ETL 1110-2-550
30 May 97
e. Additional columns are required to sum
condition is modeled assuming that only three units
O&M, repair, and rehabilitation costs for any given
are available. Subsequent scenarios are run
year. Again, subroutines must be used to prevent
removing a unit at a time until all four units are
double counting of normal maintenance costs if the
considered to be off-line. This process results in
unit is considered to be out of service for an
construction of a system production cost curve
extended period of time.
assuming a full range of unit availability in the
without-project condition. This production cost
f. Columns must be added to the spreadsheet
curve is then used in the economic model to
to account for specific alternatives and conditions.
quantify the production cost consequences of unit
For example, in an alternative that includes a
availability for any potential combination of
planned sequence of rehabilitation, if a unit outage
randomly generated unit outages.
occurs within a year of the planned rehabilitation,
b. Additional production cost curves are
the unit would not be repaired or returned to service
prior to the rehabilitation. This would be the proper
constructed to assist in modeling the alternative
sequence of events assuming that it is more cost
rehabilitation and repair scenarios. As units are
effective to leave the unit off-line than to return it to
rehabilitated, unit efficiencies increase, hydropower
service and then shut it down later for a permanent
production increases, and system production costs
rehabilitation.
decrease.
g. Another column needs to account for
c. Once all of the separate cost curves and
whether or not existing spare parts are available for
previously described input values are established,
a given unit. In any simulation, if a unit with spare
the without-project and all of the with-project
parts experiences a catastrophic outage, the existing
conditions are simulated. For each iteration of a
spare parts should be assumed to be put into
simulation, potential outages are generated; O&M,
service.
repair, and rehabilitation costs are calculated; and
system production costs are estimated. The eco-
nomic consequences for each alternative over the
E-8. Cost of Replacement Power -
period of analysis are summed and described in
Hydropower Benefits
present values terms. Net benefits are computed for
each alternative, and the plan that maximizes net
a. The without-project condition must first be
benefits is recommended for implementation.
modeled as discussed in Appendix D. This pro-
Additional statistics are generated to describe the
duces an annual system production cost assuming
range and distribution of values for each
all four of the Chapman powerhouse units are avail-
component.
able for production. Next, the without-project
E-4
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