Greenhouse Gas Emissions from Building and Operating Electric Power Plants in the Upper Colorado River Basin

Transcription

1 Environ. Sci. Technol. 2002, 36, Greenhouse Gs Emissions from Building nd Operting Electric Power Plnts in the Upper Colordo River Bsin SERGIO PACCA AND ARPAD HORVATH*, Energy nd Resources Group, University of Cliforni, 310 Brrows Hll, Berkeley, Cliforni 94720, nd Deprtment of Civil nd Environmentl Engineering, 215 McLughlin Hll, University of Cliforni, Berkeley, Cliforni As demnd for electricity increses, investments into new genertion cpcity from renewble nd nonrenewble sources should include ssessment of globl (climte) chnge consequences not just of the opertionl phse of the power plnts but construction effects s well. In this pper, the globl wrming effect (GWE) ssocited with construction nd opertion of comprble hydroelectric, wind, solr, col, nd nturl gs power plnts is estimted for four time periods fter construction. The ssessment includes greenhouse gs emissions from construction, burning of fuels, flooded biomss decy in the reservoir, loss of net ecosystem production, nd lnd use. The results indicte tht wind frm nd hydroelectric plnt in n rid zone (such s the Glen Cnyon in the Upper Colordo River Bsin) pper to hve lower GWE thn other power plnts. For the Glen Cnyon hydroelectric plnt, the upgrde 20 yr fter the beginning of opertion incresed power cpcity by 39% but resulted in mere 1% of the CO 2 emissions from the initil construction nd cme with no dditionl emissions from the reservoir, which ccounts for the mjority of the GWE. Introduction In 2001, Cliforni nd the rest of the West Cost of the United Sttes strted to experience severe shortges of electricity. Investments in both renewble nd nonrenewble sources of electricity hve been plnned. Ntionwide, the demnd for renewble or green energy is incresing. For exmple, New York Stte Governor Ptki issued n executive order in 2001 requiring gencies to purchse t lest 10% of their power from renewble sources by 2005 (1). To ddress the West Cost s crisis nd the demnd for renewble power, the Ntionl Hydropower Assocition (NHA) hs urged Congress nd the Administrtion to pss hydropower licensing reform legisltion nd crete incentives for new hydroelectric cpcity through efficiency upgrdes or by dding turbines to existing dms (2). The NHA estimted tht nother 8800 MW of new cpcity (equivlent to bout 14 vergesized col-fired power plnts) could be developed ntionwide, 2500 MW in Cliforni lone, through upgrdes of existing dms. As much s MW could be gined from instlling turbines on dms tht currently hve none. * Corresponding uthor telephone: (510) ; fx: (510) ; e-mil: horvth@ce.berkeley.edu. Energy nd Resources Group. Deprtment of Civil nd Environmentl Engineering. The debte bout the environmentl impcts of different electricity genertion technologies is lso intensifying. A study by the World Commission on Dms in 2000 (3) summrized mny of the concerns ssocited with hydroelectric plnts such s ir emissions from reservoirs, loss of hbitt, reloction of popultion, problems with sediment, etc. While hydroelectric, solr, nd wind power plnts do not need fuel inputs for opertion, fossil-fueled power plnts contribute to ir pollution significntly through sustined nnul emissions. In the United Sttes, 40.5% of nthropogenic CO 2 emissions (4), 38% of toxic ir emissions (5), nd 15% of totl toxic releses (5) were ttributed to the combustion of fossil fuels for electricity genertion in As ll environmentl systems nlyses, the comprison of the environmentl performnce of vrious electricity genertion technologies requires life cycle perspective. This pper compres greenhouse gs (GHG) emissions from three renewble (hydro, solr, nd wind) nd two nonrenewble sources (col nd nturl gs), including not only the opertions phse of electricity genertion (where the fossilfueled plnts hve distinct disdvntge s result of fuel burning) but lso the construction of the fcilities s well s the emissions from the hydroelectric plnt s reservoir. (The end-of-life phse of the fcilities ws not ssessed due to dt unvilbility.) The hypotheticl power plnts were locted in the sme geogrphicl re (since locl conditions ffect the design nd opertion of hydro, solr, nd wind plnts) nd scled to hve