Tables II and III report the net annual benefit, the
incremental kWh cost and simple payback for the four
solutions considered for sites 1 and 2. The net benefit
reported in the Tables is electric savings minus O&M,
incremental fuel expenses and annual capital cost, and is
then the annual equivalent of the NPV (Net Present Value)
of the investment. Note that incremental kWh costs for the
four solutions considered are lower than the value for
uncooled plant. Evaporative cooling (Case C) is an
extremely cost-effective solution, and payback is less than
one year, even for a continental climate and cold sites (Site
1). Its installation is advisable for all gas turbine plants, if
great electricity increases are not required. Both the
single- and two-stage systems have a payback of c. 2 years,
and their power gain is approximately double that of
evaporative cooling. It must be added that payback
oriented analysis can be misleading, since it gives priority
to short-term investment. Since we are dealing with
paybacks considerably smaller than the lifespan of the
components (from 15 to 20 years), the greater yearly saving
of the absorption unit leads, in the long run, to higher
benefits than those of evaporative cooling. We chose to
report our data in terms of simple payback instead of IRR,
since use of the former is more widespread, though it is less
accurate. The integrated solution (Case D), which proved
to be the most effective from the power increase
standpoint, is also more economical, since it guarantees