The total installed capacity of the large pumped storage schemes (PSSs) in South Africa is at present some 2910 MW. There are four large PPSs operating currently around the country, with the Steenbras (180 MW) being the municipal asset of the City of Cape Town, and three plants owned by the national entity Eskom namely the Drakensberg (1000 MW), Palmiet (400 MW) and now new Ingula (1330 MW).
The utility has a few another conventional hydropower plants owned and administered together with the Department of Water and Sanitation (DWS), two situated on the Orange River and others attached to the dams on the perennial rivers in the Eastern Cape Province. These hydropower plants do not have the same function as the pumped storages, but all can generate hydro-energy within a few minutes contrary to the coal-fired energy generation plants, most of the located in one specific area of South Africa.
All installed PSSs are serving South Africa as conventional energy storage sites supplementing hydro-energy to the national grid in the specific times of the high demand for electricity. A PSS comprises two large water storage areas (typically two sizeable dam facilities), one lower and the other at the upper elevation providing usually for static head between 100 and 700 m. The choice of a location of a PSS is depending on the availability of fresh or saline water (if a plant is located on the sea coastline) and a suitable geo-morphological configuration.
However, a PSS requires certain amount of energy for pumping of raw water to the upper storage which is effectively a battery of energy ready to be utilized when needed. The requirements for essentially two storage reservoirs (on an ocean coast not absolute necessity) and associated pumping and generation infrastructure together with typically large penstocks (i.e. connecting pipeline between lower and upper storages), dictate for rather extensive initial capital costs, but ongoing benefits outweigh typically the capital invested.
There are four large PPSs operating currently around in South Africa, with the Steenbras (180 MW) being the municipal asset of the City of Cape Town, and other three plants are owned by the national entity Eskom SOC namely the Drakensberg (1000 MW), Palmiet (400 MW) and now new Ingula (1330 MW). Since early 1980 the Drakensberg PSS has been for many years listed amongst the top twenty PSSs globally installed, sharing fifteenth place for many years with another 1000 MW PSS capacity installed in Iran.
In recent twenty years the capacity of pumped storages increased several fold with China having
now some 23 100 MW installed (accounting only for the PSSs above or equal to 1000 MW), with another 6600 MW under construction. The USA with some total installed pumped storage capacity of 14 800 MW at present, identified another 40 viable sites to be developed, primarily at existing lower dam to economize on the costs and optimising on utilisation of infrastructure assets and water resources.
The tendency worldwide is to develop PSSs in conjunction with a development of other renewable resources as wind and solar PV. The coastline PSS locations are investigated in several countries as well as at several island locations to avoid the costs of the lower dam storage, using the saline water and other renewable in pumping. The examples which can given are: first PSS using saline water in Okinawa, Japan; seawater PSS on the Isle of Lewis in Outer Hebrides, Scotland; a hybrid hydro-wind PSS on Canary Islands; etc.
|Ranking amongst other PSSs||Pumped Storage Scheme (PSS)||Installed capacity (MW)||Country of installation location|
|8||Grand Maison Dam||1800||France|
|9||La Muela II||1772||Spain|
|USA (1652 MW), Taiwan (1602 MW), Japan (1600 MW), USA (1566 MW), China (1500), Japan (1500 MW), Bulgaria (1455 MW), India (1450 MW) (Wikipedia 2017).|
|Between SA’s Ingula and Drakensberg pumped storages (accounting for the PSSs above or equal to 1000 MW), China has installed pumped storage capacity of some 10 900 MW and another 4 000 MW capacity is listed after the Drakensberg PSS)|
|NB: There are eight PSSs under construction at present, with Fenguing PSS in China with capacity to be installed at 3600 MW to be the largest in the world when completed.|
It is estimated that the overall pumped storage capacity worldwide is at present some 165 000 MW with China leading the development. The development of pumped storages on the African continent is presently far behind, with South Africa leading at present with a 2910 MW of PSS capacity installed
History of development and key parameters of existing PSSs in South Africa
The South Africa’s hydro-electricity generation sector has a legacy of almost fifty years since early 1970 when the Gariep Hydro had been commissioned at the large dam on the Orange River. The sector benefited (now already for some 35 years), besides generating hydro-electricity from a few conventional hydropower plants owned and administered together between the Department of Water and Sanitation (DWS) and Eskom also for its energy storage and a peak supplementary supply from the country’s existing pumped storage schemes (PSS).
