PUBLIC REVIEW DRAFT, SEPTEMBER 2008CD/K/04-4:2003 
ICS 27.160.20 
 
© EAC 2008 First Edition 2008 
 
 
 
 
   
 
 
EAST AFRICAN STANDARD 
 
Batteries for use in photovoltaic power systems —   
Part 4: 
Recommended practice for si zing lead acid batteries for 
photovoltaic (PV) systems 
 
 
 
  
 
PUBLIC REVIEW DRA FT, SEPTEMBER 2008  
 
 
  
 
 
  
 
   
 
  
EAST AFRICAN COMMUNITY  
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008CD/K/04-4:2003  
ii © EAC 2008 — All rights reserved  
 
Foreword 
 
Development of the East African Standards ha s been necessitated by the need for harmonizing 
requirements governing quality of products and serv ices in East Africa. It is envisaged that through 
harmonized standardization, trade barriers which are encountered when goods and services are 
exchanged within the Comm unity will be removed.  
 
In order to meet the above objectives, the EAC Partner States have enacted an East African 
Standardization, Quality Assurance, Metrology an d Test Act, 2006 (EAC SQMT Act, 2006) to make 
provisions for ensuring standardization, quality as surance, metrology and testing of products 
produced or originating in a third country and traded in  the Community in order to facilitate industrial 
development and trade as well as helping to protect the health and safety of society and the 
environment in the Community. 
 East African Standards are formulat ed in accordance with the proc edures established by the East 
African Standards Committee. The East Afri can Standards Committee is established under the 
provisions of Article 4 of the EAC SQMT Act, 2006. The Committee is composed of representatives of the National Standards Bodies in Partner States, t ogether with the representatives from the private 
sectors and consumer organizations. Draft East African Standards are circ ulated to stakeholders 
through the National Standards Bodies in the Pa rtner States. The comments received are discussed 
and incorporated before finalization of standards, in accordance with the procedures of the 
Community.   Article 15(1) of the EAC SQMT Act, 2006 provides t hat “Within six months of the declaration of an 
East African Standard, the Partner States shall adopt, without deviation from the approved text of the 
standard, the East African Standard as a nationa l standard and withdraw any existing national 
standard with similar scope and purpose”. 
 
East African Standards are subject to review, to keep  pace with technological advances. Users of the 
East African Standards are therefore expected to ensure that they  always have the latest versions of 
the standards they are implementing.  
 
© East African Community 2008 — All rights reserved
* 
East African Community  
P O Box 1096  
Arusha  
Tanzania  Tel: 255 27 2504253/8 
Fax: 255-27-2504481/2504255 
E-Mail: eac@eachq.org
 
Web: www.each.int 
                                                 
* © 2008 EAC — All rights of exploitation in any form and by an y means reserved worldwide for EAC Partner States’ NSBs.  
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008CD/K/04-4:2003  
© EAC 2008 — All rights reserved iii  
Introduction 
 
This recommended practice describes a method fo r sizing both vented and valve-regulated lead-acid 
batteries used in terrestrial photovoltaic (PV) sy stems. Installation, maintenance, safety, testing 
procedures, and consideration of battery types ot her than lead-acid are beyond the scope of this 
document. Recommended practices for the remainder of the electrical systems associated with PV 
installations are also beyond the scope of this document. PUBLIC REVIEW DRAFT, SEPTEMBER 2008CD/K/04-4:2003  
iv © EAC 2008 — All rights reserved  
Contents 
 
