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Renewable and Sustainable Energy Reviews

journal homepage: www.elsevier.com/locate/rser

A review of seasonal pumped-storage combined with dams in cascade inBrazil

Julian David Hunt⁎, Marcos Aurélio Vasconcelos de Freitas, Amaro Olímpio Pereira Junior

Energy Planning Program/COPPE/UFRJ, Brazil

A R T I C L E I N F O

Keywords:Energy storagePumped-storageEnergy efficiencyEnergy conservationEnergy securitySeasonal generation

A B S T R A C T

In order to maintain greater control over the country's water resources and reduce the vulnerability of theBrazilian electricity sector, this paper presents a review of the Seasonal-Pumped-Storage (SPS) potential inBrazil, its benefits and the different ways in which SPS can be integrated with hydroelectric dams in cascadedownstream. In addition to increasing the Brazilian energy storage potential, SPS has the potential to: regulateriver flows allowing the control of hydropower generation; reduce the spillage and increase power generation inthe hydroelectric dams in cascade; turn the construction of new dams more viable where there is no suitablegeology for the construction of conventional storage reservoirs; control floods when the geology does not permitthe construction of storage reservoirs; decrease the evaporation of accumulation reservoirs; store the electricitygenerated from intermittent renewable sources; store energy for peak generation; reduce transmissionbottlenecks; decrease the cost of electricity transmission from hydroelectric plants in the Amazon; decentralizethe energy storage capacity in Brazil to increase energy security and to reduce the risk of electricity rationing.

1. Introduction

Brazil has just came out of a severe energy crisis and severalregional water crisis, which started in 2013 and lasted until the end of2015. The level of the stored energy in the reservoirs was reduced to19% of total capacity in January 2015 [1]. The energy crisis resulted inan average 52% increase in electricity prices between October 2014 andOctober 2015 [2], which influenced on worsening the economic crisisin the country. In the end of 2015, the rain returned to the South ofBrazil and an average of 3 GWmed1 of hydropower potential bypassedthe dams without generating electricity in the Iguaçu River during 4months. As the economic crisis reduced the electricity consumption in2015 by 0.6% in comparison to 2014 [1], it is expected that more waterwill bypass the dams in 2016 without generating electricity due to thelow electricity demand during the next few years. The electricity supplyand demand imbalance will worsen with the operation of new dams inthe Amazon that will generate most of their energy during the wetperiod [3]. The Government has stated that there is the need toincrease the storage capacity [4], however no viable solution to increasethe countries energy storage potential has been proposed. Electricitydemand is set to increase by 44.9% and energy storage will increase byonly 0.9% over the next 10 years [4].

An efficient solution to the frequent variation between low elec-

tricity generation and excess of energy for any country is to increase itsenergy storage capacity. This paper develops and discusses differentprojects for the implementation of Seasonal-Pumped-Storage (SPS).SPS is an innovative technology, firstly proposed in Hunt et al. 2014[5,6], to increase energy storage in a seasonal fashion. It storespotential energy during the wet season, when there is excess flow inthe river, or when there is excess energy in the grid, pumping water toan upper reservoir. During the dry season, or when there is lack of flowin the river, or when there is lack of energy in the grid, the stored watergenerates electricity in the SPS and in the dams in cascade (two ormore hydroelectric dams in series). Although, a conventional pumped-storage plant has an average energy efficiency of 75%, the combinationof a SPS with hydropower dams in cascade, can increase the totalstorage efficiency to around 90%, without including the reduction ofspillage in the dams in cascade. In cases where a SPS decreases thespillage or evaporation in the hydropower dams in cascade, the SPSmay result in an overall energy gain, rather than a loss, to the system.

The aim of this paper is to review the potential of SPS in Brazil, thedifferent approaches of combining SPS and dams in cascade, andfurther benefits of SPS, such as, reduce the vulnerability of a country'senergy and water sectors, increasing its energy and water storagecapacity; decentralize the storage potential of Brazil, increase thesecurity of the electricity sector, remove the intermittency of renewable

http://dx.doi.org/10.1016/j.rser.2016.11.255Received 2 April 2016; Received in revised form 1 October 2016; Accepted 22 November 2016

⁎ Corresponding author.E-mail addresses: [email protected] (J.D. Hunt), [email protected] (M.A.V.d. Freitas), [email protected] (A.O. Pereira Junior).

1 1GWmed is equivalent to an average generation of 1GW during a month.

Renewable and Sustainable Energy Reviews 70 (2017) 385–398

Available online 28 November 20161364-0321/ © 2016 Elsevier Ltd. All rights reserved.

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sources, generate electricity during peak hours, decrease transmissionline costs and reduce de spillage in the dams in cascade. Furtherbenefits of SPS are presented in the following sections.

This article is structured as follows. Section 2 presents a review ofexisting pumped-storage and seasonal-pumped-storage schemes in theworld, pointing out the differences between conventional and seasonalpumped-storage schemes. Section 3 explains in details the SPSmethodology, reviews the seven different SPS types, gives an exampleof SPS project and shows how the efficiency of these systems arecalculated. Section 4 reviews the potential of SPS projects in Brazil withthe intention to resolve the energy imbalance, which resulted in thecrisis in Brazil. It also presents the projects located in environmentalprotected areas, where SPS projects should not be constructed. Section5 reviews the many benefits of SPS: low storage costs, multiple uses ofwater, decentralize energy storage, reduce transmission costs, reducespillage and evaporation in downstream dams and reduced floodedarea to store energy. Section 6 concludes the paper.