Eskom together with the DWS generate hydroelectricity from several conventional hydroelectric plants, two situated on the Orange River and others attached to the dams on the perennial rivers in the Eastern Cape Province. These hydropower plants do not have the same function as the pumped storages, but all can generate hydro-energy within a few minutes contrary to the coal-fired energy generation plants and even the nuclear energy generation.
|Hydroelectric plant||Location, river or town (province)||Owner/administrator/operator||Installed capacity (MW)|
|Ncora||Ncora River (E. Cape)||Eskom||2|
|First Falls||Umtata River (E. Cape)||Eskom||6|
|Second Falls||Umtata River (E.Cape)||Eskom||11|
|Colley Wobbles||Mbashe River (E. Cape)||Eskom||42|
|Vanderkloof||Orange River (N. Cape)||DWS/Eskom||240|
|Gariep||Orange River (N. Cape)||DWS/Eskom||360|
|Steenbras PSS||Cape Town (W. Cape)||City of Cape Town||180|
|Drakensberg PSS||Bergville (KZulu-Natal)||DWS/Eskom||1000|
|Palmiet PSS||Grabow (W. Cape)||DWS/Eskom||400|
|Ingula PSS||Van Reenen (KZulu-Natal)||DWS/Escom||1332|
|NB: There several hydro-electric schemes of significance (e.g. Stortemelk, Neusberg, etc.) connected recently to the national grid developed under the DoE’s REI4Ps and owned by the IPPs.|
Steenbras pumped storage scheme
The installation is located some 60 km from Cape Town at the foothill of the Sir Lowry’s Pass. The planning and design processes had taken six years. It is a first PSS installed in South Africa and also the first on the African continent. The Steenbras Power Station (180 MW) is owned and operated by the City of Cape Town and it is in operation since 1979. The scheme comprises upper dam storage with water run to the lower dam through turbines coupled to generators.
The hydro-electricity generated is absorbed into the local (municipal) grid. Two dam storages at different elevations of some 300 m are connected by a low-pressure tunnel installed through the mountain range connected to the high-pressure tunnel connected to a steel penstock of 3,5 m in diameter. Most of the penstock is buried below the ground to reduce the environmental impacts.
Four 45 MW pump/turbine machines are located in pairs, each pair situated at the bottom of a shaft 40 m deep to provide for necessary minimum submergence when pumping 27 m below the surface of the lower storage dam. The transient pressure effects (e.g. water hammer and surges) caused while changing from pumping to generating modes are compensated through the surge shaft situated at the end of the low pressure tunnel. The maximum water flow when generating is 75 m3/sec, if all four turbines operating at the same time. Water can be pumped back to the upper storage at the rate
60 m3/sec and it will take 12 hours to fill the upper dam.
The Steenbras PSS is serving in reducing the peak loads of the metropolitan electricity supply system. The generation output is automatically controlled so as to maintain the Eskom power in-feed to the CT Metro constantly at a predetermined monthly target demand. This way the PSS serves to the CT City for almost 40 years for the initial investment cost of R 60-million in 1979.
As far as critical maintenance is concerned, the steel pipe of penstock was refurbished with new epoxy lining after some 18 years in operation. The hydraulic machines have been subjected to extensive refurbishment due to wear and tear between 1990 and 1996.
Drakensberg pumped storage scheme
The scheme is situated between the foothill and upper plateau of the lower Drakensberg with the upper storage in the Free State and lower storage in the KwaZulu-Natal provinces of South Africa. This is the first large PSS in SA installed in collaboration between the Eskom and DWS. The PSS has a dual purpose. The primary purpose is to generate hydro-energy when Eskom is experiencing the peak demands within the national electricity grid. The second very important purpose is to supplement the water collected in the KwaZulu-Natal by the system of canals, weirs and dams for the inter-basin water transfer to Sterkfontein Dam impoundment which is an integral component of the Thukela-Vaal Water transfer Scheme (WTS), one of the largest and most complex in SA.
