Temperature - European Investment Bank

WEST AFRICAN POWER POOL (WAPP) PÖYRY ENERGY LTD.
Mount Coffee HPP ESIA and RAP 2012-09-18
ESIA Report Page 45
The horizontal lines in the graph indicate water requirements for operating one unit at
full capacity (100%, 85 m³/s) or at minimum capacity (40%, 34 m³/s), and the three
values identified above for residual flow (1 = 22 m³/s, 2 = 8 m³/s, and 3 = 4 m³/s). The
flow duration curves indicate water available for turbine operation under the different
scenarios.
It is quite obvious from this Figure that the difference in water availability is rather
small between cases 2 and 3 (residual flow of 8 or 4 m³/s, respectively), but quite
considerable for case 1 (22 m³/s). This is illustrated further in the following Table.
Table 8-3: Consequences of applying different residual flow regimes
Residual flow
Exceedance time for operating one
unit at (in % of time)
Loss* (in days on average per year)
m³/s 100% 40% for 1 @ 100% for 1 @ 40%
0 83.9 92.8 0 0
4 82.9 92.6 4 1
8 82.3 92.2 6 2
22 78.3 90.9 20 7
* "Loss" here is expressed as the number of days per year during which the respective operation pattern
cannot be maintained in comparison with the base case (0 m³/s); it has however to be noted that even in
the basecase there are on average 59 days per year (16.1%) with a discharge of less than 85 m³/s, i.e. not
enough for operating one turbine at full capacity, and 26 days (7.2%) with less than 34 m³/s.
In addition, the costs of the loss in million USD and the CO2 production, if this loss of
energy will have to be generated with a Thermal Power Plant using Light Fuel Diesel
with an efficiency of 3.33kWh/litre (12.6kWh/gallon) is shown in following Table.
For the calculation on CO2 emission it has been assumed that 1 litre of diesel contains
733g of carbon, which results in the production of 2.68 kg CO2/l. With an efficiency of
3.3 KWh el. per litre this would result in an emission of about 807 kg CO2 per produced
MWh. Furthermore, 10 kg CO2/MWh which are generated by Hydro Power Plants have
been deducted. For the calculation of cost of loss 0.45 USD/kWh (the actual tariff
applied by LEC) has been used.
Table 8-4: Loss in energy production assuming different residual flows
Residual
flow m³/s
Mean annual
electricity
production
GWh
Loss
GWh
Loss
%
Value in
million
USD
Loss in
million
USD
CO2 emission for the
replacement of the loss with
diesel (TPP) [t]
0 364 0 0 163.80 0 0
4 360 4 1.1 162.00 1.80 3’189
8 357 7 1.9 160.65 3.15 5’580
16 351 13 3.6 157.95 5.85 10’363
22 346 18 4.9 155.70 8.10 14’349
30 340 24 6.6 153.00 10.80 19’131
Source: Stanley Consultants