Costs of Designs Chosen for Analysis

Transcription

1 Appendix XI-C Costs of Designs Chosen for Anlysis LOW-TEMPERATURE DESIGNS The design chosen for hot wter storge is tnk which is buried in the ground, surrounded by lyer of polyurethne insultion (where necessry) nd vpor brrier which protects the insultion from ground moisture. (See figure xi-2). If the collector uses fluid other thn wter, het exchnger is lso required. Het exchngers would lso be required if the storge were pressurized while the other prts of the system were not under pressure. The primry costs re divided into three ctegories: the tnk itself, the excvtion nd bckfill, nd the insultion. Costs presented here exclude the contrctor s overhed nd profit (25 percent), which is dded lter. Excvtion, Bckfill, nd Soil Compction. Figure Xl-5 shows s solid line the excvtion, bckfill, nd compction cost per cubic meter of tnk volume s function of tnk volume. Costs were derived from Mens using the following ssumptions: Excvted volume is 1.3 times the tnk volume to llow for clernce, insultion, etc. Bckfill volume is 0.3 times tnk volume. Becuse there is mobiliztion nd demobiliztion chrge for hevy equipment, smli jobs cn be done less expensively by hnd lbor. For tnks greter thn 3.35 m 3, excvtion is done with trckmounted, 3½-cubic-yrd, front-end loder. Bckfill is done by bulldozer for tnks greter thn 28 m 3, Soil compction in ll cses is done in 12-inch lyers with vibrtory plte compctors. Hot Wter or Oil Tnks Figure Xl-5 lso plots instlled tnk costs, excluding excvtion nd insultion, for vriety of types of tnks suitble for storing heted or chilled wter or other fluids. These prices exclude pumps nd piping, It cn be seen tht for the rnge O to 1,000 m 3 it is possible to hve tnk instlled, including excvtion nd bckfill, for $80/m 3 or less. The bseline design ssumes $80/m 3 for this size rnge. The ssumed cost is plotted s the dshed line in the figure. Insultion Insultion costs depend strongly on the temperture of the storge nd the length of time needed for storge, The insultion chosen for nlysis is polyurethne. This mteril cn be fomed on in plce for pproximtely $0,24/bord foot ($101.71/m 3 ). 9 (A thin polyethylene vpor brrier dds negligible cost.) This cost might be reduced if plnt dedicted to producing storge equipment mnufctured preinsulted tnks. The conductivity of urethne protected by good vpor brrier is pproximtely 0.13 Btu inch/hr ft 2 o F. Anlysis Two cses re considered: 1 ) cse which pplies to storge for use with systems designed to supply domestic heting nd hot wter (therml energy supplied between 2000 nd 1200 F nd returned t 900 F); nd 2) systems designed to supply bsorption irconditioners nd other industril processhet lods (therml energy supplied between 2700 nd 2200 F nd returned t 2000 F). Cse I requires storge volume of m 3 /kwh t if mixing is ssumed, or m 3 /kwh t if there is no mixing in single tnk. The cost of insultion in these Bui/dIrJg Construction Cost Dt 1976, Robert Snow Mens Compny, Inc, R S Godfrey, ed, pp 18, 22, John L Renshw of john L Renshw, Inc (n insulting firm [n the metropolitn Wshington, D C re), privte communiction, August 1976.