the sme output. Frmework for Comprtive Assessment of Globl Wrming Effects To ssess the greenhouse effects of constructing nd operting vrious power plnts, the mounts of the mjor mteril nd energy inputs were obtined, nd life cycle ssessment (LCA) ws used. LCA is method tht ttempts to systemticlly quntify the environmentl effects of the vrious stges of product s or process entire life cycle: mterils extrction, mnufcturing/production, use/opertion, nd ultimte disposl (or end-of-life). There re mny efforts worldwide to produce LCA studies tht re comprehensive nd useful. The chllenge is to mp the production processes so tht they re ccurte nd representtive of the industry trends. Severl LCA tools provide process descriptions nd librries of dt to users. Existing studies differ in the number of environmentl effects quntified nd in the scope of the nlysis (where the boundry of the nlysis is drwn). Currently, there re two mjor pproches to boundry setting: process-bsed model developed most intensively by the Society of Environmentl Toxicology nd Chemistry (SETAC) nd the U.S. Environmentl Protection Agency (EPA) (6) nd n economic input-output nlysis-bsed model clled EIO-LCA (7, 8). The SETAC-EPA pproch divides ech product into individul process flows nd strives to quntify their environmentl effects. For exmple, in the mnufcturing stge of products, it ttempts to go s fr bck ( upstrem ) in the flow s possible. This ssessment is typiclly limited by dt vilbility, time, nd cost nd includes the first tier (direct) suppliers but seldom the complete hierrchy of suppliers, i.e., ll the suppliers of suppliers (nd thus the indirect effects). In contrst, the EIO- LCA model uses the economic input-output commodity by commodity mtrix of the U.S. economy ( generl interdependency model) to identify the entire chin of suppliers (both direct nd indirect) of commodity, thus setting the boundry of the ssessment t the level of the ntionl economy. The mtrix is bsed on ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 36, NO. 14, /es CCC: $ Americn Chemicl Society Published on Web 06/11/2002

2 commodities such s cement, steel, col, sugr, etc. To obtin the totl (direct plus indirect) economic demnd, finl purchse (finl demnd) mounts re input into the model. The results re then multiplied by mtrixes of energy use nd emission fctors clculted on economic sector level (e.g., energy use per dollr). The bse yer for EIO-LCA dt is currently The EIO-LCA model hs been pplied to number of product ssessments (see, e.g., refs 9-11). The EIO-LCA method ws used to estimte the mount M of ech GHG emissions (CO 2,CH 4,N 2O) from constructing nd operting power plnts bsed on the mounts nd costs of the mterils nd energy inputs. The construction ssessment included mteril inputs (extrction, processing, nd trnsporttion) nd equipment use (combustion of fuel). For the opertions stge of the fossil-fueled power plnts, fuel inputs were quntified in ech yer of the service life. Air emissions were estimted from the fuel extrction, trnsporttion, nd combustion phses. The temporl effects of different GHGs on globl (climte) chnge re ccounted for by using the globl wrming effect (GWE), which is the sum of the product of instntneous GHG emissions (M) nd their specific time-dependent globl wrming potentil (GWP). Since GWP compres the effect of GHG emissions to the emission of similr mount of CO 2 over chosen time horizon, it is intended for use in studying reltive rther thn bsolute impcts of emissions (12). The GWP for prticulr GHG nd given time horizon is (13) TH x [x 0 (t) ]dt GWP ) TH r [x 0 (t) ]dt where x is the rditive efficiency of given GHG, which represents the rditive forcing [rditive forcing mesures the importnce of potentil climte chnge mechnism; it represents the perturbtion to the energy blnce of the tmosphere following chnge in the concentrtion of greenhouse gses] divided by the chnge in its tmospheric concentrtion since before the industril revolution (14) up to 1992 (the bse yer of the EIO-LCA dt); r is the rditive efficiency of CO 2, which is ssumed to be 1 becuse ll other GHGs re compred to CO 2; x (t) in the numertor is response (decy) function using GHG-specific e-folding time (tht represents the time required for gs to get to 1/e of its initil