of a stand-alone photovoltac system n Turkey. Dependng on the selected locaton, materal and crtera, the proposed software mplements the lfe cycle analyss of the system. Replacement number and costs are also calculated. Addtonally, the quantty and cost of conventonal fuel savngs by the usng of PV system are calculated. The database and fxed constants of proposed software can be updated and new elements can be added at any tme. Present value algorthm s descrbed n prevous secton s used for cost calculaton. Inapproprate selecton of components s blocked by the software. Also, too large selecton of partcular elements such as nverter and batteres s blocked for optmal szng of the system. All calculated values can be saved and prnted. Delph programmng language s used n the software desgn. Informaton for database has been obtaned from the nternet and Turksh State Meteorologcal Servce [9]. Flowchart of the program s shown n Fgure 2. Fgure 3, and 4 shows the edtng wndows of constants and database respectvely. Man wndow of proposed software and an example calculaton are gven n Fgure 5. ISSN: 179-595 35 ISBN: 978-96-474-93-2
Fgure 4 Database edtng wndow Fgure 5 Man wndow of proposed software Fgure 2 Flowchart of software Fgure 3 Fxed values edtng wndow of software 5 Conclusons In ths study, software desgned to perform the lfe cycle cost analyss for stand-alone PV systems nstalled n Turkey. For system desgn, daly mnmum peak sun hours values are used that has been obtaned from statstcal data of the Turksh State Meteorologcal Servce. Cost analyss method s based on the present worth algorthm. Addtonally, the quantty and cost of conventonal fuel savngs by the usng of PV system are calculated by the proposed software. As a result of the calculatons were performed usng software desgned, n terms of lfetme cost and unt energy costs of PV systems most sutable provnces are Mersn, Antalya, Adana, Mardn, Adıyaman and Kls respectvely. In the opposte, the hghest costs are n Gümüşhane, Yalova, Ağrı, Çankırı and Kastamonu provnces. Desgned software can be used for educatonal purposes n PV system desgn courses. By expand of database the analyss can be made for any regon n the world. The results of the cost effects of varous system parameters and the envronmental mpact of conventonal fuel savngs may be analyzed. ISSN: 179-595 351 ISBN: 978-96-474-93-2
References [1] J. Perln, From Space to Earth: The Story of Solar Electrcty, AATCC Publcatons, 1999. [2] A. Luque, S. Hegedus, Handbook of Photovoltac Scence and Engneerng, Chapter-19, John Wley and Sons, Ltd, pp.1-43, 23. [3] J.W. Amulf, PV Status Report 23: Research, Solar Cell Producton and Market Implementaton n Japan, USA and the European Unon, European Commsson, Insttute for Envronment and Sustanablty, Renewable Energes Unt, p.2, 23. [4] S.K. Fuller, S.R. Petersen, Lfe-Cycle Costng Manual, Chapter:1, U.S. Government Prntng Offce, pp.1-5, 1996. [5] R. Messenger, J. Ventre, Photovoltac System Engneerng, CRC Press LLC, Florda, 2. [6] B. McNELIS, The Drect Converson of Solar Energy to Electrcty, Unted Natons Publcaton, New York, 1992. [7] J. Amt, S.C. Trpathy, R. Balasubramanan, Relablty and Economc Analyss of a Power Generaton System Includng a Photovoltac System, Energy Converson and Management, Vol.36, No.3, p.183-189, 1995. [8] Y. Sukamongkol, S. Chungpabulpatana, W. Ongsakul A smulaton model for predctng the performance of a solar photovoltac system wth alternatng current loads, Renewable Energy, Vol.27, p.237-258, 22. [9] Statstcal data of Turksh State Meteorologcal Servce, 26. ISSN: 179-595 352 ISBN: 978-96-474-93-2