1. Photovoltaic Systems Engineering
SEC598F18
Photovoltaic Systems Engineering
Session 08
Storage for PV Systems
Batteries – Part 1
September 17, 2018

2. Session 08 content PV System Storage Options New Approaches Batteries
Possibilities
Operation, reliability
Batteries
Construction, types
Operation, reliability, failure mechanisms

3. Learning Outcomes Introduction to storage science and technology
Recognition of value of storage in PV system design and operation

4. PV Systems – Storage Technologies
Electromechanical Approaches
Pumped water storage
Flywheel
Other potential energy systems
Chemical Approaches
Hydrogen generation (Solar electrolysis)
Electrical Approaches
Capacitors
Inductors

5. PV Systems – Storage Technologies
Electromechanical Approaches
Pumped water storage

6. PV Systems – Storage Technologies
Electromechanical Approaches
Flywheel

7. PV Systems – Storage Technologies
Electromechanical Approaches
Other potential energy systems

8. PV Systems – Storage Technologies
Electromechanical Approaches
Other potential energy systems

9. PV Systems – Storage Technologies
Chemical Approaches
Hydrogen generation: en.wikipedia.org/wiki/Polymer_electrolyte_membrane_electrolysis

10. PV Systems – Storage Technologies
Electrical Approaches
Capacitors

11. PV Systems – Storage Technologies

12. PV Systems - Batteries
The battery remains the most common technological approach for storing energy in PV and other electrical systems. It is by no means an ideal solution, but in the absence of a true electricity storage technology, it is a viable solution
A battery is a transducer – it converts electrical energy to chemical energy, or chemical energy into electrical energy
The driving force in the battery is the chemistry of reduction-oxidation (redox) reactions

13. PV Systems - Batteries
The battery is an electrochemical cell that consists of two half-cells, each of which has an electrode and an electrolyte. The electrodes in each half-cell are different materials
C.S.Solanki, Solar Photovoltaic Technology and Systems

14. PV Systems - Batteries
The operation of the cell involves two chemical reactions:
Oxidation: Reductant  Oxidized product + e (Loss of electrons)
Reduction: Oxidant + e-  Reduced product (Gain of electrons)
The two together are called a redox reaction

15. PV Systems - Batteries While charging: While discharging:
Oxidation takes place at the negative terminal (cathode) and reduction takes place at the positive terminal (anode)
While discharging:
Oxidation takes place at the positive terminal (anode) and reduction takes place at the negative terminal (cathode)
oxidation
reduction
C.S.Solanki, Solar Photovoltaic Technology and Systems

16. PV Systems - Batteries Types of batteries
Non-rechargable, or primary, batteries
Zinc-Chloride (common AAA, AA, C, D)
Rechargable, or secondary, batteries
Lead-Acid
Nickel Cadmium (NiCd)
Nickel Metal Hydride (NiMH)
Lithium Ion
Lithium Ion Polymer

17. PV Systems - Batteries Parameters of batteries
Battery terminal voltage (V)
Charge storage capacity (Ah)
State of charge (%)
Depth of discharge (%)
Number of charge-discharge cycles
Life cycle
Self discharge

18. PV Systems - Batteries Lead-Acid Battery
The battery that has seen the widest application in PV systems is the tried-and-true lead-acid embodiment
It consists of two (lead-based) electrodes separated physically, but chemically connected by means of a liquid electrolyte (dilute sulfuric acid) that allows conduction of ions and chemical reactions at the electrodes

19. PV Systems - Batteries A discharged battery Voc = 0 V H2O anode
PbSO4
PbSO4
Voc = 0 V
H2O
anode
cathode

20. PV Systems - Batteries The charging process
At the cathode (oxidation, loss of electrons)
PbSO4 + 5H PbO2 + 3H3O+ + HSO4- + 2e-
At the anode (reduction, gain of electrons)
PbSO4 + H3O+ + 2e Pb + H2O + HSO4-
Charging requires the injection of electrical energy into the battery

21. PV Systems - Batteries A charged battery Voc = 2.0 V anode cathode
PbO2 Pb
Voc = 2.0 V
weak
H2SO4
anode
cathode

22. PV Systems - Batteries The discharging process
At the anode (oxidation, loss of electrons)
PbSO4 + 5H PbO2 + 3H3O+ + HSO4- + 2e-
At the cathode (reduction, gain of electrons)
PbSO4 + H3O+ + 2e Pb + H2O + HSO4-
Discharging is spontaneous

23. PV Systems - Batteries A discharged battery Voc = 0 V H2O anode
PbSO4
PbSO4
Voc = 0 V
H2O
anode
cathode

24. Step 3: Battery Selection
PV Systems - Batteries
Step 3: Battery Selection
In summary

25. PV Systems - Batteries Lead-Acid Battery
Since the electrolyte itself takes part in the charge and discharge reactions, the charge level can be determined by measuring the specific gravity of the electrolyte
Charge and
discharge at
constant rate

26. References for Batteries
R.Messenger and A.Abtahi, Photovoltaic Systems Engineering, 4th Ed., CRC Press, Boca Raton, 2017
J.Jung, L.Zhang, J.Zhang, Lead-Acid Battery Technologies, CRC Press, Boca Raton, 2016
X.Yuan, H.Liu, J.Zhang, Lithium-Ion Batteries, CRC Press, Boca Raton, 2012
C.S.Solanki, Solar Photovoltaic Technology and Systems, PHI Publishing, Bombay, India, 2015