Pathways to a fully sustainable electricity supply for Nigeria in the mid-term future

This is a e sion o a publica ion in Please ci e he publica ion as ollows: DOI: Copy igh o he o iginal publica ion: This is a pa allel published e sion o an o iginal publica ion. This e sion can di e om he o iginal published a icle. published by Pa hways o a ully sus ainable elec ici y supply o Nige ia in he mid- e m u u e Oyewo Ayobami Solomon, Aghahosseini A man, Bogdano Dmi ii, B eye Ch is ian Oyewo A.S., Aghahosseini, A., Bogdano , D., B eye , C. (2018). Pa hways o a ully sus ainable elec ici y supply o Nige ia in he mid- e m u u e. Ene gy Con e sion and Managemen , ol. 178, pp. 44-64. DOI: 10.1016/j.enconman.2018.10.036 Au ho 's accep ed manusc ip (AAM) Else ie Ene gy Con e sion and Managemen 10.1016/j.enconman.2018.10.036 © 2018 Else ie L d. UNCORRECTED PROOF Ene gy Con e sion and Managemen xxx (2018) xxx-xxx Con en s lis s a ailable a ScienceDi ec Ene gy Con e sion and Managemen jou nal homepage: www.else ie .com Pa hways o a ully sus ainable elec ici y supply o Nige ia in he mid- e m u u e Ayobami Solomon Oyewo, A man Aghahosseini, Dmi ii Bogdano , Ch is ian B eye Lappeen an a Uni e si y o Technology, Skinna ilanka u 34, 53850 Lappeen an a, Finland ARTICLE INFO Keywo ds: Nige ia Ene gy ansi ion Desalina ion Pho o ol aic Ene gy sys em S o age Deca bonisa ion ABSTRACT Ambi ious ac ions ocused on apid de ossilisa ion o oday’s ene gy sys ems equi e g ea e u gency, in o de o a e unmanageable impac s o clima e change. T ansi ioning o a cos -e ec i e and ca bon-neu al ene gy sys em in Nige ia and ac oss he globe by he second hal o his cen u y is i al. This s udy explo es a pa adig- ma ic pa hway o a ully sus ainable ene gy sys em o Nige ia, by 2050. The esea ch app oach is o simula e a cos -op imised ansi ion pa hway owa ds 100% enewable ene gy based powe sys em o Nige ia, using a linea op imisa ion model. The model is based on hou ly esolu ion o an en i e yea . The coun y esea ched is s uc u ed in o 6 sub- egions. The op imisa ion o each o he 5-yea ime pe iods is ca ied ou based on assumed cos s and echnological s a us un il 2050 o all ene gy echnologies in ol ed. The le elised cos o elec- ici y declines om 54 €/MWh in 2015 o 46 €/MWh in 2050 o he powe sec o in he Bes Policy Scena io and u he declines o 35 €/MWh wi h sec o coupling. Whe eas, he cos o elec ici y inc eased o 75 €/MWh in he Cu en Policy Scena io wi hou g eenhouse gas emission cos . The esul s clea ly e eal ha in eg a ing a enewable ene gy echnology mix wi h a wide a ie y o s o age echnologies is he mos compe i i e and leas cos elec ici y op ion o Nige ia in he mid- e m u u e, as indica ed by he Bes Policy Scena io. In pa icula , he compa ibili y and p edominan ole o sola pho o ol aics and ba e ies is pa amoun owa ds a apid an- si ion o Nige ia’s powe sec o , due o highly a ou able economics. This s udy concludes wi h he implica ions o a s able and suppo i e policy en i onmen , ansi ioning o a de ossilia ed ene gy sys em in Nige ia could be achie ed in he mid- e m u u e. This s udy is he i s o i s kind in ull hou ly esolu ion o Nige ia, and demons a es he need o ca ying ou de ailed analyses in examining gaps in ene gy ansi ion unde s anding based on a ious policy cons ain s o de eloping coun ies in compa able clima es. Nomencla u e A-CAES adiaba ic comp essed ai s o age BPS bes policy scena io CAPEX capi al expendi u e CCGT combined cycle gas u bine CHP combined hea and powe CPS cu en policy scena io CSP concen a ing sola he mal powe DISCOs Elec ici y Dis ibu ion Companies in Nige ia ECN Elec ici y Co po a ion o Nige ia ESPR elec ic powe sec o e o m FMWR Fede al Minis y o Wa e Resou ces GENCOs powe gene a ion companies in Nige ia GT gas u bine HVDC high ol age di ec cu en LCOC le elised cos o cu ailmen LCOE le elised cos o elec ici y LCOS le elised cos o s o age LCOT le elised cos o ansmission NDA Nige Dams Au ho i y NEEAP Na ional Ene gy E iciency Ac ion Plan NEPA Na ional Elec ic Powe Au ho i y NESI Nige ian Elec ici y Supply Indus y NREEP Na ional Renewable Ene gy and E iciency Policy OCGT open cycle gas u bine OPEX ope a ional expendi u e PHCN Powe Holding Company o Nige ia PHS pumped hyd o s o age PV pho o ol aic RE enewable ene gy RoR un-o - i e SHS sola home sys em SNG syn he ic na u al gas SSA Sub-Saha an A ica Email add esses: [email p o ec ed] (A.S. Oyewo); ch is ian.[email p o ec ed] (C. B eye ) h ps://doi.o g/10.1016/j.enconman.2018.10.036 Recei ed 10 Augus 2018; Recei ed in e ised o m 11 Oc obe 2018; Accep ed 13 Oc obe 2018 A ailable online xxx 0196-8904/ © 2018. UNCORRECTED PROOF A.S. Oyewo e al. Ene gy Con e sion and Managemen xxx (2018) xxx-xxx ST s eam u bine SWA S a e Wa e Agency TRANSCO T ansmission Company o Nige ia TES he mal ene gy s o age UN Uni ed Na ions VRE a iable enewable ene gy WACC weigh ed a e age cos o capi al 1. In oduc ion T ansi ioning away om he con empo a y o a ne ze o emission ene gy sys em a ound he middle o he 21s cen u y is o pa amoun impo ance [1], in o de o keep global empe a u e ise well below 2°C abo e p e-indus ial le els and pu suing e o s o limi his o 1.5°C [2]. S aying unde 2°C equi es an u gen shi owa ds de ossilia ed en- e gy sys ems [3]. Renewable ene gy (RE) sou ces a e i al o a oid he unmanageable impac s o clima e change [4]. In addi ion, RE sou ces could add ess he cu en elec ici y supply gaps and u u e demands in many coun ies in Sub-Saha an A ica (SSA), as well as in Nige ia [5]. Elec ici y demand in Wes A ica g ew om 29 TWh in 2000 o 61 TWh in 2012; he highes demand in he egion is in Nige ia, which accoun s o abou 50% o he o al demand [6]. By 2040, o al elec ici y de- mand in Nige ia is expec ed o each 291 TWh acco ding o he In e na- ional Ene gy Agency (IEA) [6]. Nige ia aces an eno mous challenge wi h access o elec ici y [7]. In spi e o he coun y’s abundan oil and gas esou ces, i s ill su e s om huge unde -capaci y in elec ici y gene a ion, wi h equen powe ou - ages d i ing consume s owa ds wide-sp ead use o cos ly backup gen- e a o s [6]. The Nige ian powe sec o is no ye able o mee he en i e powe needs o he coun y [8]. As Aku u e al. [7] ques ion, whe he he e could e e be s able and cos -e ec i e elec ici y in Nige ia. Nige- ia’s on-g id elec ici y consump ion is low, a 126 kWh pe capi a com- pa ed o o he de eloping coun ies [9]. The pe capi a elec ici y con- sump ion o Ghana and Sou h A ica a e 2.9 imes (361 kWh) and 31 imes (3926 kWh) highe han ha o Nige ia, espec i ely [9]. Mo e han 90 million people in Nige ia s ill lack access o g id elec ici y, which ep esen s 55% o he coun y’s popula ion [6]. Unme powe demand esul s in load shedding, blackou s, and eliance on expensi e diesel backup gene a o s [10]. In 2012, an es ima ed amoun o 16 TWh elec ici y demand was se ed by backup gene a o s in SSA, and Nige ia accoun s o abou h ee-qua e s o he elec ici y supplied by backup gene a o s in he egion [11]. The cos o elec ici y om gene - a o s (0.14–0.22 €/kWh) a e mo e han wice as expensi e as g id-based powe (0.06–0.09 €/kWh) in Nige ia [9]. Fu he mo e, he coun y’s economic g ow h is hampe ed by he p e alen ene gy c isis [11]. The Nige ian go e nmen aims a a holis- ic economy ans o ma ion and ha e iden i ied a ious ba ie s o he coun