1. Photovoltaic Systems Engineering
SEC598F18
Photovoltaic Systems Engineering
Session 09
Storage for PV Systems
Batteries – Part 2
September 19, 2018

2. Session 09 content PV System Storage Components Batteries
Construction, types
Operation, reliability, failure mechanisms

3. PV Systems - Batteries

4. PV Systems - Batteries

5. PV Systems - Batteries
Heat Spring, S+S short course

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

7. 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

8. PV Systems - Batteries The overall redox process: +
PbSO4 + 5H20 = PbO2 + 3H3O+ + HSO4- + 2e- +
PbSO4 + H3O+ + 2e- = Pb + H2O + HSO4- or
2PbSO4 + 5H20 + H3O+ + 2e- =
PbO2 + 3H3O+ + HSO4- + 2e- + Pb + H2O + HSO4-
2PbSO4 + 2H20 = Pb + PbO2 + 2H2SO4

9. PV Systems - Batteries Lead-Acid Battery
During the charging process, especially with excess “overvoltage”, or after the charging is complete, electrolysis of the H2O can take place producing H2 gas!
Lead-acid batteries eventually lose the ability to “hold” a charge, generally due to sulfation, the crystallization of PbSO4. At the start of the battery life, the lead sulfate is an amorphous film, easily dissolved, reverting to lead and lead oxide. But crystalline PbSO4 is stable, doesn’t dissolve during recharging. It reduces available Pb and can crack the electrodes. Sulfation can be minimized with careful attention to both the charging and discharging procedures.

10. PV Systems - Batteries Lead-Acid Battery
Lead acid batteries are less prone to electrolysis and sulfation if the charging protocol does not employ a constant rate. The optimized charging profile looks like this:
This current profile
is produced by a
“charge controller”

11. PV Systems - Batteries Lead Acid Battery
Lead acid batteries had to be redesigned for PV system applications. They have been used in the automotive world for decades, and were designed with thin lead plates with high surface area – to produce high surge currents for the starter motor. The high currents actually help reduce sulfation, but the thin plates disintegrate with repeated deep charge and recharge cycles.
Lead-acid batteries used in PV systems will generally go through deep cycles, so much thicker lead plates are employed. This reduces the peak currents but also enhances the durability.

12. PV Systems - Batteries
Lead Acid Battery

13. PV Systems - Batteries Types of lead-acid batteries Flooded Gel
Absorption Glass Mat (AGM)

14. PV Systems - Batteries Lead Acid AGM Battery
C.S.Solanki, Solar Photovoltaic Technology and Systems

15. PV Systems - Batteries Other batteries for PV system applications
Nickel Cadmium (NiCd)
Nickel Metal Hydride (NiMH)
Lithium Ion
Lithium Ion Polymer
Flow Batteries

16. PV Systems - Batteries Li-Ion Battery Operation
Li-ion batteries store electrical energy in electrodes made of lithium-intercalation (or insertion) compounds
On charging, Li+ ions are deintercalated from the layered LiCoO2 cathode, transferred across the electrolyte, and intercalated among the graphite layers in the anode.
On discharging, these processes are reversed, with electrons flowing through the external circuit

17. PV Systems - Batteries Li-Ion Battery
X.Yuan et al., Lithium-Ion Batteries

18. PV Systems - Batteries

19. PV Systems - Batteries
Li-Ion Battery

20. PV Systems - Batteries Li-Ion Battery Components Discharge reactions
LiCoO2 or LiFePO4 or LiMnBO3 (cathode)
Graphite or TiO2 or Bi (anode)
Liquid containing a Li salt (LiPF6) (electrolyte)
Polymeric membrane or fabric mat (separator)
Discharge reactions
Anode (oxidation): LixC6  xLi+ + xe- + C6
Cathode (reduction): Li1-xCoO2 + xLi+ + xe-  LiCoO2
Redox: LiC6 + CoO2 = C6 + LiCoO2

21. PV Systems - Batteries

22. PV Systems - Batteries Flow Battery
Rechargeability is provided by two chemical components dissolved in Liquids contained within the system and most commonly separated by a membrane.
One of the biggest advantages is the ability to be almost instantly recharged by replacing the electrolyte liquid, while simultaneously recovering the spent material for re-energization (like refilling a fuel tank)

23. PV Systems - Batteries

24. PV Systems - Batteries C-Rate
If a load is connected to a fully charged battery which causes the battery to discharge in N hours, the discharge rate is defined as:
C/N
The charging rate is defined in the same fashion
High discharge rates result in less charge being available for a load
High charge rates, a small fraction is used for charging and a larger fraction is dissipated as heat in the battery

25. PV Systems - Batteries
C-Rate
M&A, Ch3

26. PV Systems - Batteries
C-Rate
M&A, Ch3

27. PV Systems - Batteries
C-Rate

28. PV Systems - Batteries Performance (Degree of Discharge)
C.S.Solanki, Solar Photovoltaic Technology and Systems

29. PV Systems - Batteries

30. 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