2 Appendix Xl-C 497 cses is $ V i, where V I is the volume of insultion in m 3. Cse 1: C, where E is the storge cpcity in kwh th nd tht if the bove equtions yield negtive result, the erth lone provides sufficient insultion nd C, = O. The instlled cost of buried tnks is ssumed to be $80V s for tnks less thn 1,000m3. For tnks with volumes greter thn 1,000m 3, n pproprite cost per cubic meter ws tken from figure Xl-22. Cse 1: Ct = $80x E Cse I 1: Ct = $80 X E (Systems lrger thn 1,000m3 would substitute n pproprite tnk cost for $80 in the lst eqution. ) HIGH-TEMPERATURE DESIGNS Since very few of the concepts which hve been suggested for high-temperture therml storge hve ever been fbricted s complete systems, it is difficult to estimte wht they would cost if they were produced commercilly. An ttempt hs been mde to select for the nlysis systems which re s simple s possible, both becuse such systems show the gretest promise of reching the mrket in the next decde nd it is much esier to estimte the potentil cost of these systems. The nlysis is firly conservtive, nd my be used to provide n upper limit for future high-temperture therml storge costs. in cses where the mterils require fctory work done off site, the bre mterils cost is multiplied by 1.6 to ccount for overhed, wges, nd profit in the fctory. This number is obtined from the Deprtment of Commerce input-output tbles for Sector 40: Heting, Plumbing, nd Structurl Metl Products. 10 Cost of onsite ssembly nd instlltion (excluding the contrctor s overhed nd profit, which is dded lter) is ssumed to be 32 percent of the cost of the components from the fctory. This comes from the Deprtment of Commerce tbles for Sectors 11, 12: All New Construction. Thus, in cses where better estimtes of ssembly nd instlltion were not vilble, bre mterils costs hve been incresed by 211 percent for mterils which require dditionl fctory work, or 32 percent for systems which do not. Oil Storge for Residentil Orgnic Rnkine Devices The highest tempertures used in the bseline-design orgnic Rnkine engines for the single fmily house re 4200 F (216 o C). For storge t this temperture, sensiblehet storge system using fuel oil hs been chosen. The oil is Iiquid t ll tempertures of interest nd thus cn be used s hettrnsport system for conveying het from the coiiector to the tnk s weli s serving s the storge medium. Het exchngers re only needed to trnsfer het to the het engines used to generte electricity, The storge system opertes t tmospheric pressure. Since het engines operting t the smll temperture differences vilble for the single fmily system re lredy operting t reltively low efficiencies, the system is not ble to tolerte lrge drop of temperture t the input of the het engine, For this reson, seprte tnks re used for hot fluids emerging from collectors nd cold liquids returned from the therml lods to ensure constnt high temperture to the inlet. The ssumptions nd resuiting costs re summrized in tble XI-9 Costs re computed s shown in tble Xl-C-1. Input-Output Structure of the U S Economy 1963, Survey of Current Business. U S Deprtment of Commerce, Ntionl Economics Dlvlslon, November 1967, pp Ibid

3 498 Solr Technology to Tody s Energy Needs Tble Xl-C-1. Assumptions for Hot Fuel Oil Therml Storge, Single Fmily House [420 F orgnic engine] Two-tnk system No het exchnger to collectors Het engine tempertures (orgnic Rnkine) = 420 to 90 F (216 to 32 o C) Het exchnger temperture drop to het engine: 10 o c (18 F) Storge temperture swing: 439 to 108 F (226 to 42 C) Het cpcity of storge medium (refined fuel oil) = kwh th /m 30 C b Therml conductivity of insultion (fom glss): k = 0.5 Btu in/ ft2hr F Ground temperture = 55 F (13 C) Credit for erth s insultion: equivlent to insultion thickness of (0.0833)R Het exchnger constnt = 4.5 kw/m 20 C clns.tiled cost of insultion (fom glss) = $1 14/m3 Of insultion = $3.24/ft 3 Instlled cost of buried tnks nd excvtion = $160/ m 3 of oil Instlled cost of storge medium (refined fuel oil) = $146/m 3 lnstlled cost of het exchnger to het engine = $80/ m 2 of het exchnger Tnks, excvtion, oil = 2.092E$ Het exchngers = 1.78P$ NOTE Costs exclude contrctor s overhed nd profit (ZSo/O), which IS dded lter. E IS storge cpcity in kwhth. d Is storge Intervl In hours. R IS storge