The original WTS was completed in 1979 without of the PSS. Subsequently, Eskom together with DWS redesigned the original pumping component of the Thugela-Vaal WTS, replacing the Jagersrust pumping station and adjacent feeding canals to Sterkfontein Dam with the underground pumped storage system and installing 27-million m3 Driekloof Dam situated at the very upper reaches of the Sterkfontein Dam. The Drakensberg PSS was commissioned in 1982 comprising extensive underground excavations of tunnels, halls, chambers and shafts. The machine hall contains four
250 MW reversible turbine/generator units. The vertical surge shaft of 14 m in diameter is excavated to a height of 86 m above the headrace tunnels.
During the generating mode water is drawn from the upper located storage of the Driekloof Dam situated in the Sterkfontein Dam and discharged into the lower 29-million m3 Kilburn Dam located at the bottom of the escarpment. The Driekloof Dam is pumped full, mainly during the nights (at the low demand periods) with certain amount of water overflowing into the Sterkfontein Dam to supplement the key stand-by storage of the T-V WTS. When a pumping rate head is 71 m3/sec, it takes about
35 hours to pump the Driekloof Dam full against 41l m net head. The original type of cycle operation is weekly and the cycle efficiency of about 73%.
According to Moodley (2002) the operation and maintenance processes at the Drakensberg PSS started to be hampered around 1995 (i.e. after some 13 years in operation) by repeated failures of the plant’s excitation control system causing significant production and rehabilitation losses. An refurbishment project was implemented between 1999 and 2001, which restored the installation’s excitation control system to near-100 percent reliability. At present three of four Drakensberg generator units are being modernized by a contractor from overseas, to be fully operational in 2018.
Palmiet pumped storage scheme
The 400 MW pumped storage scheme is an integral to the Palmiet River GWS situated near Grabow in the Western Cape Province. The scheme has also dual purpose similar as the Drakensberg PSS, providing for the generation of hydro-energy between the upper 17-million m3 Rockview Dam and lower 15-million m3 Kogelberg Dam storages and supplementing water to nearby Steenbras Dam PSS reservoir. The overspill water from the Rockview Dam is to supply the water supply system of Cape Town Metropolis. This is then also an inter-basin water transfer scheme. The scheme has been developed jointly by Eskom and DWS and commissioned in 1988 after some 5 years of construction predominantly within the Kogelberg Nature Reserve.
The connecting conduit between upper and lower dam comprises a headrace tunnel, which is 750 m long and 6,2 m in diameter. Water flows through a 130 m deep shaft to a pressure tunnel of 482 m long and 5,4 m in diameter and reaching subsequently cut-and-cover steel penstock, 561 m long and 5,4 m in diameter. Two reversible 200 MW pump/generator units are housed on the right bank of the Kogelberg River. From the operation point of view, the time required to pump 15-million m3 is about 40 hours. The original type of operational cycle is weekly with the cycle efficiency of some 78%.
The International Hydropower Association (IHA) awarded to the Palmiet PSS its 2003 Blue Planet Prize for a contribution to sustainable development and good practice in utilising hydropower resources.
Ingula pumped storage scheme
This scheme is situated not very far from the Drakensberg PSS and is also located between lower Drakensberg plateau and its foothills some 23 km from Van Reenen Pass. The upper 19-million m3 Bedford Dam and lower 22-million m3 Braamhoek Dam are situated at some 470 m difference in elevation. The dams are connected by a system of underground waterways with a powerhouse hall housing four reversible 333 MW pump/turbine units. Two 6,1 m in diameter inclined headrace tunnels, each 1940 m long provide for the flow of water to the turbine/generator units. The underground system comprises twin surge chambers, twin extended draft tubes and a single tailrace tunnel.
The upper storage dam can be pumped by all four units within 21 hours and is designed to provide for 16 hours of generation. The overall efficiency of the scheme is determined at 76%.
The Ingula PSS installation has been finalized in the middle of 2016 after some ten years under construction. Eskom synchronised Unit 1 with the national grid in June 2016. The pumped storage peaking capacity in South Africa has thus increased by 333 MW to present operational 1733 MW. The full connection to the national grid, by remaining 1000 MW, is anticipated by late 2017 or early 2018 when all units will be synchronised with the national grid.