2. Pumped-storage and seasonal-pumped-storage

Pumped-storage plants (PS) are widely used to store energy [7,8].At night, when electricity demand is low, excess generation is stored bypumping water from a lower reservoir to a higher reservoir. During theday, when demand increases, the stored energy is transformed intoelectricity. However, there is an energy loss of 15–30% during thestoring process and electrical generation systems. These losses areusually 13,6% for pumping, where 0,5% is lost in the transformer, 3%in the motor, 9,6% in the pump, 0,5% in the pipes, and 9,1% forgeneration, where 0,4% is lost in the transformer, 1,4% in thegenerator, 6,5% in the turbine and 0,8% in the pipes [9].

Pumped-storage has been used in China [10,11], India [12,13],Japan [14], Europe [15–17] and the United States [18,19]. Table 1shows the installed and under construction Pumped-Storage capacity.Underdeveloped countries, which have less strict energy securitypolicies, are still sluggish on the development of pumped-storagepotential. There is a proportionally higher concentration of pumped-storage plants in countries with a high share of Nuclear (France andJapan) and Coal (USA, China) power generation. Nuclear and Coal areinflexible, base load generation sources and generate a constantamount of electricity throughout the day [20]. In order to adjust thechanges in demand between night-time and daytime, conventionalpumped-storage schemes where installed with the intent to storeenergy during the night, when demand is low, and generate energyduring the day, when demand is higher. Fig. 1 presents a typical powergeneration load curve in countries with high Nuclear and Coalgeneration share. Pumped-storage turbines operate at low capacityfactors with the intent to guarantee the supply of electricity.

The last decade had an increase in pumped-storage plants with the

intention to store energy coming from intermitted sources such as wind[22–24] and solar [25] in a gird scale [26] and in the insular scale(wind power [27–29] and solar power [30–32]). These schemes havethe intent to optimise the operation of intermittent renewable sources,reducing losses when there is excess generation and complementingthe supply of electricity when there is lack of wind and solar generation.Pumped-storage has proven to be a viable alternative to store energy ona grid scale [33] and 97% of the energy storage capacity (in MW) in theworld consists of pumped-storage [34].

There are innovative approaches to apply pumped-storage, forexample, using underground reservoirs, which brings the benefit ofnot flooding new areas, as the water reservoir is located underground[35]. Another innovative approach is to use seawater in the pumped-storage system [36]. Using seawater increases the possibility ofimplementing pumped-storage systems, where there is water shortage,close to the coast.

The Seasonal-Pumped-Storage concept, which consist of operatinga pumped-storage plant in a yearly cycle instead of a daily cycle, wasfirstly presented in (Hunt et al. 2014) [5] and has the objective to storeenergy during months of high electricity generation or low energydemand and generate electricity during months of low electricitygeneration or high energy demand. For example, it can be used incountries where power generation is based on hydropower, biomass,wind or solar sources, with high seasonality variations. Alternatively, itcan reduce the consumption of fuel during months when prices areusually higher. On the demand side, energy can be stored during thesummer, when the demand is lower and generate electricity during thewinter, when demand increases, or vice-versa.

One pumped-storage plants, which operates similarly to a SPSplant, is the Tonstad III plant located in South Norway. The powerplant is an intermingled connection between several lakes, rivers andreservoirs, with eight hydropower plants (each with several turbines).The overall storage capacity of this complex is of 6 TWh, equivalent to a5% of Norway's yearly electricity production [37]. The pumped-storagefacility intends to store energy during years with high hydropowergeneration and generate electricity in years with low hydropowergeneration.

A project that would result in several plants similar to Tonstad III isthe North Seas Countries Offshore Grid Initiative (NSCOGI). TheNSCOGI intends to promote de implementation of wind power in theNorth Sea and use the hydropower and pumped-storage potential ofNorway to reduce the intermittency from wind power generation [38–41].

Another interesting existing arrangement for pumped-storage,which has similarities with seasonal-pumped-storage sites, is theShoalhaven Hydro Pump Storage Scheme, NSW, Australia, which hasa capacity of 240 MW and generates electricity during peak hours. The

Table 1Pumped-storage capacity installed and under construction in 2013 [21].

PS projectsaround the world

Installed PScapacity in 2013(GW)

PS capacity underconstruction in 2013 (GW)

Africa 1.6 1.3Middle East & North

Africa1.5 0

Latin America 1.0 0North America 20.6 0Europe 51.4 9.0Asia – South &

Central5.1 1.7

Asia – East 56.3 12.8Asia – Southeast &

Pacific4.6 0

Total 142.1 24.8

Fig. 1. Power generation load curve in countries with high nuclear and coal generationshare [20].

J.D. Hunt et al. Renewable and Sustainable Energy Reviews 70 (2017) 385–398

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facility is also used to supply water to Sydney during times of drought[42]. Managing water with pumped-storage has many benefits, forexample, it is not required to obstruct the course of the river, reducingenvironmental impacts, the flooded area required to store the sameamount of water is smaller due to the higher reservoir level variationand consequently the evaporation in the reservoir.