y’s economic de elopmen , which includes he e a ic powe sup- ply, poo and c umbling in as uc u e and o e - eliance on he oil sec- o [11]. To add ess he e a ic powe supply, he Nige ian elec ici y ision 30:30:30 ecognises he signi icance o RE sou ces o comple- men he cu en ossil uel consump ion and gua an ee ene gy secu- i y. By 2030, on-g id capaci y is expec ed o each 30 GW, o which RE will con ibu e a 30% sha e o he o al elec ici y mix [12]. The e a e plans unde way o build nuclea and coal powe plan s in Nige ia [12]. Beyond en i onmen al and public heal h isk o building ossil- u- elled powe plan s [13], mos nuclea powe plan s incu ed cons uc- ion pe iod o e uns [14] and subs an ial cos escala ion [15]. Acco d- ing o [16], 180 nuclea eac o s ep esen ing 178 GW and 459 bUSD wo h o in es men , incu ed almos 231 bUSD in cos o e uns. In ad- di ion, he cos o p o iding elec ici y om RE echnologies in pa icu- la sola pho o ol aic (PV) and wind a e inc easingly compe i i e wi h ossil-based powe plan s. The global weigh ed a e age le elised cos o elec ici y (LCOE) o u ili y-scale sola PV ell by 68% be ween 2010 and 2017 [17]. Fo ins ance, he cu en a i s o new sola PV and wind (0.041 €/kWh) a e now 40% cheape han new baseload coal (0.069 €/kWh) in Sou h A ica [18]. A ecen s udy on cos compa ison o a ious powe echnologies o Nige ia e eals ha RE echnologies a e one o he s onges op ions o mee he powe need o Nige ia in he mos cos compe i i e way [19]. Recen s udies ha e demons a ed he possibili y o achie ing a 100% enewables based powe sys ems o cases such as Nige ia [5], SSA [10], No heas Asia [20], Eu ope [21] and global [22]. These s ud- ies ha e shown ha deep deca bonisa ion o he u u e powe sys em is possible aking in o accoun echnical, economic and socie al con- s ain s, bu i is also he leas cos elec ici y op ion wi h u mos soci- e al wel a e. In addi ion, he Pa is Ag eemen and he Sus ainable De- elopmen Goal 7 (SDG 7) can be well suppo ed by he deploymen o small and la ge scale RE echnologies, in iew o ackling he wo main challenges aced globally; clima e change and widesp ead ene gy po e y [3]. The cu en elec ici y de ici and ising demand in Nige- ia necessi a es apid esponse in b idging he gap be ween demand and supply [12], due o i s g owing popula ion and unp eceden ed economic p og ess [10]. The e o e, ackling he plague o ecu en powe ou ages and ising elec ici y demand in a way ha is economically sus ainable and sa egua ds li elihoods in Nige ia [7], which equi es he deploy- men o RE in as uc u e as a key solu ion wi h bene i s ha a e mul- i ace ed [10]. Nige ia has as un apped RE esou ces [8], in eg a ing RE echnology mix wi h a wide a ie y o s o age echnologies could be compe i i e and he leas cos elec ici y op ion o Nige ia [19]. This esea ch p esen s he impo ance o ca ying ou an analy ical and comp ehensi e in es iga ion, when assessing leas cos elec i ica- ion op ions and ansi ion pa hways o de eloping coun ies, like Nige- ia, unde a ious policy cons ain s. The analysis o Nige ia is exem- pla y o de eloping coun ies o compa able clima es. To be e unde - s and he ansi ion pa hways, eigh scena ios ha e been de ined based on go e nmen al in ended ansi ion plans (Cu en Policy Scena ios) and ze o emission scena ios (Bes Policy Scena ios), which ull ma ch he a ge s o he Pa is Ag eemen . Fu he , he impac o a ious ac o s such as g eenhouse gas (GHG) emissions cos and sec o coupling a e as- sessed as well. The chosen op imisa ion modelling app oach syn hesises and e lec s in-dep h insigh s on how demand o di e en ene gy sec o s such as powe , non-ene ge ic indus ial gas and desalina ion can be me . The op imisa ion o each pe iod, modelled in 5-yea in e als, is ca ied ou based on assumed cos s and echnological s a us un il 2050. The pa- pe is s uc u ed as ollows: Sec ion 2 p esen s an o e iew o he Nige - ian powe sec o . The esea ch me hodology is desc ibed in Sec ion 3. Resul s a e p esen ed and analysed in Sec ion 4. In Sec ion 5, he esul s a e discussed and compa ed wi h ela ed s udies. Conclusion and policy implica ions a e p esen ed in Sec ion 6. 2. The Nige ian powe sec o The his o y o elec ici y gene a ion in Nige ia da es back o 1886, when wo gene a ing plan s we e ins alled o se e he Lagos Colony. In 1929, Nige ia’s i s u ili y company, he Nige ian Elec ici y Sup- ply Company was es ablished [23]. Fu he de elopmen in he sec- o , led o he es ablishmen o he Elec ici y Co po a ion o Nige ia (ECN) in 1951 o o e see elec ici y dis ibu ion in he coun y [23]. In 1962, he Nige Dams Au ho i y (NDA) was es ablished o o e - see hyd opowe de elopmen [24]. The NDA o e saw powe gene a- ion, while dis ibu ion and sales we e unde aken by ECN. Howe e , he ECN and NDA we e me ged in 1972 and esul ed in he o ma ion o he Na ional Elec ic Powe Au ho i y (NEPA), which was esponsi- ble o gene a ion, ansmission, and dis ibu ion o elec ici y o he en i e coun y. Re o ms in he powe sec o in 2005 esul ed in un 2 UNCORRECTED PROOF A.S. Oyewo e al. Ene gy Con e sion and Managemen xxx (2018) xxx-xxx bundling o he NEPA and a enaming o Powe Holding Company o Nige ia (PHCN) [25]. In spi e o he long exis ence o elec ici y in he coun y and e- o ms, he powe sec o de elopmen has been a a slow a e. To- day, gas and hyd opowe plan s domina e he on-g id powe gene a- ion capaci y in Nige ia, which ep esen 86% and 14% o he o al in- s alled capaci y, espec i ely [19]. The coun y’s powe sec o consis s o h ee main sub-sec o s [8], namely; gene a ion companies (GENCOs), ansmission company (TRANSCO) and dis ibu ion companies (DIS- COs) as shown in Fig. 1 [26]. Cu en ly, he e a e 22 gas and 3 hyd o on-g id gene a ing plan s ope a ing in he Nige ian elec ici y supply indus y (NESI) as shown in Fig. 2, concen a ed in Sou he n Nige ia, wi h a o al ins alled capaci y o 12,522MW, and a ailable capaci y o 7141MW [9]. The managemen o T ansmission Company o Nige ia is con ac ed o Mani oba Hyd o In e na ional (Canada). The na ional g id consis s o abou 5524km o 330kV and 6802km o 132kV ansmis- sion lines [12]. The elec ici y dis ibu ion company o Nige ia consis s o 11 companies ac oss he coun y, as shown in Fig. 1 [8]. The dis ibu- ion g id is ope a ed mainly on 33kV (medium ol age) and 11kV (low ol age), comp ising a ne wo k o o e 24,000km [23]. The a ailable capaci y could be used o elec ici y gene a ion, bu is cons ained by in e nal plan issues, majo ly main enance and epai issues. In addi ion, Nige ia’s powe g id aces daily challenges [27], due o wa e sho age, high equency due o demand imbalances, in Fig. 1. O e iew o Nige ia’s gene a ion, ansmission and dis ibu ion sec o [26]. Fig. 2. Nige ia’s 25 on-g id powe plan s loca ions [9]. 