Saft Sunica.plus User manual

May 2007
Sunica.plus
Technical manual

1. Introduction 4
2. The photovoltaic application 5
3. Construction features of the Sunica.plus
battery 6
3.1. Plate assembly 7
3.2. Separation 7
3.3. Electrolyte 8
3.4. Terminal pillars 8
3.5. Venting system 8
3.6. Cell container 8
4. Benefits of the Sunica.plus battery 9
5. Operating features 10
5.1. Capacity 10
5.2. Cell voltage 10
5.3. Internal resistance 10
5.4. Effect of temperature on performance 11
5.5. Short circuit values 12
5.6. Open circuit loss 12
5.7. Cycling 12
5.8. Effect of temperature on lifetime 14
5.9. Water consumption 15
6. Battery charging 16
6.1. Charging generalities 16
6.2. Charge efficiency 17
6.3. Temperature effects 18
6.4 Regulators 19
7. Special operating factors 20
7.1. Electrical abuse 20
7.1.1. Ripple effects 20
7.1.2. Over-discharge 20
7.1.3. Overcharge 20
7.2. Mechanical abuse 20
7.2.1. Shock loads 20
7.2.2. Vibration resistance 20
7.2.3. External corrosion 20
8. Battery sizing principles 21
8.1 Introduction 21
8.2 The basic principles 21
8.3 Battery sizing example 22
9. Installation and storage 23
9.1. Receiving the shipment 23
9.2. Storage 23
9.3. Installation 23
9.3.1. Location 23
9.3.2. Ventilation 23
9.3.3. Mounting 23
9.3.4. Electrolyte 23
9.4. Commissioning 24
9.4.1. Cells stored up to 6 months 24
9.4.2. Cells stored more than 6 months
and up to 1 year 24
10. Maintenance of Sunica.plus batteries
in service 25
Contents

1. Introduction
The nickel-cadmium battery is
the most reliable battery system
available in the market today. Its
unique features enable it to be
used in applications and
environments untenable for
other widely available battery
systems.
It is not surprising, therefore,
that with the emergence of the
photovoltaic (PV) market and its
rigorous requirements, the
nickel-cadmium battery has
become an obvious first choice
for users looking for a reliable,
low maintenance, system.
This manual describes the
introduction of an upgraded
photovoltaic battery product with
major improvements including:
■up to 4 years without topping-
up at + 20°C (+ 68°F)
■extended cycling at high
temperature throughout
seasonal variations of high
and low temperature and state
of charge.
Sunica.plus is built upon solid
Saft expertise with more than
20 years field experience with
Sunica, one of the most reliable
batteries under the sun, and
ultra-low maintenance Ultima
batteries used in industrial
stand-by applications.
This publication details the
design and operating
characteristics of the Saft
Sunica.plus battery to enable a
successful photovoltaic system
to be achieved. A battery
which, while retaining all the
advantages arising from nearly
100 years of development of
the pocket plate technology,
can be so worry free that the
only maintenance requirement
is occasional topping-up with
water.
4

The typical requirements for
photovoltaic (PV) applications are
ruggedness, environmental
flexibility, unattended operation,
ease of installation, and reliability.
Photovoltaic applications can
cover many applications including:
Navigational Aids: offshore,
remote lighthouses, beacons
Telecommunications: emergency
telephone posts, radio repeater
stations, base stations
Rail Transport: crossing guards
lighting, signalling, isolated
telephone stations
Oil and Gas: cathodic protection
for pipelines, emergency lighting
on offshore platforms
Utilities: electrification in remote
areas
A photovoltaic system is made up
of three distinct parts:
■The photovoltaic array which is
built to give up to 20 years of
service life
■Electronic components such as
blocking diodes and logic
circuits in power conditioners
and as controllers or voltage
regulators
■The battery must assure the
autonomy required by the
installation. Systems are often
installed in remote areas, at
sites accessible only by foot,
helicopter or boat, in good
weather conditions and with only
limited skilled labour available.
Thus, the ideal photovoltaic power
system is a reliable installation
which requires only infrequent
maintenance calls and, clearly,
the battery plays a crucial part in
this requirement as premature
failure of the battery results in a
total failure of the system.
The most important
characteristics required in a
battery for photovoltaic
applications are:
■ability to withstand cycling, daily
and seasonal
■ability to withstand high and low
environmental temperatures
■ability to operate reliably,
unattended and with minimal
maintenance
■ruggedness for transportation
to remote sites
■easily installed with limited
handling equipment and
unskilled labour
■reliability and availability during
the 20 years service life of the
photovoltaic modules
■resistance to withstand failure
of electronic control systems
■no need for refreshing charges
■high charge efficiency during
periods of low insolation
(typically cold winter seasons)
2. The photovoltaic
application
Solar panels
Sunica +
=~
REGULATOR
DC load
AC load
5