The important aspects of the technology involved in Seasonal-Pumped-Storage has already being explored in conventional dams andconventional pumped-storage systems. However, unlike PS plants thatoperate over the cycle of a day, a SPS operates over the cycle of a yearor more. This operational difference results in important differencesbetween PS and SPS projects, for example:

– The SPS upper reservoir stores a volume of water hundreds of timesgreater than PS upper reservoirs, with the intent to operate in ayearly cycle instead of a daily cycle.

– The elevation of the upper reservoir of a SPS ranges from 100 to250 m. Due to environmental restrictions, new reservoirs shouldflood small areas and store large amounts of energy, see Fig. 9.

– The tube that connects the upper and lower reservoirs in SPS plantsare usually 10–20 km long, which is longer than PS plants tubes.

– A SPS upper reservoir dam is considerably longer and higher thanthat of a PS plant, due to the need of a larger reservoir.

– The turbo-pumps operate with a head variability between 100 and250 m efficiently. There are existing pumped-storage plants thathave such high head variation. For example, the Nant de Drancepumped-storage site has a 164 m head variation, as shown inTable 2. The ‘Variation Percent’ (Head Variation/Maximum Head)reaches 37% for Limberg II, which has a head variation of 159 m,and 43% for Tehri, which has a head variation of 94 m. In order todevelop reasonably efficient SPS projects, the minimum ‘VariationPercent’ assumed in this review study is 50%. The upper reservoirlevel variation should be as high as possible, with the intention toreduce the flooded area per energy storage as much as possible.

In order to have the highest head variability as possible, the heightof the dam should be as large as possible. The highest proposed SPSdam was a height of 300 m, which could be smaller if necessary.Table 3 presents the tallest dams in the world for comparison.

3. Methodology: seasonal-pumped-storage

SPS involves the construction of an upper reservoir, with a stablegeological formation, connected by a tube to a reservoir located nearthe top of a river with a series of hydroelectric dams in cascadedownstream. The SPS reservoir should be at 200 m or more above thelower reservoir height. This is because the upper reservoir should storeas much water as possible, so that it would flood a small area andstorage a lot of energy.

A cascade of hydropower dams works as shown in Fig. 2(a) wherethe blue arrow represents the direction and the flow of water. The damswith reservoirs has the potential to store water and energy, altering thenormal flow of the river, the run-of-the-river dams do not changesignificantly the river flow. The planning of reservoirs and turbinestakes into account the optimum power generation during the year withthe lost cost.

With the combination of a SPS and hydroelectric dams in cascade,in Fig. 2(b) and (c), it is possible to change the flow of a river basin inaccordance with the need for energy storage and power generation [6].Fig. 2(b) represents the energy storage process that happens whenthere is high water availability in the basin in question and/or whenthere is excess energy in the National Interconnected System (SIN).The excess energy of the grid is used to pump water for the SPS upperreservoir with the consequent reduction of the generation of electricityin the cascade. The energy storage in SPS has a 70–75% efficiency.With the inclusion of the cascade, the overall storage efficiencyincreases considerably and may even result in a net generation gain.This happens if the increase in storage reduces the water spillage orwater evaporation of the dams in cascade. During periods of low wateravailability in the basin or when there is a shortage of energy in thegrid, SPS generates electricity using the stored water and increases thegeneration of the dams in cascade downstream, as shown in Fig. 2(c).Table 4 shows a summary of the operating characteristics of thedifferent alternatives presented in Fig. 2.

SPS systems add several benefits to the operation of dams incascade. Apart from the inherited benefits of PS such as to store energyfrom renewable sources, generate electricity during peak hours, andreduce transmission costs, each SPS project adds specific benefits tothe system. There are different types of SPS plants, each possessing aspecific characteristic. These are presented below in Table 5. Note thata SPS project can be of more than one type.

The Cascade, Spillage, Seasonal and Annual SPS types are similar.All have the objective to increase the energy storage of the SPS &cascade system. They differ in the overall storage capacity of thesystem. The Cascade type proportionate a minimum storage capacity tothe system, the Spillage type results on a medium storage capacity, theRegulation type results on a high storage capacity and the Annual typeresults on a very high storage capacity. The Cascade SPS happens inrivers with no dams in cascade and is used to create a minimum storagecapacity so that a new cascade downstream the SPS can become viable.The Spillage SPS reduces the spillage on the dams in cascade. TheSeasonal SPS allows the operator to store energy from the wet period to

Table 2Pumped-storage sites with high head variation [43,44].

Name Units Head (m) Head variation (m) Variation percent (%) Power (MW) Speed (rpm) Country

Nant de Drance 6 250–390 140 35.9 157 428.6+/-7% SwitzerlandLinthal 4 560 – 724 164 22,7 250 500+/-6% SwitzerlandTehri 4 127 – 221 94 42,5 255 230.8+/-7,5% IndiaLimberg II – 273–432 159 36,8 240 428.6 Austria

Table 3Tallest dams in the world [45].