3 UNCORRECTED PROOF A.S. Oyewo e al. Ene gy Con e sion and Managemen xxx (2018) xxx-xxx su icien gas supply, and line cons ain s due o inadequa e g id in a- s uc u e as shown in Fig. 3 [9]. These cons ain s ha e led o a mis- ma ch in demand and supply, and o e - eliance on backup gene a o s, among o he issues. In addi ion, he powe indus y loses an a e age o 6m€(1.4 billion Nai a) in e enue daily, due o hese cons ain s. Fig. 4 shows he e enue los o a ious cons ain s in he Nige ian powe indus y. Fo many yea s, he powe sec o was owned, managed and con- olled by he go e nmen . The s a e-owned monopoly u ili y NEPA, h oughou i s exis ence, ailed o mee he coun y’s elec ici y need [25]. Upon he ad en o he democ a ic go e nmen in 1999, he Fed- e al Go e nmen o Nige ia has commi ed huge inancial in es men s o abou 14 b€ o e u bish he powe sec o , bu wi hou p opo ion- a e ou comes [25]. One o he key measu es aken by he go e nmen o e amp he powe sec o was p i a isa ion o powe asse s [8]. To his end, a ious policy measu es we e es ablished in iew o he p i- a isa ion [23]. In 2005, he Elec ic Powe Sec o Re o m (ESPR) Ac was enac ed o allow p i a e in es o s in ol emen in he p e ious go - e nmen s’monopolised sec o . Fig. 5 shows he s uc u e o he pos - e- o m powe sec o [29]. Besides hyd opowe , Nige ia does no ye ha e any la ge RE-based gene a ing plan s, con ibu ing o i s on-g id elec- ici y, in spi e o he coun y ha ing huge RE po en ial and ene gy ma - ke p ospec s. Fig. 6 shows he sola and wind esou ces maps o Nige ia. The da a a e p o ided by NASA [30,31], ep ocessed by he Ge man Ae o- space Cen e [32] and con e ed o ull load hou s acco ding o Bog- dano and B eye [20] and A anasye a e al. [33]. Howe e , a un- damen al ac ion owa ds RE de elopmen in Nige ia lies in a s a egic and suppo i e policy di ec ion by he Nige ian go e nmen owa ds a p og essi e RE mas e plan [7]. Such policy, legal and ins i u ional amewo k a e a hei nascen s age in Nige ia [8] and a e o eseen o os e RE de elopmen [12]. In 2015, he Fede al Go e nmen o Nige ia app o ed he Na ional Renewable Ene gy and E iciency Policy (NREEEP), which is he coun y’s i s e e RE-speci ic policy, which p o ides he desc ip i e amewo k o ene gy e iciency and RE de el- opmen in Nige ia. The coun y a ge s o inc ease i s o al on-g id ca- paci y om 4 GW in 2015 o 30 GW by 2030 [12]. This a ge was de e mined h ough he p ocess o de eloping he Na ional Renewable Ene gy Ac ion Plan (NREAP) and Na ional Ene gy E iciency Ac ion Plan (NEEAP), as s a ed in he NREEEP 2015. The sha e o on-g id RE Fig. 3. Elec ici y gene a ion and cons ain s (C ) in Nige ia [28]. Fig. 4. Re enue los o cons ain s in he Nige ia powe sec o [28] (1 billion Nai a is equi alen o 2m€). 4 UNCORRECTED PROOF A.S. Oyewo e al. Ene gy Con e sion and Managemen xxx (2018) xxx-xxx Fig. 5. Pos - e o m powe sec o s uc u e [29]. Fig. 6. Maps o Nige ia showing annual ull load hou s o sola PV single–axis acking (le ) and onsho e wind ( igh ) o he yea 2005. supply is expec ed o inc ease om i s p esen 1.3% in 2015 o 16% by 2030 in he NREEEP 2015. Howe e , upon he comple ion and endo se- men o NREAP 2016, he a ge was e ised o a 30% sha e o RE sup- ply by 2030. 3. Resea ch me hods The esea ch app oach applies linea op imisa ion modelling in de- e mining he op imal in es men and elec ici y gene a ion echnology mix, needed o sa is y elec ici y demand in Nige ia by 2050 [22]. A linea op imisa ion ene gy sys em ool, he LUT Ene gy Sys em T an- si ion model [20], is used o simula e he Nige ian powe sys em. The model was designed and de eloped o analyse an ene gy ansi ion om he cu en (as o he beginning o 2015) ossil based-sys em o a 100% RE-based powe sys em by 2050, co e ing he demand o powe , non-ene ge ic indus ial gas and desalina ion sec o s. The ansi ion is modelled in 5-yea s eps om 2015 o 2050, and is ca ied ou based on assumed cos s and echnological s a us o all ene gy echnologies in ol ed. The elec ici y gene a ing plan s equi ed o he ene gy an- si ion om 2015 o 2050 is conside ed acco ding o Calde a e al. [34] and based on Fa an and B eye [35]. Two essen ial cons ain s a e aken in o conside a ion as he basis o he ene gy sys em ansi ion modelling. Fi s ly, a e 2015, no new ossil-based powe plan s a e in- s alled. The exis ing ossil-based powe plan s a e g adually phased ou based on hei echnical li e imes. Howe e , he ins alla ion o gas u - bines is pe mi ed a e 2015 due o lowe ca bon emission, high e i- ciency o he echnology, and in pa icula ly due o he possibili y o accommoda e bio-me hane and syn he ic na u al gas in he sys em, so ha a uel shi owa ds sus ainable uels can be ealised. Secondly, RE capaci y g ow h canno exceed 4% pe yea , in o de o p e en sys em dis up ions. 3.1. Model s uc u e The LUT Ene gy Sys em T ansi ion model is de eloped o comp e- hensi e analyses o ene gy ansi ion om cu en ene gy sys ems o 100% RE-based sys ems. The model is based on linea op imisa ion wi h an hou ly esolu ion o he ene gy sys em pa ame e s o an en i e yea , unde a se o applied cons ain s, assump ions o he u u e RE pow- e ed sys em and demand. De ailed model desc ip ion, equa ions and ap- plied cons ain s can be ound in [20]. The model is compiled using MATLAB [36], while he op imisa ion is ca ied ou in MOSEK [37]. Fig. 7 shows he low diag am o he main inpu pa ame e s and ou - pu s o he model. A ull se o echnical and inancial assump ions used in his s udy a e p esen ed in he Supplemen a y Ma e ial (Table S1). The a ge unc ion o he model op imisa ion is o minimise he o- al annual ene gy sys em cos , which is calcula ed as he sum o an- nual cos s o he ins alled capaci ies o each echnology, cos s o ene gy 5 UNCORRECTED PROOF A.S. Oyewo e al. Ene gy Con e sion and Managemen xxx (2018) xxx-xxx Fig. 7. Main inpu s and ou pu s o he LUT Ene gy Sys em T ansi ion model [22]. gene a ion, and cos s o gene a ion amping. In addi ion, he ene gy sys em consis s o dis ibu ed gene a ion and sel -consump ion o es- iden ial, comme cial and indus ial consume s. The ansi ion analysis conside s he po en ial o he p osume ma ke segmen as an essen ial aspec o sys em planning. Thus, ano he mini- ansi ion hou ly model desc ibes he p osume s PV sys ems and ba e y de elopmen capaci y. P osume s can ins all oo op PV and li hium-ion ba e ies, depending on he cos , o buy elec ici y om he g id. The a ge unc ion o he p osume s is he minimisa ion o cos o elec ici y consumed. This cos is calcula ed as he sum o sel -gene a ion cos , annual cos , and cos o elec ici y consumed om he g id. Excess elec ici y gene a ed by p o- sume s can be sold o he o e all ene gy sys em o 0.02 €/kWh. 3.2. Applied echnologies The main echnologies applied o he Nige ian ene gy sys em mod- elling can be di ided in o ou main ca ego ies: •Elec ici y gene a ion echnologies •Elec ical ene gy s o age echnologies •Elec ici y ansmission echnologies •Ene gy sec o b idging echnologies o p o ide mo e lexibili y o he ene gy sys em Fig. 8 shows he block diag am o he ene gy model and all applied echnologies o he ansi ion. The RE gene a ion echnologies in o Fig. 8. Block diag am o he LUT Ene gy Sys em T ansi ion model used o Nige ia [22]. 