3. Construction features of
the Sunica.plus battery
6
Saft’s automated
integral water filling system
is available as an option for
Sunica.plus cell types
from 185 Ah to 1110 Ah.
Automated integral
water filling system
Plate tab
Spot welded to the plate side frames, to
the upper edge of the pocket plate and to
the plate group bus.
Plate group bus
Connects the plate tabs with the terminal
post. Plate tabs and terminal posts are
projection welded to the plate group bus.
Plate
Horizontal pockets of double-perforated steel strips.
Separators
These separate the plates and insulate the
plate frames from each other. This special
type of separator improves the internal
recombination.
Plate frame
Seals the plate pockets and serves as
a current collector.
Cell container
Made of tough polypropylene.
Flame arresting vent
With transport seal protection.
Protective cover
Prevents external short-circuits.
Handles
Moulded polypropylene handles allow
Sunica.plus batteries to be easily manoeuvred
and installed.

The construction of the Saft
Sunica.plus cell is based upon
the proven Saft pocket plate
technology but with special
features to enhance its use in
the specialised photovoltaic
application.
3.1. Plate assembly
The nickel-cadmium cell consists
of two groups of plates, one
containing nickel hydroxide
(the positive plate) and the other
containing cadmium hydroxide
(the negative plate).
The active materials of the Saft
Sunica.plus pocket plate have
been specially developed and
formulated to improve its cycling
ability, a specific need for
photovoltaic applications. These
active materials are retained in
pockets formed from nickel
plated steel which is double
perforated by a patented
process. The pockets are
mechanically linked together, cut
to the size corresponding to the
plate length and compressed to
the final plate dimension. This
process leads to a component
which is not only mechanically
very strong but also retains its
active material within a steel
boundary which promotes
conductivity and minimises
electrode swelling.
These plates are then welded to
a current carrying bus bar
assembly which further ensures
the mechanical and electrical
stability of the product.
Nickel-cadmium batteries have
an exceptionally good cycle life
because their plates are not
gradually weakened by repeated
cycling as the structural
component of the plate is steel.
The active material of the plate
is not structural, only electrical.
The alkaline electrolyte does not
react with steel, which means
that the supporting structure of
the Sunica.plus battery stays
intact and unchanged for the life
of the battery. There is no
corrosion and no risk of “sudden
death”.
In contrast, the lead plate of a
lead acid battery is both the
structure and the active material
and this leads to shedding of the
positive plate material and
eventual structural collapse.
3.2. Separation
The separator is a key feature
of the Sunica.plus battery. It is a
polypropylene fibrous material
which has been used and proven
by Saft in the Ultima ultra-low
maintenance product over more
than 20 years and has been
further developed for this
product to give the features
required. Using this separator,
the distance between the plates
is carefully controlled to give the
necessary gas retention to
provide the level of
recombination required.
By providing a large spacing
between the positive and
negative plates and a generous
quantity of electrolyte between
plates, the possibility of thermal
runaway, a problem with VRLA
cells, is eliminated.
7