The cost of this PSS amounted to-date to R25-billion, increased from the original estimate by at least R7-billion.
According to the technical paper by Otieno, et al (2017) discusses the likely attack of soft water on the Ingula’s concrete tunnel lining. Numerous samples were laboratory tested. The samples tested indicated possible reduction of tunnel system efficiency by about 3% down to about 93% over some ten years of water tunnels in operation. The results are a warning that in years to come the water conduit tunnels will have to be likely relined to maintain the integrity of tunnel infrastructure and required efficiencies.
As-built characteristics and parameters of pumped storage schemes in South Africa
The characteristics and essential parameters gathered from as-built PSSs in South Africa together with the time series of PSSs outputs since installation of the Drakensberg PSS in the early 1980 are summarized in the following tables:
|Name of PSS (owner)||Installed capacity (MW)||Names of PSS upper and lower reservoir||Active storage (106 m3)||Type of upper and lower storage dam walls||Purpose of PSS installation|
|Upper Steenbras||31||Earth-fill embkmt. wall||Power gen. & water transfer|
|Steenbras (lower)||3||Earth-fill embkmt. wall|
|Driekloof (upper)||27||Rock-fill embkmt wall||Power gen. & water transfer|
|Kilburn (lower)||29||Earth-fill embkmt wall|
|Rockview (upper)||17||Rock-fill with clay core||Power gen. & water transfer|
|Kogelberg (lower)||15||Concrete gravity arch|
|Bedford (upper)||22||Concrete faced rock-fill||Power generation|
|Bramhoek (lower)||26||Rollcrete gravity wall|
|Sources of info: Generated from various public domain documentation available at the ESKOM, Cape Town City Council (CTCC), SA Institution of Civil Engineers (SAICE) and Dept. of Water and Sanitation (DWS).|
The energy generation sector in SA represented by the Department of Energy and executed by the Eskom recognises the advantages in having hydro-pumped storages as the energy storage provision, a stand-by and peaking generation facilities to some 40 000 MW base-load thermal (coal-fired) plants (ten plants are in operation at present, three plants are return-to-service and two new plants are being build). It takes a hydro-pumped storage plant two to three seconds of a hydraulic starting time and some 15 seconds to get into full load production. The PSSs are still to date the most efficient storages (i.e. batteries) of energy. Table 4 below illustrates the details on pumping/generating equipment for existing plants and the newly developed Ingula PSS.
|Name and (owner) of PSS||Total peaking capacity (MW)||Average gen. head (m)||Pump/turbine unit flow rates (m3/sec)||Type of reversible unit||Year of plant commission|
|Steenbras (CTCC)||4 units at 45 MW
|Drakensberg (Eskom)||4 units at 250 MW = 1000||
|Palmiet (Eskom)||2 units at 200 MW = 400||
|Single stage Francis p/turbine||
|Ingula (Eskom)||4 units at 333 MW = 1332||
|Francis pump/turbine||Unit 1 in 2016|
|NB: Very little information is available on the maintenance of particularly the PSSs belong to Eskom.|
From the analysis of the characteristics and as-built parameters of the PSSs developed to-date in South Africa the general planning/design guidelines applied by the planners and designers adhered primarily to the following:
Ntsone, et al (2016), established that Eskom is finding difficult to cope with the demands for electricity, which are notoriously outstripping (almost daily) the conventional supply options. The existing PSSs are to generate far more frequently than they were operationally designed for (i.e. weekly operational cycle). This implies that Eskom pumped storage installations are forced to change from a weekly balance to be balanced on a daily basis.