6 UNCORRECTED PROOF A.S. Oyewo e al. Ene gy Con e sion and Managemen xxx (2018) xxx-xxx duced in he model include a ious PV echnologies (g ound-moun ed and oo op sola PV sys ems), hyd opowe ( un-o - i e and ese - oi based), biomass plan s (solid biomass and biogas), wind onsho e u bines, geo he mal powe plan s, concen a ing sola he mal powe (CSP) and was e- o-ene gy powe plan s. While he ossil gene a ion echnologies a e coal, oil, open cycle gas u bines (OCGT) and combined cycle gas u bines (CCGT), as well as nuclea powe . Due o he a iabil- i y o RE and o ensu e a s eady supply o elec ici y, he RE echnolo- gies a e complemen ed by a ious s o age echnologies. These echnolo- gies include pumped hyd o s o age (PHS), Li-ion ba e ies assumed o se e esiden ial and sys em s o age, he mal ene gy s o age (TES), adi- aba ic comp essed ai ene gy s o age (A-CAES) [38] and powe - o-gas (P G) [39]. Ene gy sec o b idging echnologies such as gas om P G p ocess and seawa e e e se osmosis (SWRO) desalina ion [34] p o ide mo e lexibili y o he ene gy sys em. P G includes syn he ic na u al gas (SNG): me hana ion, wa e elec olysis, gas s o age, ca bon dioxide (CO⁠2) di ec ai cap u e, and gas u bines (OCGT and CCGT). Due o he absence o hyd ogen and CO⁠2 s o age, P G echnologies ope a e in syn- ch onisa ion. In addi ion, he model uses a 48-hou biogas bu e s o - age, and pa o he biogas can be upg aded o biome hane and is in o- duced in o he gas s o age. 3.3. Coun y di ision The mul i-node app oach used in he model enables desc ip ion o any desi ed con igu a ion. Based on his app oach, Nige ia is di- ided in o six sub- egions, acco ding o poli ical zoning o he coun- y, namely, No h-Eas (NIG-NE), No h-Wes (NIG-NW), No h-Cen al (NIG-NC), Sou h-Eas (NIG-SE), Sou h-Sou h (NIG-SS) and Sou h-Wes (NIG-SW). Each o he sub- egions ep esen s a node. The nodes a e in e connec ed ia ansmission lines, wi hin he coun y bo de s, as shown in Fig. 9. 3.4. Financial and echnical assump ions The inancial and echnical assump ions o all he ene gy sys em componen s a e made in 5-yea ime s eps, which include capi al expen- di u es (CAPEX), ope a ional expendi u es (OPEX) and li e imes, om 2015 o 2050, and a e p o ided in he Supplemen a y Ma e ial (Table S1). Weigh ed a e age cos o capi al (WACC) is se o 7% in his s udy, bu o esiden ial PV p osume s, WACC is se a 4% due o lowe i- nancial e u n equi emen s. The echnical assump ions conce ning s o - age echnologies, e iciency numbe s o gene a ion, and powe losses in HDVC powe lines and con e e s, can be ound in he Supplemen- a y Ma e ial (Tables S2–S4). The elec ici y p ices o esiden ial, com- me cial and indus ial consume s o he yea 2015 we e e ie ed om elec ici y DISCOs a i documen a ailable online a he Nige - ian Elec ici y Regula o y Commission (NERC) websi e [40]. The elec- ici y p ice was calcula ed un il 2050 acco ding o Ge lach e al. [41] and B eye and Ge lach [42]. The elec ici y p ice o all sub- egions a e a ailable in he Supplemen a y Ma e ial (Table S5). The uppe limi s o all RE echnologies we e es ima ed acco ding o Bogdano and B eye [20] and lowe limi s a e ob ained om Fa an and B eye [35]. Uppe and lowe limi s o RE and ossil uels a e p o- ided in he Supplemen a y Ma e ial (Tables S6 and S7). Fo all o he echnologies, uppe limi s a e no speci ied. Howe e , o solid biomass esidues, biogas and was e- o-ene gy plan s i is assumed, due o en- e gy e iciency easons, ha he a ailable and speci ied amoun o uel is used du ing he yea . Key powe capaci ies equi ed o he ene gy an- si ion o Nige ia a e p o ided in he Supplemen a y Ma e ial (Tables S8–S13). The cu en ansmission line capaci ies connec ing he sub- e- gions wi hin he coun y we e aken om [43]. The exis ing powe g id, i s de elopmen , and o e all impac on elec ici y ansmission and dis- ibu ion losses we e aken in o accoun in he s udy. Fig. 9. Nige ia sub- egions and ansmission lines con igu a ion. 7 UNCORRECTED PROOF A.S. Oyewo e al. Ene gy Con e sion and Managemen xxx (2018) xxx-xxx 3.5. Renewable esou ce po en ial The eed-in p o iles o PV op imally il ed, PV single-axis acking, wind ene gy and CSP a e calcula ed acco ding o Bogdano and B eye [20] and A anasye a e al. [33], based on esou ce da a p o ided by NASA [30,31], ep ocessed by he Ge man Ae ospace Cen e [32]. The eed-in alues o hyd opowe a e compu ed based on mon hly esol ed p ecipi a ion da a o he yea 2005 as a no malized sum o p ecipi a- ion in he sub- egions. Such an es ima e leads o a good app oxima ion o he annual gene a ion o hyd o powe plan s [44]. Full load hou ly da a o a ious esou ces a e p esen ed in he Supplemen a y Ma e ial (Tables S14–S19). The esou ce p o iles isualised in an hou ly esolu- ion can be ound in he Supplemen a y Ma e ial (Figs. S1 and S2). In addi ion, he s o age h oughpu is a ailable in he Supplemen a y Ma- e ial (Tables S20–S25). The po en ials o was e and biomass esou ces o Nige ia a e aken om Ge man Biomass Resea ch Cen e [45] and classi ied acco ding o Bogdano and B eye [20]. The cos s o biomass a e calcula ed using da a om he IEA [46] and In e go e nmen al Panel on Clima e Change (IPCC) [47]. Fo solid was e, a 50 €/ on ga e ee was assumed o 2015, which inc eased up o 100 €/ on in 2050. The geo he mal po en ials a e calcula ed o he sub- egions based on he a ailable in o ma ion ela ed o hea low a e [48] and ambi- en empe a u e o he su ace o he yea 2005 [49]. Fo he sub- e- gions whe e he hea low da a we e no a ailable, ex apola ion was pe o med o ge he equi ed da a. The po en ial is es ima ed based on he a ailable da a [50], di e en empe a u e le els [51] and a ailable hea a he mid-poin o a 1km hick deep laye and be ween he dep hs o 1–10km globally wi h 0.45°×0.45° spa ial esolu ion [52]. 3.6. Demand Elec ici y demand da a a e aken om [11], and a e e i ied wi h da a p o ided in [12]. The elec ici y demand un il 2050 is p o ided in he Supplemen a y Ma e ial (Table S5). The hou ly load p o iles o elec ici y a e calcula ed as a ac ion o he o al demand in each sub- egion based on syn he ic load da a weigh ed by he sub- egions popula ion [53]. Fo seawa e desalina ion, SWRO is mainly used in his s udy due o i s low-cos and ene gy e iciency ad an ages om 2020 onwa ds [54]. None heless, mul iple e ec dis illa ion (MED) domina es in he s a o he ansi ion and complemen s om 2020 onwa ds. The equi ed desalina ion capaci y, echnical cons ain s and inancial as- sump ions om 2015 o 2050 a e calcula ed by using he me hodol- ogy desc ibed in [54]. The non-ene ge ic indus ial gas demand da a a e aken om IEA s a is ics websi e [55] and ex apola ed un il he yea 2050 based on IEA’s assump ion o non-ene gy gas demand g ow h a e o Nige ia [6]. 3.7. Scena ios In his s udy six scena ios ha e been de eloped, which a e b ie ly desc ibed in Table 1. The scena ios explo e pa hways o a 100% RE sys- em in he mid- e m u u e, co e ing he demands o he powe , non-en- e ge ic indus ial gas and desalina ion sec o s. 4. Resul s This sec ion p esen s he indings o he modelling ou comes o he Nige ian ene gy ansi ion pa hways in he mid- e m u u e. Financial implica ion o he ene gy ansi ion, ins alled capaci ies, elec ici y gen- e a ion mix, ansmission and s o age a e analysed in his sec ion. O de o he igu es in he en i e pape a e as ollows: Figu e (a) is assigned o BPS-1, Figu e (b) o BPS-2, Figu e (c) o BPS-3, Figu e (d) o CPS-1, Figu e (e) o CPS-2, and Figu e ( ) o CPS-3. Table 1 O e iew o he s udied scena ios. Scena io name Desc ip ion Bes Policy Scena io (BPS-1) – Powe only scena io The a ge o he LUT model is o each 100% RE by 2050. In addi ion, GHG emission cos is applied in he model o es ic ossil powe plan s. In his scena io, only elec ici y demand is co e ed Bes Policy Scena io (BPS-2) – Powe only scena io (planned hyd opowe capaci y conside ed) This scena io is he same as he abo e scena io. In addi ion, he planned hyd opowe capaci y is also conside ed. Fo ins ance, Zunge u hyd