3.3. Electrolyte
The electrolyte used in
Sunica.plus, which is a solution of
potassium hydroxide and lithium
hydroxide, is optimised to give the
best combination of performance,
life, cycling ability, energy efficiency
and wide operational temperature
range. The concentration is such
as to allow the cell to be operated
to temperature extremes as low
as – 20°C (– 4°F) and as high as
+ 50°C (+122°F). This allows the
very high temperature fluctuations
found in certain remote regions to
be accommodated. For
continuous temperatures below
– 20°C (– 4°F) a special high
density electrolyte can be used.
It is an important consideration of
Sunica.plus, and indeed all nickel-
cadmium batteries, that the
electrolyte does not change during
charge and discharge. It retains
its ability to transfer ions between
the cell plates irrespective of the
charge level. In most applications
the electrolyte will retain its
effectiveness for the life of the
battery and will never need
replacing.
3.4. Terminal pillars
Short terminal pillars are welded
to the plate bus bars using the
well established block battery
construction. These posts are
manufactured from steel bar,
internally threaded for bolting on
connectors and are nickel plated.
The terminal pillar to cover seal
is provided by a compressed
visco-elastic sealing surface held
in place by compression lock
washers. This assembly is
designed to provide satisfactory
sealing throughout the life of the
product.
3.5. Venting system
Sunica.plus is fitted with a flame
arresting flip-top vent to simplify
topping-up and is supplied with a
transportation plug to ensure
safe transportation. There is also
an option of a water filling system
which has been proven by Saft in
railway applications over many
years. This gives semi-automatic
filling and an effective and safe
venting system.
3.6. Cell container
Sunica.plus is built up using the
well proven block battery
construction. The tough
polypropylene containers are
welded together by heat sealing
and the assembly of the blocks
are completed by a clip-on
terminal cover which gives
protection to IP2 standard for
the conductive parts.
8

Complete reliability
Does not suffer from the sudden
death failure associated with
other battery technologies.
Long cycle life
Sunica.plus has a long cycle life
even when the charge/discharge
cycle involves full discharges and
will give up to 8000 cycles at
15 % depth of discharge during a
twenty year life.
Exceptional long life
Sunica.plus incorporates all the
design features associated with
the conventional Saft twenty year
life products to ensure that, in
many applications, it can achieve
or exceed this lifetime.
Low maintenance
With its special recombination
separator and generous
electrolyte reserve, Sunica.plus
reduces the need for topping-up
with water. It can be left in
remote sites for long periods
and will, depending upon
application demands, give up to
4 years without the need for
topping-up.
Charge efficiency
Good charge efficiency at normal
temperatures and excellent
charge efficiency at low
temperatures ensure that the
battery is charged during the
winter period.
Wide operating
temperature range
Sunica.plus has a special
optimised electrolyte which
allows it to have a normal
operating temperature of from
– 20°C to + 50°C (– 4°F to +122°F),
and accept extreme
temperatures, ranging from as
low as – 50°C to up to + 70°C
(– 58°F to up to +158°F).
Resistance to mechanical
abuse
Sunica.plus is designed to have
the mechanical strength required
to withstand all the harsh
treatment associated with
transportation over difficult terrain.
High resistance to
electrical abuse
While the use of a voltage
regulator is recommended to
obtain maximum overall
efficiency of the system, the
failure of this component will not
damage the battery. It will simply
cause an overcharging of the
battery and so use extra water.
The Sunica.plus battery is
resistant to overcharge and
over-discharge conditions.
Low installation costs
Sunica.plus can be used with a
wide range of photovoltaic
systems as it produces no
corrosive vapours, uses
corrosion free polypropylene
containers and has a simple
bolted assembly system.
Well proven pocket plate
construction
Saft has nearly 100 years of
manufacturing and application
experience with respect to the
nickel-cadmium pocket plate
product and this expertise has
been built into the twenty plus
years design life of the
Sunica.plus product.
4. Benefits of the
Sunica.plus battery
9

