pumped hydro energy storage system

1. Energy storage systems
Pumped Hydro Energy Storage System
Dr. Mohamed Hassanain

2. Pumped-Hydro Energy Storage
 Potential energy
storage in
elevated mass is
the basis for
pumped-hydro
energy storage
(PHES)
Energy used to
pump water from
a lower reservoir to

an upper reservoir
Electrical energy input
mechanical energy
Pumps transfer energy
potential energy
to motors converted to rotational

to the water as kinetic, then


3. Pumped-Hydro Energy Storage
 Energy stored in
the water of the
upper reservoir is
released as water
flows to the lower
reservoir
Potential energy
converted to
kinetic energy
Kinetic energy of falling

water turns a turbine

Turbine turns a generator
Generator converts mechanical energy to electrical

energy


4. Pumped-Hydro Energy Storage
• Typically, pumping would take place
by buying electricity during times
when prices are low, which is when
demand is low or the availability of
electricity from other sources is high
(e.g. a windy and sunny day).
• Generation would take place during
times of high demand (such as
during evenings) when prices are
high. This pattern of buy-low and
sell-high is called arbitrage.
• The power companies make a lot of
money by selling the generated power
during peak hours at higher rates.

5. • Typically, pumping would take place by buying
electricity during times when prices are low,
which is when demand is low or the availability of
electricity from other sources is high (e.g. a windy
and sunny day).
• Generation would take place during times of high
demand (such as during evenings) when prices
are high. This pattern of buy-low and sell-high is
called arbitrage.
• The power companies make a lot of money by selling
the generated power during peak hours at higher
rates.
Pumped Storage Hydro Power Plants

6. HISTORICAL DEVELOPMENT
The history of pumped storage plant can be traced as far back
1st
as 1882, in which year the hydroelectric plant making use of
pumped storage started functioning at Zurich in Switzerland.
1st
In 1931, the reversible pump-turbine was installed at
Baldeneyesee in Germany.
1st
The major reversible diagonal turbine (Deriaz) was
installed at Niagara in 1955.
In Europe, in 1962, Ffestiniog (Great Britain) with a total
capacity of 360 MW and Provindenza (Italy) with a head of
284 m, were the major landmarks in the progress of pumped
storage plants.

7. Conventional river-based PHES (open-loop)
• Many existing PHES systems have been
developed in conjunction with a
conventional river-based hydroelectric
system.
• Two reservoirs are created, at different
altitudes, but close to each other.
• Often, the lower reservoir is large and
located on a substantial river, while the
upper reservoir is smaller, and located
higher up on the same river or in a
high tributary or parallel valley.
• Most river water passes through the
system, generating electricity, and
then flows on down the river. Some
water is cycled between the two
reservoirs to create energy storage.

8. • There are alternative methods of constructing
PHES that do not require significant
modification to river systems. One method is to
connect closely spaced existing reservoirs using
underground tunnels and powerhouses. With
care, there is low disturbance at the surface
• An off-river PHES system comprises a pair of
artificial reservoirs spaced several kilometers
apart, located at different altitudes, and
connected with a combination of aqueducts,
pipes and tunnels.
• The reservoirs can be specially constructed
('greenfield') or can utilize old mining sites or
existing reservoirs ('brownfield’).
• Off-river PHES utilizes conventional
hydroelectric technology for construction of
reservoirs, tunnels, pipes, powerhouse,
electromechanical equipment, control systems,
switchyard and transmission, but in a novel
configuration.
Off-river (closed-loop) pumped hydro systems

9. • An off-river PHES system has the advantage that flood
mitigation costs are minimal compared with a river-based
PHES system.
• Heads are generally better than river-based systems
because the upper reservoir can be on a high hill rather
than higher in the same valley as the lower reservoir.
• Environmental costs of damming rivers are avoided with
off-river PHES, which helps with social acceptance.
• The much greater number of off-river sites compared with
on-river sites allows much wider site choice from
environmental, social, geological, hydrological, logistical
and other points of view.
• Another advantage is that construction of off-river
pumped hydro can be much faster than other storage
methods
• Work can proceed in parallel on the two reservoirs, the
water conveyance, the powerhouse and the transmission
Off-river PHES vs river-based PHES

10. • The first requirement is to find places where reservoirs can be constructed that store a large amount of water
compared with amount of rock and other material used to construct the reservoir walls.
• The second requirement is to find closely spaced pairs of sites that have large differences in altitude ('head').
The former requirement is because pipes and tunnels connecting the two reservoirs are expensive, and the
latter requirement is because doubling the head doubles the storage energy volume and storage power
capacity but does not double the system cost.
Off-river PHES location requirement

11. Components of a PHES Plant
Lower
reservoir

12. PHES Components – Reservoirs

 Upper and lower
reservoirs separated by
an elevation difference
 Two configurations:
Open-loop:
 At least one of the
reservoirs connected to a
source of natural inflow
 Natural lake, river, river-fed reservoir, the sea
Closed-loop:
 Neither reservoir has a natural source of inflow
 Initial filling and compensation of leakage and evaporation
provided by ground water wells
 Less common than open-loop