Name Height (m) Type Country River Year ofoperation

Jinping-I 305 Concrete arch China Yalong 2013Nurek 300 Embankment,

earth-fillTajikistan Vakhsh 1972

Xiaowan 292 Concrete arch China Lancang 2010Xiluodu 285.5 Concrete arch China Jinsha

Jiang2013

GrandeDixence

285.5 Concretegravity

Switzerland Dixence 1964

Inguri 271.5 Concrete arch Georgia Inguri 1987Vajont

Dam261.6 Concrete arch Italy Vajont 1959

ManuelMorenoTorres

261 Embankment,earth-fill

Mexico Grijalva 1980

NuozhaduDam

261 Embankment China LancangRiver

2012


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generate during the dry period. The Annual SPS has the storagecapacity to do all of the above and can store and generate energy forone or more consecutive years.

3.1. Seasonal-pumped-storage example

The Palmital SPS will allow its lower reservoir, Governador BentoMunhoz Dam (GBM) and the dams in cascade to generate most of theirenergy during the dry period. As shown in Fig. 3, the catchment area ofthe GBM Dam and the catchment area of the dams in cascadedownstream have similar sizes. This is an advantage because, withthe construction of Palmital SPS, the flow of the dams in cascade willhave a similar flow to the GBM Dam.

Given the mountainous geology around the GBM Dam, a number ofdifferent locations and projects could be developed using the GBMDam as the lower reservoir of a SPS site. Fig. 4 presents three differentSPS projects around the GBM Dam. Each project has problems andbenefits and for the case of exemplifying the technology, Palmital SPSwas preliminary selected, as it requires a low dam and short tube.

Fig. 5 shows the operation of the SPS Palmital in the Iguaçu RiverBasin. This project consists of building a SPS where the lower reservoirconsists of the G. B. Munhoz Dam and an upper reservoir with a dam oftwo kilometres in length and a maximum height of 220 m. The upperreservoir has a storage capacity of 13700 hm3 and 23.8 TWh, which isequivalent to 11.4% of the storage capacity of the Brazilian Grid.

With the Palmital SPS plant, 2 GW of electricity can be pumped tothe new Palmital reservoir for 6 months to fill most of the reservoirsuseful volume. The electricity used for pumping may come from futureplants in the Amazon that will generate a surplus of electricity duringthe wet season [46]. Note that energy loss from pumping happenswhen the system has an excess of energy (instead of wasting hydro-power potential, it is stored). With the increased water storage,hydropower generation in the dams in cascade downstream the SPSPalmital decrease by 2.3 GW (including gains on the water that wouldhave been spilled, if storage has not been increased), as shown inFig. 5(a). This results in a total generation reduction of 4.3 GW duringthe wet season.

During the dry season, Fig. 5(b), the Palmital SPS generates 1.5 GWfor 6 months (including losses from the storage process) until theupper reservoir is empty, and increases the hydroelectric generation inthe dams in cascade in 3.3 GW (including gains from the water thatwould have been spilled without the increase in storage). This results ina total increase of 4.8 GW of generation during the wet season.Compared to the reduction in the wet season, there is a net gain of0.5 GW per year including losses from pumping. Storage costs arerelatively low because the investment is only on the 2 GW SPS project,but the final storage is 4.8 GW. This reduces storage costs more than

Fig. 2. Operation of (a) conventional hydroelectric plants (b) SPS during periods of high water availability (c) SPS during periods of low water availability. Note that the same legend isused in other figures. (For interpretation of the references to color in this figure, the reader is referred to the web version of this article.)

Table 4Operation scheme for SPS.

Wet period Dry period

High water availabilityin the watershed

Low water availability inthe watershed

High energyavailability in the SIN

Low energy availability inthe SIN

NoSPS

With SPS No SPS With SPS

Dams inCascadegeneration

High Low (Energy isConserved)

Low High (Generatein scarcity)

Losses due tospillage

High Low (Water isStored)

Low Low

Losses due topumping

Zero 25% (EnergyLosses Reduced)

Zero Zero

Losses withsmaller head

Low Low High (LessPower perFlow)

Low (EfficientGeneration)

Table 5Types of seasonal-pumped-storage plants.

SPS Type Specific benefit Proposed SPS

Cascade Adds a minimum storage capacity required to turn viable the construction of dams in cascade downstream of the SPSsite.

Peçanha, Raizama (Section 5.2)

Spillage Adds a medium storage capacity to reduce losses with spillage of the dams in cascade downstream of the SPS site. Estrela, Careca, Paranorte (Section 5.2)Seasonal Adds a high storage capacity to allow most of the electricity in the cascade to be generated during the dry season. Palmital (Section 3.1)Annual Adds a very high storage capacity to the system, so that electricity can be stored or generated for more than a year. Canastra (Section 5.1)Transposition Allows water to be transposed from one river to the other to optimise the hydropower generation in both rivers. Preto, JardimEvaporation Allows high evaporation reservoirs downstream the SPS to be kept at their lowest level to reduce evaporation. Muquém, Pardo (Section 5.2)Water Stores water to avoid water shortage. BarreiroFlood SPS Stores water to reduce the impact of floods. Macacos


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Fig. 3. GBM Dam catchment area and downstream dams in cascade in the Iguaçu River.

Fig. 4. Three possible SPS projects around the GBM Dam.