mss) (14); x (t) in the denomintor represents the CO 2 response function (13); nd TH is the time horizon between the instntneous relese of the GHG nd the end of the nlysis period. Therefore, the globl wrming effect (in metric tons of CO 2 equivlent, MT of CO 2 is where M j is the mount of the instntneous emission of ech GHG j (in metric tons, MT); GWP j,th is the globl wrming potentil for ech GHG j over the time period TH clculted using eq 1. For exmple, the GWE of CH 4 emissions over 20 yr is equl to the mounts of releses in yers 1, 2, 3, multiplied by methne s GWP when the TH is 20, 19, 18,..., 1 yr nd summed for the totl. Therefore, the globl impct of ech electricity genertion technology over time is function of the frction of gs remining in the tmosphere in the future s compred to the effect of CO 2 remining in the tmosphere in the future. In ddition to GWP clcultions for CH 4, it is ssumed tht fter tmospheric decy ll CH 4 oxidizes into CO 2, which is cptured by the rditive efficiency of CH 4, nd thus is ccounted for s dditionl CO 2 (12). The CO 2 response (1) GWE ) M j GWP j,th (2) function is used to determine the future concentrtion of crbon in the tmosphere. The opertion of fcility depends on the obsolescence of the structures nd technology. Consequently, the nlysis periods depend on upgrdes, chnges in technology, societl preferences, resource vilbility, etc. To ccount for different service lives of vrious power plnts, this nlysis looked t four periods: 10, 20, 30, nd 40 yr fter construction. Next, the cse studies of the five electricity genertion technologies re presented. Hydroelectric Plnt: The Cse of Glen Cnyon Dm Hydropower is the United Sttes leding renewble electricity source (round 7% of genertion cpcity) (15). In 1978, s direct response to the oil crisis, the U.S. Bureu of Reclmtion, the second lrgest hydroelectricity producer in the ntion with 58 power plnts (16), estblished hydroelectric plnt upgrde progrm. The primry gols of upgrding re incresed power output nd improved relibility of the system. Through October 1995, 55 genertor units hve been upgrded, corresponding to n dded cpcity of 1783 MW. Ech upgrded unit incresed in cpcity by n verge of 48%, t cost of $69/kW, nd it hs been estimted tht three-qurters of the dms operted by the Bureu of Reclmtion now contin high-efficiency genertor windings (17). The Glen Cnyon hydroelectric plnt on the Colordo River is the second lrgest operted by the Bureu (17). It begn opertion in The reservoir, the 300-km-long Lke Powell, formed by flooding the Glen Cnyon nd displcing m 2 of lnd (18), is the second lrgest in the United Sttes. It provides dditionl services such s wter for irrigtion, recretion, nd flood control nd mngement. Between 1984 nd 1987, the genertors were upgrded by 338 MW to 1296 MW. The fcility upgrde consisted of rewinding the genertors nd reducing the size of ech penstock (the tube trnsferring wter into turbine) from 15 to 14 in. dimeter (19). The fcility hs 8 units; five genertors re presently rted t 165 MW ech, nd three genertors re rted t 157 MW ech. The upgrde of the existing dm hs resulted in 39% dditionl power (17). Additionl energy produced from the upgrded hydroelectric plnt corresponded to 1.48 TWh, for totl of 5.55 TWh in 1999 (19). The contrct cost to upgrde units 1, 3, 5, nd 6 ws $ ($26/kW) while it cost $ ($30/kW) to upgrde units 2, 4, 7, nd 8, for totl upgrde cost of $ in 1987 dollrs (17). The cost clcultions do not include the offset in upgrde cost by routine opertion nd mintennce costs. Nmely, norml mintennce costs would hve been incurred to replce worn genertor winding even if the upgrde hd not occurred. This considertion would mke upgrde costs significntly smller. On the bsis of detiled technicl records (20), eqs 1 nd 2, nd the CO 2 response function (13), the estimted GWE of Glen Cnyon s construction is MT of CO 2 equiv (fter 20 yr). The contribution of construction mterils, processes, nd power plnt components is shown in Tble 1. Emissions from excvtion were clculted bsed on the fuel consumption of the construction equipment, ssuming tht ll fuel ws converted to CO 2. The GHG emissions from the upgrde were estimted ssuming tht ll replced prts cme from the sector tht produces turbines nd turbine genertor sets. Since EIO- LCA in its current version (7) uses 1992 dollrs, we converted the upgrde costs from 1987 to 1992 dollrs using the Consumer Price Index (CPI) (21). The upgrde, which incresed power cpcity by 39%, resulted in MT of CO 2 emissions, or bout 1% of the estimted CO 2 emissions from Glen Cnyon s initil construction ( MT of CO 2). VOL. 36, NO. 14, 2002 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