1 Scope ....................................................................................................................... ...................... 1 
2 References .................................................................................................................. ................... 1 
3 Defini tions ................................................................................................................. ...................... 1 
4 Outline of sizi ng methodology ............................................................................................... ......... 2 
5 Battery reserve considerations .............................................................................................. ......... 3 
6 Load determ ination .......................................................................................................... ............... 3 
6.1 General cons iderations .................................................................................................... ...... 3 
6.2 Load da ta ................................................................................................................. .............. 4 
6.3 Data an alysis ............................................................................................................. ............ 5 
7 Battery capacity and functional -hour rate det ermination ................................................................ 5 
7.1 Unadjusted capacity ....................................................................................................... ....... 6 
7.2 Battery type selection .................................................................................................... ........ 6 
7.3 Capacity adjustment ....................................................................................................... ....... 6 
7.4 Functional-hour rate ............................................................................................................... 7 
8 Determining number of se ries-connected cells .............................................................................. 7  
8.1 Nominal system voltage ......................................................................................................... 7 
8.2 Voltage window ............................................................................................................ .......... 7 
8.3 Calculating the number of  series-connected cells ................................................................. 8 
9 Battery size determination .................................................................................................. ............ 9 
9.1 Cell size selection ....................................................................................................... ........... 9 
9.2 Number of pa rallel strings ................................................................................................ ...... 9 
9.3 Final number of cells .............................................................................................................. 9 
9.4 Final battery  capacity .................................................................................................... ....... 10 
9.5 Checks and considerations .................................................................................................. 10 
10 Battery sizi ng worksheets .................................................................................................. ...... 10 
Worksheet 1 — Battery sizing .................................................................................................. ........ 16 
Worksheet 2 — Supplemental battery sizi ng for duty cycle pe riods > 24 h ..................................... 20 
Worksheet 3 — Summary ................................................................................................................. 20 
Annex A (informative)  Battery characteristics ............................................................................................ 21 
Annex B (informative)  Examples ............................................................................................................. 25 
B.1 Refrigerator/freezer fo r vaccine storage .............................................................................. 25 
B.2 Remote communications system ......................................................................................... 30 
B.3 Remote residence .......................................................................................................... ...... 35 
Annex C (informative)  Bibliography ........................................................................................................... 43 
 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008CD/K/04-4:2003  
© EAC 2008 — All rights reserved  1  
Batteries for use in photovoltaic power systems — Part 4: 
Recommended practice for si zing lead-acid batteries for 
photovoltaic (PV) systems 
 
 
1 Scope 
 
This recommended practice describes a method fo r sizing both vented and valve-regulated lead-acid 
batteries in photovoltaic (PV) systems. Installation, maintenance, safety, testing procedures, and 
consideration of battery types other than lead -acid are beyond the scope of this document. 
Recommended practices for the remainder of the electrical systems associated with PV installations are 
also beyond the scope of this document. 
 
Sizing examples are given for various representative system applications. Iterativ e techniques to optimize 
battery costs, which include consideration of the in terrelationship between ba ttery size, PV array size, 
and weather, are beyond the scope of this document. 
 
This recommended practice is meant to assist syst em designers in sizing lead-acid batteries for 
residential, commercial, and industrial PV systems. 
 
2 References 
 
This recommended practice shall be used in conjunction with the following publications. When the following 
standards are superseded by an approved revision, the revision should be used. 
 
EAS 389-1, Solar photovoltaic power systems — Design, installation operation monitoring and 
maintenance — Code of practice — Part 1: Design of solar PV power systems  
 
EAS 363-2, Solar photovoltaic power systems — Test procedures for main components — Part 2: 
Installation, maintenance, test ing and replacement of batteries  
 
3 Definitions 
 
The following definitions apply specifically to this recommended practice.  
 
3.1 
array-to-load ratio 
The array-to-load ratio is the average photovoltaic  ampere hours available divided by the average daily 
load in ampere hours (Ah). The average daily PV am pere hours is calculated by taking the average 
daily solar resource for the month of inte rest in kilowatt hours per square meter (kWh/m2) times the 
array current at its maximum power point under a solar irradiance of 1000 watts per square meter 
(W/m ). 
 
3.2 
cycle life 
The number of cycles (discharges and recharges) , under specified conditions, that a battery can 
undergo before failing to meet its specified end-of-life capacity. 
 
33 
days of battery reserve 
The number of days a fully charged battery can sa tisfy the load with no contribution from the 
photovoltaic array or auxiliary power source. 
 