opowe p ojec o 0.7 GW and Mambilla p ojec o 3.0 GW a e o be ins alled in 2020 and 2025 [56], espec i ely, du ing he ansi ion and acco ding o he espec i e planning [12] Bes Policy Scena io (BPS-3) – In eg a ed scena io In his scena io, powe , SWRO desalina ion and non-ene ge ic indus ial gas sec o s demand is co e ed Bes Policy scena ios wi hou GHG emission cos (BPSnoCC) In hese scena ios, GHG emission cos is no conside ed o he Bes Policy Scena io 1 and 2. The inancial implica ion, ins alled capaci ies and gene a ion o Bes Policy Scena io 1 no GHG emission cos (BPS-1noCC) and Bes Policy Scena io 2 no GHG emission cos (BPS-2noCC) a e only discussed in Sec ion 4.9 Cu en Policy Scena io (CPS-1) In his scena io, he coun y’s a ge ela ing o elec ici y capaci y mix up o 2030 is conside ed acco ding o [12]. Howe e , he pos -2030 capaci y mix is ex apola ed up o 2050. Cu en Policy Scena io (CPS-2) –no GHG emission cos This scena io is he same as he p e ious desc ibed scena io, excep ha in his scena io GHG emission cos is no conside ed in he modelling Cu en Policy Scena io (CPS-3) A e 2030, no new ossil powe plan s a e allowed excep nuclea powe plan s, because he coun y aims a eaching 4.8 GW ins alled capaci y o nuclea by 2035 4.1. Le elised cos o elec ici y The LCOE ob ained o all he scena ios a e shown in Fig. 10. The a - e age inancial esul s o he scena ios a e exp essed as LCOE, which in- cludes all gene a ion, s o age, cu ailmen , ansmission, uel and GHG emission cos s. The LCOE end om now un il 2050 a ies o he di - e en scena ios. Fi s ly, he sys em LCOE end du ing he ansi ion o he Bes Policy Scena ios is obse ed as shown in Fig. 10(a)–(c). In he BPS-1 and BPS-2, he LCOE inc eased sligh ly a ound 2025, beyond 2025 he sys em LCOE u he declines o 48 €/MWh and 46 €/MWh by 2050, espec i ely. Howe e , he LCOE emains s able un il 2030 and u he declines o 34 €/MWh by 2050 in he BPS-3. The inc ease obse ed in he LCOE end in he Bes Policy Scena ios, pa icula ly in BPS-1 and BPS-2, a ound 2025 a e due o in es men equi emen s. F om 2030 onwa ds, he sys em LCOE s eadily declines, signi ying he impac o low-cos RE echnologies, in pa icula sola PV and ba e y echnologies in he Bes Policy Scena ios. By 2050, he sys em LCOE is mainly domina ed by cos o gene a ion and s o age, as sola PV con- ibu es o he la ges sha e o elec ici y gene a ion and i s comple- men a i y by ba e y s o age. Fig. 10(d)–( ) p esen s he co esponding LCOE o he Cu en Policy Scena ios. Fuel and GHG emission cos s con ibu e o mo e han hal o he o al LCOE by 2050 in he Cu - en Policy Scena ios, excep in CPS-2 because GHG emission cos was no aken in o accoun . This also led o LCOE de ia ion in 2015 o he CPS-2 in compa ison o o he scena ios. By 2050, he LCOE is 120 €/MWh, 75 €/MWh and 100 €/MWh in CPS-1, CPS-2 and CPS-3, espec- i ely, as shown in Fig. 10(d)–( ). Addi ional inancial esul s o all he scena ios a e a ailable in he Supplemen a y Ma e ial (Figs. S3–S5). 8 UNCORRECTED PROOF A.S. Oyewo e al. Ene gy Con e sion and Managemen xxx (2018) xxx-xxx Fig. 20. To al gas demand (le ) and gas inpu by sou ce ( igh ) om 2015 un il 2050. Fig. 21. Hou ly esolu ion o s a e o cha ge o gas s o age and p oduc ion o me hana ion uni s in 2050. Fig. 22. Elec ici y gene a ion and demand p o ile in ull hou ly esolu ion o he Bes Policy Scena io 1 o he NIG-NE in 2050. a e discha ged du ing he nigh hou s as shown in Fig. 22. Fig. 23 p e- sen s he hou ly gene a ion p o ile in NIG-SW du ing a week in he ainy season. Du ing his week he ole o gas u bines is obse ed in p o- iding lexibili y o he powe sys em due o low gene a ion om RE. Howe e , PV p osume s, elec ici y impo s and ba e y discha ge du - ing nigh hou s ha e a subs an ial in luence in his sub- egion. Fig. 24 shows he ene gy low in he Bes Policy Scena io 3 (In- eg a ed scena io). I shows he RE gene a o s, s o age echnologies, ansmission g ids, o al elec ici y demand o each sec o and sys em losses. The po en ial usable hea and sys em losses include he di e - ence be ween he elec ici y gene a ion and inal elec ici y demand. Bo h includes cu ailed elec ici y, he hea eleased om biomass, bio- gas and was e- o-ene gy powe plan s, cha ge and discha ge om s o - age echnologies, elec olyse s and me hana ion p ocesses. Sola PV mee s addi ional demand due o sec o coupling in he In eg a ed sce- na io. 4.9. Compa ison o key di e ences in all scena ios by 2050 This sec ion p esen s key di e ences in all scena ios examined by 2050 as p esen ed in Table 2. The o al annualised cos o sys em a- jec o y om 2015 o 2050 is shown in Fig. 25. The modelled inan- cial ou comes e eal ha a ully deca bonised ene gy sys em is he leas cos op ion o Nige ia. The o al annualised cos o sys em o all Cu - en Policy Scena ios a e highe han in he Bes Policy Scena ios, ex- cep in he BPS-3 due o sec o coupling. The a e age o al annualised cos o sys em in all Cu en Policy Scena ios a e 42% highe han in Bes Policy Scena ios. The o al annualised cos o sys em anges om 15 UNCORRECTED PROOF A.S. Oyewo e al. Ene gy Con e sion and Managemen xxx (2018) xxx-xxx Fig. 23. Elec ici y gene a ion and demand p o ile in ull hou ly esolu ion o he Bes Policy scena io 1 o he NIG-SW in 2050. Fig. 24. Ene gy low o he sys em o he In eg a ed scena io in 2050. Table 2 Di e ence in key pa ame e s and inancial ou comes in 2050 o all scena ios. BPS-1 BPS-2 BPS-3 BPS-1noCC BPS-2noCC CPS-1 CPS-2 CPS-3 Financial ou come To al annualised cos o sys em [b€] 16.6 15.8 27.2 16.2 15.5 42.2 26.4 35.0 LCOE [€/MWh⁠el] 48 46 35 47 45 120 76 100 Elec ici y pa ame e Demand [TWh⁠el] 347 347 637 347 347 347 347 347 Gene a ion [TWh⁠el] 398 396 697 395 383 353 353 353 Ins alled capaci y [GW] 198 194 351 192 190 68 64 95 15 o 42 b€in all he scena ios. The LCOE ob ained in he Cu en Pol- icy Scena ios a e highe han in he Bes Policy Scena ios. The LCOE is ound o be in he ange o 34.5–120.4 €/MWh. The capaci y e- qui emen s a e highe in he Bes Policy Scena ios han in he Cu en Policy Scena ios. This is due o lowe FLH o sola PV ha domina es he o e all capaci ies in Bes Policy Scena ios, while he Cu en Pol- icy Scena ios a e domina ed by he mal gene a o s ha un on highe FLH. On a e age, capaci y equi emen s in all Bes Policy Scena ios a e abou 70% highe han in he Cu en Policy Scena ios. Highe gene a ion is obse ed in he Bes Policy Scena ios han in he Cu en Policy Scena ios. Fu he mo e, he Bes Policy Scena io 1 no GHG emission cos (BPS-1noCC) and he Bes Policy Scena io 2 no GHG emission cos (BPS-2noCC) a e examined in his esea ch. The Bes Policy Scena io no GHG emission cos modelling ou come e eals ha a RE-based en- e gy sys em would ye be mo e compe i i e in he mid- e m u u e in Nige ia. By 2050, RE elec ici y gene a ion eaches 97.8% o o al elec- ici y gene a ion in BPS-1noCC and BPS-2noCC. In bo h scena ios as 16 UNCORRECTED PROOF A.S. Oyewo e al. Ene gy Con e sion and Managemen xxx (2018) xxx-xxx Fig. 25. Compa ison o o al annualised cos o sys em o all scena ios in 2050. GHG emission cos is no applied, na u al gas is allowed o be used in gas u bines. Howe e , he RE ins alled capaci ies sligh ly d op in bo h scena ios, due o inc eased FLH o gas u bines. The o al annualised cos o sys em and LCOE dec ease sligh ly in BPS-1noCC and BPS-2noCC as GHG emission cos is assumed o be ze o h oughou he ansi ion o bo h scena ios as shown in Table 2. Addi ional in o ma ion on hese scena ios a e a ailable in he Supplemen a y Ma e ial (Tables S11–S12, S22–S23, S30–S32 and Figs. S16–S19). 