Determining the Cost of Electricity of a Natural Gas Generator

Determining the Cost of Electricity of a Natural Gas Generator

Nicholas Kenny, P.E. ? Extension Irrigation Specialist, Texas A&M University

As water well production declines across many parts of the Texas High Plains, many pumping plants currently using natural gas engines are becoming better suited for smaller submersible pumping units driven by electricity.

Infrastructure costs associated with delivering necessary electrical power from the grid often make this conversion to properly sized, efficient pumping plants an economic compromise. An alternative method for electrical power delivery in these scenarios is the installation of an onsite natural gas generator that can power multiple smaller electrical pumping plants.

The following information contains a basic method for determining the fuel costs associated with producing electricity at an on-site natural gas generator. This cost can be directly compared to the market price of electricity purchased from a commercial provider.

To determine total costs associated with onsite power generation,

Natural gas Caterpillar 3306TA driving a Marelli three-phase generator, providing power to three irrigation wells.

operation and maintenance expenses and amortized capital expenses tied to the purchase of the natural gas generation unit also must be considered. For practical comparative evaluations, the capital expenses associated with on-site generation usually are similar to or less than the capital expenses related to delivering power from the existing commercial electrical

grid to a pump location. Further, comprehensive maintenance costs associated with one natural gas generator typically are much less than the costs associated with multiple natural gas wells. Upgrade costs at individual pumping plants also will need to be included in a comprehensive economic evaluation related to this conversion.

1 LSU AgCenter Pub. 3241-D: Determining the Cost of Electricity at a Natural Gas Generator

The feovlaloluwaitniognisn,ftohremcaatipointacl oenxtpaeinnsseasbaasssioccmiaetethdowd iftohrodne-tseirtme igneinnegrathtieonfuuelsucaolslyts aarsesoscimiatieladr wtoithorplreosdsutchinang ethleecctraipciittyalaetxapnenses on-sirteelantaetdurtaol gdaeslivgeerninegratpoor.weTrhifsrocmostthceanexbisetindgireccotlmy mcoermcipaalreedlectotritchael gmraidrketot paricpeumopf eloleccattriiocnit.yFpuurtrhcehra,secdomfrpormeheansive commmearicnitaelnparnocveidceors.ts associated with one natural gas generator typically are much less than the costs associated with multiple

Method of Calculating Costs natural gas wells. Upgrade costs at individual pumping plants also will need to be included in a comprehensive economic

To deetvearlmuaintieotnortaellactoedststoasthsioscciaotnevdewrsiitohno. n-site power generation, operation and maintenance expenses and amortized capital eermexvalapailentuentadestneiosatonntscid,eeedtchlioevtsoetcrsaitnpahoigisentsfaotplpeMacoueirwaxresvctpeeahpaerdasnelsfwsuecrieosiristfmo,ehiafetsotstdhtnhhhoeeeecevinaoemnaetxealtuluidtosaurtmarrwipanlelsigegtehaagcsodacoosfgcnmte-ungisnmmieraetneaertraeetcugtreoiaeraitrnnalitoethlyenrsapligeetsiuiccaocnatmnrsoilitlcynu(eaasdtlaaluhsrsagseoelrulmfiymdorluoeaurctrnsmohectgolsaebeeinNpwmesnrphseasitaultclttusluamhosehwrr.manapgenlstieoligpndlltaoheoetsrceriraCeoatcldtoaneiotr.ose,snsrtpFps.rtoiohlaFrlvaasuinrsdpro3irtntch3ahgi0ceae6trpti,TeoccdwaAacploewdirmtcriatiotopvlhmirtneehmpxghreapueaerenlaMtnisitrpisiravvielrgeeesealtliiotnhreenevaatulurMaalteigothansordewloaeftlelCsd.atUlocbnputeahgliar)tsatu.idcnreoTganhcvlCoieogssrtsssatimsosaynte.cianodsniuvsirudeummalpeptunimotnpiis.ngAupssleaandtsntaoolstoeca,wlmiclluonlaseettdentoathtbueeriranalctlguedaeosdf in a comprehensive economic

Measure accurate

tthhiesemlamrepeaseaseudtdreetiinrmmsgeeniitinnswstmeihlcloeubnledTt)si.epfTxolhiareicssdomnHbseiuaygmshuaprtePicmolonaenroirntfeisascsrutpieseoecqdnifuiteoifrdaeccvaotltcolhuurmlaaNpttheaeoatoasutefrhaandgelceagircntsaaueosptrreaauCltlaooangtrfye,tarepnspfraid(oolttlvuharirreda3illn3ogg0na6pgsToewArcoetdhrnretsiovuiintmnhtgreperatevioMiarnlra.iirgseAa,ltlstiihotanehrmneeoo-tree,

most natural glaos cmaeltecros nindtihteioTnesxa(sfoHrigehxPalaminsplreq:ugireasthatteamdpiseprlaaywteeudllrsre.e,adainlgtitisudmeu,ltiplied by a correction factor to

MethaocdcooufnCtafolcrulloactpainlrgceoCsnosdsiuttsiroyens, (efotrce.x)a.mple: gas temperature, altitude, pressure, etc.).