3.4 
depth of discharge (DOD) EAST AFRICAN STANDARD PUBLIC REVIEW DRAFT, SEPTEMBER 2008CD/K/04-4:2003  
2 © EAC 2008 — All rights reserved The ampere hours removed from a fully charged ba ttery, expressed as a percentage of its rated 
capacity at the applicable discharge rate. 
 
3.5 
discharge rate 
The rate, in amperes, at which cu rrent is delivered by a battery. See also: hour rate.  
 
3.6 
energy capacity 
The energy, usually expressed in watt hours (Wh), that a fully charged battery can deliver under 
specified conditions. 
 
3.7 
hour rate 
The discharge rate of a battery expressed in terms of the length of time a fully charged battery can be 
discharged at a specific current before r eaching a specified end-of-discharge voltage. 
 
3.8 
rated capacity (C) 
The capacity, in ampere hours (Ah), assigned to a cell  by its manufacturer for a given constant-current 
discharge rate, with a given discharge time, at a spec ified electrolyte temperature and specific gravity, 
to a specific end-of-discharge voltage. 
 
3.9 
regulation voltage 
The maximum voltage that a charge controller will allow the battery to reach under charging 
conditions. At this point the charge controller w ill either discontinue charging or begin to taper the 
charging current to the battery. 
 
3.10 
self discharge 
The process by which the available capacity of a battery is reduced by internal chemical reactions 
(local action). 
 
3.11 
self-discharge rate 
The amount of capacity reduction in a battery occurri ng per unit of time as the result of self-discharge. 
 
3.12 
valve-regulated lead-acid cell (VRLA) 
A lead-acid cell that is sealed except for a valve t hat opens to the atmosphere when the internal gas 
pressure in the cell exceeds the atmospheric pressure by a preselected amount. Valve-regulated cells 
provide a means for recombinati on of internally generated oxyg en and the suppression of hydrogen 
gas evolution to limit water consumption. 
 
3.13 
vented battery 
A battery in which the products of electrolysis and evaporation are allowed to escape freely to the 
atmosphere. These batteries are commonly referred to as "flooded." 
 
4 Outline of sizing methodology 
 
The function of a battery used in a PV system is to supply power when the system load exceeds the output 
of the PV array. For a satisfactory PV battery system , many factors should be considered to determine the 
necessary capacity and the number of cells composi ng the battery. These factors, as follows, will be 
discussed in subsequent clauses: 
 
⎯ Battery reserve considerations (Clause 5). The length of time that the load should be supported solely 
by the battery is established by system design requirements. 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008CD/K/04-4:2003  
© EAC 2008 — All rights reserved  3 ⎯ Load determination (Clause 6). Requirements of the application determine the amount of current that 
is to be supplied by the battery over a period of  time. The peak current and the operational voltage 
window are determined by the system's load devices. 
 
⎯ Battery capacity and functional-hour rate determination (Clause 7). The battery capacity and its 
discharge functional-hour rate are determined by the specific application load, days of battery 
reserve, and battery characteristics (see Annex A). 
 
⎯ Determining number of series-con nected cells (Clause 8). The syst em's voltage limits (voltage window) 
determines the required number of cells in series. Several criteria should be examined to assure a 
workable system. 
 
⎯ Cell capacity and battery size determination (Clause 9). Once the overall battery capacity and number 
of cells in series have been determined, the final selection of a specific cell can be made and the final 
battery size can be calculated. 
 
NOTE Because of the interaction of these factors, an iterative process may be needed to determine the optimum 
battery for the application. 
 
⎯ Battery sizing worksheets (Clause 10). Worksheets t hat provides a systematic approach to the sizing 
of a battery for a PV system is presented. The application of the worksheets is explained in 
accompanying text. 
 
⎯ Battery characteristics (Annex A). System perfo rmance, life, maintenance, and cost are influenced 
by the type of battery selected for a PV applic ation. Information regarding lead-acid battery 
characteristics is presented. 
 
⎯ Examples (Annex B). Presented are examples de monstrating various aspects of battery sizing. 
 