tnk rdius P IS dischrge rte In kwth R w Hll~t nd R L Gervls, Cert(r/ Rece~ver Solr Therml power System, Phse 1, F(n/ Report, MDC G6040, McDonnell. Dougls Astronutics Compny, Jnury 1976 %ee figure Xl-B-1 cmens Bu//d/ng Cons frucf/on COSf Dt, 1976, P. 111 Therminol-55/Rock Storge The TherminoI-55/rock-storge system is similr to the hot fuel oil system just exmined. Two tnks re used to mintin high dischrge temperture nd thus high temperture efficiency (for het engines). The rocks re ssumed to occupy 70 percent of the storge volume. The ssumptions nd resulting costs re summrized in tble XI-C-2. Storge in Steel Ingots The steel-ingot system cn eliminte the need for het exchngers, but this requires the use of 150 psi stem in the collector Tble Xl-C-2. Assumptions for Therminol-55/ Rock Therml Storge [600 F het engine] Two-tnk system: no het exchnger to collectors; 70% rocks by Volume Het engine tempertures: 600 to 100 F (316 to 38 C) Het exchnger temperture drop to het engine: 10 C (18 F) Storge temperture swing: 618 to 118 F (326 to 48 o C) Het cpcity of Therminol-55: 31 Btu/ft3 F (0.577 kwh/m3 C) Het cpcity of rocks: 27.3 Btu/ft3 F (0.509 kwh/m3 C) System het cpcity: 28.4 Btu/ft3 F (0.529 kwh/m3 c) b Therml conductivity of insultion (fom glss): k = 0.6 Btu in/hr ft 2 F Het exchnger constnt = 4.5 kw/m 2 C Ground temperture: 55 F (13 C) Credit for erth insultion: equivlent to insultion thickness of (0.1)R c lnstlled cost of insultion (fom glss) = $114/m 3 of insultion = $3.24/ft 3 lnstlled cost of het exchngers to het engine = $80/m 2 of het exch. Instlled cost of rocks = $0.01/lb x 140 lb/ft 3 x 70% = $0.98/ft3 storge = $34.61/m3 Instlled cost of Therminol-55 = ($.38mtl + $.05 shipping)/lb x 43 lb/ft3 x 30% = $5.55/ft3 = $195.89/m 3 storge Instlled cost of buried tnks nd excvtion = $160/ m3 of storge: Tnks, excvtion, Therminol, rock = 2,655E$ Het exchngers = 1.78P$ NOTE: Costs exclude contrctor s overhed nd profit (250/.), which IS dded lter. E IS storge cpcity in kwh 8 is.sforge intervl In hours R is storge tnk r~us. P IS dischrge rte In kw th H[let nd Gervls, MDC G6040. b%e figure Xl- B-1 cmens, 1976, Q. 111 system. This is ssumed to be cceptble since the het engine will operte t this pressure, nd thus n opertor fmilir with the engine should be ble to supervise the stem trnsport system. The ingots could be integrted into the structure of the building or buried in the erth. Erth buril is ssumed for the following clcultions, lthough individul instlltions my present other opportunities. Excvtion nd bckfill costs re tken from figure XI-5. The Jet Propulsion Lbortory (JPL) hs clculted tht

4 Appendix XI-C 499 system operting between 9500 nd 1000 F (510 0 nd 38 C) cn be dischrged by bout 68 percent of its totl sensible-therml cpcity before the output stem strts to fll below 950 F. 12 The nlysis therefore reduces the therml cpcity of the steel ccordingly nd ssumes tht l I of the dischrge stem is t 9500 F. The following cost ssumptions were lso tken from the JPL study: steel ingots t $.15/lb; welded heders t $50/hole ($25 ech end); ril trnsporttion of mterils t $.01/lb; miscellneous (flow vlves, controls, sensors, wetherproofing, etc. ) t $.0067/lb of ingots. It lso is ssumed tht the ingots re piled in stck whose shpe is close enough to cylinder (with length = 4R) tht the insultion clcultions cn be done using equtions lredy developed for cylindricl tnks. The ssumptions used re shown in tble Xl-C-2. High-Temperture Phse Chnge Storge Severl designs for storing therml energy in the het of fusion of sodium hydroxide hve been exmined, nd operting units of t lest two different pproches hve been 3 constructed. These units use electricity to chrge the storge to bout 9000 F. Totl system cost for these devices is estimted to be between $1.35/MBtu nd $1.50/MBtu ($ /kWh th). Exmining figure XI-19, it cn be seen tht the vilble energy for use t 9000 F is pproximtely twice the vilble energy for the temperture swing between 6200 nd 4200 F which is required for the het engine. The price pproprite for the on site ppliction wouid thus be pproximtely $3/MBtu ($10.24/kWht) JPL hs designed sodium hydroxide storge system R H Turner () PL), Therml Energy Storge Using Lrge Hollow SteeJ Ingots, Shring the Sun: So/r Techrto/ogy in the