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half.Eq. (1) is used to estimate the energy stored in the Seasonal-

Pumped-Storage sites:

∑EnergyStored h f c gρ=i

n

i i i=1 (1)

where, Energy Stored is in Joules (J); h is the average height differencebetween the upper reservoir and the lower reservoir of the SPS and theaverage head of the series of dams in cascade (m); n is the number ofdams in cascade plus the SPS plant; i is each dam; f is the flow of waterequivalent to each dam (kg); c is the electricity generation efficiency ofeach dam; g is the acceleration of gravity (m/s2); ρ is the density ofwater (kg/m3). The volume of water stored in the SPS is estimatedusing the topographic map of the location [47].

The efficiency is estimated using Eq. (2) and (3) below. The flowratedata used to calculate the spilled water was taken from [1], where thereare existing lower reservoir dams, and from [48], where there are noexisting lower reservoirs.

EnergyStored LosswithStorage LosswithSpillage

LosswithEvaporationEnergyStored

Overall Efficiency =

− + +

(2)

H H H F g V EH H F g

Overall Efficiency =( + −0, 25× )× × + +

( + ) × ×SPS jSPS SPS

SPS j (3)

where:

F=flow rate of water pumped into the SPS (m3/s).HSPS=SPS average operation height (meters).HjSPS=Dams in cascade average head downstream the SPS (meters).

Hj=Dams in cascade average head without SPS (meters)V=Electricity generation gain due to spillage reduction (in kWmed)E=Electricity generation gain due to evaporation reduction (inkWmed)g=Gravitational acceleration (m/s2).

Even though a conventional pumped-storage plant has an averageefficiency of 75%, the combination of a SPS system with hydropowerdams in cascade can increase the total storage efficiency to about 90%,without including the reduction of spillage in the dams in cascade. Incases where an SPS decreases the spillage or evaporation in thehydropower dams in cascade, the SPS may result in an overall energygain, rather than a loss to the system. For example, the Palmital SPSpresented above has a total reduction of 4.3 GW during the dry periodand a total increase of 4.8 GW during the wet period. Thus, the overallefficiency is equal to 112% (4.8/4.6=1.12).

4. Results

This section presents the results of the proposed SPS projects andhow these projects enhance the hydropower generation in the dams incascade. Around a hundred possible SPS systems were investigated.Fig. 6 locates thirteen of these projects. The colour of the catchmentarea corresponds to the energy storage capacity of the SPS.

Table 6 presents the details of each project, such as storage volume,flooded area, dam height, tube length, upper reservoir maximum andminimum levels, lower reservoir level, pumping capacity to fill thereservoir in six months, energy storage capacity, catchment area andestimated efficiency.

Table 7 presents the head of the dams in cascade built, planned orthose that would be made viable with the construction of the SPS plant.In addition, it shows the total head loss with the depletion of the

Fig. 5. Diagram representing the operation of Palmital SPS in the Iguaçu River Basin (a) during the wet period and (b) during the dry period.


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reservoirs of the dams in cascade built, planned or made viable with theSPS system. The ‘Percent to the built’ column in Table 7 shows theamount of head that needs to be built for the SPS project to be reachthe storage efficiency presented in Table 6. In addition, it presents thefurther investment required to complete the SPS projects and thehydropower dams downstream. The ‘Percent of head loss’ shows thehead reduction when all storage reservoirs of a river reaches theirminimum level. SPS projects can reduce the head loss of the dams incascade, as it will increase the energy and water storage of the cascade.

An important aspect of the development of SPS projects is theirenvironmental and social impact. The map in Fig. 7 shows the areas ofBrazil with conservation units, Indian territories, Marron territoriesand Agricultural Settlements, and the proposed SPS projects.

As shown in Table 8, the Palmital SPS project on the Iguaçu River islocated in an Environmental Protection Area (EPA) [52,53], whichmakes it a non-viable project. However, the Palmital SPS project hasthe same lower reservoir as the Areia and Iratím SPS projects, as showin Fig. 4. Thus, Areia or Iratím projects can be constructed instead of

the Palmital SPE project.The Canastra, Barreiro and Raizama SPS projects are also located in

two National Parks and an EPA respectively. This turns the CanastraProject not viable. The similar Barreiro and Raizama SPS projectscould be build outside the National Park and EPA, with differentreservoirs and longer tubes. This would increase the price of theprojects. Regarding Indian Land, only the Peçanha SPS project islocated inside an Indian Land. Permission for the Indians communitiesis required for this project. This permission can be difficult to attainand can be controversial [54–56].

5. Discussion

Seasonal-Pumped-Storage systems bring many benefits to theenergy sector and society. This section presents the main benefits ofthe technology.

Fig. 6. Catchment area of SPS projects and their respective storage capacities. (For interpretation of the references to color in this figure, the reader is referred to the web version of thisarticle.)


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5.1. Reduced flooded area (Annual SPS type example)

SPS upper reservoirs have a head variability of 100–250 m and arebuilt at the first dam of a hydroelectric cascade. For these reasons, theflooded area of SPS is much smaller than conventional storagereservoirs. For example, the Canastra SPS project, an Annual SPStype, with a flooded area of 168 km2, stores the same amount of energyand floods an area 54 times smaller than the summed total of theSobradinho, Tucuruí and Serra da Mesa dams, which flood an area of9003 km2, as shown in Fig. 8.

