Solar energy storage

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:- Thermal energy storage Sensible heat – i)Water Storage ii) Packed bed storage Latent heat. Electrical storage Capacitor b. Inductor c. Battery Chemical Storage Chemical b. Thermochemical Mechanical Pumped hydro-electric b. Compressed air c. Flywheel Electromagnetic Storage

3. Sensible heat storage: W here 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. I t is low in cost and has a high specific heat. C onvenient 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 100 C 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 , H cap = ½ x V ε E 2 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 H ind = ½ VµH m 2 µ is permeability of material H m is magnetic flux density For H ind to be large both µ and H m 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 – 263 o C Electromagnetic field produced by an electric current flowing through wire coil can store energy.