IEEE Power & Energy Magazine - September/October 2020 - 47

Results for New Plants
In addition to the life-extension options analyzed for the
existing facilities, new development options were also investigated for adding capacity to the system with a new powerhouse at the Acaray dam and also with a new powerhouse
at the Yguazú dam. To determine the costs of construction
for the cost-benefit evaluation, conceptual layouts of the
Acaray III and Yguazú plants were developed. For Acaray
III, the cost estimates were based on the bill of quantities
included in the contract documents for the construction of
the Acaray II plant applying current construction costs, with
adjustments for increased penstock lengths and other variations and with prorating based on the installed capacity and
the number of units. This cost was compared to the actual
benchmark cost of construction within Hatch's internal database and applied to the Yguazú cost estimate based on footprint and unit sizing.
For Yguazú, the following various alternative layouts for
the new facility were developed to help identify the most
cost-effective arrangement:
✔ Use the existing bottom outlet of the dam to construct
a new intake for a new powerhouse downstream of the
september/october 2020

dam. This option was limited by the existing size of
the bottom outlet, which would limit the flow.
✔ Construct a new intake structure on the free-flow spillway section at the left side of the dam. The water
conveyance system will lead the water to a new powerhouse on the left side of the dam.
✔ Construct a new intake from the gated spillway with
a steel penstock to a new powerhouse in the toe of the
dam. This option will be limited by constructability aspects.
All of the options consider vertical Kaplan units that will
allow for operation during low-flow seasons and will not
require deeper excavation, which can increase construction costs.

Results for New Development at Acaray III
After combining the construction cost estimates with the
estimated revenues determined in the long-term energy
market analysis, the results show that under the current
projected load growth, the development of the Acaray III
project will have a BCR greater than one and would be recommended. Figure 13 shows that the BCR peaks between
90 and 110 MW and decreases beyond this size. When
performing a sensitivity analysis, it was found that for the
2,025 load projections, the BCR decreased below one and
negative NPV values were obtained. This indicates that
the results are highly sensitive to the energy benefits as
affected by the future system demand and that Acaray III
should not be developed unless the load projection exceeds
the forecast for year 2025 level derived under the highgrowth scenario.

Results for New Development at Yguazú
A similar cost-benefit analysis was conducted on the Yguazú
future development. The development costs were estimated
to be slightly lower than those of Acaray III, with their benefits far less sensitive to the future load projections because

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0.06

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20
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25
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tated before construction begins for the new Yguazú
facility in 2025
✔ a full plant outage would occur coincidently with the
first unit outage at each plant (2021 and 2023); the rehabilitation of common plant components would be
scheduled during this time period to minimize the
following outage costs:
* penstocks and surge tanks
* intake, hoists, and trashracks
* main inlet valves
* hydraulic draft tube gates (Acaray I)
✔ powerhouse crane overhauls conducted prior to first
unit overhaul
✔ stop logs and gantry cranes overhauled prior to unit
overhauls, where they will be required
✔ related components with interventions suggested in
similar years forced into a concurrent intervention
(same year); the similar groups of components include:
* turbine components and governor components
* generator windings and core and rotor poles
* gates and hoists.
The levelization methodology resulted in a CAPEX plan
with a major refurbishment of units 1 and 2 at Acaray I in
2021 and 2022 and the refurbishment of units 3 and 4 at
Acaray II in 2023 and 2024. The expenditures in 2023 and
2024 deal with the Acaray II upgrades and are significantly
less than those of the previous two years because the generators have already been purchased and are not included
in the plan. The CAPEX profile for modeled components is
expressed as a percentage amount of the next 20 years, as
displayed in Figure 12.

CAPEX (%)

✔ the existing Yguazú spillway gates are to be rehabili-

Year

figure 12. The recommended CAPEX profile for components modeled from simulations, including constraints and
excluding engineering costs and contingencies.
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IEEE Power & Energy Magazine - September/October 2020

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