Temperature - European Investment Bank

WEST AFRICAN POWER POOL (WAPP) PÖYRY ENERGY LTD.
Mount Coffee HPP ESIA and RAP 2012-09-18
ESIA Report Page 40
Based on these figures, in the following Table a comparison is made between turbine
output on the one hand and inflow into the reservoir under certain conditions on the
other.
Table 8-2: Comparison between turbine output and inflow to the reservoir
Turbine output per second per hour per day daily output in % of
m³/s cfs M m³ M cf M m³ M cf
1 unit @ 40% 34 1'200 0.12 4.32 2.94 103.68 3.3
@ 65% 55 1'950 0.20 7.02 4.77 168.48 5.3
@100% 85 3'000 0.31 10.80 7.34 259.20 8.2
4 units full (400%) 340 12'000 1.22 43.20 29.38 1'036.80 32.6
reservoir volume
Inflow to reservoir Comment
yearly average 564 19'917 2.03 71.70 48.73 1'720.84 full operation of all units
av. dry season flow 184 6'500 0.66 23.40 15.89 561.60 sufficient for 2 units
av. wet season flow 835 29'500 3.01 106.20 72.13 2'548.80 full operation of all units
av. wettest month 1'617 57'103 5.82 205.57 139.71 4'933.68 full operation of all units
av. driest month 108 3'814 0.39 13.73 9.33 329.52 sufficient for 1 unit
av. driest month on record 58 2'048 0.21 7.37 5.01 176.97 at limit for 1 unit @ 65%
av. driest day on record 2 71 0.01 0.25 0.17 6.10 no operation possible
The relevant points of this comparison are as follows:
� During the dry season, there is on average not enough water for operating the
plant at full capacity.
� On average, during the driest month of the year, there would be enough water
for operating one turbine at 100% capacity.
� In extremely dry months, with average flows of 34 m³/s (1'200 cfs) or less, there
would be barely enough water for operating one turbine at 40% capacity. During
the 18 years of records, this has never happened, the driest month recorded ever
had a mean flow of 58 m³/s (2'045 cfs).
� Still, there can be days with flows considerably lower than the minimum
requirements for turbine operation. This situation occurs on average on
approximately 4 days per year.
As shown in the flow exceedance curve (Figure 8-4) during much of the time (47%),
there will be some amount of spilling and the scheme can be operated as a run-of-river
plant at full capacity. During the remaining time (53%), all available water would be
used for energy production, and during much of this time the plant will not operate at
full capacity. Without spilling, the original river bed below the spillway would remain
completely dry.