5 Battery reserve considerations 
 
Photovoltaic power systems may require some battery reserve, both for reliability of service and to provide 
time for intervention in the event of an unanticipated o ccurrence such as unusually poor weather or failure of 
a system component. The number of days of battery  reserve is commonly specified as a system 
design requirement, and is based on several considerations including the following: 
 
a) System application. Critical load applications generally require mo re days of battery reserve than 
noncritical applications. 
 
a) System availability. System availability is the minimum percentage of the time that the PV system 
should be able to satisfy the system loads. 
 
b) Solar irradiance variability. Daily and seasonal vari ations in solar irradiance affect the required number 
of days of battery reserve. 
 
c) Predictability of load. The load may or may not be predictable; also, there may be the possibility of 
adjusting the loads, e.g., dropping nonessential loads. 
 
d) Backup power provisions. If the PV system includes provisions for backup power, the desired 
frequency and duration of operation of the backup power source needs to be considered. 
 
e) Accessibility of site. The wo rst-case time required for co rrection of any problem should be 
considered. 
 
6 Load determination  
 
6.1 General considerations 
 
The overall duty cycle imposed on the battery is the descr iption of the dc load current and its duration within 
the days of battery reserve, during which it is assum ed that no power is provided by the PV array or auxiliary PUBLIC REVIEW DRAFT, SEPTEMBER 2008CD/K/04-4:2003  
4 © EAC 2008 — All rights reserved power source. For ac loads supplied through an inverter, these loads should be tabulated separately, 
totaled, and combined with the inverter losses to determine the actual dc load on the battery. 
 
The system's load can be expressed in a tabular or  graphical form. As both descriptions start with a 
tabulation of the individual loads and their durations, the tabular form is more general. The load-profile 
diagram, the graphical representation, is necessary to visualize the interrelationships of the individual 
loads. For both load descriptions, all loads expected during a 24 h period are tabulated along with their 
anticipated durations. Worksheet 1 in Clause 10 provides  a convenient method of tabulating load data in 
accordance with the sizing method of this document. 
 
It may be necessary to consider a longer period of time when a 24 h period does not accurately describe 
the load profile. For those cases where the load pr ofile exceeds 24 h, an average and a maximum daily 
load should be determined for subsequent battery capacity determinations. Worksheets 2 and 3 in 
Clause 10 provide a convenient method for determining these loads. The average daily load is used in 
the initial determination of the battery size. 
 
Once the battery has been sized, the maximum daily load is used to determine the ability of this battery to 
sustain it. If the maximum daily load sequence cann ot be established, the days should be arranged in 
the worst possible order, generally with the maximu m load day last. The battery's capacity may need to 
be increased to satisfy the maximum daily load in this partially discharged state. 
 
A load-profile diagram is a necessary aid in determining those areas where the battery's performance 
needs to be checked to assure load satisfaction. To make a load profile diagram, do the following: 
 
a) Tabulate all the individual loads along with their starting and stopping times. 
 
b) Total the coincident loads for their respective periods of time. 
 
c) Plot the resulting total load versus time of day or elapsed time, as appropriate. 
 
The resulting curve is the load-profile diagram. If the daily loads vary during the days of battery reserve, the 
individual daily load-profile diagrams, plotted in seque nce, constitutes the syst em's load-profile diagram. 
See Annex B for examples. 
 
6.2 Load data 
 
The information that should be gathered for each load is discussed in 6.2.1 through 6.2.6. 
 
6.2.1 Momentary current  
 
Loads lasting one minute or less are designated "momentary" loads and are given special consideration. 
The ampere hour requirements of this type of load are us ually very low, but their effect on battery terminal 
voltage may be considerable and should be taken into  account. Momentary loads can occur repeatedly 
during the duty cycle. Typical momentary loads are as follows: 
 
a) Motor starting currents 
 
b) High inverter surge currents 
 
6.2.2 Running current  
 
Running current is the current required by a load afte r its starting current has subsided. Certain devices 
require a constant power, thus the current required will rise as the  battery voltage falls. Since the battery 
voltage remains relatively constant until near the end of discharge, the running current may be 
approximated as the current required at 95% of the system voltage. 
 