5. Discussion This s udy p esen s pa hways o ansi ioning o a ze o GHG emis- sion ene gy sys em o Nige ia unde he de ined scena ios. The key ob- jec i es o his esea ch is o show ha a ully sus ainable ene gy sys- em is echnically and economically easible and he espec i e inancial consequences in compa ison o a ossil-based powe sys em. Such an en- e gy sys em can be achie ed wi h abundan RE esou ce a ailabili y in he coun y, enabled by s ong poli ical suppo o enewable ene gy de elopmen . A 100% RE-based ene gy sys em is achie able in Nige ia. This s udy is he i s o i s kind o be conduc ed o Nige ia. The LCOE alues ob- ained in his s udy indica e ha cos o elec ici y could dec ease om 54 €/MWh in 2015 o 46 €/MWh in BPS-1, 48 €/MWh in BPS-2 and 35 €/MWh in BPS-3 by 2050. Whe eas in he Cu en Policy Scena ios, he LCOE inc eased om 54 €/MWh in 2015 o 120 €/MWh in CPS-1, and 100 €/MWh in CPS-3 by 2050. Howe e , he LCOE ob ained by he no GHG emission cos scena ios declined om 51 €/MWh in 2015 o 47 €/MWh in BPS-1noCC, 45 €/MWh in BPS-2noCC and 76 €/MWh in CPS-2 by 2050. Resul s ob ained in he ully enewable end-poin sce- na ios o Nige ia in e ms o LCOE a e compa able o he global a - e age LCOE ob ained using he LUT model, which shows a ange o abou 50–70 €/MWh [22]. The dec easing cos s o RE echnologies ex- pec ed du ing he ansi ion, pa icula ly sola PV, con ibu es o he de- c easing cos o elec ici y o e he ansi ion in he Bes Policy Scena - ios. In addi ion, sec o coupling o seawa e desalina ion, non-ene ge ic indus ial gas and elec ici y demand esul s in a u he educ ion in LCOE by 22% in 2050 as obse ed in BPS-3. Sec o coupling p o ides addi ional lexibili y o he powe sys em. In addi ion, a highe sha e o low-cos gene a ion leads o he LCOE educ ion. The addi ional de- mand equi ed due o sec o coupling is mainly sa is ied by ins alla ion o low-cos sola PV. P G echnology enables he co e age o gas de- mand o he in eg a ed scena io (BPS-3) c ea ing addi ional elec ici y demand o 290 TWh⁠el in he yea 2050, which esul s in inc eased gen- e a ion capaci y. The ou s anding ole o PV echnologies and ba e ies needs o be highligh ed in he ully enewable end-poin scena ios in Nige ia. By 2050, PV single-axis acking domina es he sys em in he Bes Policy Scena ios. While he es o he PV capaci y is me by PV p osume s. P osume s con ibu e 22% o o al gene a ed PV elec ici y in 2050. PV-ba e y p osume s will educe dependency on he cen alised sys em in he nea es u u e in Nige ia acco ding o he esul s o his esea ch. In compa ison o he Cu en Policy Scena ios, PV capaci y ange om 11 GW o 52 GW in 2050, he highes sha e o PV ins alled capac- i y is obse ed in he CPS-3. By 2050, PV echnologies gene a e 364 TWh (93% o o al gene a ion), 350 TWh (89%) and 667 TWh (96%) in BPS-1, BPS-2 and BPS-3, espec i ely. The inc eased gene a ion in BPS-3 is due o demand o h ee ene gy sec o s. Whe eas in he Cu en Pol- icy Scena ios, PV gene a ion anged om 22 TWh o 112 TWh, accoun - ing o 6–32% o he o al elec ici y gene a ion in 2050. The highes ins alled PV capaci ies we e ound in he no he n sub- egions in pa - icula he NIG-NW and NIG-NE, due o excellen sola esou ce condi- ions in he no h o Nige ia and espec i e low cos o PV echnology. In addi ion o he o egoing analysis, sola PV echnology will play a majo ole in he Nige ia u u e powe sys em, based on he esul s o his esea ch and om esou ce poin o iew as discussed in [58]. Mos s udies on u u e ene gy sys ems in Nige ia ha e a emp ed o analyse enewables po en ial in mee ing he g owing elec ici y demand o he coun y [8], bu did no in es iga e wha his may mean in conc e e powe gene a ion mix op ions. B immo e al. [59] p o ided an in-dep h e iew on wind, hyd opowe , geo he mal and nuclea ene gy op ions in Nige ia. Sola ene gy esou ce cu en applica ion and he ex en o u ilisa ion is p esen ed in [58], while Aku u e al. [7] based on li e - a u e, modeled scena ios and ield expe ience conclude ha 100% RE in Nige ia could be d i en by indi iduals a he han sole dependence on go e nmen ac ions. The es o he gene a ion is supplied by wind ene gy, hyd opowe , geo he mal and biomass in he 100% RE-based scena ios conside ed in his esea ch. In he BPS-2, hyd opowe p o- jec s unde cons uc ion such as Mambilla hyd opowe p ojec in Ta aba S a e and Zunge u hyd opowe p ojec in Nige S a e we e conside ed. Hyd opowe has been a majo pa o he Nige ian powe lee . The Go e nmen o Nige ia also plans o build mo e hyd opowe capaci y in he nea es u u e. Inc eased hyd opowe capaci y is one ma ked ea u e o he BPS-2. Howe e , dispa chable hyd opowe con ibu es o lowe s o age needed in BPS-2. By 2050, hyd opowe capaci y is 1.7 GW in BPS-1 and BPS-3, while i eaches 5.3 GW in BPS-2. The hyd opowe ins alled capaci y is 12.1 GW each in CPS-1 and CPS-2, while ins alled capaci y eaches 5.9 GW in CPS-3 in 2050. Acco ding o IEA New Pol- icy Scena io, hyd opowe capaci y is expec ed o inc ease om 2 GW (11%) in 2012 o 15 GW (19%) in 2040 [6]. The high sha e o hy- d opowe in BPS-2 esul s in lowe LCOE and s o age equi emen , as hyd o ese oi s se es as i ual s o age [60]. One o he main con- s ain s o hyd opowe de elopmen is cos o e uns and schedule spills [14], especially la ge hyd opowe p ojec s [15]. Acco ding o [16], 61 hyd opowe dams we e analysed ep esen ing 114 GW and 271.5 bUSD wo h o in es men expe ienced a mean cos o e un o 231 bUSD [16]. These p ojec s exhibi ed a mean cos o e un o 70% [16]. An- o he s udy epo s an a e age 96% cos o e un on hyd opowe de el- opmen , whe e he au ho s epo ha he cos o e uns igu es exclude in la ion, deb , en i onmen al cos and social cos [61]. The speci ic capaci y densi y de i ed in he LUT Ene gy Sys em model is 75MW/km⁠2 o op imally il ed PV and 8.4MW/km⁠2 o on- sho e wind in [20]. Hence, he o al a ea o land equi ed in Nige- ia o sola PV and wind capaci ies in 2050 is 2409km⁠2 (0.3% o o- al land a ea) and 361km⁠2 (0.04%) o BPS-1, 2317km⁠2 (0.3%) and 53km⁠2 (0.01%) o BPS-2, and 4369km⁠2 (0.5%) and 209km⁠2 (0.02%) o BPS-3. The land a ea equi emen o achie ing a 100% RE sys em should be no limi ing ac o , acco ding o he esul s o his esea ch. Fu he mo e, he e a e plans unde way in Nige ia o build new he - mal powe plan s [19], mainly nuclea and coal powe plan s [12]. The Cu en Policy Scena ios a e mainly domina ed by he mal plan s, which include gas u bines, nuclea and coal powe plan s. In 2017, he Nige ian go e nmen signed a mul i-billion dolla con ac wi h 17 UNCORRECTED PROOF A.S. Oyewo e al. Ene gy Con e sion and Managemen xxx (2018) xxx-xxx Rosa om, a Russian nuclea company o build ou nuclea plan s in Akwa Ibom and Kogi S a e o con ibu e 4.8 GW o Nige ian elec ici y by he yea 2035 [62]. In 2000, Rosa om es ima ed cos o build wo new p essu ised wa e eac o s o he VVER se ies a he Lening ad nu- clea powe plan 2 a 1.74 b€ o 2.17 GW. By 2011, Rosa om se p ice o his ype o p ojec was es ima ed a 3.73 b€, mo e han wice he o iginal p ice [63]. The cos o Olkiluo o 3, Finland, which was planned o begin ope a ion in 2009, ha e inc eased om 3.2 b€ o 8.5 