Seventies. J olnt Conference, Americn Section, Interntionl Solr Energy Society nd Solr Energy Society of Cnd, Inc, Wlnnlpeg, Cnd, Aug 15-20, 1976, Vol 8, pp R E Rice, Therm/ Storge for Appliction to Energy Conservtion, Comstock nd Wescott, Inc, April 1975, Cited In Brmlette, et l, (Sndl Lbortories, Llvermore) SAN D for use with solr system which opertes between 6500 nd 4000 F for cost of pproximtely $3.7/MBtu ($12.63/kWhJ. The system which will operte with the Stirling cycle will hve very similr design. The costs of the two systems re estimted in prliel in the following discussion. The het of fusion storge system is ssumed to be produced in fctory-ssembled modules. Ech modulr tnk contins within it bundle of seled, long, nrrow, cylinders full of the storge mteril. The cylinders occupy three-fourths of the tnk volume, nd het-pipe fluid circultes in the spce round the cylinders, s shown in figure IV-20. During chrging, the het-pipe fluid is heted directly in the solr collector, nd during dischrging, the het-pipe fluid condenses t the het engine, eliminting the expense of seprte het exchngers. Ech cylinder is ssumed to be 4 feet long nd 3 inches in dimeter. There re 60 cylinders per tnk, nd the tnks re 59 inches long nd 27 inches in dimeter. The cylinder wlls re inches thick. This is thick enough to contin the weight of the storge mteril if dequte room is provided for expnsion during phse chnges. The volume of continment mteril per cylinder is thus 302 cm 3, nd ech cylinder cn contin 5,260 cm 3 of storge mteril. The chrcteristics of potentil continer mterils re shown in tble Xl-C-3. The cylinders re ssumed to be mde of stinless steel. Although stinless steel is not completely resistnt to corrosion by pure fluorides, N. V. Philips reports tht by dding smll mount of luminum to the melt, ll corrosion is eliminted. Corrosion testing ws done for more thn 14,000 hours t 850 C with ordinry 18/8 stinless steel. 5 Ech tnk is double-wll pressure vessel, insulted by vcuum nd multifoil super- 14) Schroder (N V Phliips Achen Lb ), Therml Energy Storge nd Control, journ/ ot Engineering for /ndustry, August 1975, pp j Schroder (N V Philips Achen Lb ), privte communlctlon, jn 13, 1977

5 500. Solr Technology to Tody s Energy Needs Tble Xl-C-3. Assumptions for Steel-Ingot Therml Energy Storge Stem Rnkine engine: no het exchngers Het engine tempertures: 950 to 10O F (510 to 38 o C) Storge temperture swing: 950 to 100 F (510 to 38 C) Storge temperture swing: 950 F to 100 F (510 o C to 38 C) Storge medium: cst steel ingots, 60 ft long, 1 ft wide, 1 ft high; 9 xil holes, 2 in dimeter per ingot Heders: 2 in dimeter, low-lloy, semless pipe Schedule 50, formed into therml stress expnsion loop nd welded to ingot holes Steel het cpcity = 58 Btu/ft3 F System het cpcity (20% holes; 32% unrecoverble) = kwhth/m3 C sumed to be ¼-inch stinless steel, fbricted t $2.00/lb. 8 The two het pipes re ssumed to dd $200 ech to the cost of ech tnk. 9 The instlled cost of the cylinders is estimted using the mterils costs in tbles Xl-4 nd Xl-C-4, dding $().1()/kg for shipping, nd multiplying by the fctor of 2.11 to ccount for fctory nd onsite fbriction nd instlition. The cost ssumptions re summrized in tbles Xl-C-5 through Xl-C-7. BATTERY STORAGE COSTS See figure Xl- B-1 b Mens, 1976, p 111. NOTE Costs exclude contrctor s overhed nd profit (2s0/.), which IS dded lter. E IS storge cpcity In kwh storge Intervl In hours. R IS rdius of the p~~e ;~I ; ;; possible to use concrete or some other Inexpensive mteril insted of steel, the cost could be reduced by fctor of three or more insultion. This type of insultion hs therml conductivity of Btu in/hr ft 2 o F. 16 The cost of the metllic foil insultion is estimted t $2.00/ft 2 of surfce re, nd the resultnt therml conductivity is so low tht even sesonl storge results in very smll het losses. 7 The tnk wlls re s- N. E. Polster nd W R. Mrtini (University of Wshington), Self-Strting, Intrinsiclly Control/cd Stirling Engine, 11th I EC EC. R L, Pens nd R. J. Fox (Aeronutronic Ford Corp. nd Wlt Disney Productions), A So/r/Stir/ing Tot/ Energy System, unpublished, The costs of bttery storge used in the nlysis conducted in this study re summrized in figure Xl-28 nd tble XI-11. There ppers to be resonble concensus tht costs s low s $55/kWh re fesible in the intermedite term, but considerble mount of disgreement bout how fr prices will fll in the long term. The Bechtel summry of bttery costs estimted tht dvnced btteries could be produced for $10 to $25/kWh 20 while other sources hve estimted tht prices below!