5.1. Capacity
The Sunica.plus battery capacity
is rated in ampere hours (Ah)
and is the quantity of electricity
it can supply for a 120 hour
discharge to 1.0 volts after
being fully charged. This figure
was chosen as being the most
useful for sizing photovoltaic
applications.
5.2. Cell voltage
The cell voltage of nickel-
cadmium cells results from the
electrochemical potentials of the
nickel and the cadmium active
materials in the presence of the
potassium hydroxide electrolyte.
The nominal voltage for this
electrochemical couple is 1.2 volts.
5.3. Internal resistance
The internal resistance of a cell
varies with the type of service
and the state of charge and is,
therefore, difficult to define and
measure accurately.
The most practical value for
normal applications is the
discharge voltage response to a
change in discharge current.
The internal resistance of a
Sunica.plus cell when measured
at normal temperature is
approximately 300 m
Ω divided by
the capacity (Ah). This value is
for fully charged cells and for
lower states of charge and
temperature the value will
increase. For cells 50 %
discharged the internal
resistance is about 20 % higher
and when 90 % discharged it is
about 80 % higher. The internal
resistance of a fully discharged
cell has very little meaning.
Reducing the temperature also
increases the internal resistance
and, at 0°C (+ 32°F), the internal
resistance is about 40 % higher.
Table 1 shows typical values for
a 100 Ah cell (values in m
Ω ).
5. Operating features
10
Table 1 - Internal resistance for a 100 Ah cell (in milliohms)
for different conditions
Temperature Fully charged 50 % discharged 90 % discharged
20°C (+ 68°F) 3.0 3.6 5.4
0°C (+ 32°F) 4.2 5.0 7.6

5.4. Effect of temperature
on performance
Variations in ambient
temperature affect the
performance of Sunica.plus and
this must be allowed for in the
battery engineering.
Low temperature operation has
the effect of reducing the
performance but the higher
temperature characteristics are
similar to those of normal
temperatures. The effect of
temperature is more marked at
higher rates of discharge.
The factors which are required in
sizing a battery to compensate
for temperature variations are
given in a graphical form for cells
with standard electrolyte in
Figure 1 for operating
temperatures from – 20°C to
+ 40°C (– 4°F to +104°F). These
factors can be applied for daily
depth of discharges (DOD) of up
to 15 %.
When the special high density
electrolyte is used, for operating
temperatures from – 40°C (– 40°F)
to room temperature, the
factors which are required in
sizing a battery to compensate
for temperature variations are
given in a graphical form in
Figure 2.
Figure 1 - Temperature de-rating: standard electrolyte for operating
temperatures from – 20°C to + 40°C (– 4°F to + 104°F)
11
Temperature
De-rating factor
De-rating factors to apply on RT performance
according to temperature and end voltage
End voltage 1.20 V
End voltage 1.18 V
End voltage 1.16 V
End voltage 1.14 V
– 30°C
– 22°F
0.6
0.7
0.8
0.9
1.0
– 20°C
– 4°F
0°C
+ 32°F
+ 10°C
+ 50°F
+ 20°C
+ 68°F
+ 30°C
+ 86°F
+ 40°C
+ 104°F
– 10°C
+ 14°F
Temperature
De-rating factor
0.03 C A
0.02 C A
0.015 C A
0.01 C A
0.005 C A
–50°C
–58°F
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1.1
–45°C
–49°F
–35°C
–31°F
–30°C
–22°F
–25°C
–13°F
–20°C
–4°F
–15°C
+ 5°F
–10°C
+ 14°F
–5°C
+ 23°F
0°C
+ 32°F
–40°C
–40°F
De-rating factors to apply on RT performance
according to temperature and discharge rate; end voltage 1.14 V
Figure 2 - Temperature de-rating: special electrolyte for operating
temperatures down to – 40°C (– 40°F)

5.5. Short circuit values
The typical short circuit value in
amperes for a Sunica.plus cell is
approximately 9 times the
ampere-hour capacity, e.g. for a
100 Ah cell the short circuit
value would be 900 amperes.
The Sunica.plus battery with
conventional bolted assembly
connections will withstand a
short circuit current of this
magnitude for many minutes
without damage.
5.6. Open circuit loss
The state of charge of the
Sunica.plus cell on open circuit
stand slowly decreases with time
due to self discharge. In practice
this decrease is relatively rapid
during the first two weeks but
then stabilises to about 2 %–3 %
per month at + 20°C (+ 68°F).
The self discharge
characteristics of a nickel-
cadmium cell are affected by
the temperature. At low
temperatures the charge
retention is better than at
normal temperature and so the
open circuit loss is reduced.
However, the self discharge is
significantly increased at higher
temperatures.
The open circuit loss for
Sunica.plus for normal
temperature and the higher
temperature which may be
experienced in a photovoltaic
application is shown in Figure 3.
5.7. Cycling
Sunica.plus is designed to
withstand the wide range of
cycling behaviour encountered in
photovoltaic applications. This
can vary from low depth of
discharges to discharges of up
to 100 % and the number of
cycles that the product will be
able to provide will depend on
the depth of discharge required.
Figure 3 - Open circuit loss at + 20°C and + 40°C (+ 68°F and + 104°F)
12
Days
Charge retention of Sunica.plus
% of available capacity C5
+ 20°C (+ 68°F)
+ 40°C (+ 104°F)
0
0 %
20 %
40 %
60 %
80 %
100 %
120 %
50 150 200 250 300 350100

