Solar Energy Storage:- Methods of storage such as sensible, latent heat & thermochemical storage,selection of method of storage, properties of storage materials and different arrangements of storages

1. SOLAR ENERGY STORAGE
By
Prof. Ashish Bandewar

2. Unit 3 Solar Energy Storage system:-
1. Thermal energy storage
a. Sensible heat – i)Water Storage ii) Packed bed storage
b. Latent heat.
2. Electrical storage
a. Capacitor b. Inductor c. Battery
3. Chemical Storage
a. Chemical b. Thermochemical
4. Mechanical
a. Pumped hydro-electric b. Compressed air c. Flywheel
5. Electromagnetic Storage

3. Sensible heat storage:
Where the addition or removal of heat results in a
change in temperature.
Latent heat storage: (phase change energy storage)
Energy absorbed or released during a change in
phase, without a change in temperature (isothermal).

4. Sensible Storage - Water Storage
• Water is the ideal material which store useable heat.
• It is low in cost and has a high specific heat.
• Convenient when water is used also as the mass and heat
transfer medium in the solar collector and in the load heat
exchanger.

5. Sensible storage - Packed Bed Storage
• It is a large insulated container filled with loosely packed
rocks.
• Circulation of air through the void of the packed is done
• Which results in natural or forced convection between the
air and the rocks.

6. Few points for Bed Storage :-
• Rock is more easily contained than water
• Rock acts as its own heat exchanger
• For storage more than 1000C it can be used, as
water cannot be used.
• Heat transfer coefficient between air and solid is
high
• Low cost storage
• Conductivity of bed is depend on air flow/air
velocity
• Can be used in solar houses or hot air collector
system.

7. Latent heat Storage
• Heat is stored in material when it melts and
extracted from the material when it freezes.
• Material that undergo phase change in suitable
temp range is useful in energy storage if following
criteria satisfied for phase change :-
• Must be accompanied by high latent heat effect
• Must be reversible without degradation
• Must occur with limited super cooling
• Material must be available in large quantities
• Material must be harmless (non toxic, non
inflammable)
• Must have high thermal conductivity in both phase

8. Electric Storage
• Capacitors could store large amount of electrical
energy, Energy stored is , Hcap = ½ x VεE2
• V is Volume of dielectric
• ε is constant
• E is Electric field strength
• Electric energy storable in dielectric (material-mica)
is limited
• Capacitive storage is economical for times no
longer than 12 hours
• Capacitors store electrical energy at high voltage
and low current.

9. • Inductor storage is at low voltage and high current
• Hind= ½ VµHm
2
• µ is permeability of material
• Hm is magnetic flux density
• For Hind to be large both µ and Hm should be large
• High magnetic fields are required
• Reverse operation in case of inductor can discharge
stored energy

10. • Battery is combination of individual cells
• Cell is the combination of material and electrolyte
where energy is stored electrochemically
• This energy is regained as electrical energy
• Secondary batteries are important for solar
application (Re-Chargeable batteries)
• Exa – lead-acid , nickel-cadmium, iron-air, nickel-
hydrogen, sodium-suplhur etc
• Anode and cathode immersed in electrolyte

11. • Chemical storage in the form of fuel
• To store in battery by photochemical reaction
brought about by solar radiation
• This battery is charged photochemically and
discharged electrically whenever needed
• Thermochemical energy storage are suitable for
medium or high temp applications
• For storage, reversible reactions appear to be
attractive A+B AB
• Forward reaction takes place with absorption of
heat from solar energy ( Heat is stored )
• Reverse reaction caused to liberate heat.

12. Mechanical energy storage
1. Pumped hydroelectric storage
• In hydroelectric power plants, once the water has
been run downhill to turn the turbines it flows out to
sea; pumped hydro lets us pump that water back up
hill, to re-use for power generation again and again.

13. 2. Compressed air energy storage
• A compressor/wind turbine is used to store
compressed air in pressurized storage tank.
• Later this compressed air is used to drive turbine
which will generate electricity when there is demand

14. 3. Flywheel storage
• Flywheel is driven by electric motor during off peak
hours stores mechanical energy
• The rotation of flywheel can be used to operate a
generator to produce electricity when required

15. Electromagnetic energy storage/ Superconducting
magnetic energy storage (SMES)
• SMES material suddenly loose all resistance to the
flow of electricity when cooled below very low
temp
• If maintained below this can carry strong electric
currents
• Superconducting materials like niobium titanium
alloy at temp – 263oC
• Electromagnetic field produced by an electric
current flowing through wire coil can store energy.