Photovoltaic Systems Engineering SEC598F17 Photovoltaic Systems Engineering Session 10 Storage for PV Systems Batteries – Part 1 September 21, 2017

Session 10 content PV System Storage Options New Approaches Batteries Possibilities Operation, reliability Batteries Construction, types Operation, reliability, failure mechanisms

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

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

PV Systems – Storage Technologies Electromechanical Approaches Pumped water storage

PV Systems – Storage Technologies Electromechanical Approaches Flywheel

PV Systems – Storage Technologies Electromechanical Approaches Other potential energy systems www.aresnorthamerica.com

PV Systems – Storage Technologies Electromechanical Approaches Other potential energy systems www.aresnorthamerica.com

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

PV Systems – Storage Technologies Electrical Approaches Capacitors

PV Systems – Storage Technologies

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

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

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

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

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

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

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

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

PV Systems - Batteries The charging process At the cathode (oxidation, loss of electrons) PbSO4 + 5H20 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

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

PV Systems - Batteries The discharging process At the anode (oxidation, loss of electrons) PbSO4 + 5H20 PbO2 + 3H3O+ + HSO4- + 2e- At the cathode (reduction, gain of electrons) PbSO4 + H3O+ + 2e- Pb + H2O + HSO4- Discharging is spontaneous

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

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

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

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