NOTE For certain loads, it is necessary to consider both the momentary and running current components of the load. For 
example, it' an electric motor starts during the duty cycle, bot h the starting (momentary) current and running current need to be 
considered. The starting current need not be considered if the lo ad was operating at the beginning of the duty cycle, i.e., at the 
beginning of the days of battery reserve. 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008CD/K/04-4:2003  
© EAC 2008 — All rights reserved  5 6.2.3 Parasitic current  
 
Parasitic losses, such as those resulting from tare  losses of charge controllers and inverters, should 
be included as currents. These currents should be included as part of the running-current loads. 
Consideration of the battery's self-discharge is recommended as a check (see 9.5) after the battery is 
selected. 
 
6.2.4 Load duration  
 
The load duration is the time, in hours, of operation of each load. For PV systems, it is very common for load 
duration to be expressed in terms of a daily cycle th at repeals over the days of battery reserve. If the 
inception time of a load is known, but the shutdown time is indefinite, it should be assumed that the load will 
continue through the remainder of the days of battery reserve. 
 
6.2.5 Load coincidence  
 
Each load current (momentary or running) is classified  as to whether or not it is coincident with any other 
loads, and tabulated accordingly. Loads that occur at  random are assumed to be coincident loads. This 
information, portrayed in the load-profile diagram, is  later used in battery selection and to check discharge 
rate (see 6.3). 
 
6.2.6 Maximum and minimum load voltage  
 
The maximum and minimum voltage at which each load operates properly should be determined and 
tabulated (see 8.2). Voltage drops, such as those associated with cabling, overcurrent protection, and 
connectors, between the battery and the loads are not to be considered as an adjustment to a load's 
maximum voltage. This is because the current and resulting voltage drops can be very low at times, thus 
exposing the device to battery terminal voltage. Ho wever, these voltage drops should be determined 
individually for each load device and added to its minim um operating voltage to ensure that the required 
minimum voltage will be present at the load. 
 
6.3 Data analysis 
 
6.3.1 Ampere hours  
 
It is usually possible to calculate an equivalent daily  load by multiplying each load current by its daily 
duration, and summing the results. If the duration of the momentary load is known, calculate the ampere 
hour load by multiplying this duration by the momentar y current. If the duration of the momentary load is 
not known, assume the time to be 1 min and calculate the load accordingly. For voltage-drop 
considerations, a full-minute duration is used in either case. 
 
If the duty cycle does not repeat each day, it is necessary to describe the load over all the days of 
battery reserve. Worksheet 2 in Clause 10 is provided for this purpose. If the graphical form of the load 
description is used, the ampere hour load is the total area under the load-profile curve. 
 
6.3.2 Currents  
 
The maximum momentary and maximum running currents are determined and are used to calculate 
the battery's maximum discharge current. Sinc e the system loads may operate in various 
combinations, the maximum current (momentary or running) is the largest summation of the individual 
loads that can occur simultaneously.  
 
7 Battery capacity and func tional-hour rate determination 
 
The required battery capacity for a PV application is de termined by the number of days of battery reserve 
and by the characteristics of the load, battery, and inst allation. A functional-hour rate for the application is 
determined by capacity and load calculations. 
 
 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008CD/K/04-4:2003  
6 © EAC 2008 — All rights reserved 7.1 Unadjusted capacity 
 
The unadjusted capacity, in ampere hours, is calculated by  multiplying the days of battery reserve by the 
average daily load (in ampere hours/day as determined in  Clause 6). This capacity will be adjusted in 7.3 for 
battery characteristics and operating conditions. 
 
7.2 Battery type selection 
 
A trial battery type should be selected before proceeding with the sizing process. This is necessary 
because performance characteristics, such as desi gn depth of discharge and cycle life, are different for 
the various battery types. 
 