3 TABLE 1. Mjor Construction Inputs nd GWE (fter 20 yr) for Glen Cnyon Hydroelectric Plnt inputs totl MT unit cost (1992 $/MT) totl cost GHG emissions (MT of CO 2 (1992 $) CO 2 + CH 4 + N 2O ) GWE concrete b excvtion (m 3 ) n turbines nd turbine genertor sets n n power distribution nd trnsformers n n steel c copper c luminum c totl Totl emissions re rounded to one significnt digit. MT, metric ton; GWE, globl wrming effect; n, not vilble. b Ref 39. c Ref 40. While hydroelectric plnts do not use fossil fuels in opertion, they emit GHGs from biomss decy in the dm s reservoir, subject of debte ltely (22, 23, 3). Yerly biomss emissions re reduced s the flooded vegettion decys over time. Colder climtes hve slower decy rtes nd thus lower nnul emissions (23). For Glen Cnyon, the ssumptions were tht () the re of the flooded lnd is similr to the surfce re of the reservoir, Lke Powell ( m 2 ), (b) originlly the lnd ws covered by desert scrub tht hs crbon density of 0.3 kg of C/m 2 (24), (c) the e-folding time for the biomss decy is 7 yr, nd (d) 10-30% of the crbon ws subject to nerobic decomposition nd relesed s CH 4 (22). Accordingly, the GWE is estimted to be MT of CO 2 equiv (fter 20 yr). [The CO 2 response function ws used to clculte these vlues.] In ddition, the formtion of Lke Powell displced n ecosystem nd resulted in forgone crbon uptke mesured by net ecosystem production (NEP). NEP is the difference between net primry productivity (NPP), which bsorbs crbon from the tmosphere, nd heterotrophic respirtion in the bsence of disturbnces, which releses crbon to the tmosphere (25, 26). NEP is clculted s NEP ) NPP - C τ where C is the mount of crbon stored in the terrestril ecosystem; τ is the verge turnover time, which is clculted s (27, 28): Using 298 K for the locl men nnul temperture (MAT), τ ws clculted s 15 yr. On the bsis of nnul NPP of kg of C/m 2 (24) nd crbon density in the desert scrub ecosystem (0.3 kg of C/m 2 ; 24), the nnul NEP ws clculted s 12 g of C/m 2. Assuming constnt crbon sequestrtion rtes, the estimted GWE due to the forgone crbon uptke of the flooded re is MT of CO 2 equiv (fter 20 yr). Summing the two GHG emission sources (construction of the dm nd biomss decy from the reservoir) nd the forgone NEP, the totl GWE of the Glen Cnyon Dm fter 20 yr (t the time of the upgrde) is estimted t MT of CO 2 equiv. Decy from flooded biomss ccounts for 67-83%, NEP loss ccounts for 7-13%, nd construction ccounts for 8-17% of the totl GWE (percentges my not sum due to rounding). Hydroelectric plnts hve been intensely criticized for chnging nd destroying the physicl environment, such s destroying nturl hbitt (e.g., of Pcific Northwest slmon) nd species, being unsightly (such s the flooding of Glen Cnyon), silttion, dislodging indigenous popultions, etc. While undoubtedly importnt, these issues re not the subject of this pper. (3) τ ) 42.8 e -1921[1/( ) - 1/(MAT )] (4) In the following, the comprison of Glen Cnyon Dm to two renewble (solr nd wind) nd two nonrenewble (col nd nturl gs) power sources is presented. It ws ssumed tht ll the other power plnts cn meet Glen Cnyon s 1999 output (5.55 TWh) nd re locted in the sme geogrphicl re (ner the border of Uth nd Arizon). This is importnt for the solr nd wind options s the locl conditions ffect the design nd opertion of such fcilities. Solr Power Plnt Medium-sized photovoltic (PV) plnts of 1 MW cpcity re considered the functionl unit (29). Ordinrily, lrge cpcity solr plnts re designed s therml systems insted of incorporting photovoltics. These plnts use reflective surfces to focus sunlight on collector tht contins working fluid (e.g., n oil-filled tube). The het from the working fluid is trnsferred to wter, nd the resulting stem powers turbine-genertor set to produce electricity (30). This setup would be more pproprite t the scle under considertion