High Demand Season Low Demand Season
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the local grid. The electricity consumption was also looked at to assist with the project feasibility by offsetting the reservoir usage with the electricity generated. Once commissioned these micro hydro turbines will then feed the electricity needs of the reservoir and export the excess to the municipal grid. [18]
Figure 3.19: Proposed micro hydro turbine installation at reservoirs around the city [18]
Table 3.15: List of reservoirs assessed and generation potential at eThekwini Municipality [18]
Name of Reservoir Size of Hydro Turbine
Theomore Reservoir 71 kW
Stone Bridge Drive Reservoir 104 kW
Umhlanga Rocks Reservoir Between 26 and 177 kW
Yellowfin and Escolar Reservoir Between 26 and 177 kW
Avocado and Pomegranate Reservoir Between 26 and 177 kW
Western Aqueduct Hydro Project
The Western Aqueduct Hydro Project is a water pipeline (aqueduct) project that is been implemented by the eThekwini Municipality Water Department for the sole purpose of transferring water from the Umlass Road reservoir to new and existing reservoirs in and around the city of Durban to meet growing water demands as shown in Figure 3.20. The first
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phase of the Western Aquaduct covered 19 km from Umlass to Inchanga Station whilst the second phase covered 55 km from Inchanga Station to Umlazi. The project completion is expected in 2017.
During the project feasibility study, it was then realized that there was a need for break pressure tanks to be installed at two sites as calculations showed high water pressures due to the hilly terrain that the aqueduct traverse through. It was at this stage when the thought of installing hydro generators at these two sites with opportunity to generate additional revenue from the electricity sales and possible Carbon credits. Together with the national electricity shortages, recent spate of load shedding and additional revenue generated from selling the Carbon credits from this project, the project soon looked financially attractive and it was then decided that two hydro generators will be installed on route as part of the Western Aqueduct Pipeline Project. Two sites were identified to install hydro turbines. Water flow rate calculations indicated that a 3.6 MW hydro turbine could be installed at the first site whilst calculations showed a 3 MW hydro turbine could be installed at the second site. [38].
Figure 3.20: Pipeline to be installed for the Western Aqueduct Project [38]
There are many industries that have the potential and opportunity to generate electricity from their existing plant and processes. This can then be used to supply their own electricity needs whilst exporting the excess to the local grid. Durban currently has two companies that have Power Purchase Agreements to sell excess power that is co-generated via their processes.
91 Tongaat Hullets
The Tongaat Hullets Maidstone Sugar Mill has the capacity to crush 475 tons of raw sugar cane per an hour. This then produces 150 tons of bagasse an hour when the mill is crushing at full capacity. Bagasse is a by-product of sugar cane which can be considered as a free energy resource. The calorific value of bagasse at the Maidstone Mill is 7.7 GJ/ton. Bagasse is currently used as a fuel in the boilers at the Maidstone Mill to produce steam only during the sugar crop season. Sugar Mills across South Africa have historically utilized this bagasse by- produce as a source of fuel to raise their internal steam and electrical requirements. The Tongaat Hullets Mill currently exports about 1 MW of electricity to the eThekwini Electricity grid. [43]
NCP Alcohols
NCP Alcohols is an extra neutral ethanol manufacturer located in Springfield Park in Durban. They currently uses gas fired high pressure boilers to produce steam which then drives a 3 MW steam turbine. This then produces the plant electricity requirements and low pressure steam from the turbine exhaust. The co-generation currently supplies 98% of their electricity requirements whilst the excess is exported to the eThekwini Electricity grid. NCP Alcohols are also planning on converting one of its coal fired boilers to gas which will enable them to generate a further 2.6 MW electricity to export to the grid. [44].