If a vented battery is used, it should be selected for the intended application by considering watering 
intervals, the consequences of hydrogen and oxygen evolution, and wear-out mechanisms. 
 
If a valve-regulated battery is used, it should be se lected for the intended application by ensuring that 
recombination is effective and that dry-out, therma l runaway, and the consequences of hydrogen and 
oxygen evolution are considered (see A.4.3). 
 
Annex A provides a more detailed catalog of bat tery characteristics that should be considered. 
Reevaluation of the applicability of the trial battery  is recommended throughout the sizing process. 
Refer to manufacturer's literature for spec ific data on the type of battery selected. 
 
7.3 Capacity adjustment 
 
7.3.1 Discharge adjustments  
 
The unadjusted capacity should be modified to assure satisfacto ry battery cycle life. Battery 
manufacturers rate lead-acid cells for maximum depth of discharge (MDOD), maximum daily depth 
of discharge (MDDOD) and end-of-life (EOL) capacity. The battery capacity should be adjusted in the 
following ways:  
 
a) The capacity adjusted for MDOD is obtained by  dividing the unadjusted capacity by MDOD (in 
percent).  
 
b) The capacity adjusted for MDDOD is obtained by dividing the maximum daily ampere hours by 
MDDOD (in percent).  
 
c) The capacity adjusted for life is obtained by divi ding the unadjusted capacity by the end-of-life 
capacity expressed in percent of the rated capacity, commonly 80%.  
 
The largest of these three capacities will satisfy the depth-of-discharge and end-of-life adjustments.  
 
7.3.2 Temperature adjustment  
 
The available capacity of a battery is affected by it s operating temperature. Cell capacity ratings are 
generally standardized at 25 °C. Capacity increase s at temperatures above 25 °C and decreases at 
temperatures below 25 °C. Capacity is rarely  adjusted for warm temperature operation, but 
adjustments are routinely made for cold weather app lications. Refer to the battery manufacturer's 
literature for temperature correcti on factors. The adjusted capaci ty determined in 7.3.1 should be 
corrected by this factor to yield capacity adjusted for temperature. 
 
7.3.3 Design margin adjustment  
 
It is prudent design practice to provide a capacity margin to allow for uncertainties in the load 
determination, e.g., less-than-optimum conditions and load growth. A common practice to provide this 
design margin is to add 10—25% to the capacity as determined in 7.3.2. PUBLIC REVIEW DRAFT, SEPTEMBER 2008CD/K/04-4:2003  
© EAC 2008 — All rights reserved  7  
7.4 Functional-hour rate 
 
In order to correctly size the battery, the disc harge rate and ampere hour capacity should be 
considered together. In continuous load applicat ions, the battery should have sufficient capacity to 
supply the constant discharge rate over the num ber of days of battery reserve. However, in 
noncontinuous load applications, the discharge rate varies and could include high rates of discharge 
periodically throughout the days of battery reserve.  Using an average rate to size the battery could 
result in insufficient capacity to supply high curr ents above the minimum voltage late in the battery 
discharge. The functional-hour rate conservative ly approximates a single discharge rate that is 
equivalent to the varying discharge rates of a partic ular duty cycle. The functional-hour rate used in 
9.1, for cell selection, may be greater  than the period of battery reserve. 
 
The functional-hour rate can be calculated as follows: 
 
a) Compare the sum of coincident running currents ( Icoin) with the maximum noncoincident running 
current ( Inoncoin) and select the larger. 
 
b) Divide the adjusted capacity as determined in 7. 3.3 by the maximum running current selected in 
step a). 
 
EXAMPLE 1 The adjusted battery capacity in a system with 5 days of  battery reserve is 150 Ah, with a maximum current drain of 2 5 A. 
The functional-hour rate is 150 divided by 25, or 6 hours. 
 
EXAMPLE 2 The adjusted battery capacity in a system with 5 days of  battery reserve is 150 Ah with a continuous current drain of  1 A. The 
functional-hour rate is 150 divided by 1, or 150 hours. 
 