13. PHES Components – Penstock
 Penstock
Conduit for water flowing
between reservoirs and to
the pump/generator
Above-ground pipes or
below ground shafts/tunnels
 5 -10 m diameter is common
 One plant may have several penstocks
 Typically steel- or concrete-lined, though may be unlined
Flow velocity range of 1 – 5 m/s is common
Tradeoff between cost and efficiency for a given flow rate,
 Larger cross-sectional area:
 Slower flow
 Lower loss
 Higher cost



 𝑄
𝑄

14. PHES Components
 Tailrace tunnel
 Typically, larger diameter
than penstocks
 Lower pressure
 Lower flow rate
 Downward slope from lower
reservoir to pump/turbine
 Inlet head helps prevent
cavitation in pumping mode
 Surge tanks
 Accumulator tanks to absorb high pressure transients during
startup and mode changeover
 May be located on penstock or tailrace
 Especially important for longer tunnels
 Hydraulic bypass capacitors

15. PHES Components – Power House
 Power house
Contains pump/turbines
and motor/generators
Often underground
Typically below the level
of the lower reservoir to
provide required pump
inlet head
Three possible configurations
 Binary set: one pump/turbine and one motor/generator
 Ternary set: one pump, one turbine, and one motor/generator
 Quaternary set: separate pump, turbine, motor, and generator





16. Power Plant Configurations – Quaternary Set
 Quaternary set
Pump driven by a motor
Generator driven by a turbine
Pump and turbine are
completely decoupled
Possibly separate
penstocks/tailrace tunnels
Most common configuration
prior to 1920
High equipment/infrastructure
costs
High efficiency
 Pump and turbine designed to
optimize individual performance








17. Power Plant Configurations – Ternary Set
 Ternary set
Pump, turbine, and
motor/generator all on a single
shaft
 Pump and turbine rotate in the
same direction
Turbine rigidly coupled to the
motor/generator
Pump coupled to shaft with a
clutch
Popular design 1920 – 1960s
Nowadays, used when head exceeds
stage pump/turbine




the usable range of a single-

 High-head turbines (e.g., Pelton) can be used
Pump and turbine designs can be individually optimized


18. Power Plant Configurations – Ternary Set
 Ternary set
Generating mode:
 Turbine spins generator
 Pump decoupled from the shaft
and isolated with valves
Pumping mode:
 Motor turns the pump
 Turbine spins in air, isolated with
valves
Both turbine and pump can
operate simultaneously
Turbine can be used for pump startup
 Both spin in the same direction
 Turbine brings pump up to speed and synchronized with grid, then
shuts down
 Changeover time reduced





19. Power Plant Configurations – Binary Set
 Binary set
Single reversible
pump/turbine coupled to a
single motor/generator
Most popular configuration
for modern PHES
Lowest cost configuration
 Less equipment
 Simplified hydraulic pathways
 Fewer valves, gates, controls, etc.
Lower efficiency than for ternary or



quaternary sets

 Pump/turbine runner design is a compromise between pump and
turbine performance

20. Power Plant Configurations – Binary Set
 Binary set
Rotation is in opposite
directions for pumping and
generating
Shaft and motor/generator
must change directions
when changing modes
 Slower changeover than for
Pump startup:


ternary or quaternary units

 Pump/turbine runner dewatered and spinning in air
 Motor brings pump up to speed and in synchronism with
grid before pumping of water begins
the

21. Turbines
 Hydro turbine design selection based on
 Head
 Flow rate
 PHES plants are typically sited to have large
 Energy density is proportional to head
 Typically 100s of meters
 Reversible Francis pump/turbine
 Most common turbine for PHES applications
head
 Single-stage pump/turbines operate with heads up to
 For higher head:
 Multi-stage pump/turbines
 Ternary units with Pelton turbines
700 m

22. Turbine Selection
Source: rivers.bee.oregonstate.edu/turbine-sizing

23. Francis Turbine – Components
 Volute casing (scroll casing)
Spiral casing that feeds
water from the penstock
to the turbine runner
Cross-sectional area
decreases along the
length of the casing
 Constant flow rate
maintained along the
length

Francis turbine casing – Grand Coulee:


24. Francis Turbine – Components
 Guide vanes and stay vanes
Direct water flow from the casing into the runner
Stay vanes are fixed
Guide vanes, or wicket gates, are adjustable



Open and close to control flow rate
Power output modulated by controlling flow rate
Set fully open for pumping mode



Source: Stahlkocher Source: Stahlkocher

25. Francis Turbine – Components
 Turbine runner
 Reaction turbine
 Pressure energy is extracted from
the flow
 Pressure drops as flow passes
through the runner
 Flow enters radially
 Flow exits axially
 Typically oriented with a
vertical shaft
 Draft tube
 Diffuser that guides exiting
to the tailrace
flow
Source: Voith Siemens Hydro Power