The less deeply a battery is
cycled then the greater the
number of cycles it is capable of
performing before it is unable to
achieve the minimum design
limit. A shallow cycle (say 10 %)
will give more than 10000
operations, whereas a deep
cycle (say 80 %) will give about
1000 operations.
Figure 4 gives the effect of depth
of discharge on the available
cycle life and, it is clear, that
when sizing the battery for an
application, the number and
depth of cycles have an
important consequence on the
predicted life of the system.
In practice, in photovoltaic
applications, the battery is
exposed to a large number of
relatively shallow cycles operating
at different states of charge and,
often, this will be at high
temperatures. In order to simulate
this, the IEC Standard 61427
incorporates an accelerated
cycling test procedure which
replicates a photovoltaic energy
system operating in very severe
conditions. The test consists of a
period with a high state of
charge, to simulate the effect of
overcharge on the lifetime of the
battery, and a period with a low
state of charge, to simulate the
effect of a poor state of charge
on a battery. This mix of high and
low state of charge cycling is
difficult for a battery and allows
evaluating the ability of the
battery to meet the requirements
of the photovoltaic application.
In testing to this standard,
Sunica.plus has demonstrated
that it can achieve more than
12 periods each of 150 cycles,
i.e. more than 1800
charge/discharge cycles,
without reaching the
requirements of the end of test
criteria (see Figure 5).
Number of cycles
Battery capacity evolution when cycled as per IEC 61427
% of the initial battery capacity
0
0
20
40
60
80
100
120
150 450 600 750 900 1050 1200 1350 1500 1650 1800 1950300
13
Depth of discharge (% C5Ah)
Life time criteria:
Capacity = 70 % of rated capacity
Number of cycles
+ 20°C (+ 68°F)
0°C (+ 32°F)
+ 40°C (+ 104°F)
0
100
1000
10000
100000
10 30 40 50 60 70 80 90 10020
Figure 4 - Typical cycle life values at different temperatures
Figure 5 - Sunica.plus cycling to IEC Standard 61427

5.8. Effect of temperature
on lifetime
Sunica.plus is designed as a
twenty year life product but, as
with every battery system,
increasing temperature reduces
the expected life. However, the
reduction in lifetime with
increasing temperature is very
much lower for the nickel-
cadmium battery than the lead
acid battery.
The reduction in lifetime for both
the nickel-cadmium battery and,
for comparison, a lead acid
battery is shown graphically in
Figure 6.
In general terms for every
+ 10°C (+ 18°F) increase in
temperature over the normal
operating temperature of + 20°C
to + 25°C (+ 68°F to + 77°F), the
reduction in service life for a
nickel-cadmium battery will be
20 % and for a lead acid battery
will be 50 %. In high temperature
situations, therefore, special
consideration must be given to
dimensioning the nickel-cadmium
battery. Under the same
conditions, the lead acid battery
is not a practical proposition due
to its very short lifetime.
14
Figure 6 - Lifetime reduction with temperature
Temperature
Percentage of + 25°C (+ 77°F) lifetime
Lead acid
Nickel-cadmium
+ 25°C
+ 77°F
0
10
20
30
40
50
60
70
80
90
100
+ 30°C
+ 86°F
+ 35°C
+ 95°F
+ 40°C
+ 104°F
+ 45°C
+ 113°F
+ 50°C
+ 122°F
+ 55°C
+ 131°F

