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Page 25-30 © MAT Journals 2021. All Rights Reserved
e-ISSN: 2456-9860
Volume-6, Issue-3 (September-December, 2021)
Journal of
Instrumentation and Innovation Sciences
www.matjournals.com
Solar Energy Batteries-A Critical Review
Samhar Saeed Shukir
Electrical Department, Technical Institute- Kut, Middle Technical University, Baghdad, Iraq
Corresponding Author: samharalwandi@gmail.com
ABSTRACT
Solar power has numerous benefits, it is a
clean and renewable energy resource that can
help us to reduce carbon emissions from fossil
fuel use and mitigate climate change.
However, solar energy production is limited
to daytime hours when sunlight is abundant,
and for solving the intermittency problem
batteries bank has been used, where it store
electricity for later use, so you can keep
appliances running during a power outage,
and use more of the solar energy that you
produce at your home. Solar batteries are a
deep cycle batteries, as the current flows from
the battery in small quantities and evenly.
This article represents; difference between
automotive batteries and a solar batteries, a
brief explanation of the different types of
solar batteries and a comparison between
them in terms of price, depth of discharge ,
service life, charge and discharge
temperature, and energy density. The article
also introduces an electrical representation of
the battery, criteria that are taken into
account when choosing the appropriate
battery such as battery capacity, battery
efficiency, depth of discharge of the battery,
the time required for charging the batteries,
and connect batteries in series and in parallel,
where it is necessary to know this information
to choose the appropriate battery for
designing the solar systems.
Keywords: Flooded batteries, Gel batteries,
AGM batteries, Lithium batteries, Electrical
models of batteries, Battery energy, Series and
parallel connection of batteries
INTRODUCTION
Automotive batteries also known as
starting, lighting, and ignition (SLI) batteries
have a very low internal resistance (50 milliohm)
to produce a burst of energy. Low internal
resistance is achieved by adding extra plates and
the lead is applied in a sponge-like form that has
the appearance of fine foam for maximum
surface area (Figure 1). The plates are thin
(1mm), which make the discharge is short
Figure 1: Starting battery
The deep-cycle batteries have an internal
resistance that is ten times that of the automotive
batteries which is achieved by making the lead
plates thick (figure 2). These batteries are
characterized by a maximum capacity and a high
cycle count, and this makes it ideal for solar
energy systems.
Figure 2: Deep-cycle battery
Solar Batteries are a deep cycle batteries
used to store the direct current generated by the
solar panels, which is converted into alternating
current by the inverter to operate the various
loads. The battery (12v) generally consists of (6)
cells, each of these cells consists of, anode,
cathode, and the conductive material (the
electrolyte).
26
Page 25-30 © MAT Journals 2021. All Rights Reserved
e-ISSN: 2456-9860
Volume-6, Issue-3 (September-December, 2021)
Journal of
Instrumentation and Innovation Sciences
www.matjournals.com
There are many types of solar batteries (figure
3), which differ among themselves in the materials from which the anode and cathode are
made and the type of electrolyte.
Figure 3: The different types of solar batteries
The most common types of solar
batteries are:
1 – lead-acid batteries that include:
Liquid lead-acid batteries (flooded)
Gel Batteries
AGM batteries
2- Lithium batteries
The flooded batteries
It is the oldest type of batteries, the
cheapest and the most widespread. It is called
―liquid‖ because the conductive material
between the anode and cathode plate is a liquid
substance, which is sulfuric acid diluted with
water, concentration ratio 3:1. Flooded batteries
need maintenance, which includes replacing the
acid and adding distilled water once or twice a
month to compensate for the water evaporating
from the batteries. Figure 4 demonstrates the
components of a single cell of a flooded battery,
which consists of sponge lead which represents
the cathode electrode and a clip of lead, and
behind the clip a plate of dioxide Lead, which
represents the anode electrode, and these cells
are immersed in acid diluted with water
Figure 4: The liquid lead -acid battery
27
Page 25-30 © MAT Journals 2021. All Rights Reserved
e-ISSN: 2456-9860
Volume-6, Issue-3 (September-December, 2021)
Journal of
Instrumentation and Innovation Sciences
www.matjournals.com
The gel battery
A gel battery has the same design and
functionality as a traditional flooded battery. The
gel battery differs from the liquid battery in that
the conductive material contains silica in the
electrolyte, which creates a gel-like substance.
