Electrochemistry and Corrosion: PV Battery System Design Report

This report presents a comprehensive design of a 5kW PV battery system, focusing on electrochemistry and corrosion principles. The design centers on a rechargeable battery, specifically exploring the technical aspects of a Red Flow's Zn-Br battery module. The report details the electrochemical reactions within the battery cells, including the oxidation and reduction processes, and the role of the electrolyte and external circuit. It provides a detailed methodology for determining the number of cells required, considering voltage and current requirements, and explains the arrangement of cells in series. The report also discusses the working mechanism of the battery, comparing it to a capacitor, and covers charging, discharging, and safety considerations. Furthermore, it provides a cost analysis and concludes with a summary of the key design elements and potential benefits of the PV battery system for household energy storage.

Running head: ELECTROCHEMISTRY AND CORROSION 0
ELECTROCHEMISTRY AND CORROSION
Name of Student
Institution Affiliation

ELECTROCHEMISTRY AND CORROSION 2
Executive summary
This PV battery system is the rechargeable battery which can be charged from solar
panels. Storage of electrical energy has been a major challenge since the invention of electrical
power, many attempts have been put in place to ensure that storage is realized. In this report, we
will design a battery system for a typical Queensland household having a power of 5kW
(Knibbe, 2012). In this report paper, technical review for the Red Flow’s Zn Br battery module
will be fully covered. In each cell of Zn Br battery of two electrolytes moving past carbon
plastics composite electrode in two different compartments disjointed by a microporous
polyolefin membrane.
During charging the Br and Zn combines into zinc bromide, which will generate about
1.8 volts per cell. This will upsurge the zinc ion Zn2+ and the bromide ion Br- density in both
electrolyte tank. While during the charge of this battery, metallic part (zinc) will be plated as a
thin film on one side of the carbon- plastic electrode composite. While the other part (bromine)
evolves as a dilute on the other side of the membrane. Bromine will react with other agent known
as the organic amine to create a thick oil of bromine which helps in sinking down of the amine to
the bottom of the electrolytic tank (Konarova, 2011). With this design of this battery which gives
a power of 5 kW from 1.8 Voltage in each cell at a current say x current. So the amount of
current generated will determine the number of cells of the battery.
From P= IV,
Where P= power generated, I= current, V= voltage
If the current generated is 2A, then the power generated per cell is given by
P= 2×1.8 = 3.6 Watts. Therefore for this the number of the cells required will be obtained as;

ELECTROCHEMISTRY AND CORROSION 3
3.6n= 50000
n= 5000
3.6 = 1388.88 cells, this gives around 1400 cells
A higher number of cells (slightly above the calculated one) is recommended since there are
losses between cells (Luo, 2013).
Introduction
The reaction in the battery cell is a reduction-oxidation (Redox) where there both
oxidation and reduction of chemical reaction occurs at the same time. The anode is electrode
where the oxidation occurs, Cathode is the electrode where the reduction occurs, an electrolyte is
a liquid where the current flows internally and finally, the external circuit which is basically
electrical conductor which permits the flow of electrical currents generating energy in a galvanic
cell (Butler, 2011). The Electrical power in the battery is generated from the two combined half-
cell equations of zinc and bromine. And the reaction at the anode is referred to as oxidation since
the zinc metal is taken into the electrolyte and form two zinc ions as shown below;
Zn (s) Zn2+ (aq) + 2e- ( aq)
While on the cathode side the reaction is referred to as reduction since the Bromine ion is
reduced from two anions to zero (bromine liquid) as seen below;
2Br- + 2e- 2Br (l)
The above two half-cell equation are combined make one general equation which then helps to
generate electrical energy and the storage of electric power (Mbadi, 2010). The combined
equation is shown below;

ELECTROCHEMISTRY AND CORROSION 4
Zn ( s) + 2 Br- (aq) Zn2+ (aq) + 2 Br (l)
For this design the cell reaction is separated by a membrane or a salt bridge represented by the ||,
the electrodes always appeared on the outer side while the reactions of the electrolyte are on the
inner side (Johnston, 2010). These two phases are separated with |. The species in the same state
is separated with a semicolon (;) and the concentrations are shown in (). A summarized Notation
is illustrated below
Zn| Zn2+ || 2 Br- |2 Br
In this type of battery, we can use any strong acid as the electrolyte, for example, Sulphuric acid
(H2SO4).
The following diagram clearly illustrates the configuration of this type of battery being
designed;
Fig1: Configuration of a PV battery (Knibbe, R. 2012)

ELECTROCHEMISTRY AND CORROSION 5
A battery is like a capacitor having two plates having negative and positive charges
(being at the cathode and anode) separated by a distance d as shown in figure two below (Dubey,
2014);
Fig 2: showing charges in a battery Konarova, M. 2011)
The concept of charging and discharging a capacitor will clearly explain how and that this
battery can be recharged. As in capacitors the following expressions are employed (Shaw, 2013);
V = Qd
Ɛ r A
K = Ɛr/Ɛ0
C = ( Ɛ0 A k )/ d
Q= CV = ( Ɛ0 Ak )/d
Where; Ɛr is relative permittivity of dielectric material Ɛ0 is relative permittivity of vacuum k is
a dielectric constant of a material ( dielectric ) and C is the capacitance given in Farads
( Coulomb/ volt).