$25/kwh re unlikely The long-term cost $11/kWh shown in the tble reflects n ssumption tht low-cost iron-redox system hs been developed. Neither estimte of O&M cost given in tble Xl-8 would dd pprecibly to the overll costs of bttery storge. Even if O&M costs for dvnced btteries re fctor of 2 higher, the O&M costs would still be minor. Consequently, /kWh hs been used for ll three cses in tble Xl-11. Ibid, Ibid ~OAn Engineering Study of 20 M W,.200 MWh f-=d- Acid Bttery Energy Storge Demonstrtion P/nt, Bechtel Corportion, ANL Contrct No , October * Jmes Birk (E PRI), privte communiction, Jn. 20,1977. ZZAn Assess~enr of Energy Storge S ysterns suitble for Use by Electric Utilities, Fin/ Report by PSEG on ERDA Contrct No. E (11-1 }2501, Vol. 11, July 1976, pp

6 Appendix XI-C. 501 Tble Xl-C-4. Continment Mterils Density 3 Yield strength cost Mteril (kg/m ) (N/m2) ($/kg) crbon steel X x stinless steel b x X Steelite X x bcde.. Inconel ce X X Hstelloys bcde x X Room temperture vlues Oxldtton resistnt bhlgh.temperture l IOY CReSIStnt to chemicl ttck dreslstnt to most fluorldes ereslstnt to fluorldes If Al IS dded to the fluorlde SOURCES T T Brmlette (Sndl Lbortories, Livermore), compiled for OTA, Note e dded by J Schroder (N. V. Philtps Achen Lb ), Dnvte communl - ction, Jn 13, 1977 The slvge vlue (or reduced replcement cost) for ner-term btteries is principlly the vlue of the led in the bttery. The replcement price for intermediteterm btteries is bsed on crude verge of the frctionl replcement prices projected in tble Xl-8. Most of the dvnced btteries use inexpensive mterils which wouid hve negligible slvge vlue. Consequently, no slvge vlue is ssumed. If one of the btteries contining Iithium were used, the replcement price would clerly be less thn the initl price, since lithium cn be effectively recycled. Bttery storge systems for utility pplictions re expected to use lrge number of cells which hve individul storge cpcities of 5 to 40 kwh. 23 These re the systems for which virtuliy li of the vilble cost projections pply. It is expected tht smller systems will require somewht smller cells to obtin resonble system voltges Detiled studies of the reltive cost of such systems hve not been completed. However, the direct product cost ($/kwh) for 7 kwh mss-produced cell would probbly be bout 14 percent higher thn 50 kwh cell, nd btteries in the 20 kwh size rnge my cost 20 to 25 percent more thn btteries for lrge storge fcilities. Detiled design studies now underwy my chnge this estimte. 24 Tble Xl-C-5. Ltent-Het Storge Tnk Assumptions Volume of stinless steel in tnk wll = m3 Surfce re of tnk = 38.48ft2 Tnk wll cost = ( m3)(7,900kg/m3)( 2.2lb/kg) ($2/lb) = $1,560 Insultion cost = (38.48ft2)($2.00/ft2) = $77 Het pipe cost = $ cylinders per tnk Cylinder cost = (302cm3)(.0079kg/cm3)($1.86/kg) (2.1 1) = $9.36/cylinder NOH cost + ( m3)(1,784kg/m3)($0.65/kg) (2.11 = $12.87/cylinder NF/MgF2 t $0.50/lb = ( m3)(2190kg/m3) ($1.20/kg)(2.11) = $29.17/ cylinder NF/MgF2 t $0.25/lb = ( m3)(2190kg/m3) ($0.65/kg)(2.11) = $15.80/ cylinder Volume of storge mteril per tnk = m3 Overll volume of tnk = 0.60m3 Totl instlled tnk, NOH: $3,371 plus excvtion nd bckfill Totl instlled tnk, $0.50 NF/Mg F2: $4,349 plus excvtion nd bckfill Totl instlled tnk, $0.25 NF/Mg F2: $3,547 plus excvtion nd bckfill J jmes R [31rk, The Led-A c/d Bttery for E/ectr/c Uti//t/e~ A ReL Iew nd An/ysIs, presented t the ER- DA EPRI Led-Acid Bttery Workshop 11, Dec 9, Nlck Msk lick (Westinghouse Corportion), privte communiction, Jn. 31, 1977

