There are nearly
300 pumped storage
projects in the world,
and 40 in the United
States.
The facility
in Bath County
Virginia is the
largest one now,
-- it can generate
3,003MW
(megawatts)
when all six
generators
are operating
at full power.
Within the
United States,
only Grand
Coulee Dam
has more capacity
to generate electricity
fro, flowing water.
A 4,000MW project
at Lake Revelstoke
in British Columbia
has been proposed.
In 2017 the largest
pumped storage
in Europe was the
Cortes-La Muela
hydroelectric project
in Spain, which was
rated at 1,762MW.
The largest in China
was the Cuntangkou
Pumped Hydro Power
Station in Sichuan,
rated at 2,000MW
The Snowy Hydro 2.0
pumped storage project
in Australia completed
a feasibility study in 2017
that proposed to expand
the existing network
of hydropower dams
to provide up to
6,000MW of electricity
generating capacity.
At the Bath County Virginia
Pumped Storage Station,
Dominion Energy moves
water between their
uphill and downhill
reservoirs, to create
a "giant battery",
for providing electricity
at times of peak demand
To generate electricity,
water is released from
an upper reservoir
created by damming
Little Back Creek.
The water drops
1,262 feet from
the upper reservoir
to the lower reservoir.
Water moves down
through three tunnels,
or "penstocks",
carved through Little
Mountain, which
separates Little Back
Creek and Back Creek.
There are six turbines:
Two at the bottom end
of each of the three
penstocks.
Turbines are reversible,
and serve as uphill
water pumps, as well
as downhill water flow
electricity generators.
The penstocks are
3,780 feet long,
and 28.5 feet
in diameter.
They have
concrete walls
18-24 inches thick.
The water
level in the
upper reservoir
can drop
105 feet,
and the
lower reservoir
can rise
60 feet.
The dam on
Little Back Creek,
creating the
upper reservoir,
is 460 feet high.
The dam
on Back Creek,
creating the
lower reservoir,
is 135 feet high.
But ...
a pumped storage
station uses more
electricity than
it generates.
Pumping water to
an uphill reservoir
requires
more electricity
than the turbines
can generate when
gravity is allowed
to let the water
go downhill to spin
the six turbines
on the way to the
lower reservoir.
This Virginia plant
is 80% efficient.
For every
four kilowatts
of electricity
generated,
five kilowatts
are consumed.
The facility serves
as a "battery", which
can be started quickly
as demand shifts,
4,500 times per year.
If the
upper reservoir
was fully drained,
over 11 hours,
it could produce
24,000 megawatt
-hours of electricity.
The 500MW
turbines
can start
exporting
significant
amounts
of electricity
into the grid
within 5-10
minutes.
Note:
A coal-fired,
or nuclear power
generating plant,
would have
long delays for
"warming up".
Peak power can be
generated for only
three hours.
Once the
upper reservoir
has emptied,
the turbines
need to be
reversed
to pump water
uphill and
"recharge
the battery."
Maximum
power
generation
of 3,003MW
is possible
only when
the reservoir
is full.
As the
upper reservoir
drains, the
elevation of the
water drops
and the turbines
spin at slower
speeds.
The water flow is timed
to provide electricity
when demand peaks,
typically in the summer
when air conditioners
kick on between lunch
and early evening.
At times of
low demand,
such as
in the middle
of the night,
the water flow
is reversed.
The price of
a kilowatt-hour
of electricity
sold in the
afternoon
is high.
The cost of
a kilowatt-hour
used to pump
water uphill
before dawn,
is low.
Water flow
when generating
is 13.5 million
gallons per minute.
The flow when pumping
uphill is slightly lower,
at 12.7 million gallons
per minute.
During the summer,
there may not be
enough time to pump
all the water back uphill
before electricity demand
rises again (and the flow
needs to be downhill
to generate power).
Plant operators
normally catch up
by refilling the upper
reservoir on the
weekends.
When completely full,
the upper reservoir
has the capacity
to provide 24,000
megawatt-hours
of electricity.
The Bath County
Pumped Storage
Station does not
use fossil fuels
to produce
the electricity
it uses to pump
water uphill,
so it does not add
greenhouse gases
to the atmosphere.
Because water levels
in the two reservoirs
change so much,
and so rapidly,
they are not safe
for recreational use.
The two pumped
storage reservoirs
eliminated five miles
of natural stream
habitat.
The flooding
of 950 acres
and five miles of
Little Back Creek
and Back Creek
was "offset" by
Dominion Energy
building two
recreational ponds
and a campground.
The recreational ponds
offer warm water fishing
opportunities for
bass, sunfish, and
channel catfish.
CONSTRUCTION:
The bedrock
in the valley
of Little
Back Creek,
in which the
upper reservoir
was constructed,
is shale.
The bedrock
in the valley
of Back Creek,
in which the
lower reservoir
was constructed,
is limestone.
Little Mountain,
through which
the "penstocks"
were excavated,
is also limestone.
When one
of the penstocks
carved through
Little Mountain
was first filled
up with water,
there was
enough leakage
and pressure
changes through
the limestone
to buckle
a steel liner
in an empty,
adjacent
penstock.
At Gathright Dam,
grouting was injected
into the bedrock
to seal it.
HISTORY:
In 1971, the
Virginia Electric and
Power Company
(VEPCO),
now "Dominion Energy",
obtained preliminary
permits from the
Federal Power
Commission for two
pumped storage
projects.
They were for peak
demand periods
(typically from
11:00am to 8:00pm),
but would have
surplus capacity
during nights.
Pumped storage was
a proven technology,
with a track record
of meeting electricity
peak demand
requirements
in Virginia.
At the time,
natural gas
prices were high
( long before the
fracking boom ),
otherwise a new
natural gas plant
would have
been built.
Construction
started in 1977,
but stopped
three years later,
because the growth
in peak demand
for electricity
had not grown
as projected
by VEPCO.
The utility
then sold
Allegheny
Power
System
(now FirstEnergy)
a 40% share,
and completed
the construction.
Sharing the power,
and the costs,
made the Virginia
pumped storage
project feasible,
and it started
generating
electricity
in 1985.
National Public
Radio titled a story
on the project
"The World's
Biggest Battery."
Allegheny Power
had proposed to build
its own pumped storage
project in West Virginia.
The Federal Energy
Regulatory Committee
approved their pumped
storage project,
but the U.S. Army
Corps of Engineers
denied the needed
Clean Water Act
Section 404 permit
to allow construction.
And In 1988,
the Supreme
Court finally
ruled that the
Corps' denial
of that
Section 404
permit would
stand.
Allegheny Power
sold its 12,000 acres
in Canaan Valley
to the US Fish
and Wildlife
Service in 2002.