ELECTROCHEMISTRY AND CORROSION 6
This battery also employs the concept of the capacitor to help store electric energy (Mubarak,
2010). As in the capacitor electrical energy (electric potential) which is simply work required to
move one unit charge (q)
V = E/q
Electrostatic potential energy = dE/Vdq
And the Capacitance in capacitor, C= Q/ V
Therefore the energy in a single cell E= ½ C (V cell) 2
During charging of this battery an external source of voltage will pull electrons from the
negative electrode of the battery (cathode) via an external circuit (conducting wires) to the
positive electrode ( anode) and this will make Li-ion flow from the negative terminal( cathode)
to the positive terminal ( anode ) (Deambi, 2011). This movement occurs within the liquid
electrolyte Sulphuric acid (H2SO4). While during the discharge of this battery, the process of
charging is reversed (Spagnuolo, 2013). The Li-ions travel from the anode and cathode via the
liquid electrolyte Sulphuric acid (H2SO4). And the electrons flow via the external circuit
(conducting wire) to the cathode from anode resulting in the generation of electrical power
(Sonnenenergie, 2012). This movement of electrons in a single can be illustrated using the
diagram below;

ELECTROCHEMISTRY AND CORROSION 7
Fig 3: Showing the movement of electrons Konarova, M. 2011)
The figure below shows a discharging battery (working battery);
Fig 4: Showing a battery during discharging Konarova, M. 2011)

ELECTROCHEMISTRY AND CORROSION 8
Design methodology
The basic unit of this battery are the cells, so the first design consideration should focus
on the cells of the battery. The electrochemical reaction that releases and stores energy occurs in
the cells which include the separator, bipolar electrodes, electrolyte storage and the aqueous. The
standard half-cell equations are shown below;
The arrangement of the cells in wet/rechargeable battery is shown in the figure below;

ELECTROCHEMISTRY AND CORROSION 9
Fig 5: Shows the arrangement of battery cells (Konarova, M. 2011)
In this design we have to we have to consider some basic factors of the battery like the battery
type, battery bank DC voltage, type of the charge controller, module type among other
specifications. For this design, we will use the battery type as a flooded type or wet cell. The
battery bank Dc voltage used will be 48 V voltage DC. 48 type is employed since it gives an
output power of more than 2kW (Snow, 2013).
The number of battery required for this design is obtained as follows; From the above Net
cell reaction of a given cell we can see that we produce 1.85 V between Zn and Br, therefore a
single battery of 26 cells is used to produce;
1.85*26 = 48.1 voltage for a single battery. These cells are connected in series to ensure that the
overall voltage is the sum of all the voltage produced by each cell. Each battery is assumed to
give about 14 A. This will give a power of 48.1× 14 = 673.4 the banks of the batteries are

ELECTROCHEMISTRY AND CORROSION
10
arranged in series so the total number of batteries needed to be connected in series is given below
(Solanki, 2014);
673.4n= 5000 watts
n= 5000/673.4
n= 7.425
This can be rounded off to 8 batteries put in series.
The number of the batteries = 8 (The number of batteries is surrounded off to the next number
since there are losses between a battery to another. The diagram below shows how the batteries
can be arranged in series;
Fig 6: Showing batteries arranged in series (Spagnuolo, G. 2013)
This battery with the selections of 26 cells per battery with each battery producing 48.1 Voltage
DC, will be installed in the household to serve the six individual of 4 adults and 2 children. For

ELECTROCHEMISTRY AND CORROSION
11
this 26 cell module design, maximum power point tracking controllers (MPPT) will be
employed. This is because these controllers have optimum energy harvest as well as wider input
range of voltage which is between 48 voltages to 60 voltage even though they are relatively
expensive. For this design, the amount of electricity consumed per day is of a great importance
(DeBlasio, 2012).
Working mechanism of this battery
The cathode and the anode are made from a collector of particles of powder that are bonded
together into a three-dimension electrode. During the discharging, the battery begins in the bulk
of anode particle, then undergoes diffusion of solid-state particles and at the surface, it dislodges
the electrons enters the electrolyte that occupies the pores of the electrode. The ion will then be
moved via the electrolyte (diffusion) to the cathode (Sayigh, 2012). As the ions enter the cathode
it will undergo solid state diffusion in the cathode. The electrons will have to go through the
collection of the solid-state particle to the collector at the metal current where it is extracted and
employed to power the device.
Zn/Br batteries usually discharge at a relatively low rate of 15-30mA /cm2. A discharge – charge
profile of 26 cell stack is illustrated in the diagram below. The amount of the charge is put on the
zinc loading which is well-defined at 100 %. The amount is always lower than the total Zn2+
dissolved in the electrolyte charge duration and efficiency of charging are obtained at the end of
the charge. This can be illustrated using the graph below;

ELECTROCHEMISTRY AND CORROSION
12
Fig 7: showing the charging and discharging of Zn/Br battery (Konarova, M. 2011)
The above design will work best for this small household of size individual with 4 adult and 2
children, but when more electrical power is required then I would recommend the addition of
cells in the battery or designing producing more batteries which are connected in series to the
already 7 connected ones. This will ensure that the amount of power produced will highly
increase. And since these batteries are charged using PV the solar which charges them should be
exposed to the sunlight to attain the optimum design specifications of 5000 watts.
For the safety considerations of this battery is that at high temperature, some battery components
and cells will break down and this will result in an exothermic reaction which in turn may cause
accidents. To avoid this accident from occurring I would recommend that if this battery is used
in a hot environment then the battery must be put under the shade a place which is cool and dry
all the times. The cost of all components required for the design of this PV battery system is
relatively cheaper as compared to paying the bill monthly. Averagely the household can use