POWER July 2015 - 65

GENERATION TRANSITIONS
TVA's Generating Resources
Tennessee Valley Authority (TVA) has its
roots in water-hydropower was its calling
card in the beginning. Over time, it has
used almost every resource available. Here's
how its portfolio breaks out today, according
to the draft Integrated Resource Plan.
Nuclear. TVA operates six reactors:
three at Browns Ferry, two at Sequoyah,
and one at Watts Bar, with a second Watts
Bar unit likely to come online this year
after 36 years of construction (see " Watts
Bar Unit 2: A 'Deferred Nuclear Plant' Gets
Back into the Game " in the June issue of
POWER or in the online archives at powermag.com).
The current nuclear units have
a capacity of 6,700 MW; Watts Bar 2 would
add another 1,150 MW.
Coal. The TVA coal system consists
of 10 coal-fired stations with 41 active
generating units, totaling about 11,900
MW. In recent years, TVA has retired 11
coal-fired units and idled another seven.
According to the utility's draft Integrated
Resource Plan, by 2016 the coal fleet will
decrease to about 32 units with a total
capacity of 10,300 MW " as a total of 16
units are expected to be idled to comply
with environmental requirements. "
Natural Gas. TVA runs 87 combustion
turbines at nine power stations with
a combined capacity of about 5,400 MW
and 11 combined cycle units at five plants
with some 3,900 MW of generating capacity
(Figure 1). That combined cycle figure
increased immediately by 700 MW with
the recent purchase of an existing plant
in Ackerman, Miss.
Hydro. The TVA hydro system is made
up of 109 conventional units at 29 dams,
with generating capacity of about 5,400
MW. TVA also has a long-term power purchase
agreement with the U.S. Army Corps
of Engineers at eight dams on the Cumberland
River system for another 400 MW.
Storage. Raccoon Mountain is a
pumped storage project-TVA's largest
hydro facility at 1,616 MW-which stores
water off peak for release when demand
is high.
Wind. TVA buys all the power prothat
already provides electricity to TVA at a
price that is significantly less than it would
cost to build a comparable plant. "
As the IRP modeling scenarios play out,
July 2015 | POWER
1. Big on gas. The Lagoon Creek Combustion
Turbine Plant in west Tennessee is
one of TVA's nine combustion turbine facilities
and one of four combined cycle sites.
The colocated units have a joint capacity
of 1,444 MW, making the site TVA's largest
gas-fired facility. Courtesy: TVA
vary more significantly than other resources. "
The analysis suggests an addition of 4.8 GW
of combustion turbines at the highest demand
scenario to 800 MW at the lowest; the need
for additions of combined cycle generation
are consistent over the five models.
The Coal Plan
Gas prices and environmental regulations will
determine how TVA will deal with its coalfired
plants " in the mid-2020s. " Johnson said,
" By the end of this decade, we will have retired
40% of our coal fleet, " in part because of a
settlement with the Environmental Protection
Agency on coal ash storage, following a massive
2008 coal ash pond spill at the agency's
Kingston coal-fired plant in Tennessee.
Johnson noted that " the average age of
duced by the Buffalo Mountain wind farm
in Anderson County, Tenn., with 27 MW of
nameplate capacity from 18 turbines. The
agency also has a long-term power purchase
agreement with eight wind farms in
Illinois, Kansas, and Iowa, with 1,500 MW
of nameplate capacity, and TVA estimates
that about 14% of that will be available
for summer peaks.
Solar. The agency owns 16 photovoltaic
arrays with a combined nameplate
capacity of about 300 kW. TVA also buys
solar output through several long-term
contracts with 72 MW of nameplate capacity;
TVA expects about half of that to be
available at summer peaks.
Biomass. At the Allen Fossil Plant,
TVA cofires methane from a nearby sewage
treatment plant and also cofires wood
waste at the Colbert Fossil Plant. TVA says,
" The co-firing is more like a fuel switch
for coal and does not provide additional
capacity at either of these plants. " The
agency buys about 49 MW of biomass generation
from non-utility providers.
Oil. TVA owns five diesel generators, and
several others are under contract, providing
a total of about 120 MW of capacity.
Energy Efficiency. TVA's efficiency
and demand response programs focus on
peak demand reduction. The power agency
says that from fiscal 2012 to fiscal 2014,
it has seen peak reductions of 451 MW, or
1,843 GWh in energy demand.
most of the variations in plant expansions
relate to tradeoffs between energy efficiency
and natural gas. Across the scenarios, says
the IRP, " The addition of natural gas units
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TVA's coal units is 55 years, and some are in
good shape; some are not. " What remains on the
TVA system, he said, " will be fully scrubbed,
fully controlled, and producing only dry ash. "
The Obama administration's Clean Power
Plan to reduce carbon dioxide from existing
coal plants is likely to be less of a headache
for TVA than for some other coal-heavy utilities,
Johnson said. He said TVA already has
reduced CO2
emissions by 30% from 2005
levels. The utility is on track for a 40% reduction
by 2020. He added that the least-cost
planning approach in the resource plan helps
guide where TVA can find carbon reductions,
including opportunities to use its extensive
hydro system more efficiently.
Selective Renewables
When it comes to renewables, the IRP says,
" Solar resources begin appearing in the resource
plans in the mid 2020s; wind resources
appear in the late 2020s. " A recent article in the
Chattanooga Times Free Press raised the possibility
that TVA might become a customer of
the 700-mile high-voltage, direct-current Clean
Energy Line bringing Western wind power to
the TVA region. It's a $2 billion project.
TVA quickly reacted. The IRP states that
" generally the HVDC wind option is not selected
until the early 2030s, " and Joe Hoagland,
the TVA vice president who presided over the
IRP, told the newspaper the agency wasn't all
that bullish on wind. " The wind blows when
the wind blows. What we're trying to maintain
is a balanced portfolio of power. " TVA
currently has 1,500 MW of (nameplate) wind
capacity, most of it under contract from nonutility
suppliers. " We don't get a lot of energy "
from that, Johnson said.
Last February, when the nine-member
TVA board authorized the purchase of the
Mississippi combined cycle gas plant, it also
approved a power purchase agreement with
NextEra Energy for electricity from a planned
80-MW utility-scale solar farm in Lauderdale
65
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POWER July 2015

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