Economic Evaluation of Pumped Storage Power Plant Complexes and Comparison with other Candidate Pumped Storage Power Plants Proposed for Sri Lanka

The daily electricity demand in Sri Lanka varies significantly with the time. The maximum demand occurs between 0630pm to 0930pm and the lowest demand occurs between 0030am to 0430am. The maximum demand is more than twice the lowest demand. According to the Ceylon Electricity Board (CEB) Long Term Generation Plan 2013~2032, sixteen coal power plants amounting to 4,700MW capacity will be added to the Sri Lanka power system in future. For economic operation of coal power plants in a power system which has significantly varying load throughout the day, energy storage mechanisms such as Pumped Storage Power Plant (PSPP) are required. The studies reveal that Sri Lanka has several attractive natural sites for Pumped Storage Power Plants, among them two sites can be developed as Pumped Storage Power Plant Complexes (PSPPC). This paper present the economic evaluation of possible sites and the findings shows that developing 1,000MW Maha Pumped Storage Power Plant Complex would be the most economical candidate site when considering the capacity requirement with the time.


Calculation Method
The calculations were done by the measured values based on layouts done on 1:10,000 scale topographical maps and formulae based on the quantities of existing facilities. These formulae used were developed in Japan for the purpose of the hydropower potential studies. They are prepared for each facility considering factors such as intake weir, intake, and headrace etc. The quantities of civil works are calculated for main work items such as excavation, concrete, embankment, reinforcement bars, gates, screens, and steel conduits. Quantities of work items other than main work items are not calculated. However, their costs are calculated as "others" in a lump-sum at a certain ratio against the total cost of main work items. Quantities of works of headrace tunnels and penstock are calculated based on their inner diameters.

Conditions for Construction Cost Estimate
Construction costs calculations are described in Table 5 for Maha PSPPC. In the preparatory works, costs of access roads, camp & facilities are calculated based on quantity of civil works, and the percentage cost are calculated making reference to actual costs of similar projects. For access road as 5% for pumped storage type of the total cost of civil works is estimated. While camp & facility cost as 3% and Environment mitigation cost as 3%. The cost of civil works and hydraulic equipment are calculated by multiplying the quantity of main items of works by unit cost which is described in Table 3 and Table 4 for Maha PSPPC. The work quantity is obtained from tables, diagrams and numerical formula. In this evaluation, the main work items of structures of civil works are excavation, concrete, embankment, and reinforcement bars and those of hydraulic equipment are gate, screen, and steel pipe. The costs of rest of the items of work, other than the main items, are calculated as "Others" in a lumpsum at a certain ratio against the total cost of the main work items. Unit costs are obtained by making reference to the latest data of similar works in Sri Lanka's Upper Kotmale Hydropower Project.
The construction costs of turbines, generators, control devices and main transformers, etc. are appropriated in a lump-sum in "Electromechanical equipment". There is a relationship that it is almost a straight line on logarithmic paper between electro-mechanical equipment cost DOI: http://doi.org/10.4038/slemaj.v18i2.16 according to each turbine type and P /√ (P: maximum output in kW), He (:effective head in meters), as shown in the example in Figure 1 and escalated as required.
In this paper, the construction cost of transmission lines is not considered. The following are included in the costs of "administration", "engineering service", "contingencies", which are calculated by multiplying the direct construction cost by an appropriate ratio.
The administration cost includes personnel expense and expenses to maintain the construction office. The engineering service cost includes expenses related to technical services such as design work and construction supervision conducted by consultants. In this evaluation, 15% of the direct construction cost is appropriated as the cost of administration and engineering service. The contingency includes physical contingency which is the increase of quantities of work, and 10% of the direct construction cost is appropriated for the contingencies. Interest during construction is calculated based on the following conditions.

Figure 1 -Example of Electro-Mechanical Equipment Cost
Weighted average interest rate (i) is calculated taking into account the ratio of local currency and foreign currency. For example, if the local and foreign currency portions are 25% and 75% respectively the calculation is as follow.   Cost of other items of works such as grouting not included in the main items described above is estimated at 20% of the cost of the main items.
ii) Spillway In the case of a fill type dam, the quantity of work of the spillway is calculated by the design flood discharge.
The excavation volume, concrete volume, weight of reinforcement bars, and weight of gates are calculated according to the following equations. Cost of other items of works which is not included in the main items described above is estimated at 20% of the cost of the main items.

Allugolla PSPP -Upper Dam
(1) Structural Design Concrete gravity type dam is adopted because of the following reasons. Possible to obtain the sound rock for the dam foundation, River span is narrow, Easy to overflow during the flood period, Easy to transport concrete.  V e ≈ 106, 600.00 m 3 V c ≈ 69,929.60 m 3 W g ≈ 33.7 ton Cost of other items of civil works such as grouting and coffering not included in the main items above, is estimated at 20% of the main items.