Fig. 9 shows the amount of flooded area to store 1 TWh for theproposed SPS projects and the existing conventional reservoirs in thegrid. It also shows the names of conventional reservoir dams with theirrespective flooded area. The SPS projects flood a small area of between2.5 and 31 km2 to store 1 TWh. For example, the best SPS project, SPSBarreiro, floods 2.5 km2/TWh, which is 10 times less than the NovaPonte dam, the dam that stores energy with the smallest flooded area ofthe Brazilian Grid, 26.7 km2/TWh. The SPS with the greatest floodingindex, Careca SPS with 31.1 km2/TWh, floods 135 times less thanBalbina Dam, with 4924.3 km2/TWh, which is the second plant thatfloods the most area per TWh stored. In comparison with the best SPSdam (SPS Barreiro), Balbina floods an area 1692 larger to store thesame amount of energy. It should be noted that some dams were

designed with a large flooded area with the intention to increase itsgeneration head and not to store energy, for example, Ilha Solteira andItaipú Dams.

5.2. Reduced spillage and evaporation in the dams downstream theSPS (Cascade and evaporation SPS type example)

SPS projects have the potential to reduce the amount of water thatbypass dams without generating electricity. SPS projects increase theamount of electricity that a river can generate by storing water whenthere is excess of rain.

In the Cascade SPS, the river flow on the lower reservoir variesconsiderably during the wet and dry periods and there is no appro-priate location to build a conventional hydropower storage damupstream to regulate the flow. The Cascade SPS can regulate the riverpumping water during the wet season and generate electricity duringthe dry season. This SPS operation would contribute to regulate theflow and make economically viable the construction of the Vão dasAlmas Dam (lower reservoir of the SPS system), as well as turneconomically viable the construction of dams in cascade below theVão das Almas Dam, see Fig. 9.

Another possible benefit of SPS projects is to reduce the evapora-tion of dams downstream of SPS projects. Examples are the Muquém

Table 6Description of SPS projects in Brazil.

Plant River Volume(hm3)

Floodedarea(km2)

Index(km2/TWh)

Damheight(m)

Tubelength(km)

Level (m)minimum&maximum

Ave. lowerreservoirlevel (m)

Pumpingflow (m3/s)

Storage(TWh &% doSIN)

Catchmentarea (km2)

Efficiency (%)

Palmital Iguaçu 13,700 177 7.4 220 4 870–1,000 742 868.8 23.8/11.4 30,100 112%Estrela Uruguai 5100 85 11.2 190 12/10 800–900 647 323.4 7.6/3.6 27,300 119%Preto Ivaí e

Tibagi7280 104 7.9 250 40 900–1,000 430/475 461.7 13.2/6.3 34,500 137%

Raizama Paranã 12,130 286 11.4 100 14 830–870 386 769.3 25.0/11.9 31,245 128%Jardim Verde e

Claro5551 61 8.5 155 13/11 700–830 560/550 352.0 7.2/3.4 15,700 123%

Canastra Grande 28,110 168 2.9 300 12 1050–1250 660 1782.7 58.2/27.7 59,500 92%Barreiro Paraíba

do Sul4000 29 2.5 260 12 1200–1450 460 253.7 11.4/5.5 13,400 89%

Muquém SãoFrancisco

7800 52 5.2 230 9 550–700 411 494.7 10.0/4.8 326,000 95%

Pardo Velhas 16,500 150 4.9 175 10 950–1100 540 1046.4 30.6/14.5 19,000 92%Peçanha Xingu 36,400 615 18.1 122 9 440–530 260 2314.8 34.0/16.6 169,000 129%Careca Teles

Pires21,390 508 31.1 102 17 360–420 302/292 1368.8 16.3/7.8 37,400 125%

Paranorte Tapajós 61,250 875 17.8 100 14 350–450 217 3938.4 49.1/23.3 156,000 128%Macacos Mortos 8400 204 25.3 100 9 550–620 480 540.1 8.1/3.9 16,000 115%Total 215,493 3314 11.86 409/140 935,145

Table 7Head of the dams in cascade downstream from the SPS site..

Plant Head of dams Head loss of dams in Cascade

Built (m) Planned (m) Madeviable (m)

Total head(m)

Percent to bebuilt (%)

Built (m) Planned (m) Madeviable (m)

Total headLoss (m)

Percent of headloss (%)

Palmital 480.8 15.5 – 496.3 3.1 72 1 – 73 14.7Estrela 397.47 111.12 – 508.59 21.8 46 4.21 – 50.21 9.9Preto 289.43 56.84 – 346.27 16.2 16 0 0 16 4.6Raizama 139.79 70.72 112 322.51 56.7 24.4 7 17 48.4 15.0Jardim 286.03 81.96 – 367.99 22.3 20 – – 20 5.4Canastra 520.25 – – 520.25 0 59.3 – – 59.3 11.4Barreiro 214.4 45.77 – 260.17 17.6 22.5 1.7 – 24.2 9.3Muquém 306.9 18.88 – 325.78 5.8 17 – – 17 5.2Pardo 306.9 18.88 – 325.78 5.8 17 – – 17 5.2Peçanha 86.9 – 115 201.9 57.0 0 – – 0 0Careca 118.41 77.3 – 195.71 39.5 10.4 0.4 – 10.8 5.5Paranorte 112.2 77.3 – 189.5 40.8 0.4 0.4 – 0.8 0.4Macacos 65.5 41.88 225 332.38 80.3 22.4 – 20 42.4 12.8


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and Pardo SPS projects in the São Francisco River, where Sobradinhoand Três Marias reservoirs are located. The flooded area and evapora-tion in Sobradinho and Três Marias reservoir is shown in Table 9.(Fig. 10).

