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)