On Mike Gillespie's
“dam facts” web page, it is
stated that Bagnell Dam operates eight turbines, each producing a maximum of
21,500 kilowatts (KW), for a total of 172 Megawatts (MW). While a bit simplistic, this stated capacity has
the virtue of at least getting the basic math right (8 turbines x 21.5KW = 172MW). If we include the two “house” generators each
producing an additional 2,100KW, we arrive at what the Federal Energy Regulatory Commission calls the “authorized
installed capacity” of 176.2MW. However,
this is not the current maximum capacity of Bagnell Dam.
LakeOzark.com/FunLake.com provides a
more enigmatic number, “The
facility with eight generators has a maximum capacity of 215 megawatts”. But the Tri-County Lodging Association that
runs FunLake.com is more interested in promoting tourism than quoting facts so
we’ll give them a pass.
There
are several other lake area sites that provide slight variations on this
number, but from the International Water Power
and Dam Construction, 2005 comes another number, “Completed in 1931, the 226MW Osage Plant and
Bagnell dam created Missouri’s Lake of the Ozarks”. Again, how this number was reached is left
unsaid.
Another outside source Hydroworld, an industry website, hints
at a possible reason for the various numbers, quoting power generation for
three different times in the life of the dam:
1931: 201MW
Quoted in a Feb 2009 article: 231MW
Quoted in 2014:
242MW
The 1931 capacity of 201MW
is a perplexing numbers since it is far more than the quoted “install capacity”, and even
more strange when considering only six of the eight turbines were even installed prior to
1953. The 2009 stated capacity of 231MW can
be attributed to upgraded Units 3 and 5 completed in 2002, along with upgrades
to Units 1, 6, 7 and 8 in 2008. These
upgrades increased each unit’s capacity from 26MW to 33.5 MW. Again however the numbers don’t quite add
up as accounting
for all 8 turbines, including the six unit upgrades from 26MW to 33.5MW, the total
output power comes to 253MW.
Ameren UE, being a publicly
traded company, provides its own information regarding Bagnell Dam’s energy
capacity. In its corporate fact sheet,
Ameren UE rates power generation at 240MW, producing 500 million Kilowatts
(500,000MW) per year. The 2007 FERC license quotes the total annual production
at 636,397MWh but recent turbine and generator upgrades have increased this
output. As reported in Hydroworld, “The
upgrades should increase the project's maximum hydraulic capacity by 1,580
cubic feet per second, resulting in a 6.5 percent increase in annual generation
of about 41,600 megawatt-hours.” When
added to Ameren’s stated energy production, the improved performance brings the
total annual production to about 678,000MWh
An important distinction
between total annual production and output capacity can be seen in the units
used to express power. Whereas capacity
is rated in essentially “watts” (the standard unit for electrical power),
production is expressed in “watt-hours”, adding the dimension of time to the
rating. The watt-hour rating for any
energy production facility is not to be confused with total capacity, it is typically only used to express actual energy
sales but can still provide some useful insight. Using the latest stated capacity of 678GWh
the amount of time needed to produce that much energy can be calculated by
simply dividing total energy produced by the maximum stated capacity of 240MW.
Considering
a year as consisting of 8760 hours, Bagnell Dam must generate the equivalent of
maximum output nearly 1 hour of every 3 on average to meet this sales potential. But why build a dam capable of generating
almost three times the amount of energy only to utilize it a third of the
time? Why not simply design the dam to
operate with the same outflow as average inflow and run it continuously? Understanding
how hydroelectric dams work, from the basics of the energy potential of gravity
to the practicalities of kinetic flow and usable energy, we can apply basic
engineering analysis to dissect the current energy production of Bagnell Dam,
as well as it limitations.
Next: Energy of the Osage
