KHOLOMBIDZO HYDROPOWER PROJECT

The African Development Bank supported the Government of Malawi through the Ministry of Natural Resources, Energy and Mining to conduct the Feasibility Study of the Kholombidzo hydro power electric plant with the objective of evaluating the energy generation potential and feasibility of the development of this hydropower scheme. The main objective of the Feasibility Study was to assess project viability, determine optimum project layout, estimate investment requirements and all other requirements to support whether to proceed to project financing (appraisal and due diligence by financial institutions).

The Kholombidzo falls are located in the middle Shire River, upstream of Nkula Falls and the first falls downstream of Liwonde. Kholombidzo Power Plant will rely on water from the Shire River, which is the only outlet of Lake Malawi. The Shire River has a natural discharge curve that is directly related to the lake level but controlled under certain conditions by Kamuzu barrage at Liwonde.Kholombidzo HPP concept is governed by the prevailing topographic, hydrological, geotechnical and environmental and socio-economic conditions at site. The hydropower scheme is utilizing a natural head of 55 m and can provide 210 MW of power generation capacity.

The  projects key technical characteristics is as follows:

  • The total hydropower cost is approximately USD 511.5 million corresponding to a project specific cost of 2401 USD/kW.
  • The tentative schedule envisages a period of 66 months (5.5 years) for project implementation including a development phase of 18 months and a construction period of 48 months.
  • The Kholombidzo HPP has an assessed average continuous generation potential of 138 MW (1212 GWh/year) corresponding to a plant factor of 0.65.
  • The average revenues, for a unit energy price of 6 cUSD/kWh, are estimated at USD 70.5 million
  • It is capable of generating an estimated NPV, for a discount rate of 8 %, of USD 127 million over the 50 year evaluation period, having a B/C ratio of 1.2 and an IRR of 10.8 %.
  • The levelized cost of energy generation is 4.9 cUSD/kWh. These favourable financial indicators are resilient to construction delays and to some extent to higher investment costs but sensitive to   material changes in electricity prices and energy generation (water availability).
  • The total length of the power waterway is 4.2 km.
  • The surface powerhouse is equipped with four 53.3 MW class Francis turbine coupled to a 63 MVA generator, operating at a rated net head of 58.8 m.
  • The rated flow is 100 m3/s per machine, totalling 400 m3/s.
  • The switchyard for a voltage level of 132 kV is located in an excavated platform between the powerhouse and the surge chambers.
  • The electrical network connection is assured by two 132 kV Overhead Transmission Lines with approximately 16 km long between HPP and Phombeya substation.
  • The run-of river development involves the construction of a diversion dam and appurtenant structures, the left bank waterway and the power generation system.
  • The dam with central gated spillway is located 160 m downstream of the existent Matope Bridge and consists of a 16.8 m high concrete gravity dam founded on a gneiss rock mass outcropping in the river bed.
  • The total crest length is 265 m at elevation 470 m.a.s.l. The dam with full supply water level at 468 m.a.s.l. impounds a reservoir of 26.7 million m3 capacity and an inundated area of 21.7 km2.

The power waterway, designed for a flow rate of 400 m3/s, comprises the following major components:

  • Intake at tunnels portal near the dam left abutment;
  • Two headrace tunnels, circular section (inner diameter 8.0 m), concrete lined and constant slope. Each tunnel supplying water to two of the four generating units;
  • Two cylindrical surge chambers, one per tunnel, with 32.0 m of internal diameter and 38 m high, to provide protection against transient events and ensure stability of operation;
  • The headrace tunnels end with steel lined sections that bifurcate into four tunnels upstream the four generating units installed at the powerhouse;
  • Four tailrace tunnels, circular section (inner diameter 7.4 m), concrete lined, that connect the draft tubes of the powerhouse to the outlet portal near Mkundi river;
  • Unlined tailrace canal, trapezoidal section with bottom width of 40 m and constant slope, conveying water back to Shire River.

The development of the project comprises establishment of design criteria for dimensions of the different project components and study of design variants in project components to optimize the final solution. The layouts are developed using topographic mapping and geological/geo-technical information obtained in previous tasks of the present study.