5.9. Water consumption
During charging, more ampere
hours is supplied to the battery
than the capacity available for
discharge. These additional
ampere-hours must be provided
to return the battery to the fully
charged state and, since they are
not all retained by the cell and do
not all contribute directly to the
chemical changes to the active
materials in the plates, they must
be dissipated in some way.
This surplus charge, or
overcharge, breaks down the
water content of the electrolyte
into oxygen and hydrogen, and
pure distilled water has to be
added to replace this loss.
Water loss is associated with
the current used for
overcharging. A battery which is
constantly cycled i.e. is charged
and discharged on a regular
basis, will consume more water
than a battery on standby
operation.
In theory, the quantity of water
used can be found by the Faradic
equation that each ampere hour
of overcharge breaks down
0.366 cc of water. However, due
to the recombination separator
used in the Sunica.plus battery,
the water usage will be
considerably less than this.
The consumption of water used
by the battery varies according
to the voltage, temperature and
the level of cycling which occurs
in the application.
Table 2 gives typical water
consumption values over a range
of voltages corresponding to daily
depth of discharges at two typical
photovoltaic temperatures.
Table 2 - Typical water consumption values at different voltages
Charge voltage 1.5 V 1.55 V 1.6 V
Daily DOD 5 % to 10 % 10 % to 15 % 15 % to 25 %
Topping-up interval at + 20°C (+ 68°F) 4 year 3 year 2 year
Topping-up interval at + 40°C (+ 104°F) 2 year 1.5 year 1 year
15

6.1. Charging generalities
The photovoltaic array converts
solar irradiance into dc electrical
power at a predetermined range
of voltages whenever sufficient
solar radiation is available.
Unlike a mains connected
system, the output from a
photovoltaic array is variable
and, to obtain the best efficiency
from the system, it is quite
normal to have some form of
charge control.
In general the solar panels are
sized in such a way that they can
provide the requested energy to
the load during the season of low
solar radiation and the extra
energy obtained during the
season where the solar radiation
is at its highest is then available
for recovering full battery
capacity.
Depending on the season, the
battery in solar application cycles
is either at high state of charge
or at low state of charge and, as
a consequence, the charge
parameters are never well
defined in solar applications.
In practice, as the charging
current depends on the sun
irradiance and the charging time
on the light duration, the charge
voltage is left as the main
parameter which can be used to
optimise the battery state of
charge for a given solar
application.
The optimised charge voltage is
linked to the daily depth of
discharge (which is in
relationship with the battery
autonomy) and the target is to
maintain a high state of charge
cycle after cycle with low water
consumption.
6.1.1 The Daily Depth of
Discharge (DOD)
In order to define the optimised
charge voltage, it is necessary
to define the Daily DOD. This is
obtained from the fact that the
battery is cycling every day; it is
charging during the day and is
discharging during the night.
In general the daily discharge
is going to fall between
5 to 20 % DOD.
The following example gives an
illustration.
The battery has to be defined to
give 5 days back up time with a
load of 50 W. Thus the battery
requirement is
5 x 24 x 50 W = 6000 Wh
The daily discharge of the battery
during the night is 50 W for
about 12 h. So, each day the
battery has to supply
50 W x 12 h = 600 Wh.
From this it can be seen that the
daily DOD is
600 Wh / 6000 Wh i.e. 10 %
6. Battery charging
16

6.1.2 Optimum charge voltage
It is now necessary to define the
optimum charge voltage when
the battery is cycling at high
state of charge.
This can be carried out by
checking the values of the
stabilised state of charge in
cycling according to different
daily DOD, charge voltage and
temperature and the values are
summarised in Figure 7.
When cycling with the
recommended charge voltage
corresponding to the daily DOD,
it is expected that a stabilised
state of charge of 90 % will be
achieved providing the solar
panels are correctly sized for the
load and the site conditions.
6.2. Charge efficiency
The charge efficiency of
Sunica.plus is dependent on the
state of charge of the battery and
the temperature. For much of its
charge profile it is recharged at a
high level of efficiency. In cycling
at 20°C (+ 68°F), with the advised
charge voltage corresponding to
the daily DOD, the Ah efficiency is
close to 100 % at a 50 % state
of charge, and it is better than
90 % at a 90 % state of charge.
At higher temperatures the Ah
efficiency is reduced and at
+ 40°C (+ 104F°) the values are
respectively 96 % and 82 %.
When the charge voltage is less
than or more than the
recommended value the
stabilised state of charge and the
Ah efficiency will be modified.
Figure 7 - Charge voltage required for high state of charge
Daily DOD in %
Recommended charge voltage
according to the daily DOD and at + 20°C (+ 68°F)
Charge voltage per cell (V)
Minimum voltage level
0
1.3
1.35
1.4
1.45
1.5
1.55
1.6
1.65
1.7
1.75
515 20 25 30
10
17