The South African Electricity Grid Background
“Most of South Africa’s base generation is thermal coal fired power stations located in the northern and north east regions of South Africa namely Limpopo and Mpumalanga Provinces respectively shown in Figure 3.21 and Table 3.16. A nuclear power station with two 955 MW units is also situated in the Western Cape Province. There are pumped storage schemes at Drakensburg (1000 MW) and Palmiet (400 MW) and to be further supplemented by Ingula (1300 MW) under construction, situated in KwaZulu Natal Province. There is also Open Cycle Gas Turbines (OCGT) providing 2415 MW installed capacity. South Africa is also a net exporter of (2000 MW) and interconnected with five neighboring countries; Namibia at 220 kV and 400 kV, Botswana at 400 kV, Swaziland at 400 kV, Mozambique via two 533 kV DC lines (1700 MW). The 2012 National peak demand was 38 GW. Power transmission voltage levels in South Africa are at 765 kV, 400 kV, 275 kV and 220 kV. The responsibility for distribution of electricity is shared between Eskom, the municipalities and other licensed
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distributors. About 180 municipalities distribute 40% of electricity sales to 60% of the customer base. Sub-transmission and distribution voltage levels are 132 kV, 88 kV, 66 kV, 44 kV, 33 kV, 22 kV, 11 kV and 6.6 kV.” [5]
Figure 3.21: Location of Eskom Power Stations [5]
Table 3.16 shows the Eskom’s generation fleet in South Africa.
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Table 3.16: Break down of Eskoms generation fleet in South Africa [5]
Name of Station Type of Station Sets (MW)
Total Capacity
(MW)
Commencement of Operation Arnot
Candem Duvha Grootvlei Hendrina Kendal Komati Kriel Lethabo Majuba Matimba Matla Tutuka Koeberg Gariep Vanderkloof Drakensberg Palmiet Darling Klipheuwel Acacia Port Rex Ankerlig Gourikwa Medupi Kusile
Coal Coal Coal Coal Coal Coal Coal Coal Coal Coal Coal Coal Coal Nuclear Hydro Hydro
Pumped Storage Pumped Storage Wind
Wind OCGT OCGT OCGT OCGT Coal Coal
2 x 960
6 x 800 6 x 800
2100 1600 3600 1200 2000 4116 1000 3000 3708 4110 3990 3600 3654 1920 360 240 1000 400 5.2 3.2 171 171 1338 746 800 -
1975 1967 1980 1969 1970 1988 1961 1976 1985 1996
1983 1985 1984 1971 1977 1981 1988 2008 2002 1976 1976 2007 2007 2015 - Total installed Capacity 44832.40 MW
The installed generation capacity in SA is 44832.40 MW. Bulk of this capacity comes from base load coal fired power stations. This generation capacity is then distributed to a wide sector of customers all around SA.
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Background to the eThekwini Electricity Grid
eThekwini Electricity supplies more than 723 593 customers in an area covering nearly 2 000 square kilometers in and around the city of Durban. In 2014 eThekwini Electricity purchased a total of 11 236 882 178 MWh of electricity from Eskom. The maximum demand peaked at 1 756 MVA. [17] eThekwini Electricity currently purchases just over 5% of the total energy generated by Eskom in South Africa. This is purchased from Eskom at 275 kV at three in- feed points namely Georgedale Major Substation (400/275 kV), Hector Major Substation (400/275 kV) and Avon Major Substation (400/275 kV). This is then fed into the five 275 kV in feed points at eThekwini Electricity namely Durban North Major Substation (275/132 kV), Durban South Major Substation (275/132 kV), Klaarwater Major Substation (275/132 kV), Lotus Park Major Substation (275/132 kV) and Ottawa Major Substations (275/132 kV). [5]
Figure 3.22: eThekwini Electricity infeed and transmission networks (45)
Figure 3.22 and Figure 3.23 shows the eThekwini Electricity transmission (33 – 275 kV) and distribution (11 kV) network. At the transmission level, there is in excess of 100 Major Substations, 650 km of overhead line and 400 km of underground cables. At distribution level, there is in excess of 15 000 substations, 3 500 km of overhead line and 17 000 km of underground cables. [46]
Electricity from the 275kV in feed substations is then transformed to 132 kV which then supply about one hundred and five Major Substations within the eThekwini electricity area of supply. These substations then transformer the voltage from 132kV to either 33 kV or directly to 11 kV. The 33 kV substations then further transformer the voltage to 11 kV. The
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11 kV, 400V and 230V is then used to distribute electricity to residential, commercial and business customers. There are a few large industrial customers that purchase electricity at 132 kV and 33 kV. Electricity is currently purchased from Eskom on the Eskom 275 kV Megaflex TOU tariff structure.