here; however, solr industry trends point towrd PV module production. Mnufcturing nd constructing PV plnt for the required nnul electricity output (5.55 TWh) would result in GWE of MT of CO 2 equiv fter 20 yr of opertion (Tble 2). The totl cost of mterils nd construction energy is $ (in 1992 dollrs), excluding lnd purchses, lbor/instlltion, nd mintennce costs. The 100-W pnels of dimensions m (31) re used in nonconcentrting rry (n unrelistic configurtion in prctice, but suitble for this nlysis; such lrge rrys would lmost lwys tke dvntge of concentrting lenses), with rry units of 3 10 pnels, ech hving its own concrete foundtion, for surfce re of m, sited t 30 ltitude, t 30-deg tilt (pproximtely 1.2 m of dditionl width is needed to ccount for shding by the rry due to the sun s ngle). There is 0.9 m between ech of these rry units for personnel ccess. Ech djcent unit covers lnd re of m 2 nd hs cpcity rting of 3 kw. Some of these 3 kw units re required (32). The upgrded Glen Cnyon plnt yields 5.55 TWh of energy ech yer from cpcity of 1296 MW. Since the photovoltic plnt will hve smller cpcity fctor (due to solr resource vilbility), the necessry instlled cpcity to chieve the sme delivered energy is 4118 MW, more thn three times the hydroelectric plnt s cpcity. By comprison, the world production of PV modules ws 125 MW in 1997 (33), thus meeting the cpcity with PV is unrechble without mjor investments in production cpcity or new technologicl brekthroughs. The PV rry required in this nlysis would demnd pproximtely m 2 of lnd re. Lnd costs will vry depending on loction. A PV plnt of this mgnitude must be constructed in remote re such s desert where lnd prices re low nd solr resource is high. Given rnge ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 36, NO. 14, 2002

4 TABLE 2. Mjor Construction Inputs nd GWE (fter 20 yr) for Photovoltic Plnt construction inputs totl MT unit cost (1992 $/MT) GHG emissions (MT of CO2 totl cost (1992 $) CO 2 + CH 4 + N 2O ) GWE steel b copper b electricity (MWh) c luminum b cement b glss b totl Totl emissions re rounded to one significnt digit. b Ref 40. c Ref 41. TABLE 3. Mjor Construction Inputs nd GWE (fter 20 yr) for Wind Frm construction inputs totl MT unit cost (1992 $/MT) GHG emissions (MT of CO2 totl cost (1992 $) CO 2 + CH 4 + N 2O ) GWE steel b electricity (MWh) c d concrete e luminum b plstics f copper b glss b oil d snd b totl Totl emissions re rounded to one significnt digit. b Ref 40. c Derived by ssuming tht ll energy input is electricity, then excluding embedded mteril energy from Tble 6 from ref 36, ssuming 67% construction nd 33% decommissioning energy requirements, nd scled up to 4480 turbines. d Ref 41. e Ref 39. f Ref 42. of prices between $250 nd $1200 per h, the required lnd would dd n dditionl $ to the cost of the PV plnt, n insignificnt mount given the totl life cycle cost of $3.6 billion. The cost of lnd would be reduced if the PV system were distributed, i.e., the generting cpcity required would be spred over lrger number of smll systems (e.g., existing rooftops). The solr plnt displces n ecosystem similr to wht Glen Cnyon Dm s reservoir flooded. The NEP loss is estimted t MT of CO 2 equiv, nd the decy of the biomss removed from the site during construction mounts to MT CO 2 equiv (ssuming the sme ecosystem conditions s for the Glen Cnyon site, mesured fter 20 yr). Therefore, the totl GWE of the PV plnt (ccounting for the mnufcturing, construction, biomss removl, nd NEP loss) would mount to MT of CO 2 equiv 20 yr fter construction. It ws ssumed tht fter 30 yr of opertion (34) ll PV pnels hd to be replced (but not the concrete nd steel bse) nd tht the required construction energy ws 100% of the originl due to n energy-intensive PV mnufcturing process. The electricity output of the fcility remined constnt. The refurbishment resulted in MT of CO 2 emissions, fifth of the originl emissions from mnufcturing nd construction ( MT of CO 2). Wind Frm A wind frm producing 5.55 TWh of electricity per yer ws ssumed to be in southern Uth, t n elevtion of 2134 m (7000 ft), close to the Esclnte Desert where the verge wind speed is 6.5 m/s (35). A turbine of 600 kw (36) ws used s the unit for the frm s totl of 4480 turbines tht would occupy n re of m 2 (37). The