Temperature - European Investment Bank

WEST AFRICAN POWER POOL (WAPP) PÖYRY ENERGY LTD.
Mount Coffee HPP ESIA and RAP 2012-09-18
ESIA Report Page 47
The two specific recommendations, small unit in the spillway structure and additional
study of river flow conditions during operation in order to maximise the benefit of the
residual flow, are discussed shortly.
8.2.3.5 Small Unit for Turbining Residual Flow
One very valid argument against a residual flow of 8 m³/s is the costs - or the loss -
caused by this measure, estimated to be 3.5 million USD annually.
Here, first of all, it has to be stated that the actual cost might in reality be very much
lower. As noted above and explained with more detail in Chapter 25, present tariffs are
extremely high, due to the high costs caused by using fuel oil for energy production.
Depending on the financing model for MC HPP, generation costs and tariffs might
decrease very considerably, to about half of the tariffs applied today (see Table 25-8).
This would mean that the "value" accorded to electricity in Table 8-4, as well as the
calculated loss, would diminish accordingly.
On the other hand, it would certainly be possible to install a small unit for using the
residual flow of 8 m³/s. The result would be as shown in the following Table (it should
be noted that investment costs and power generated are rough estimates and not based
on a detailed analysis).
Table 8-5: Esitmated costs and benfits of a small unit
Item Unit Amount
Installation of turbine of 900 kW Million USD 4
Yearly generation GWh/year 7.8
Value of production Million USD/year 3.51
Loss (acc. to Table 8-4) GWh/y 7.0
Costs (acc. to Table 8-4) Million USD/year 3.15
Net benefit Million USD/year 0.36
Note: investment costs are calculated on the basis of 4000 USD/kW installed. Annual
monetary gains and losses are calculated assuming the same tariff as was used for Table
8-4.
The small unit would have a head of approximately 51 m (as compared to the 22 m of
the main turbines) and would therefore produce less energy per m³ of water than the
main turbines. However, while the loss caused by the residual flow is restricted to the
dry season (no loss during the time when there is spilling), the small unit would be
operating the whole year round, during the dry season using an additional 8 m³/s of
water which would otherwise be spilled. This explains the fact that overall, gain would
be slightly higher than the loss, resulting in a small net benefit.
If in addition this electricity could be used for electrification of nearby settlements, this
would be an additional benefit for the local population, a measure entirely in the sense
of sharing benefits.