Figure 3.23: Voltage levels at eThekwini Electricity [45]
In order to carry out the required studies, we will utilize a typical 132/11 kV and a 33/11 kV eThekwini Electricity distribution grid to carry out the studies upon. Currently all of the EG connections or proposed connections at eThekwini Electricity is either at 11 kV, 400V or 230V hence the focus area for this study will look at connections at these voltage levels. For larger projects such as wind and solar farm, the connection voltage level will be either 33 kV or 132 kV. The distribution grid selected and modelled for the study will depict a typical MV network at eThekwini Electricity that EG will connect onto. The primary focus of these studies is to understand how the distribution network design and performance will be affected with the increased levels of EG penetration.
eThekwini Electricity currently has 723 589 customers on 15 different tariffs structures as depicted in Table 3.17.
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Table 3.17: Breakdown of eThekwini Electricity customer base [24]
Tariff Scales
Descriptions 2013/2014 – Number of Customers
1 Business and General 40 524
2 Business and General (Two Rate) – Obsolete 1 234
21 Business and General (Two Rate) – Obsolete 258
5 Business and General – Discontinued 865
6 Business and General – Discontinued 98
7 Business and General – Discontinued 14
3&4 Single and three phase credit residential 319 875
8&9 Residential Prepaid 358 411
10 Business and General - Prepaid 1 142
11 Business and General - Prepaid 209
LV3 Low Voltage 3-part – obsolete 132
CTOU Commercial Time of Use 96
ITOU Industrial Time of Use 731
Others Eskom Megaflex TOU 4
Total 723 589
The current eThekwini Electricity (EE) residential single and three phase tariffs are R1.5878/kWh. There are presently 319 875 (44%) single and three phase credit residential customers that utilize an average of 700 kWh a month. There are also 358 411 (49%) prepaid customers that utilize an average of 200 kWh on average a month. The relatively low electricity usage can be attributed to many factors including the fact that of the base of pre- paid electricity users, about 100 000 consumers qualify for free basic electricity of 65 kWh per month. These are for electricity users who utilise below 150 kWh a month. Bulk of the pre-paid electricity users are residents from informal settlements, rural areas and transit camps. Their electricity needs and monthly usages are relatively low as they rely on the free basic electricity tokens. Based on their consumption figures, dwelling sizes and income levels, credit customers are most likely to install rooftop PV systems. [38]
Figure 3.24 provides a breakdown of the eThekwini Electricity sales amongst the different category of customers whilst Figure 3.25 provides the revenue distribution amongst the different category of customers at eThekwini Electricity.
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Figure 3.24: Distribution of energy sales for 2014/2015 at eThekwini Electricity [24]
Figure 3.25: Distribution of revenue from total electricity sales at eThekwini Electricity [24]
Simulation studies are required to be able to predict the behaviour of the eThekwini Electricity distribution network with the introduction of EG. In order to carry out these simulations, a power system analysis tool is required to model the existing electrical networks thereafter various different studies can be carried out to predict the behaviour of the electrical network with the introduction of EG. There are a number of Power System simulation
PRIVATE RESIDENCES
25%
OTHER 1%
BULK 45%
PREPAID 9%
BUSINESS &
GENERAL 20%