Lower Dam -Arama Lower Dam
(1) Structural Design Concrete gravity type dam is adopted.

Uduwella PSPP -Intake
(1) Structural Design A pressure type is adopted. The inner diameter of waterway is obtained from Figure 2. by using the maximum plant discharge. Inner Diameter: 6.9 m Maximum plant discharge: 152 m 3 /s

Uduwella PSPP -Headrace
(1) Structural Design A circular fully lined pressure tunnel is adopted. Diameter of tunnel is calculated assuming that a flow velocity in the tunnel is 6.0 m/s.

5.7
(2) Quantity of work The excavation volume of the pressure tunnel, concrete volume and weight of reinforcement bars are calculated by the following equations. V 68,435 V =21,250 =850 Cost of other items of works such as grouting, adit, ect. Not included in the main items stated above is estimated at 15% of the cost of the main items.

Uduwella PSPP-Headrace Surge Tank
(1) Structural Design Surge tank shall be provided to protect the headrace tunnel against the pressure of water hammer.
(2) Quantity of work The excavation volume, concrete volume, and weight of reinforcement bars are calculated in accordance with the following equations.

Uduwella PSPP -Penstock
(1) Structural Design A circular fully steel lined pressure tunnel is adopted. The inner diameter of penstock is calculated assuming that a flow velocity in the penstock is10 m/sec.   (1) Structural Design Underground type is adopted for Powerhouse.
(2) Quantity of work The excavation volume, concrete volume, and weight of reinforcement bars are obtained by the following equations.

Uduwella PSPP -Tailrace Tunnel
(1) Structural Design A circular fully lined pressure tunnel is adopted. Diameter of tunnel is calculated assuming that a flow velocity in the tunnel is 6.0 m/sec. Diameter: (4×Q max /6.0π) 0.5 = (4×152/6.0π) 0.5 = 5.7 m (2) Quantity of work The excavation volume of the pressure tunnel, concrete volume, and weight of reinforcement bars are calculated by the following equations. Cost of other items of works such as grouting, adit, etc. not included in the main items stated above is estimated at 15% of the cost of the main items.

Figure 3 -Relationship between Inner Diameter of Tunnel and Lining Concrete Thickness
(2) Quantity of work The excavation volume, concrete volume, and weight of reinforcement bars are calculated in accordance with the following equations.

Uduwella PSPP -Tailrace Outlet
(1) Structural Design A pressure type is adopted same as the intake.

Uduwella PSPP -Miscellaneous Works
Cost of miscellaneous works such as the disposal area and landscaping work is estimated at 10% of the total civil work cost.

Alugolla PSPP -Intake
Inner Diameter : 6.4 m (1) Quantity of work V e = 26,310 m 3 V c = 9,674 m 3 W r = 387 ton W g =194 ton W s = 108 ton Cost of other items of works such as coffering and trash rack, rake, etc. not included in the main items above are estimated at 25% of the main items.

Alugolla PSPP -Headrace
(1) Structural Design 5.0 (2) Quantity of work V 67,680 V =21,561 862 Cost of other items of works such as grouting, adit, ect. Not included in the main items stated above is estimated at 15% of the cost of the main items. (1) Structural Design Underground type is adopted for Powerhouse.

Alugolla PSPP -Headrace Surge Tank
(2) Quantity of work Q : Maximum plant discharge (m3/s) = 121 m 3 /s V e = 136,570 m 3 V c = 25,931 m 3 W r =1,037 ton The cost of powerhouse building and transformer chamber is included in 50% of "Others".

Alugolla PSPP -Tailrace Tunnel
(1) Structural Design Diameter: (4×Q max /6.0π) 0.5 = 5.1 m (2) Quantity of work V e ≒12,800 m 3 V c ≒4,020m 3 W r ≒161 ton Cost of other items of works such as grouting, adit, etc. not included in the main items stated above is estimated at 15% of the cost of the main items.

Alugolla PSPP-Tailrace Surge Tank
(1) Structural Design V e =21,329 m 3 V c =6,174 m 3 W r =309 ton Cost of other works such as steel lining not included in the main items above is estimated at 20% of the main items.

Alugolla PSPP -Tailrace Outlet
(1) Structural Design A pressure type is adopted same as the intake.
(2) Quantity of work Ve =27,568 m 3 Vc =10,121 m 3 Wr =405 ton Wg = 192 ton Ws = 107 ton Cost of other items of works such as coffering and trashrack, rake, etc. not included in themain items obtained above is estimated at 25% of the cost of the main items.

