Pumped Storage for Home Energy Storage: Design and Assessment

Mechanical Engineering 1
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Mechanical Engineering 2
Pumped storage is technology which can be employed in the storage of energy in form of
water stored in the reservoir, even though this type is also not commonly employed in the home
energy storage but is used as well. Pumped hydropower makes the good use of the altitude in
the storage of energy (Petlyuk, 2012). Since this research paper was based on home energy
storage, hence the pumped hydropower technology is employed in the small streams which
stores energy to be used in the local homes which are around the stream and the power
generated is off-grid (not connected to the grid) hence it is exclusively for domestic use (Bajpai,
2016). This pumped storage is used in the places where the amount of water present is not
adequate for the full generation of electrical energy. The water moves from the reservoir to the
powerhouse through the penstock at a very high pressure. Therefore for the design of the
penstock, tensile strength must be considered to ensure that the pipe does not collapse while
water is traveling at a higher speed. The below is a prototype of how the penstock is connected
to the pumped energy storage system.
Fig 1: Showing how the penstock is connected to the pumped energy storage system.
(Webinars, 2012).

Mechanical Engineering 3
Pumped storage is employed since it is employed in the storage of water during the rainy
seasons and then used the stored water during the dry season when there is no sufficient water
for the supply of the required electric power.
THE DESIGN
For the design of the penstock the following specifications are given, this design is done to
ensure a tensile strength for a period of 50 years.
Crack length (mm) Pipe diameter (m) Static head (m) Water hammer (m)
4 2.4 534 704
For this design of the penstock, there is two case study which one of them was used in the
design (Papers, 2011). The case study (a) was selected for the design. Option (a) has the
following parameters.
Steel A (a medium strength, low-alloy, quenched and tempered steel QT 445). And the chemical
composition and specification of the steel A is given in the table below,
Composition Steel A
C 0.15-0.21
Si <0.90
S <0.04
P <0.04
Mn 0.80-1.10
Cr 0.50-0.80
Mo 0.25—0.60
Ni -
Zr 0.05-0.15
Cu -

Mechanical Engineering 4
B 0.0005-0.0000
Nb -
Yield strength 700
Ultimate tensile strength 800
Fracture toughness 100
Elongation ( in %) 18
Price of the rolled plate ( in £ per 1000 kg) 965
Density (in Kg/m3) 9750
Overload assessment:
The wall thickness of the penstock can be determined by using the design specification of the
internal diameter of 2.4 meters. So if the thickness is taken 0.25m. Then the external diameter
will be 2.9m.
Presume new pipe to be steel penstock, 704 m long, the design flow is taken as 25 m3/s and a
gross head of 534 m.
Calculate and diameter and wall thickness.
Select diameter as, D =2.4 m
Flow velocity V = 4 Q
π D2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1