totl cost of mterils nd construction of the fcility would mount to $ (in 1992 dollrs) without lbor/instlltion nd mintennce costs. Given rnge of prices between $250 nd $1200 per h, the required lnd would dd n dditionl $ to the cost. Given the lrge re, lnd between the turbines could be used for other ctivities such s griculture. No NEP loss ws nticipted. The contribution of construction mterils nd energy to the GWE of the wind frm fter 20 yr of opertion ( MT of CO 2 is shown in Tble 3. It ws ssumed tht fter 20 yr of opertion ll turbines hd to be replced (but not the concrete foundtions) nd tht the required construction energy ws 30% of the originl electricity nd 100% of petroleum used. The electricity output of the fcility remined constnt. The refurbishment resulted in MT of CO 2 emissions, two-thirds of the originl emissions from mnufcturing nd constructing the plnt ( MT of CO 2). Col-Fired Power Plnt A 1000 MW col-fired power plnt with 6.08 TWh/yr output (29) ws scled down to 5.55 TWh/yr. The technology nd design of col-fired power plnts re not site-specific. Their environmentl performnce depends on col qulity, firing configurtion, nd technology type. Its loction depends on the vilbility of col nd cooling wter. Since this lterntive could replce energy from hydropower, it could be instlled close to where the demnd is (e.g., lrge cities or industries) or to the current power trnsmission lines nd be ccessible by rilrod for col delivery. As shown in Tble 4, the GWE for this power plnt fter 20 yr of opertion (including col burning) ws estimted t MT of CO 2 equiv (38). It ws ssumed tht fter 30 yr of opertion ll boilers hd to be replced (but not the structure of the building) nd tht the required construction energy ws 50% of the originl. The electricity output of the fcility remined constnt. The refurbishment resulted in MT of CO 2 emissions, onethird of the originl emissions from mnufcturing nd constructing the plnt ( MT of CO 2). VOL. 36, NO. 14, 2002 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

5 TABLE 4. Mjor Construction Inputs nd GWE (fter 20 yr) for Col-Fired Power Plnt GHG emissions (MT of CO2 unit cost totl cost totl MT (1992 $/MT) (1992 $) CO 2 + CH 4 + N 2O ) GWE Opertionl Inputs b col combustion c col extrction c trnsporttion by rilrod Construction Inputs steel d concrete e luminum d totl Totl emissions re rounded to one significnt digit. b Includes fuel consumption over n ssumed service life of 20 yr. c Ref 43. d Ref 40. e Ref 39. TABLE 5. Mjor Construction Inputs nd GWE (fter 20 yr) for Nturl Gs Power Plnt GHG emissions (MT of CO2 unit cost totl cost totl mount (1992 $/mount) (1992 $) CO 2 + CH 4 + N 2O ) GWE Opertionl Inputs b nturl gs combustion m c nturl gs trnsporttion m nturl gs extrction m c Construction Inputs steel d concrete e luminum d totl b Totl emissions re rounded to one significnt digit. b Includes fuel consumption over n ssumed service life of 20 yr. c Ref 43. d Ref 40. e Ref 39. Nturl Gs-Fueled Power Plnt The cpcity of the fcility used s model for nturl gs power plnt is 1000 MW (6.34 TWh/yr output scled to 5.55 TWh/yr) (29). The technology nd design of combined cycle gs turbines re not site-specific. Its loction depends on the vilbility of nturl gs nd cooling wter. If this lterntive is to replce energy from hydropower, it should be instlled close to where the demnd is or to the current power trnsmission lines. As shown in Tble 5, fter 20 yr, the GWE (including nturl gs burning) ws estimted t MT of CO 2 equiv. It ws ssumed tht fter 30 yr of opertion ll boilers hd to be replced (but not the structure of the building) nd tht the required construction energy ws 50% of the originl. The electricity output of the fcility remined constnt. The refurbishment resulted in MT of CO 2 emissions, bout 60% of the originl emissions from mnufcturing nd constructing the plnt ( MT of CO 2). Discussion of Results Meeting the incresing electricity demnd is n importnt strtegic gol tht should be chieved by building the lest economiclly nd environmentlly costly new power plnts nd upgrding existing ones. As the U.S. Bureu of Reclmtion hs suggested, upgrding hydroelectric genertor nd turbine units t existing power plnts is one of the most immedite, cost-effective, nd environmentlly cceptble