If the Muquém and Pardo SPS projects stored the water over thewet period, the Sobradinho reservoir would not be necessary. Thus, itcould be kept at its minimum level. This would considerably reduce theevaporation in the Sobradinho reservoir. The water could then be usedfor other uses or to increase the electricity generated in São FranciscoRiver.

5.3. Reducing transmission costs

SPSs can store energy near the run-of-the-river dams in theAmazon [57]. Thus, the capacity of transmission lines of hydropowerdams in the Amazon can decrease after it reached the SPS. Forexample, Fig. 11 shows an 800 kV cc transmission line with thecapacity to transmit the 11 GW generated from Belo Monte Dam tothe C Hub in the map. As the Peçanha SPS could have a storagepotential of 4 GW, the transmission line to the consumer centre (SãoPaulo) would only need a 7 GW capacity, as 4 GW would be used topump water in the Peçanha SPS system. In the dry period, the

Fig. 7. Map with conservation units, Indian land and proposed SPS projects [49–51].

Table 8SPS projects on conservation units, Indian lands, marrons and settlements.

Conservation units Indian land Maroons Settlements

Iguaçu Palmital Sustainable use EPA Serra da Esperança – – –

Areia – – – –

Iratím – – – –

Estrela – – – –

Preto – – – –

Raizama 1 Sustainable use EPA Pouso Alto – – –

2 –

Jardim – – – –

Canastra Integral protection Canastra National Park – – –

Barreiro 1 Integral protection Bocaina National Park – – –

2 – – – –

Muquém – – – –

Pardo – – – –

Peçanha – Kayapó Regularized – –

Careca – – – –

Paranorte – – – –

Macacos – – – –


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generation in Belo Monte is around 3 GW and the Peçanha SPS 4 GW.Thus, the transmission line required to transmit the generation fromBelo Monte Dam and Peçanha SPS to Sao Paulo could have a capacityof 7 GW instead of 11 GW.

In addition, the Barreiro SPS located close to the main demandcentres, São Paulo and Rio de Janeiro, has the potential to reduce theneed for transmission lines in the country. The transmission linesystem will be able to transmit energy constantly throughout the day tothe demand centres. If the transmission lines are not used to supply thedemand with electricity, they can be used to store energy in BarreiroSPS. This would optimise the Brazilian transmission system.

5.4. Decentralize the energy storage potential

Brazil depends heavily on rainfall in the Southeast region to storeenergy until the end of the dry season. As it rained less than the averagein the region during 2012, 2013, 2014 and 2015, the reservoir levelsbecame critically low, thermal power plants operated at full capacity,which contributed to the increase in electricity prices of up to 70% andcontributed to the economic crisis in 2015 and 2016. Of the Brazilianstorage capacity, 70.1% is in the Southeast and Midwest regions, 18.0%in the Northeast, 6.9% in the South and 5.0% in the North. The areacircled in red in Fig. 6 represents more than 70% of the energy storage

capacity of Brazil. If it does not rain in this region during the wetseason, electricity generation in Brazil during the dry season iscompromised.

Given climate variability, considering climate change or not, itwould be advantageous to increase storage capacity in areas with lowstorage capacity. This would reduce the risk of not having energy storedto supply the country during the dry season, increasing energy security

Fig. 8. Flooded area of Canastra SPS project compared with three conventional dams and the same energy storage capacity.

Fig. 9. Comparison of flood area required to store energy in SPS dams and conventional reservoir dams.

Table 9Characteristics of Sobradinho and Três Marias reservoirs [1].

Dam Floodedarea (m3)

Evaporationa

(m3/s)Energylossesb

(GWmed)

Volume(hm3)

Sobradinho(3925 m)

4.196 262,1 0,754 34.116

Sobradinho(3805 m)

1.145 72,3 0,201 5.447

Três Marias(5725 m)

1.064 14,8 0,049 19.528

Três Marias(5492 m)

368,6 5,1 0,016 4.250

a The total evaporation was calculated assuming which full or empty reservoir all yearround.

b The energy losses only take into account the evaporated water in the reservoirs.


394

and reducing the risk of energy rationing. SPS has the potential todecentralize and increase the energy storage potential of Brazil.

5.5. Remove the intermittence of renewable sources

SPS projects have the ability to remove the intermittency ofrenewable sources such as wind and solar with the same efficiencypresented in Table 6. In order to achieve this, during the wet season,the SPS will pump more water when there is more wind and solargeneration in the Grid. When there is less wind and solar generation,the SPS will pump less water. During the dry season, the SPS willgenerate more electricity to the Grid when there is less wind and solargeneration and will generate less electricity when there is more windand solar generation in the system.