Alugolla PSPP -Access Tunnel to powerhouse
(1) Quantity of work V e = 2,250 m 3 V c = 500 m 3 W r = 15 ton Cost of other items of works such as grouting, adit, etc. not included in the main items stated above is estimated at 15% of the cost of the main items.

Alugolla PSPP -Miscellaneous Works
Cost of miscellaneous works such as the disposal area and landscaping work is estimated at 10% of the total civil work cost.

Benefit-Cost Method (B/C Method)
The economics of the project is analyzed on the basis of maximum output, energy output and the construction cost obtained.

Methodology of Analysis
An economic analysis of the hydro power project is made by a method to compare its benefit (B) and cost (C). The benefit of a hydro power project is the avoided cost of an alternative thermal power that supplies electric power equivalent to the hydro power project, and the cost is derived from the construction cost of the hydro power project. In the case of benefit cost ratio (B/C) is 1.0 or over, hydro power is economically better than the alternative thermal power. It is also possible to judge that a certain hydro power project is economically attractive if the B/C value is outstanding among a number of hydro power projects that are compared. Yet another method is to use the latter method and calculate the Economic Internal Rate of Return (EIRR).

Selection of Alternative Thermal Power
The alternative thermal power plants are gas turbine, coal fired, oil fired, liquefied gas fired, combined cycle, and diesel power plants.

(1) Standard Thermal Power
One method is to select the power source most commonly used in the electric power system. This is defined as the "standard thermal power". This method is suitable to compare the economic viability of a number of hydro power sites according to the same criteria, and this method is used for hydro power potential survey, master plan studies, etc. For example, in the case of an electric power system consisting mainly of coal fired thermal power plants or new coal fired plants are scheduled to be constructed, coal fired plants are selected as the standard thermal power.

(2) Alternative Thermal Power Equivalent to Hydropower
The other method is to select an alternative thermal power which is equivalent to the planned hydro power project, to evaluate its position as the source of supply in the electric power system. For instance, a gas turbine plant is often selected as the alternate thermal power for the reservoir type, pondage type and pumped storage type power plants that are designed to supply power for peak.

Benefit and Cost of Conventional Hydropower Projects Benefit
Annual benefit (B) of a hydro power project is obtained in accordance with the following formula, based on the fixed cost (mainly the equipment cost) and variable cost (mainly the fuel cost) of the alternative thermal power selected.
Where, B: Annual benefit of hydro power plant (monetary unit) B 1 : kW benefit (monetary unit/kW) B 2 : kWh benefit (monetary unit/kWh) Ph: Effective output (kW), maximum output is used in the case of pumped storage type E: Annual energy generation (kWh) at 2190 hours operation in a year (6hours per day) b 1 : kW value (also called capacity value), which is the fixed cost per kW for alternative thermal power (monetary unit/kW) b 2 : kWh value (also called energy value), which is mainly the fuel cost and is the variable cost per kWh for alternative thermal power (monetary unit/kWh) Loss rate and Outage rate is omitted.

Calculation of kW Value (b 1 ) and kWh Value (b 2 )
The kW value and kWh value are calculated from the following equations for the selected power source.
= Heat rate (kcal/kWh) fuel price (monetary unit/kcal) 860 (kcal/kWh)/thermal efficiency Fuel price (monetary unit/kcal) Ct: Unit construction cost of thermal power (monetary unit/kW) = Annual cost factor of thermal power = kW adjustment factor; correction factor due to the difference in reliability (station use, forced outage, scheduled outage) between hydro power and thermal power.
The annual factor and thermal efficiency for gas turbine plant is shown below.  Table 6.

Conclusion
The nature has blessed Sri Lanka with several natural locations which are suitable for developing Pumped Storage Power Plants. Few sites can be developed as Pumped Storage Power Plant Complexes which, further improve their economic viability. These will reduce the transmission costs which was not considered in this study.
Results (Table 7) show that 500 MW Maha-Alugolla Pumped Storage Power Plant is the most economical plant while 1,000MW Maha Pumped Storage Power Plant Complex is the next lowest.
The future load curve trends showed that there will be about 1,000MW PSPP capacity requirement by year 2021 [3]. By considering the economic evaluation results and PSPP capacity requirement forecasted for the future, it can concluded that the "Maha" Pumped Storage Power Plant Complex will be the best candidate plant to be installed in Sri Lanka.  Total cost 1,600,091,621 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9

Calculation of Construction Cost (Civil Cost)-Maha PSPP Complex
Install Capacity 1,000,000 (kW) Project Cost per kW 1,600 (USD/kW)

Calculation of Economic Evaluation Indices (Base Case) -Maha PSPP Complex
Year in order