1 Measure

accurate

tthhiesem1la.epasseudretimmeenitnwseilclobned)s. fTohricsomnseuamsuprte3imo6ne0notf0ias

specified volume of natural gas (the longer the interval is, the used to calculate the rate of natural gas consumption. As a

more note,

macocsotunnat tfuorrallogcWaalshcemorene:dteirtisonins

(tfhoerVNTeoGxelaxcNomGanssp==lHevn:iogaglhtuaumsrPatelelamoginfapssneacrrateoutqnurusaruielrm,egaaptlshttiicatouotndnaiesnu,dmpcisruepebdsliascdyuufereedrei,ntergeptcaet.dhr)i.ehnosgpueirsc(ifmfti3eu/hdltoitupimrli)eedpebryioad

correction (ft3)

factor

to

1.

Time=elapse3d6ti0m0e (seconds)

Calculate the Where:

hourly

fuel cost of the natural gas generator: NGcons = natural gas consumption in

cubic

feet

per

hour

(ft3/hour)

2.

CaVTlciomulNelGa==teevlaotplhusemedehtiomof uenar(tsluyercaoflnugdeassl)ccoonssutmoefdtdhurein/gn1tah0teu0srp0aeclifgieadstime period (ft3)

Whereg: eneratoNr:G Cost= cost of natural gas consumed per hour of operation ($ / hour)

Calculate the hourly fuel cost ofNthGeCnaotsuturnaitl=gapsugrcehnaesreatporri:ce of natural gas per thousand cubic feet ($ / thousand cubic feet)

2 NGcons = natural gas consumption in cubic feet per hour (ft3/hour)

Mea2su. re the electricalproductionofthegenerator usingapro/p1er0ly0ra0ted, true-rms digital clamp meter. The measurements

npeocweWesrshapreryroeda: ruectAioCn

avnodlNtsuGsaenCdtohscetu=rarcveoensrtat gionef

navmaotlputasra.gleIgt aaonsfdtceonanmsisupmewreaodgretphewrerhahidolieunrgtoso.fm(oTepaheseruasretieocnaall(lc$uth/larhetoieouners)leacrtreicfaolr

legs to ensure balanced three-phase power (the

calculation for single-pNNhGGacsCoenosps=otuwnniaet tr=udrpaoulersgcahnsaoscteoinnpcsrluiucmedepotftihonenastiuqnruacalurgbe-aicrsofpoeeterot tfphetohrurhesoaenufdrac(cftuot3br/.hi)cofuere)t ($ / thousand cubic feet)

Measure the electrical production of the generator using a properly rated, true-rms digital clamp meter. The measurements necessary are AC volts and current in amps. It often is worthwhile to measure all three electrical legs to ensure balanced power production and use the average voltage and amperage readings. (These calculations are for three-phase power (the calculation for single-phMaseeapsouwreer dtoheseneotleincctlurdiceathlepsrqouadrue-crotoiot nof othfretehfeactgore.)nerator

using a properly rated, true-rms digital clamp meter. The measurements necessary are AC volts and current in amps. It often is worthwhile to measure all three electrical legs to ensure balanced power production and use the average voltage and amperage readings. (These calculations are for three-phase power (the calculation for single-phase power does not include the square-root of three factor.)

Exercise extreme caution when working around all agricultural electrical circuits!

2 LSU AgCenter Pub. 3241-D: Determining the Cost of Electricity at a Natural Gas Generator

Exercise extreme caution when working around all agricultural electrical circuits! Determine the power generated by the generator in

kilowatt hours per hour (kwh / hour).

Determine the power generated by the generator in kilowatt hours per hour (kwh / hour).

3 Exercise

extreme

3.

cautionwhen workingaround

all

agricultural

electrical

circuits!

Exercise extreme caution when working around all agricultural electrical circuits! DeterminWe thheerpe:ower generaPVtoe=wdoeburyt=pthuketilvgooewlntaaetgrtaehtogoreunirnserkpaietlreodhwo(aAuttrChgoevunorelstrsap)teerdh(okuwrh(k/ whohu/r)h.our).