The gel battery is characterized by being suitable
for use in many positions due to its stability and
absence of any gases emitting from it, and it is a
deep cycle battery
.
Figure 5: The Jel battery
The AGM battery
A fiberglass material is placed between
the anode and the cathode, which absorbs the
electrolyte like a sponge and prevents it from
leaking or evaporating. An AGM battery is a
deep cycle discharge with the provision of
mixing the sulfate back into the hydrogen gas,
resulting in a reduction of the hydrogen released
during the discharge process.
Figure 6: The AGM lead battery
The lithium battery
An anodes consist of graphite-based
materials due to the low cost, wide spread, and
the stability to accommodate the lithium
insertion, but it carbon suffer from a low
capacity, so in recent year, the carbon-based
anode has been improved, and new types of
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Page 25-30 © MAT Journals 2021. All Rights Reserved
e-ISSN: 2456-9860
Volume-6, Issue-3 (September-December, 2021)
Journal of
Instrumentation and Innovation Sciences
www.matjournals.com
anode materials, such as silicon, alloy, and metal
oxides have been developed, which has
improved the lifetime, capacity and performance
of lithium batteries. Cathodes consist of a
complex lithium compound material, such as
LiCoO2 and LiFePO4 . Battery performance
significantly differs with different cathodes.
Cathode has been fabricated from lithium
material blending with conductive material such
as carbon due to low impedance because of high
diffusion coefficient and high ionic
conductivities compared with other materials
compound. The electrolyte in lithium batteries
includes three types liquid electrolyte, semisolid
electrolyte, and solid-state electrolytes. Liquid
electrolyte consists of lithium salts such as.,
LiBF4, LiPF6, LiN(CF3SO2)2, and LiBOB, which
are dissolved in organic carbonates such as,
ethylene carbonate, propylene carbonate, ethyl
methyl carbonate, dimethyl carbonate, and their
mixtures. While, the semisolid electrolyte, and
solid-state electrolyte are composed of lithium
salts as the conducting salts and high-molecular-
weight polymer matrices such as, polyvinylidene
fluoride and poly(ethylene oxide).
Figure 7: Lithuim-ion battery
Table 1: Comparison of different types of batteries
Lithium battery
AGM battery
Jel battery
Lead-acid battery
No need
No need
No need
Need
Maintenance
80%
50%
75%
50%
Depth of discharge
20 year
6-8 year
6-8 year
3-5 year
Lifespan
2000$
250$
300$
150$
Cost
0°C to 45°C
0°C to 50°C
20°C to 50°C-
0°C to 50°C-
Charge temperature
20°C to 60°C–
0°C620°C to -
0°C60°C to 4-
0°C70°C to 3-
Discharge temperature
20°C to 60°C-
20°C to 60°C-
40°C to 60°C-
20°C to 60°C-
Storage temperature
260W.h/kg-50
50W.h/kg
40W.h/kg
30W.h/kg
Energy density
The electrical representation of the battery
To determine the power losses and the
terminal voltage of the battery an electrical
representation has been achieved by models
based on thevenin network. The most simple
model consists of a series resistor, RC network
to describe basic charge transfer phenomenon,
and open circuit voltage (Voc) which dependent
on the state of charge (SOC) as obvious in figure
8(a). An enhancement for the batteries
simulation can be done by adding a second RC
branch as demonstrated in figure 8(b). The first
RC branch represents short-term transient
behavior, and the second RC branch represents
long-term transient behavior.