mens for developing dditionl electricl power (17). Figure 1 shows comprison of the GWE/kWh for the lterntives for four time periods fter construction. The wind frm s emissions re lower thn those of the hydroelectric plnt (provided the cpcity of the wind frm cn be scled up to 5.55 TWh nnul output), nd both hve lower impcts thn the other options. For the Glen Cnyon Dm, the effects ssocited with the reservoir re the most significnt, especilly in the short term becuse the reltively rpid initil decy of biomss in the reservoir releses CH 4 tht hs short tmospheric residence time nd high GWE in the short run (hence the exponentil decrese in GWE/kWh for the hydroelectric plnt between yers 10 nd 20). This nlysis locted the plnts in the rid Upper Colordo River Bsin. The GWE of reservoir in region with higher NEP (such s temperte nd tropicl forests) would further increse the impct of the hydroelectric option. The mounts of mterils my lso vry from dm to dm depending on design nd construction criteri. Technologicl chnges ssocited with the other electricity genertion options (such s incresed efficiency of wind nd solr energy conversion nd lower mnufcturing impcts) could chnge the results s well. For the Glen Cnyon fcility, the upgrde 20 yr fter the beginning of opertion (tht incresed power cpcity by 39%) resulted in mere 1% of the CO 2 emissions from the initil construction nd cme with no dditionl impcts from the reservoir. The upgrde of the other power plnts ppers in the 30- nd 40-yr vlues in Figure 1. The hydropower upgrde would obviously not result in dditionl lnd use. Still, the Glen Cnyon Dm uses the most lnd due to its reservoir, Lke Powell, bout one-third more thn the wind frm, which in turn would require lmost 10 times more lnd thn the PV plnt. Mesured fter 20 yr (Tbles 1-5), the GWE of construction ws insignificnt for the hydroelectric, col, nd nturl gs power plnts. (Note: construction inputs were indistinguishble from mnufcturing of electricity genertion equipment for the solr nd wind options.) Figure 2 shows discounted electricity costs including construction, opertion, nd mintennce. The hydropower option produces the chepest energy, followed by ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 36, NO. 14, 2002

6 FIGURE 1. Comprison of GWE per electricity output for vrious lterntives for four time periods fter construction (g of CO 2 equiv/kwh). FIGURE 2. Electricity cost in 2000, ssuming constnt nnul output nd 5% nnul discount rte (cents/kwh). Footnotes: (1) ref 34; (2) refs 37 nd 44; (3) ref 15, ssuming stble prices for fossil fuels; (4) refs 19 nd 20. col, nturl gs, nd wind. The PV plnt hs the highest costs. For full life cycle costs of the lterntives, the vlution of externl effects (such s emissions) should lso be included. Understnding the environmentl impcts of electricity genertion options from renewble nd nonrenewble sources is essentil for better policy- nd decision-mking. This nlysis looked t the GWE of GHG emissions ( globl concern) from five lterntives. Investment decisions ought to consider vriety of other environmentl impcts such s toxic emissions from fossil-fueled power plnts, hbitt destruction ssocited with dms, etc. However, comprison of GWE with other environmentl impcts is complicted. Acknowledgments Some of the ides for this reserch were first explored in clss project t UC Berkeley by S.P., John Gllowy, Ahmd Hy, nd Jen Ku. S.P. is grteful for the Conselho Ncionl de Desenvolvimento Cientifico e Tecnologico (Ntionl Council for Scientific nd Technologicl Development) fellowship from Brzil. Literture Cited (1) Post, N. M. ENR 2001, 247, 16. (2) Rost, P.; Armisted, T.; Ichniowski, T. ENR 2001, 247, 12. (3) World Commission on Dms. Dms nd Development: A New Frmework for Decision-Mking; Erthscn Publictions Ltd: London nd Sterling, VA, VOL. 36, NO. 14, 2002 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