b€ o 1.6 GW, and s and he isk o u he cos inc ease [64]. Coun ies like Nige- ia should be awa e o binding nuclea con ac s, simila o he con ac signed in 2014 by he Hunga ian go e nmen wi h Rosa om, incu ed inancial bu den is always bo ne by he o eign go e nmen . Rosa om nuclea cons uc ion p ojec s wi hin Russia and o he coun ies ha e no been cha ac e ised by delays and cos o e uns, bu also by lack o p ope quali y con ol and sa e y conce ns [63]. So acool e al. [16] analysed 401 powe plan p ojec s in 57 coun ies, he eo 180 nuclea eac o s ep esen ing 177 GW. These eac o s had a mean cos o e un o 117%, and mo e han 9 in 10 p ojec s su e ed om cos escala ion [16]. In addi ion, nuclea ene gy iola es all sus ainabili y c i e ia ha should o m a amewo k o a esilien ene gy sys em design discussed in [13]. Va ious isks a e associa ed wi h nuclea ene gy [65], which in- cludes en i onmen al and heal h isks as wi nessed in Fukushima and Che nobyl, i epa able impac on ecosys em esul ing om gene ic mu- a ion plan s and animals, and isk o nuclea weapons p oli e a ion and po en ial e o is a acks on nuclea acili ies [13]. The Cu en Pol- icy Scena ios a e obse ed o be expensi e due o high capi al cos s o he mal plan s in pa icula nuclea . Acco ding o [66], he LCOE me- dian alues anged om 79 o 112 €MWh, and LCOE including ex e - nal and GHG emission cos anged om 87 o 120 €/MWh [67]. Ra he han building new nuclea and coal powe plan s in Nige ia, gas u bines (OCGT and CCGT) could be an op ion alongside wi h new in es men s in RE echnologies in pa icula sola PV. In all he scena ios, gas powe plan s eme ge as he dominan he mal powe plan , pa icula ly in he Cu en Policy Scena ios. The esul ob ained in he Cu en Policy Sce- na ios, is compa able o he indings o he IEA New Policy Scena io, which epo s gas- i ed gene a ion will o m he co e o he Nige ian u- u e powe sec o [6]. Acco ding o IEA [6], gas powe plan capaci y may be 37 GW (48%) and coal may be 8 GW (10%) by 2040. Simila ly, acco ding o he IRENA Renewable P omo ion scena io abou 55% elec- ici y gene a ion is supplied by gas powe plan , hyd opowe supply is abou 35% and emaining sha e is supplied by impo s o he yea 2030 [68]. In he Bes Policy Scena ios, gas powe plan s a e used as a e y aluable and lexible balancing echnology on di e en ime scales, om days o weeks. Gas u bines can be ins alled a e 2015, because o lowe GHG emissions and he possibili y o subs i u e he ossil na u al gas wi h SNG o biome hane. S o age echnologies play a i al ole in his s udy, pa icula ly in he Bes Policy Scena ios due o high sha es o RE esou ces. Sola PV domina ed powe g ids a e usually cha ac e ised by high s o age e- qui emen s [69]. In his esea ch, high pene a ion RE sou ce, in pa - icula sola PV, is complemen ed by ba e y s o age due o daily e- qui emen . The PV-ba e y hyb id sys em eme ges o become he leas cos solu ion in a 100% RE-based powe s sys em by 2050. In addi ion, he cos o ba e ies declined by 80% in he pas 6yea s [70], u he cos educ ion is expec ed [71], policies designed o s eng hen ma - ke g ow h and inno a ion in ba e y s o age can d i e he u u e cos educ ion [72]. The con inued cos decline o PV-ba e y sys ems [22] combined wi h excellen sola esou ces in Nige ia a e he key d i e s o a high sha e o PV in all he Bes Policy Scena ios. By 2050, ba - e y s o age ou pu in he Bes Policy Scena ios anged om 157 TWh o 166 TWh and om 13 TWh o 42 TWh in he Cu en Policy Sce- na ios. The plausible eason o low s o age ou pu and equi emen in he Cu en Policy Scena ios is due o highe sha e o dispa chable hyd opowe and he mal powe plan s. Addi ional ba e y s o age de mand o 106 GWh is p ojec ed in 2050 because o highe PV p osume s ins alled capaci y. The ba e y p osume s ou pu inc eased om 0.2 TWh in 2025 o 32.1 TWh in 2050. In e ms o s o age capaci y, gas s o age domina es in he Bes Policy Scena ios, while ba e y s o age domina es in he Cu en Policy Scena ios, ollowed by TES. The ech- nology equi emen in he Bes Policy Scena ios a e highe han in he Cu en Policy Scena ios, due o lowe FLH o RE in pa icula sola PV and s ic cons ain s on ossil uel. The high gas s o age capaci y is e- qui ed o P G and gas u bines, as ossil na u al gas is eplaced by SNG. Acco ding o Fasihi e al. [73], RE-based syn he ic uels a e a eal op ion o deca bonising he powe sys em o he yea 2030 and beyond. The ole o powe g ids becomes p ominen om 2020 onwa ds, and u ilisa ion inc eases wi h pene a ion o RE sha es in he powe sys em, pa icula ly in he Bes Policy Scena ios. The g id in e connec ion en- hances he shi ing o ene gy om expo ing sub- egions wi h high e- newable esou ce po en ials o he impo ing sub- egions. Acco ding o he esul s o his s udy, ansmission g ids a e i al in eaching a ully sus ainable powe sys em in Nige ia by 2050. B own e al. [21] show ha sec o coupling, oge he wi h elec ici y ansmission ne wo ks, can educe he o al sys em cos s by up o 37% compa ed o a sys em wi h none o hese lexibili y op ions. Howe e , a mix o se e al lexibil- i y op ions such as long- and sho - e m ene gy s o age, dis ic hea ing and syn he ic uels a e ound o be mo e bene icial han powe ansmis- sion alone. In es men s in g id expansion a e i al o he de elopmen o he Nige ian powe sys em. Acco ding o he IEA New Policy Sce- na io, he a e o elec ici y access is expec ed o inc ease om 45% in 2012 o a ound 85% in 2040 h ough g id ex ension due o high popula- ion densi y and widesp ead ne wo k co e age in he coun y [6]. How- e e , g id ex ension is o en a ime-consuming p ocess, which migh lea e many people wi hou elec ici y o a long pe iod [74]. The g id ex ension app oach has no con ibu ed signi ican ly o an e adica ion o ene gy po e y in many SSA coun ies, including Nige ia [75]. Thus, o -g id solu ions based on RE echnology, pa icula ly sola PV based echnologies (sola home sys ems (SHS) and mini-g ids), p o ide solu- ions in a eas whe e g id ex ension is no cos -e ec i e [76]. Acco ding o Be heau e al. [77], wo scena ios we e modelled o unde s and he e ec s on u u e g id ex ension plans in SSA. Resul s o he modelling e eals ha abou 96 million Nige ians a e un-elec i ied. In he i s scena io based on he exis ing g id, 22.1 million people (23%), 38.5 mil- lion people (40%) and 35.6 million people (37%) can be elec i ied by mini-g ids, g id ex ension and sola home sys ems, espec i ely. The sec- ond scena io, in which modelling was based on he planned g id, 17.3 million people (18%), 51 million people (53%) and 27.9 million people (29%) can be elec i ied by mini-g ids, g id ex ension and SHSs, espec- i ely [77]. Fu he mo e, SHS can se e as sho - e m solu ion un il g id connec ion can be achie ed o economic powe makes he es ablishmen o mini-g id easible [78]. Accele a ing elec i ica ion access equi es in dep h spa ial and echno-economic analysis in iden i ying leas cos and op imal elec i ica ion mix op ions in u al a eas [79]. Oued aogo [80] highligh s ha he elec i ica ion a e in SSA has o be inc eased 40- old om oday’s elec i ica ion le el o dec ease he elec ici y po e y in he con inen . This can be achie ed by an inc ease o new RE-based powe gene a ion capaci y and o -g id sys ems. Fu he mo e, he wa e sec o is undamen al o he coun y’s de el- opmen , and he go e nmen o Nige ia has made