|Year||Coal fired stations||Nuclear station||Hydro-electric stations||Diesel & gas turbines||RE sources W + IPPs||Pumped storage stations||The commissioning date and capacity of the PSSs in SA|
|1978/79||74 485||1144||14||Steenbras (180 MW)|
|1980/81||95 675||1653||81||415||Drakensberg (1000 MW)|
|1986/87||122 947||6167||1617||2||1774||Palmiet (400 MW)|
|1987/88||123 777||10 493||3162||2||1403|
|1988/89||128 304||11 099||2759||3||1039|
|1994/05||151 730||11 301||529||0||1274|
|1995/06||163 541||11 775||1319||0||2220|
|1996/07||170 464||12 647||2092||0||2608|
|1997/08||165 473||13 601||1596||3||2420|
|1998/09||165 665||12 837||726||0||2590|
|1999/00||172 362||13 010||1343||1||2591|
|2000/01||175 223||10 719||2061||0||1587|
|2001/02||181 651||11 991||2357||0||1738|
|2002/03||194 046||12 663||777||0||2732|
|2003/04||202 171||14 280||720||0||2981|
|2004/05||251 914||16 912||903||0||Wind + IPPs||3675|
|2005/06||206 606||11 293||1141||78||3||2867**|
|2006/07||215 211||11 780||2443||62||2||2947**|
|2007/08||222 908||11 317||751||1153||1||2979**|
|2008/09||211 941||13 004||1082||143||2||2772**|
|2009/10||215 940||12 806||1274||49||1||2742**|
|2010/11||220 219||12 099||1960||197||2 + 1833*||2953**|
|2011/12||218 212||13 502||1904||709||2 + 4107*||2962**|
|2012/13||214 807||11 954||1077||1904||1+ 3516*||3006**|
|2013/14||209 483||14 106||1036||3621||2+ 3671*||2881**|
|2014/15||204 838||13 794||851||3709||1+ 6022*||3107**|
|2015/16||199 888||12 237||688||3936||311+ 9033*||2919**||Ingula Unit 1 (332 MW)|
|2016/17||200 893||15 026||579||29||345+11529*||3294**|
|Notes: * The amount of GWh obtained from the IPPs. ** The amount of GWh required for pumping is on average about 1000 GWh over above production (i.e. about 30 % on average). ***A PSS is a net consumer of energy.|
Potential for future development of pumped storages in South Africa
Firmly evaluated potential for future development of PSSs
Now, after Ingula PSS peaking capacity (1332 MW) will go fully on a stream, the future development of another PSS in South Africa appears to be postponed until 2030. Eskom already between 1985 and 1995 identified several highly potential PSS sites around South Africa. Louwinger (2008) highlights that all selected sites were scrutinised according to the environmental, technical, economical and legal requirements. The next large PSSs to be developed by Eskom after Ingula PSS, were listed the Lima PSS (renamed to Tubatse PSS) and Mutale PSS.
The layout in Fig. 1 above illustrates other six potential sites besides Ingula PSS suitable for future development. Most promising is a site named Lima (Tubatse) where it is needed only to develop an upper reservoir as the lower very large De Hoop Dam impoundment was commissioned in 2014. The purpose of this dam storage is to provide water for the residential/industrial use in the northern region of South Africa. As the water requirements of a PSS are non-consumptive, this scheme would be not impacting on the dam storage (only marginal evaporation losses at the upper reservoir) and can be likely build for some 25% less than the Ingula PSS, if implemented soon.
The development of Tubatse PSS (planned at 1500 MW capacity) has been detailed around 2008/09 and Eskom has been that far as applying for the generation license from NERSA. However, any development of this site has been put on a back-burner. In the meantime it is obvious that Eskom need more peaking capacity due to recent changes in generation patterns, connecting and receiving electricity amounts from several IPPs and grappling with reduced demands for electricity as the national economy is stagnating. See Table 5 for relevant patterns observed within energy generation mix operated by the Eskom.
Position of potential PSSs in future energy mix in SA
According to the SA’s Integrated Resource Plan 2010 (IRP 2010-2030) and its recent revision, the country is contemplating to participate in developing of a hydropower installation at Inga Falls on the Congo River in the Democratic Republic of Congo (DRC). A capacity of a 2500 MW from the overall to be installed capacity at the Inga site is offered by the DRC to SA. In the local hydropower terms, this is a capacity termed as the “imported hydropower” which would be rather expensive to pay for and particularly maintaining transmission over very long distances as well as paying for the security of supply. There are vital issues needing more explanation from the socio-political platform.
