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Photovoltaic Systems Engineering

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Presentation on theme: "Photovoltaic Systems Engineering"— Presentation transcript:

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


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