The relationship between the
charge efficiency and the daily
depth of discharge, autonomy
and charge voltage for + 20°C
(+ 68°F) is shown in Table 3.
It is important to note that the
charging efficiency of Sunica.plus
is not reduced with time and so
this does not have to be taken
into account in battery sizing.
In practice, a photovoltaic
system’s battery normally has a
state of charge between 20 %
and 80 % and so the charging
efficiency of Sunica.plus
remains high.
6.3. Temperature effects
As the temperature increases,
then the electrochemical
behaviour becomes more active
and so, for the same charge
voltage, the current at the end of
charge increases. This end of
charge increase in the current
helps to compensate for the
variation in charge efficiency at
high temperatures and allows a
high state of charge to be
achieved. For this reason it is
not recommended that
temperature compensation of
the charge voltage is used for
ambient temperatures above
0°C (+ 32°F). In terms of water
loss, this is not increased
significantly at these higher
temperatures due to the
effectiveness of the partial gas
recombination features of
Sunica.plus.
As the temperature is reduced,
then the reverse occurs and it is
recommended that, for
applications where the ambient
temperature during the critical
period of the year falls below
0°C (+ 32°F), temperature
compensation of the charge
voltage should be used to
maintain the end of charge
current at a constant value.
The change in voltage required
per cell, or “temperature
compensation”, should be
between – 2 mV and – 3.5 mV
per °C. The recommended value
is – 2.5 mV per °C and per cell.
Table 3 - Typical Ah efficiencies under different application conditions
Daily Typical Charge Expected Ah efficiency Ah efficiency
DOD autonomy voltage SOC at H SOC at 50% SOC
per cell
5 to 10 % 5 days or + 1.5 V 90 % min >90 % ≈10 0 %
10 to 15 % 3 to 5 days 1.55 V 90 % min >90 % ≈10 0 %
15 to 25 % 2 to 5 days 1.6 V 90 % min >90 % ≈10 0 %
18

6.4 Regulators
6.4.1 A pulse width modulator
(PWM) type regulator
For a PWM type regulator the
advised charge voltage should
be based on the daily depth of
discharge according to the
values in Table 4.
6.4.2 A battery regulator
based on the switching principle
For this type of regulator it is
useful to define the boost
threshold (not mandatory), the
float threshold and the charge
reconnect threshold.
Typical threshold values for a
battery system with Sunica.plus
defined for 5 days or more
autonomy is shown in Table 5.
6.4.3 Recommendation for
choosing the voltage regulators.
The charge voltages shall be
adjustable due to the wide charge
voltage range of Sunica.plus.
The low voltage disconnect shall
be adjustable or inhibit due to
the deep discharge possible of
the Sunica. plus. Regulators with
voltage regulation using PWM
systems are recommended due to
the need of maintaining the
charge voltage on the battery
during the daily charge process.
Examples of voltage regulators
- The TriStar from Morningstar
- The Enerstat from Total energie
- The Trace C40
- etc
Table 5 - Typical threshold values for switching type regulator
Voltage system 12 V 24 V 48 V
Typical number of Ni-Cd cells 9 18 36
Boost threshold
(not mandatory 14.7 V 29.4 V 58.8 V
or 1.65 V per cell)
Float threshold 14.1 V 28.2 V 56.4 V
(by 1.55 V per cell)
Battery reconnect threshold 13 V 26 V 52 V
(by 1.45 V per cell)
End of discharge threshold
(not mandatory 9 V 18 V 36 V
or 1 V per cell)
19
Table 4 - PWM regulator recommended charge voltages for different conditions
Daily DOD Typical autonomy Charge voltage per cell
5 to 10 % 5 days or + 1.5 V
10 to 15 % 3 to 4 days 1.55 V
15 to 25 % 2 to 3 days 1.6 V
Voltage system 12 V 24 V 48 V
Typical number 91836
of Ni-Cd cells