p o ision o wa e and basic sani a ion he esponsibili y o he Fede al Minis y o Wa- e Resou ces (FMWR) [81]. Wa e a ailabili y a ies ac oss he coun- y. Acco ding o [81], Nige ia No h-Wes and No h-Eas a e he main egions wi h wa e sca ci y. In he a o emen ioned egions, poli ical and economic p oblems hinde wa e se ices. The Nige ian go e n- men is commi ed o p o iding wa e co e age o 9 million people yea ly beginning om 2016 un il 2030. The es ima ed in es men e- qui emen is 378m€/yea , based on Uni ed Na ion (UN) connec ion 18 UNCORRECTED PROOF A.S. Oyewo e al. Ene gy Con e sion and Managemen xxx (2018) xxx-xxx p ice o 42 €/pe son o he wa e ne wo k. The nominal a i cha ged by he S a e Wa e Agency (SWA) anged om 1.26 o 1.68 €pe am- ily pe mon h. Wa e supply om al e na i e p o ide s anges om 5.0 o 6.7 €/m⁠3 in he No h, while p ices ange om 1.7 o 3.4 €/m⁠3 in he Sou h [81]. Acco ding o he esul s o his esea ch, LCOW declines om 0.66 €/m⁠3 in 2015 o 0.56 €/m⁠3 in 2050. The capex equi ed in 2050 o mee he Nige ian wa e demand is 14.7m€, whe eas he an- nual opex ixed and a iable is 1.1m€and 1.8m€, espec i ely. The esul s ob ained a e compa able o he indings o Ba asa e al. [5] o he SSA egion based on o e nigh app oach o he yea 2030, which conclude ha SSA coun ies will be powe ed mainly by sola PV and complemen ed by wind ene gy. In addi ion, he LCOE ob ained in he Bes Policy Scena ios a e compa able o he LCOE ob ained in [5]. Examining he applica ion o a ca bon p ice du ing he ansi ion, pa - icula ly in he Bes Policy Scena ios, led o a apid ansi ion and as GHG emissions educ ion in compa ison o no GHG emission cos sce- na ios. Howe e , he no GHG emission cos scena ios achie ed compa- able esul s in e ms o capaci y, gene a ion, cos s o elec ici y and GHG emission ajec o y o he Bes Policy Scena ios. By 2050, he RE elec ici y gene a ion eaches 97.8% in he no GHG emission cos sce- na ios, wi h abou 2% ene gy supplied by ossil gas. This indica es ha Nige ia’s ene gy ansi ion is achie able wi hou GHG emission cos im- plemen a ion. The esul s o his esea ch is ully in line wi h he e- cen ag eemen o se e al A ican ci ies, such as Lagos in Nige ia, Cape Town and Johannesbu g in Sou h A ica and Acc a in Ghana, o cu ca - bon emissions o ze o un il 2050 [82]. An ene gy sys em op imisa ion analysis o he Uni e si y o Ilo in in Nige ia unde se e al con igu a- ions show ha a hyb id PV-Diesel-Ba e y sys em is he bes solu ion o educe he GHG emissions cos signi ican ly, while he sys em cos s a e also he lowes compa ed o o he con igu a ions [83]. Howe e , he capi al cos o sola PV assumed is much highe han he cu en cos in Nige ia [84]. I he ac ual cos o sola PV was conside ed, i is likely ha hyb id PV-Ba e y sys ems will o e he leas cos , while wind en- e gy can also complemen . Aku u e al. [7] conclude ha 100% RE is possible in Nige ia wi h he coun y’s abundan RE esou ces, bu ha he igh go e nmen backing is lacking. Though he ole o he go e n- men canno be comp omised, indi iduals could d i e he ansi ion o 100% RE in Nige ia by ins alling RE sys ems in mega ci ies like Lagos, Abuja o Po Ha cou [7]. 6. Conclusion and policy implica ions T ansi ion o a ca bon-neu al ene gy sys em in Nige ia will equi e a s ong poli ical commi men a all le els o go e nance. Beyond ech- nical easibili y and economic iabili y o an ene gy ansi ion owa ds a ze o GHG emission sys em, i encompasses long- e m and well-de- signed policy in e en ions. A conce ed and consis en policy ac ion ha would es ic new in es men s in ossil powe plan s, and acili- a e RE de elopmen in a long- e m pe spec i e is exigen o he ansi- ion in Nige ia. This esea ch o e s key insigh s o ene gy sys em plan- ne s and policymake s in Nige ia, and demons a es he need o a de- ailed analysis in de e mining knowledge gaps in ansi ion pa hway op- ions unde a ious policy cons ain s o de eloping coun ies o com- pa able clima es. The esul s o his esea ch demons a e ha a deca - bonised ene gy sys em is qui e compe i i e in all Bes Policy Scena - ios in compa ison o he Cu en Policy Scena ios. The high compe - i i eness is based on an inc easing sha e o RE echnologies, pa icu- la ly he high cos compe i i eness o sola PV and suppo ing ba e - ies. Sola PV domina es all he Bes Policy Scena ios by 2050, whe e PV single-axis acking con ibu es he mos (63–83%) o he o al PV in- s alled capaci ies ollowed by PV p osume s. The high sha es o PV in he Bes Policy Scena ios a e e lec ed in an inc ease in ba e y s o age u ilisa ion. The combina ion o sola PV and ba e y s o age was ound o be e y bene icial o he powe sys em. The need o elec ici y s o - age in he ene gy sys em is a key cha ac e is ic o high pene a ion le els o VRE. Sho - e m (Li-ion), medium- e m (TES), and long- e m (gas s o age) s o age a e equi ed o balance daily, weekly and sea- sonal a iabili y o RE. Fu he mo e, ene gy s o age p o ides lexibili y o he ene gy sys em by enabling demand balancing. G id in e connec- ion wi hin he coun y allows shi ing o elec ici y om one poin in ime o ano he , enabling la ge-scale gene a ion and demand balancing be ween he di e en sub- egions. Mo eo e , gas u bines p o ide ad- di ional lexibili y o he powe sys em, whe e ossil gas is subs i u ed wi h SNG o biome hane om 2015 onwa ds in he Bes Policy Scena - ios. The p oduced gas can be ei he used in he powe sec o o balance he sys em when i is needed, o s o ed in gas s o age o mee he de- mand o non-ene ge ic indus ial gas sec o . Ene gy policy in Nige ia should place sola PV a i s co e. The cu - en pe spec i e o RE u ilisa ion, possible mo i a ion o RE de elop- men , ba ie s and challenges in Nige ia equi e delibe a e ac ions and s ong poli ical will. F om a policy pe spec i e, his esea ch iden i ies in es men equi emen s, iming and ope a ions ac oss Nige ia. Such in- o ma ion a e ele an o policy make s and ene gy planne s in Nige ia o se ing ene gy in es men a ge s. Du ing he ansi ion, sola PV and ba e ies eme ge as he mos impo an echnologies, complemen ed by wind ene gy and exis ing hyd opowe . In addi ion, gas u bines p o ide lexibili y o he powe sys em. A 100% RE-based sys em is eachable and is he eal policy op ion o Nige ia. RE esou ces can mee he elec- ici y demand o he powe , seawa e desalina ion and non-ene ge ic indus ial gas sec o s. Fu he mo e, based on all scena ios examined in his s udy, he Bes Policy Scena ios p esen he leas cos elec ici y pa hways o Nige ia in compa ison wi h he Cu en Policy Scena ios. The LCOE anges om 34 o 48 €/MWh o he Bes Policy Scena ios, whe eas he LCOE o he Cu en Policy Scena ios lie be ween 75 and 120 €/MWh. The Cu en Policy Scena ios clea ly demons a e he need o a cleane ene gy sys em, as a ossil domina ed sys em iola es all sus- ainabili y c i e ia. New in es men s in nuclea powe plan s in Nige ia a e no compe i i e and show a high isk p o ile, leading o low social accep ance. Finally, a well designed RE oadmap, an a ac i e en i onmen o local and o eign in es o s, elec ici y ma ke e o ms, esea ch and de- elopmen and o he emissions aba emen policies would be equi ed o d i e RE de elopmen in Nige ia. Inno a i e inancing mechanisms ad ancing RE de elopmen elsewhe e in he wo ld can be adop ed in Nige ia as well. 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