The Lewis River Hydroelectric Projects - PacifiCorp

Lewis River Interpretive & Education Plan
The grid does not store electricity. It is merely a transmission and distribution
system—the supply meets the demand. Power must be continually fed in to meet
continual power draw (load). The United States’ electricity-distribution system
is based on alternating current at a frequency of 60 hertz (60 cycles per second).
The goal is to maintain this frequency in electrical output from the grid. If
more electricity is flowing into the grid than is flowing out, the input must be
decreased in frequency. If output exceeds input, more power is added to prevent
the frequency from falling.
Power demand from the grid fluctuates constantly—primarily twice a day, in
morning and afternoon peaks. This means that the rate of power input into the
grid must change accordingly. Operators across the western states are constantly
fine-tuning inputs into the grid, working to maintain the optimal 60 hertz. This
is called “load-following” and is adjusted approximately every ten seconds.
Hydroelectric power plants are important tools for keeping the grid at a steady
state. Unlike coal-fired plants (which take a considerable amount of time to
come online), hydro plants can begin generating at full capacity within a very
short time. When they are not generating power, many hydropower facilities
maintain what are called “spinning reserves” where generators are kept in
motion by (drawing power from the grid rather than from flowing water, so that
the generators become motors), they are ready to be switched to back to hydrodriven
(generator) operation at a moment’s notice. This is particularly useful
when the power demand suddenly changes or a big power plant at another site
unexpectedly shuts down.
The Lewis River Project is capable of maintaining spinning reserves These
reserves are required by the Federal Energy Regulatory Commission (FERC)
to be able to respond to a demand for power within 15 minutes. This capability
comes in handy when a thermal plant trips offline; the spinning reserve can
quickly fill in the gap in power input.
Power Economics
Operating the
Three-Lake System
Electricity is a commodity, traded like other commodities, with prices
fluctuating according to supply and demand. In Portland and other major cities,
traders for utilities and power companies (overseen by FERC) meet in roundthe-clock
energy markets to buy and sell power for projects, municipalities,
and companies. These markets set both daily and spot-market prices per unit of
electricity. [Note: we may not want to discuss pricing in such specific terms on
the signs; this information is included for completeness].
If power generation were the only consideration, operators would run all the
water that enters the uppermost Lewis River reservoir through generators at all
three dams, maximizing the total power output of the river.
Sea Reach Ltd • 146 NE yamhill Street • Sheridan, OR draft 3 • November 2008 • page 74