7.1. Electrical abuse
7.1.1. Ripple effects
The nickel-cadmium battery is
tolerant to high ripple and the
only effect is that of increased
water usage. In general, any
commercially available charger
or generator can be used for
commissioning or maintenance
charging of Sunica.plus.
7.1.2. Over-discharge
If more than the designed
capacity is taken out of a battery
then it becomes over-discharged.
This is considered to be an
abuse situation for a battery and
should be avoided.
In the case of lead acid batteries
this will lead to failure of the
battery and is unacceptable.
The Sunica.plus battery is
designed to make recovery from
this situation possible.
7.1.3. Overcharge
Overcharge is the effect of
forcing current through a battery
when it is fully charged. This can
be damaging for a lead acid
battery and, due to its starved
electrolyte technology, seriously
reduce the life of a VRLA battery.
In the case of Sunica.plus, with
its generous electrolyte reserve,
a small degree of overcharge will
not significantly alter the
maintenance period. In the case
of excessive overcharge, water
replenishment is required but
there will be no significant effect
on the life of the battery.
7.2. Mechanical abuse
7.2.1. Shock loads
The Sunica.plus block battery
concept has been tested to both
IEC 68-2-29 (bump tests at 5 g,
10 g and 25 g) and IEC 77
(shock test 3 g).
7.2.2. Vibration resistance
The Sunica.plus block battery
concept has been tested to
IEC 77 for 2 hours at 1 g.
7.2.3. External corrosion
Sunica.plus nickel-cadmium cells
are manufactured in durable
polypropylene, all external metal
components are nickel plated
and these components are
protected by a rigid plastic cover.
7. Special operating factors
20

8.1 Introduction
The type of use of the PV system
and the required reliability is of
paramount importance in sizing
the system.
Professional applications
(emergency systems, sea-lights,
radio beacons etc.) have to be
oversized according to their
importance and it is necessary to
take into account the working
conditions of the system.
It is not the purpose of this manual
to give sizing methods for
complete photovoltaic systems.
However, this is an application with
specific performance requirements
and it is useful to discuss the
different factors which can affect
the design of the system and the
battery sizing. The array and
battery size are related since the
photovoltaic system must have
array and battery sizes which are
sufficient for the load to operate at
all the required times throughout
the year. The system could have a
small array and a large battery or
vice versa. However, there are
limits to these sizes as, while the
minimum array size is that which
can deliver the annual daily load in
the average daily insolation, the
minimum battery size is that which
can supply the overnight load.
8.2 The basic principles
The basic rules controlling the
calculation of the correct battery
for an application require the
calculation of the following
parameters:
Unadjusted capacity
This is the average daily load
(in Ah per day) multiplied by the
number of days of battery reserve.
This capacity has to be adjusted
according to the battery
characteristics and operating
conditions.
Discharge adjustment
This is the capacity adjusted for
life. It is obtained by dividing the
unadjusted capacity by the
required capacity at the end of
life (expressed as a percentage
of the rated capacity). Figure 4
shows the number of cycles
before reaching a capacity of 70 %.
Charge adjustment
It is recommended to use a
charge voltage optimised for the
daily DOD and temperature. With
an optimised charge voltage we
get a good state of charge with
the lowest water consumption.
As a guideline, an optimised
charge voltage will allow to keep
a state of charge by 90 to 95 %
when the battery is cycling at high
state of charge.
Temperature adjustment
Cell capacity ratings are defined at
+ 20°C to + 25°C (+ 68°F to + 77°F).
For temperatures outside this
range, it is necessary to use the
temperature correction
factor (see Figures 1 and 2).
Design margin adjustment
It is a common practice to
provide a design margin to allow
for uncertainties in the load
determination. This is usually in
the region of 10 to 25 %.
Load current calculation
The purpose of the equivalent
load current calculation is to be
able to use the performance
table data at + 20°C to + 25°C
(+ 68°F to + 77°F).
From this information it is
possible to correctly calculate a
battery capacity value from the
unadjusted capacity, to apply the
derating factors from the
capacity adjustment, to calculate
the equivalent average current in
dividing the capacity calculated
by the discharge time (number
of days x 24 h) and, using the
current value calculated, the
end voltage, and the autonomy,
to select the right battery
Sunica.plus from the
performance table.
8. Battery sizing principles
21