Chiweta

The Chiweta geothermal prospect is located in the Rumphi district (Northern Region of Malawi), 370 km north of Lilongwe. The site falls in the northern portion of the Malawi rift and is underlain by biotitic gneisses of the Basement Complex, covered by clastic sediments of the Karoo System and by a thin level of Quaternary deposits. The geoscientific investigations performed over the prospect, inclusive of geological, geochemical, gravimetric and geoelectrical surveys and allowed to elaborate the conceptual model of the field.

The main characteristics of the geothermal system, which can be summarized as follows:

  • Areal extent of the reservoir: 5 km2 (corresponding to the “probable” extent)
  • Depth of the reservoir: 500-750 m
  • Chemical composition: Na-Cl(SO4) with TDS of 1,300 ppm
  • Temperature: 130-140 °C
  • Thermodynamic state: water dominated

A volumetric estimate of the electric potential of the system indicates a likely value of 13.5 MW and a highly probable value of 10.5 MW, which was taken as a reference for selecting the capacity of the power plant. The initial step towards this goal consists of the implementation of a program of exploratory drilling, aimed at proving the existence of a geothermal system of commercial interest and at defining its thermodynamic, hydraulic and chemical features. For this purpose, it is proposed to drill three slim holes with final diameter of the slotted liner of 41/2” up to a vertical depth of 900 to 1,000 m (CW-01, CW-02 and CW-03). Two of these holes are easily accessible from highway M1, whereas the third is situated some 1.2 km to the west at elevation of 650 m a.s.l.

At completion of this exploratory stage, in case of favourable results, it will be possible to proceed with the development of the resources subject to the procurement of adequate financing. This development shall consist of four components, namely:

Drilling: In accordance with the required thermal input for the operation of the 10 MW power plant, it is foreseen to drill 9 production wells with final diameter of the slotted liner of 7” and vertical depth of 1,000 m. Wells will be located in three distinct pads (Pads A, B and C), out of which two are due to coincide with the pads utilized for drilling the slim holes of the previous stage. Four reinjection wells, all to be drilled from the same pad situated just beyond the southern limit of the probable zone (Pad D), are deemed to be necessary to dispose of the brine from the power plant.

  • Fluids conveyance system: It corresponds to the pipes due to convey the fluids from the production wells to the power plant and from the power plant to the reinjection  wells. A total length of the conveyance system of 4 km has been estimated.
  • Power plant: The power plant will be located along highway M1, some 200 m away  from the lake Malawi shore, and will cover a surface of approximately 3 ha. In  consideration of the relatively low temperature of the geothermal fluids, it is proposed to adopt an Organic Rankine Cycle (ORC) utilizing n-butane as organic fluid.
  • Transmission line: Interconnection to the national grid will be performed through installation of a new 66 kV line, leading to the existing Livingstonia substation, which  will follow the coastal road up to Khondowe and then the internal road from Khondowe to Livingstonia for a total length of about 20 km.

A period of approximately 5.5 years is needed for completion of the above described program, out of which the first 2.5 years would be dedicated to the exploratory activities and the following 3 years to the development stage. Electric generation can accordingly start at the beginning of the year 2024. Costs for the implementation of the program have been estimated grouped into two major components, that is capital expenditures (CAPEX) and operation and maintenance (OPEX), as shown here after. CAPEX amounts to 76.2 MUSD, that is to 7,600 USD/kW.

OPEX has been subdivided into four sub-components, that is:

  • Fixed O&M costs (staff salaries, insurance, head office expenses, routing maintenance of plant and field): 0.8 MUSD/year
  • Variable O&M costs (consumables, spare parts and salaries for extraordinary staff): 0.2 MUSD/year
  • Major plant overhauls. 0.5 MUSD/4 years
  • Make-up wells (to compensate for reservoir decline): 3.5 MUSD/4 years
  • The economic and financial analyses were carried out on the base of the projected work schedule and of the estimated CAPEX and OPEX, assuming a plant factor of 0.90, equivalent to 7,900 operating hours per year.
  • An Economic Internal Rate of Return (EIRR) equal to 12.63% over a period of 30 years of operation has been calculated.
  • Financial Internal Rate of Return (FIRR) of 12.7% has been calculated. 

In conclusion, it can be stated that the geothermal resources of the Chiweta prospect, due to their low enthalpy nature, are associated with higher exploitation costs than the traditional high enthalpy resources. However, it is felt that this aspect is counterbalanced by several positive parameters, namely:

  • Exploitation of low to medium enthalpy geothermal fluids is becoming more and more common in the worldwide scenario, representing the main target for future geothermal projects.
  • Power generation through geothermal resources constitutes the most reliable and constant source in terms of base load, being independent from external constraints such as climatologic conditions, fuel supply restrictions and energy market fluctuations.
  • The Chiweta prospect is located in a sector of Malawi where alternative energy sources, in particular hydroelectric ones, are not abundant.
  • The volumetric estimate of the electric potential of any geothermal system is as a rule characterized by a conservative approach, since it does not take into account meteoric recharge. Therefore, the 10 MW capacity assumed as a reference value surely falls on the low side and may result to be significantly larger.
  • It should be mentioned that any expansion of the 10 MW capacity, e.g. installation of a new 10 MW unit, would be associated with significantly lower unit costs, related in particular to the exploration phase, power plant and transmission line.
  • The Levelized Cost of Electricity (10.4 USD cents per kWh) is in line or slightly lower than the Feed-In Tariff (FIT) fixed by the Government of Malawi at 10.5 USD cents per kWh for geothermal power plants.

In consideration of the above, it is recommended to proceed with the development of the Chiweta resources by implementing the program of exploratory drilling. 

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