Determine the pow3e.r generatedbythIPe=Fgeo=nueptproauwttoecrruifnrarcektnioltorgwoefanttethrheaotgeuedrns(eaprmeartpohsr)oiunrd(ekcwimh a/lhso(utyrp).ically 85 percent or .85)

3WC.haelcrue:lateW4t.hheeCrceoa:slPVtcoou=fwlpoaeourtwte=peukrPVIPtt:ih=oFlv=owoeow=loeutauarcpttgptoot=peuwhusktgoteticeurlvuonroofrswealrfrtcepaaatnpetgotttreeorhdghogwoeo(feunAuentrerhsCerrgearp:atevgeetnoreedeldnhtr(seaoa()rtAumaertdCpogs(rev)kinownelthrdsae)/tcehidmo(uakrlw)s. h(ty/ phiocuarll)y. 85 percent or .85)

CalculateWthheecroe:stIo=f opuotwpuertE:cluercreCnot sgte=nuenraitteedle(catmricpasl) cost in dollars per kilowatt hour ($ / kwh)

4 Calculate

the

cost

o4f.

PF = powNerGfaCctoosrt

power: Power=

oe=lfentchatteruicgraaellngpeaoraswtoceorrsigtnepdneeercrhaimtoiuoarnls(r$(atty/eph(iokcuwarlhloyf/8hN5oGup)re)rcent

or

.85)

4EA. xnaamtuprlaeWl ghaesreg:eneratorseEt wleicthCoanst=85unpietrecleencttrpicoawl ecrofsatcintodr oisllagresnpeerartkinilgow48a0tt vhoolutrs (w$i/thkwa hs)ystem current load of 120 amps

from two pumping plants. NNGatuCroasltg=asnaistupruarlcghaassecdosftrpoemr hanouorf(f$-s/itheosuurpopfliNerGa)t $5 per thousand cubic feet. Measurements of

natural gas show that 20 cPuboiwcefree=t ealreectcroicnaslupmoewdeirngaen5e0r-asteiocnonradtepe(kriwodh./Dheotuerr)mine the unit electrical power cost associated

Wwhitehret:his generatoErlesectC. ost= unit electrical cost in dollars per kilowatt hour ($ / kwh)

Example

NG Cost = natural gas cost per hour ($ / hour of NG)

Example Power = electrical power generation rate (kwh / hour)

A natural gas generator set with an 85 percent power factor is generating 480 volts with a system current load of 120 amps

EAxnaamtuprlaelwfngraoiattmushrgtathelwingsoeag1rfopsaea.uftnsocmheA1rtorpaos2witenro0tgtrahwissatpaeiutltmtahg.2rna0eaptsnlncs.uge8Nbf5raariactopsutefrmieragnceleetggtnnaawtrs4eepoi8roscaw0opptneuuosrvrumrcfomhaslacpetstedsoientrdiwngiwfsraiotipgthm5elh0na-aeansarneatnsctosioyfn.nf8gs-dNs5t4iepta8eepm0trseuiuvorrpocdcapl.utellsDirengrwerettaieatnrthspm$toai5isnlwsopeyeeastrhtrdeetmhuoncuiustarreneldenctctulroibcaiacdl

feet. Measurements of

power cost associated of 120 amps

fnwraoittmuhrtathlwigsoagpseunsmheorpawitnogtrh12pfaespa.ee.tllrutaeee.2nrct0ct.scthc.roMuNiacnbsaeiascteaulufdrsepamueloftgrerwaaeodrsememiirscneopacnnuaonsrtucss5mhota0oefsadf-fe-sdsisnnsefiaotracoetcom5ui0nasr-audtasneeplcpodpogfenflaw-idrsesiiioptrteeshdarshi.uottopdDh$pw.ileD5siettereghpteareaertmmntr$5iei2ntnrhpe0eaeotrhtcutoethuhsruobeanusiniscteuadentnfl.deeictcceuturtbibciiacclfpeoewt.eMrecaossut r/aesmsoecnitasteodf

1.

12 2.

2343.... ///

3 3.

4.

/

4 4.

/

3 LSU AgCenter Pub. 3241-D: Determining the Cost of Electricity at a Natural Gas Generator



Louisiana State University Agricultural Center William B. Richardson, Chancellor

Louisiana Agricultural Experiment Station John S. Russin, Vice Chancellor and Director Louisiana Cooperative Extension Service Paul D. Coreil, Vice Chancellor and Director

Pub. 3241 D (200) 7/13 The LSU AgCenter is a statewide campus of the LSU System and

provides equal opportunities in programs and employment.

4 LSU AgCenter Pub. 3241-D: Determining the Cost of Electricity at a Natural Gas Generator

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