26. High-Head PHES
Two-stage pump/turbine:
 Options for heads in
excess of 700 m:
Two-stage Francis
pump/turbines
 Typically no wicket gates
two-stage configuration

in
 No mechanism for varying
generating power
Ternary unit with Pelton
turbine

Source: Alstom

27. Pelton Turbines
 Pelton Turbine
Suitable for heads up to 1000 m
Impulse turbine
 Nozzles convert pressure energy to kinetic
energy
 High-velocity jets impinge on the runner at
atmospheric pressure
 Kinetic energy
transferred to the
runner
 Water exits the turbine
at low velocity
Cannot be used for
pumping
 Used as part of a
ternary set


Source: BFL Hydro Power

Source: Alstom

28. PHES Losses
 Typical losses for PHES:

29. ADVANTAGES

30. Relatively low capital cost; thus economic source of
peaking capacity.
Rugged & dependable; can pick up load rapidly in a matter
of few minutes.
Readily adaptable to automation as well as remote-control.
Hydel power is free from effects of environmental
pollution—thus contributing a part in curbing air & water
pollution.
ADVANTAGES

31. Allow great deal of flexibility in operational schedules of
system.
Power required for pumping is available at a cheaper rate(slack
hours’ rate); power produced can be sold at prime rate(peak
hours’ rate) - this compensates the low hydraulic efficiency.
They allow entire thermal or nuclear power generation to take
up base load; thus load factor improves giving overall greater
system efficiency.
Little effect on the landscape.
ADVANTAGES

32. Disadvantages of PHES
 Disadvantages of PHES
 Environmental issues
 Water usage
 River/habitat disruption
 Head variation
 Pressure drops as upper reservoir drains
 Efficiency may vary throughout charge/discharge cycle
 Particularly an issue for lower-head plants with steep, narrow upper
reservoirs
 Siting options are limited
 Available water
 Favorable topography
 Large land area
 Possible alternative potential
 Rail energy storage
energy storage:

33. OBLEMS OF
PR OPERATION
Once it's used, it can't be used again until the water is
pumped back up.
Cavitation problems; powerhouse location has to be so fixed
that pump operates under submerged conditions(magnitude
depends on specific speed & net head).
Reversing of direction of flow gives rise to runner cracking
due to fatigue.
Trash racks vibrate violently during pumping operation.
Flow during pumping mode tends to lift the machine axially
causing tensile stresses in bearings; specially guide vanes.

34. • Density=mass/volume
• W=m x g
• Density of water =1000Kg/m3
• hydraulic efficiency x electrical efficiency= overall efficiency
General Formulas

35. • The power that can be extracted from a waterfall depends upon its height
and rate of flow.
• The available hydro power can be calculated by the following equation:
• P= ρ*Q*g*h
• P=available water power[W]
• Q=water rate of flow [m3/s]
• h= head of water [m]
• Ρ = water density [ kg/ m3]
• g = 9.81 [m/s2]
Available Hydro Power

36. The energy used to pump a water volume (V) to a height (h)
with a specific pumping efficiency (ηp) is given by:
Epumping =
 · g · h · V
ηp
Overall efficiency of the energy storage system
= Egenerator / Epumping
The energy supplied to the electrical network by a generator
of efficiency (ηg) can be obtained by:
Egenerator =  · g · h · V · ηg
Ppumping =
 · g · h · Q
ηp
Pgenerator =  · g · h · Q · ηg
Pumped Hydro Energy

37. • A large hydropower station has a head of 324m and an average flow
of 1370m3/s. The reservoir of water covers an area of 6400Km2.
Calculate
• the available hydraulic power
• the number of days this power could be sustained if the level of the
impounded water were allowed to drop by 1m.
Example 1

38. • The available hydropower can be found using the equation
• P= ρ*Q*g*h
• P=1000*9.8 x 1370 x 324=4350MW
• (b) we have to find the number of days ?
• Using the 1 m drop we find the corresponding volume of water
• Volume = area x height =6400x106m2 x 1m=6400x106m3
Solution

39. • Rate of flow= 1370m3/s
• By looking at the units of rate of flow we can deduce that time in
seconds would be volume divide by rate of flow
• Q=V/t  t=V/Q
• t=6400x106/1370 = 4.67x106 s = 1298h =54 days
Solution

40. 40
Assignment :

41. 41

42. • Then the power cost of the pump, the revenue generated by the turbine, and the
net income (revenue minus cost) per year become
42
Solution

43. • Discussion It appears that this pump-turbine system has a potential annual
income of about $70,000. A decision on such a system will depend on the
initial cost of the system, its life, the operating and maintenance costs, the
interest rate, and the length of the contract period, among other things.
43
Solution