IEEE Power & Energy Magazine - September/October 2020 - 48

1.4

0.2

1.35

0.15

1.3

0.1

1.25
1.2

0.05
0

BCR

NPV (% Maximum Capital)

Acaray III NPV and BCR Versus Plant Capacity

1.15
50

100
150
Plant Capacity (MW)

1.1
200

NPV (MM$: Million Dollars)
BCR

Yguazú NPV and BCR Versus Plant Capacity
20

1.5

5
0

BCR

NPV (% Maximum Capital)

figure 13. The Yguazú cost-benefit evaluation under
integrated load projections.

0.5
50

100
150
Plant Capacity (MW)

0
200

NPV (MM$: Million Dollars)
BCR

figure 14. The Yguazú cost-benefit evaluation under
integrated load projections.

Yguazú is used for both energy and peaking, as opposed to
Acaray III, which is strictly used for peaking. In general, the
NPV was always positive and the BCR always greater than
one with an optimal capacity at roughly 90 MW for the current future growth projection, as shown in Figure 14.
When performing a sensitivity analysis, it was found that
for the 2025 load projections, the BCR remained above one,
with a positive NPV for capacities between 50 and 90 MW.
With the more conservative load projection, the optimal size
was selected at approximately 70 MW.

Recommendations
Based on the simulation results, the upgrade of Acaray I and
II was recommended in the short term because both plants
are at the end of their useful lives and the financial analysis
indicates a positive NPV and BCR. Acaray I was identified
as the highest-priority project, with an increased capacity
runner replacement and complete replacement generator for

ieee power & energy magazine

both units. Recommendations were also provided for the
refurbishment/replacement of the associated hydromechanical, balance of plant, and protection and control equipment,
which would be conducted prior to, or concurrent with, the
unit upgrade projects. It was recommended that the Acaray
II runner replacement project be conducted immediately
following the Acaray I project, which consisted of a runner
replacement, with its capacity matching the recently purchased generators. It was also recommended that the bid
documents for the engineering tender be prepared within the
next few months and the preparation of documents for the
bidding of the Acaray I and II projects be prepared in the
near term so that construction could begin.
The development of a new 70-MW plant at the Yguazú
dam was recommended regardless of the future load projections, and construction could be planned for immediately following the Acaray I and II upgrade projects. Progress should
be made in the near term for conducting preliminary studies
and the collection of baseline data for environmental studies.
The construction of a new facility at Acaray III would be
profitable only under conditions of a strong and sustained
load growth resulting in higher energy revenues for the
peaking facility. This is related to the fact that under strong
system demand, any increase in Acaray's capacity would
translate into a direct reduction in capacity purchases from
Itaipú, as the available hourly contract would then be fully
utilized. The development of Acaray III would take place in
the mid to long term, provided that the increase in system
demand is sustained during that period.

For Further Reading
B. Glabau, E. Nielsen, F. Welt, and R. Allen, "Role of advanced power system modeling in strategic studies at BPA,"
in Proc. HydroVision 2016, Minneapolis, MN, 29 July 2016,
Session 61, pp. 1-14.
S. Bhan, F. Welt, J. King, A. Bridgeman, and C. R. Donnelly, "Risk-based asset management plan for the exploits river hydroelectric system," in Proc. HydroVision 2013, Denver,
CO, 23-26 July 2013, Session 7I, pp. 1-13.
H. W. de Meel, "Deciding optimal timing for equipment
rehab or replacement," Hydro Review Mag., vol. 27, no. 2,
pp. 54-59. Apr. 2008.

Biographies
Daniel Flores is with Hatch, Ontario, Canada.
Andrew Bridgeman is with Hatch, Ontario, Canada.
Francois Welt is with Hatch, Ontario, Canada.
Juan Jose Aveiro is with Manitoba Hydro International
Ltd., Paraguay.
Delfín Benítez is with Administración Nacional de
Electricidad, Paraguay.
José Vallejos is with Administración Nacional de
Electricidad, Paraguay.
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