7 (4) Crbon Dioxide Emissions from the Genertion of Electric Power in the United Sttes: 2000; U.S. Deprtment of Energy/U.S. Environmentl Protection Agency: Wshington, DC, (5) U.S. Environmentl Protection Agency, Office of Pollution Prevention nd Toxics. Toxics Relese Inventory: 1998; U.S. Government Printing Office: Wshington, DC, (6) Currn, M. A. Life Cycle Anlysis; McGrw-Hill: New York, (7) Economic Input-Output Life Cycle Assessment: 2001; Green Design Inititive; Crnegie Mellon University: Pittsburgh; (ccessed July 2001). (8) Hendrickson, C. T.; Horvth, A.; Joshi, S.; Lve, L. B. Environ. Sci. Technol. 1998, 32 (4), 184A-191A. (9) Lve, L. B.; Mclen, H.; Hendrickson, C. T.; Lnkey, R. Environ. Sci. Technol. 2000, 34 (17), (10) Horvth, A.; Hendrickson, C. T. J. Infrstruct. Syst. 1998, 4 (3), (11) Horvth, A.; Hendrickson, C. T. Trnsp. Res. Rec. 1998, 1626, (12) Houghton, J. T. Climte Chnge 2001: The Scientific Bsis; Intergovernmentl Pnel on Climte Chnge; Cmbridge University Press: New York, (13) Houghton, J. T. Climte Chnge 1994: Rditive Forcing of Climte Chnge nd n Evlution of the IPCC IS92 Emission Scenrios; Intergovernmentl Pnel on Climte Chnge; Cmbridge University Press: New York, (14) Houghton, J. T. Climte Chnge 1995: The Science of Climte Chnge; Intergovernmentl Pnel on Climte Chnge; Cmbridge University Press: New York, (15) Annul Energy Outlook: 2001; U.S. Deprtment of Energy, Energy Informtion Administrtion: Wshington, DC, (16) U.S. Bureu of Reclmtion. Reclmtion s Role in Hydropower; (ccessed June 2000). (17) U.S. Bureu of Reclmtion. Bureu of Reclmtion Genertor Power Uprte Progrm Report; dt/uprte/uprte.htm (ccessed June 2000). (18) U.S. Bureu of Reclmtion. Glen Cnyon Dm Fcts; (ccessed June 2001). (19) U.S. Bureu of Reclmtion. Glen Cnyon Power Plnt; (ccessed June 2001). (20) Glen Cnyon Dm nd Power Plnt: Technicl Record of Design nd Construction; U.S. Bureu of Reclmtion: Denver, CO, (21) Consumer Price Indexes: 2000; U.S. Deprtment of Lbor, Bureu of Lbor Sttistics: Wshington, DC, (22) Pinguelli Ros, L.; Scheffer, R. Energy Policy 1995, 23 (2), (23) Ggnon, L.; vn de Vte, J. Energy Policy 1997, 25 (1), (24) Hrte, J. Consider Sphericl Cow; University Science Books: Suslito, CA, (25) Bldocchi, D. Crbon nd Energy: Terrestril Stores nd Fluxes. In Encyclopedi of Globl Environmentl Chnge, Vol. 2; John Wiley & Sons: New York, (26) Wtson, R. T.; et l. Lnd Use, Lnd-Use Chnge nd Forestry; IPCC, WMO, UNEP/GRID-Arendl: The Hgue, Netherlnds, 2001 (CD-ROM). (27) Sndermn, J.; Amundson, R.; Bldocchi, D. University of Cliforni, Berkeley, unpublished results. (28) Lloyd, J.; Tylor, A. Funct. Ecol. 1994, 8 (3), (29) Thr, K.; et l. Energy Convers. Mnge. 1997, 38, S (30) Johnsson, T. B.; et l. Renewble Energy: Sources for Fuels nd Electricity; Islnd Press: Wshington, DC, (31) Siemens Solr. Siemens Solr Module Detils nd Specifictions; (ccessed June 2001). (32) Solr Rdition Dt Mnul for Flt-Plte nd Concentrting Collectors: 1991; Ntionl Renewble Energy Lbortory, Anlytic Studies Division: Golden, CO, (33) Eckhrt, M. T. Finncing Solr Energy in the U.S.; Technicl Report; Renewble Energy Policy Project: Wshington, DC, (34) Stronberg, J.; Virinder, S. Government Procurement to Expnd PV Mrkets; Technicl Report; Renewble Energy Policy Project: Wshington, DC, (35) Wind Energy Resource Atls of the United Sttes; Pcific Northwest Ntionl Lbortory, Solr Technicl Informtion Progrm; Solr Energy Reserch Institute: Richlnd, WA, (36) Schleisner, L. Renewble Energy 2000, 20 (3), (37) Nturl Resources Cnd, Energy Diversifiction Reserch Lbortory. Wind Energy Project RETScreen Energy Model; 1998; retscreen_new_1.html (ccessed My 2000). (38) U.S. Environmentl Protection Agency, Office of Pollution Prevention nd Toxics. Compiltion of Air Pollutnt Emission Fctors AP-42; U.S. Government Printing Office: Wshington, DC, (39) R. S. Mens Building Construction Cost Dt; R. S. Mens Co.: Kingston, MA, (40) U.S. Geologicl Survey, Minerl Resources Progrm. USGS Minerls Informtion, Publictions nd Dt Products; 2002; (ccessed Jnury 2002). (41) Retil Energy Prices in Selected Countries in US Dollrs/Unit; Interntionl Energy Agency: (42) Joshi, S. Unpublished Ph.D. Disserttion, Crnegie Mellon University, Heinz School of Public Policy nd Mngement, (43) Energy Prices; U.S. Deprtment of Energy, Energy Informtion Administrtion: Wshington, DC, (44) Sezgen, O.; et l. Wind Genertion in the Future Competitive Cliforni Power Mrket; Technicl Report; Lwrence Berkeley Ntionl Lbortory: Berkeley, CA, Received for review June 27, Revised mnuscript received Mrch 20, Accepted My 1, ES ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 36, NO. 14, 2002