Environmental Engineering Reference
In-Depth Information
Water flow, pumping
11 million gallons/minute (694 cubic meters/second)
Water flow, generating
14.5 million gallons/minute (915 cubic meters/second)
Turbine generators
Six Francis type 350 MW units manufactured by Allis Chalmers
Maximum pumping
power per unit
563,400 horsepower (420,127 kw)
PHESEfficiency
The process of pumping water up and releasing it back down to achieve the
return of energy is not 100% efficient. Some of the electric energy used to
pump the water up will not be returned as usable electric energy on the way
back down. This efficiency loss is incurred as a result of rolling resistance and
turbulence in the penstock and tail race and efficiency losses in the motor
generator and pump turbine. In addition, the water retains some energy as it
flows into the tail race. Considering all of these losses, PHES has a turnaround
efficiency ranging from 70 to 80%, dependent on design characteristics. For
example if a PHES facility were 80% efficient, that would mean for every ten
units of energy put into storage, eight can be returned on demand. Table 3.1
reflects PHES cycle efficiencies for plants constructed after the late 1970s.
2
FacilitiesinUnitedStates
Figure 3.2 is a map showing PHES facilities in the United States. Table 3.2
lists all PHES facilities (by state) as reported by the 2005 EPA EGRID.
EnergyandPowerPotential
PHES facilities require two fundamental resources: elevation change (head)
and water. By ascertaining the potential elevation change and water available,
it is possible to determine the power and energy availability of a PHES facility
with the basics of gravitational potential energy or the fluid power equation:
PE = mgH
(3.1)
where PE = potential energy in joules, m = mass [volume (m
3
) ∙ density 1000
kg/m
3
], g = acceleration due to gravity or 9.81 m/s
2
; and H = hydraulic head
height in meters (m).
