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Determining the Optimum Scheme Layout for the Sombwe Hydropower Project

Author: Edwin Lillie, Robert Greyling
Conference: Hydro 2018
Date: October 15-17, 2018

INTRODUCTION
Legislation in the DRC has recently changed to allow Independent Power Producers (IPP) to compete in the local power market. To this end, Kipay Investments appointed Knight Piésold and Ingerop Consulting Engineers to conduct a feasibility study for the proposed Sombwe Hydropower Project in late 2016. The project is located approximately 290 km north of Lubumbashi in the Katanga Province of the DRC, shown schematically in Figure 1. Two existing hydropower stations have been operating for many years upstream of the proposed Sombwe site. The 71 MW Mwadingusha hydropower plant at the Tshangalele Dam and the 36 MW Koni hydropower plant, which is located immediately downstream of Mwadingusha.

The catchment area at Sombwe is approximately 47 337 km2 and is characterised by two main sub-catchments. The Koni sub-catchment, with an area of approximately 12 877 km2 upstream of Koni Hydropower Station and the Sombwe dam incremental catchment downstream of Koni, having an area of approximately 34 450 km2. The Tshangalele Dam regulates the river flow from the Koni sub-catchment, whereas river flow in the Sombwe dam incremental catchment is unregulated. Based on available statistics of the existing upstream HPP schemes, and considering that the Sombwe site drains a significantly larger catchment, the applicable range for installed capacity is expected to lie between 80 MW and 160 MW.

It was initially envisaged that a dam with a final height of 70m to 100m would be required at Sombwe to provide sufficient head and yield for the power generation. However, as it is a Greenfield project, a number of different scheme layouts were investigated to select the most appropriate configuration for the feasibility study investigation.

To select the optimum scheme layout and component sizes, several parameters were considered before focusing the feasibility investigation on the selected option. The key output required from the options analyses study was
to determine;

  • Dam site and type,
  • Dam height,
  • Power plant capacity,
  • A single dam or a combination of dams in a cascade,
  • A surface or an underground powerhouse,
  • The initial estimated capital and operating cost estimates in sufficient detail to select a preferred option,
  • The long term average energy yield, and
  • The levelised cost of energy for all the plausible options.

There are too many parameters to optimise a scheme in a single analysis and a logical stepwise approach was undertaken to eliminate some parameters early on, but to retain those which may still influence the optimum scheme selection, until a decision could be made on the most economical solution. The objective was to select the most economical option for investigation at the feasibility level of detail with due consideration of technical, economic, environmental and social conditions.

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