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Page 25-30 © MAT Journals 2021. All Rights Reserved
e-ISSN: 2456-9860
Volume-6, Issue-3 (September-December, 2021)
Journal of
Instrumentation and Innovation Sciences
www.matjournals.com
(a) (b)
Figure 8(a) Thevenin-based model, 1RC network (b)Thevenin based model, 2RC network
Voc(soc) = K0 + K1.(soc) + K2.(soc)2 + K3.(soc)3
+ K4.(e)K5.SOC
Rcell (soc) = Rcell(0) + K5(e)K6.SOC
R1 (soc) = R1(0) + K7(e)K8.SOC
C1 (soc) = C1(0) + K9(e)K10.SOC
R2 (soc) = R2(0) + K11(e)K12.SOC
C2 (soc) = C2(0) + K13(e)K14.SOC
The coefficients K0, K1, K2,
K3,…….,K14 depend on the respective cell type
and are subjects of measurements.
For higher accuracy another RC network
is proposed, in order to describe finally short-
term, mid-term, long-term transient behavior.
However, this makes the calculation of the
associated capacitors and resistors much more
complex, also studies have shown that 2RC
model achieves good results, therefore it is
proposed in simulations of electrical power grids
The most important information about
batteries
The effectivity and performance of the
battery depend on the following parameters:
1. Capacity of battery
2. Efficiency of battery
3. Depth of discharge
Battery capacity
The amount of energy that the battery can
storage.
If a battery of (12v) has a capacity of (500 A.h)
,the energy can be storage with this battery is:
Energy = Voltage * Current * Time
= 12v * 500A.h
= 6000w.h
Battery efficiency
It is the ratio of the output energy from
the battery to the input energy that the battery
needs to charge.
If the energy that the battery needs to
charge is (6000 wh) and the energy that can be
obtained from this battery is (4800 wh), then the
efficiency of this battery is:
Battery efficiency = (output energy) / (input
energy) * 100%
= (4800 w.h) / (6000 w.h) * 100%
= 80%
Depth of Discharge (DOD)
It is the amount of capacity that can be
obtained from the battery capacity.
If the depth of discharge is equal to 50%
for a battery whose capacity is (60Ah), then the
amount of capacity that can be get it from this
battery is:
= 60A.h * 0.5
= 30Ah
The time required for charging the batteries
When the solar panels used to charge the
battery, the time required for charging the
battery is equal to (capacity of the battery / panel
current)
If the panel(9A) used in charging the
battery (200A.h) then the time that required to
charge the battery =
= 22.22h
Series and parallel connection of batteries
The batteries are connected in parallel or
in series to obtain the required current and
voltage Figure 9 shows four batteries each one
of (12v , 100Ah) connected in series
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Page 25-30 © MAT Journals 2021. All Rights Reserved
e-ISSN: 2456-9860
Volume-6, Issue-3 (September-December, 2021)
Journal of
Instrumentation and Innovation Sciences
www.matjournals.com
Figure 9. Series connection of batteries
and figure 10 obvious these foure batteries
connected in parallel
Figure 10. Parallel connection of batteries
CONCLUSION
At the present time, due to the rise in
temperatures over the past years, it is necessary
to take into account the impact of temperatures
on the performance of the battery when
choosing the appropriate battery for working on
design. Temperature, have a significant effect
on the performance, and the safety of the solar
batteries. As the temperature of the battery
increases the chemical reactions inside the
battery also quicken, and increased storage
capacity of the battery. It was found that an
increase in temperature from 25 0C to 45 0C led
to a 20% increase in maximum storage
capacity, but an available capacity
decreases over time, and the lifecycle of the
battery is decreased over time. Lithium battery
has better volume and weight, and is relatively
cheaper to maintain but the initial cost is higher,
and it is more temperature sensitive. Flooded
batteries and Jel batteries are the most using in
Iraq because they are more cost-effective, it's
price is just 1/4~1/6 of the lithium battery cost
with an acceptable limits of the discharge depth
(DOD) and it is suitable for high temperature
work,
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