The Muquém SPS project can be used to store energy fromrenewable sources because it is located close to a region with greatwind and solar potential, as shown in Fig. 12. Apart from removing theintermittency of these renewable sources of electricity, the storagescheme would reduce costs with transmission lines from where theelectricity is generated to where the electricity is consumed.

In addition, SPS has the potential to reduce the amount ofharmonics in the transmission network [58]. This happens becausethe pumps dampens harmonics when operating and when the turbinegenerates electricity, it does not generate harmonics in the system.

5.6. Multiple uses of water

There are multiple uses of water, all of which are benefited from the

increased energy storage with SPS projects. The specific benefitsdiscussed in this section are the need to store water for humanactivities, environmental requirements and to enable the constructionof waterways allowing more transport options in Brazil.

As the country relies heavily on hydroelectric generation, when thestored water is used to ensure electric generation, water supply forhuman activities and the environment can be compromised. Forexample, in 2013 and 2014 much of the water stored in theParaibuna reservoir, the head of the Paraiba do Sul River Basin wasused to generate electricity due to the energy crisis. In January 2015,the reservoir fell to below the operational level, restricting wateravailability and compromising the water quality in the Rio Paraibado Sul [59]. A similar scenario happened in the São Francisco basin[60]. Thus, policies to reduce the vulnerability of the energy sector havea positive impact on the availability of water resources in the country.

The watersheds that shows signs of not being able to attend thewater supply requirements, such as Paraíba do Sul and São Francisco,should manage their water resources prioritising water supply ratherthan energy supply. This change in paradigm is enough to resolve theirissues with water supply for several decades.

As SPS is an efficient technique for storing energy, this articlesuggests that SPS should provide seasonal energy storage in Brazil andmost conventional accumulation reservoirs should operate close totheir maximum capacity. The benefits resulting from this are to:

• Increase the generation of current hydropower dams by 2 GWmedduring normal years and 5 GWmed during drought years. This isbecause the head of the storage reservoir dams will be kept at its

Fig. 10. Flow regulation of the dams in cascade downstream of the Raizama SPS.


395

maximum.

• Influence the microclimates around the reservoirs increasing thehumidity of the land and atmosphere by keeping the storagereservoirs full. This increase in humidity would increase rainpatterns in the river bedside, where the highest hydropowerpotential in the watershed is located.

• Instead of storing seasonal energy, conventional reservoirs couldstore energy from renewable sources, thus, change their operationparadigm on the Brazilian Grid.

• Enable the use of Brazilian rivers as waterways to increase theconnectivity and reduce transport costs.

• Increase economic activities that depend on a fixed quota river. Forexample, tourism, fishing, fish farming, etc.

5.7. Low cost storage

The estimated cost of construction of the SPS projects is betweenUS$ 2000/kW and 5000/kW. However, as the operation of the SPS

projects influences the generation of hydroelectric dams in cascadedownstream the overall cost of storage reduces to US$ 1000/kW–US$3000/kW.

SPS operates with an average 40% capacity factor. This is becausehalf of the time, it will be storing and the other half generating. Thus,given the investment cost presented above the generation cost will bebetween US$ 40/MWh and U$ 120/MWh, assuming the energy usedto pump would have been wasted. In other to increase electricitygeneration during the wet period, dams in the Amazon can beconstructed at a price of U$ 60/MWh. To store this energy for thedry period, the addition of seasonal storage would result on an overalprice of U$ 100/MWh–U$ 180/MWh.

6. Conclusions

In conclusion, this article showed the need to increase the energystorage potential of Brazil and that this is viable through the construc-tion of SPS projects in combination with dams in cascade. This increase

Fig. 11. Potential transmission line capacity reduction with SPS.


396

in energy storage would decentralize the energy storage capacity inBrazil, which is focused in the Southeast region and makes theelectricity sector vulnerable to climate change. The decentralizationof the Brazilian storage potential will increase the energy security of thecountry by increasing the possibility of storing energy in differentregions of the country, thus reducing the risk of electricity rationing.

In addition, it was shown that SPS systems have the potential to:

• Regulate the flow of rivers and reduce spillage, increasing powergeneration in the hydroelectric dams in cascade, for example, theUruguay River would benefit from a SPS project because it does nothave large accumulation reservoirs.

• Facilitate the construction of new dams in cascade where there is noappropriate geology for the construction of conventional accumula-tion reservoirs, for example in the Paranã River in the TocantinsRiver Basin.

• Control floods when the geology does not permit the construction ofaccumulation reservoirs, for example, in the Araguaia River.

• Decrease the evaporation in accumulation reservoirs, for example,maintaining the Sobradinho Reservoir at its lowest level.

• Allow conventional reservoirs to operate close to their maximumcapacity without the risk of emptying, thus making possible theconstruction of waterways increasing the river transport modality ofBrazil.

• Store the excess electricity generation from renewable sources andreduce the impact of intermittent sources on the National Grid.

• Store energy to generate during peak hours thereby reducingbottlenecks in the Grid.

Acknowledgements

We would like to thank CAPES/BRAZIL for the research grant aspart of the Science Without Borders Program [61] and theInternational Virtual Institute for Global Change [62] for the possibilityto interact with experts in the field.

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