7 502 Solr Technology to Tody s Energy Needs Tble Xl-C-6. Assumptions for NOH Ltent-Het Storge [600 F het engine] Tble Xl-C-7. Assumptions for NF/MgF2 Ltent-Het Storge [1,400 F het engine] cost : (.50 NF/mg F2 $/kg) Totl storge cost : (.25NF/ F2 $/kg) NOTE Costs exclude contrctor s overhed nd profit (250/.), which IS dded lter. (E IS storge cpcity In kwht IflSultlOn IS dequte for sesonl storge Hllet nd Gervls, MDC G6@$0 bsee tble XI-7 CR L. Pens nd R J FO X. For purposes of this study, we increse the lrge system prices by 10 percent for the commercil nd multifmily residentil systems, nd 20 percent for home systems. POWER-CONDITIONING COSTS As noted erlier, the bulk of the cost of power-conditioning pprtus results from the cost of the inverter system. Estimtes of the cost of voltge regultors vry from 1 to Hllet nd Gervls, NDC G6040 b See tble Xl-7 6 percent of the cost of the inverter. The cost of the interfce vries from bout 10 to 20 percent of the inverter cost for systems in the kilowtt rnge to bout 2 percent of inverter cost for systems in the megwtt rnge. Estimtes of current nd potentil power-conditioning costs re shown in figure XI-28. The prices chosen to represent nerterm, intermedite, nd specultive technologies re chosen somewht rbitrrily to represent the spectrum of estimtes shown. The ner-term prices selected re somewht lower thn the verge prices of contemporry power-conditioner devices since mny of the units now vilble re

8 Appendix Xl-C.503 overdesigned for solr ppliction, nd mny of the smll systems shown operte t voltges much lower thn would be required for solr pplictions (low-voltge systems re usully more expensive thn higher voltge devices with similr power cpbilities). In the intermedite term, it cn be ssumed tht t the lower power levels, incresed production volume will lower prices, lthough in mny of tody s systems, stndrd components such s inductors nd cpcitors represent significnt frction of the cost, nd this will limit the production economies possible. At higher power levels, systems wili probbly continue to be essentilly custom-designed, but incresed engineering experience shouid lower costs somewht, s ssumed for the intermedite cse of figure Xl-28. in the longer term, it cn be ssumed tht power-conditioner units in the smller sizes cn be mde for substntiliy lower prices by mss-producing units designed with power trnsistors so tht the use of components such s inductors is minimized. Westinghouse hs estimted tht such units could be produced for $50 to $70/kW. 25 At intermedite nd higher power levels, mrket size nd component size will probbly prevent utomted production, nd the price my go up for some sizes s suggested by the curve sketched for the long-term cse i n figure Xl-28 It should be noted tht the prices discussed so fr hve been in terms of rted cpcities which re relted to the norml lod of the system. Most systems cn ctully supply 1.5 to 3 times the rted cpcity, depending on the specific chrcteristics of the power conditioner nd the lod. 26 I n the integrted system cost runs, it hs been ssumed tht power conditioners hve pek cpcity 1.5 times their rted cpcity. BUILDING AND OTHER COSTS I n ddition to the bttery nd power conditioner costs, there is significnt cost ssocited with instlition, electricl wiring, nd instrumenttion, nd the room in which the bttery system will be housed. No detiled estimtes of these costs were vilble for systems of the size considered in this study, It ws ssumed tht the btteries would be locted in the bsement of homes or in the equipment rooms of prtments nd shopping centers. Unfinished bsement spce in such buildings costs bout $5.00 to $7.50 per squre foot. Building nd Other Costs were ssumed to be twice the cost of the spce nd it ws ssumed tht the btteries we rrnged so there were 2 to 3 kwh per squre foot of floor spce for present led-cid bttery systems. It is ssumed tht dvnced bttery systems wiii hve higher energy densities, nd require less spce. REDOX btteries do not hve high energy density but it should be esier to integrte the liquid storge tnks which mke the system bulky into building spce thn it wouid be to find spce for more complex systems requiring high tempertures or potentilly hzrdous mterils It ws therefore ssumed tht the building nd other costs ssocited with the REDOX systems would be no greter thn those of other btteries. It ws ssumed tht the building nd other costs nd power conditioner costs scle with bttery cpcity in the sme wy (see tble Xl 1-11 ) J 5 P F Plttmdn, Progrdrn A4ndger for Westinghouse F let trlc Corport Ion Re$erch I bortorie>, F/rr/ Report on Conceprud/ Lies/gn nd S y$tems An~/\\l\ of Photovo/tlc Power $ ysterns, ERDA Contrdct N o I ( ), December 1976