Also, two coal-fired power stations (Kusile and Medupi) are nearing their completion, increasing the overall energy generation capacity of SA. These two plants are base-load installation as far a generation is concerned and their production is necessary to be supported by an additional peaking capacity, which should not come from by increasing the diesel and gas turbines generation.
|Energy sources mix||*Final policy adjusted IRP 2010 to 2030||**New capacity layout introduced/revised|
|Pumped storages (PSSs)||1332||2,4||–||–|
|SHP, biomass, landfill, etc.||465||0,8||–||–|
|Total||56 539||100||42 539||100|
|Source: *IRP 2010 (May 2011), ** Uncommitted in 2015, SHP = Small Hydro Power|
As illustrated in Table 6 above, the group of Alternatives – PSSs lists the capacity of 1332 MW which represents the Ingula PSS capacity now already installed. No further PSS capacity is listed in the New Capacity Layout and the Draft Revision 2016 of the IRP 2010 also does not indicate any PSS capacity to be developed before 2030.
The prospects in development of small scale pumped storage with other renewable
South Africa is blessed with rather extensive water supply infrastructure developed over the years in both the urban and rural context. There are several viable opportunities in developing small scale pumped storages together with other renewable energy resources and technologies (i.e. primarily PV-solar in SA). The suitable technologies are now on the market and prices becoming affordable to the municipalities and even to the rural communities, if eligible for the subsidies or grants.
Most suitable location for a small scale pumped storage within a water supply system would be already existing elevated concrete reservoir, where only a lower another concrete/steel reservoir is needed to be installed (i.e. if the potable water supply is going to be involved). The research has been done particularly in Europe and several suitable sites selected. Table 7 given below illustrates a theoretical sizing for a small scale pumped storages of 2, 5, and 10 MW.
|Item of pumped storage scheme||Size of pump as turbine (PaT)|
|2 MW||5 MW||10 MW|
|Rate of flow in PaT (m3/sec)||0,809||2,023||4,046|
|Pipeline size (mm)||700||1000||1200|
|Friction head of pipeline: steel material||
|Friction head of pipeline (fibre glass option with length of 1200 m)||
|Capacity of reservoirs (m3)||20 000||40 000||80 000|
|NB: The PaT’s pumping demand can be connected to the PV-solar systems.|
At present there is no any small scale pumped storage system installed in South Africa. However, the installation of pumps as turbines is now tested at the Annlin Reservoir by the Tshwane Metropolitan Municipality in Pretoria.
The prospects in development of PSS in Lesotho
Lesotho has already a 72 MW hydro-electric scheme installed at the Muela Dam situated at the Katse Tunnel Outlet as a component of the LHWP Phase 1.
LHWC together with the local consultants are conducting a master plan study of the Kobong (or Monont’sa) 1200 MW pumped storage scheme. The selected site in close proximity of the Katse Dam impoundment offers max gross head of 600 m. Existing Katse Dam impoundment is the location of the lower reservoir and only upper dam storage will need to be installed.
A pumped storage scheme is effectively a large energy storage battery, energy is stored in the form of water during off-peak periods and released during the peak electricity demands. A PSS using reversible pump/turbine assembly is so far most effective way to store electrical energy at acceptable costs and is the source of energy which can deliver positive or negative reserve to the grid for balancing intermittent resources such as wind and solar. A grid needs energy for rapid balancing the PSS can provide such, and new pumped storage installations benefit from the technological achievements of the recent past in the development of hydraulic and electrical machines and progresses in automatisation.
 Eskom: Annual Reports, between 1969/70 and 2016/17.
 F Louwinger: “Case study of Ingula and Lima pumped storage schemes”, Energize, May 2008.
 M Ntsoane, D Booyens and N Pillay: “Hydro Pumped Storage Dynamics”, Eskom SOS, 2016.
 M Otieno, M Alexander and J du Plessis: “Soft water attack on concrete tunnel lining in the Ingula”
 PSS: “Assessment of concrete resistance and protection”, Journal of SAICE, Vol 59, No 3, September 2017.
Contact Bo Barta, Energy and Water Resources Engineering, Tel 073 177-6045, firstname.lastname@example.org
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