8 Determining number of series-connected cells 
 
A battery is usually composed of a number of identical cells connected in series. The maximum and 
minimum system voltages determine the number  of series-connected cells of the battery. 
 
8.1 Nominal system voltage 
 
The lead-acid cell has a nominal voltage of 2 V; therefor e, the number of cells may be estimated by dividing 
the nominal system voltage by 2. It is common practice to use 6 cells for a 12 V system, 12 cells for a 24 V 
system, etc., but it is possible that the allowable volt age limits may require adjustment to this general rule. 
 
8.2 Voltage window 
 
The system equipment will always have a voltage r ange within which the equipment will operate at rated 
capacity and efficiency. If the equipment is exposed to  higher- or lower-than-specified voltages, it may be 
damaged or operate improperly. This high ( Vmax) and low ( Vmin) limit of system voltage is called the voltage 
window. The magnitude of this window has a direct  effect on the number and capacity of battery cells 
selected. The narrower the window, the larger the cell's capacity needs to be; the wider the window, 
the smaller the cell's capacity can be. 
 
From the tabulated maximum and minimum voltages in 6.2.6, the lowest maximum voltage ( Vmax) and the 
highest minimum voltage ( Vmin) define the voltage window within which all loads in the system will operate 
properly (see item 4b of Clause 10). If a charge controller is used, its setpoints should be within this voltage 
window. 
 
When a temperature-compensated charge controller is used, the setpoints vary with the temperature of 
the battery. (The temperature used for the voltage compensation should be sensed at the battery.) The 
voltages associated with the anticipated temperature extremes of the battery should be used for this 
voltage window check. Since the charging voltage of the battery increases with decreasing temperature, 
generally only the voltage associated with the lowest  anticipated temperature will be of significance. 
 
NOTE The battery may be excessively overcharged by a voltage less than Vmax. It is recommended that a charge controller be used 
to limit the charge voltage. The consequences of excessiv e overcharging are described in item a) of 9.5. 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008CD/K/04-4:2003  
8 © EAC 2008 — All rights reserved 8.3 Calculating the number of series-connected cells 
 
The number of series-connected cells is a function  of both the voltage window of the loads and the 
manufacturer's charging recommendation for the selected cell. An optimum number of cells is 
determined by iterative calculations. 
 
8.3.1 Maximum number of cells allowed  
 
The most important aspect of calculating the maxi mum number of series-connected cells is to ensure 
an optimal and safe cell recharge voltage. In determin ing the maximum number of cells allowed by the 
system, the following calc ulation is performed: 
 
Maximum number of cells (rounded down) =   voltage recharge  cellmaxV 
 
When the system has capability for cell equalization or temperature-compensated charging, the 
maximum associated voltage should be used for the above calculation provided it does not exceed 
the manufacturer's recommendations.  
 
EXAMPLE: 
 
Assume 2.4 V per cell is the maximum recommended voltage for recharging. The maximum allowable 
system voltage is 58 V dc. Then:  
 
V/cell 2.4V  58= 24.17 cells,  
 
therefore, use 24 cells.  
 
8.3.2 Minimum system voltage versus end-of-discharge voltage  
 
To ensure that the battery is not operated below the manufacturer's recommended end-of-discharge 
(EOD) voltage, calculate the voltage per cell to which the low limit of the system voltage would allow 
the cell to be discharged. This calculated EOD cell voltage should not be below the manufacturer's 
limit at the functional-hour rate. This is determined as:  
 
Calculated EOD cell voltage = 8.3.1  from calculated cells of number  minV 
 
EXAMPLE : 
Assume the minimum system voltage is 42 V dc. Then 
 
cells 24V  42= 1.75 V per cell 
 
If the calculated EOD cell voltage is not satisfacto ry (i.e., is below the manufacturer's recommended 
EOD voltage at the functional-hour rate), an adj ustment should be made to the minimum system 
voltage or a smaller number of cells should be used, or both. 
 
NOTE If the calculation results in an EOD voltage that is greater than that recommended by the manufacturer, the cell, when dis charged to 
the calculated EOD voltage, will supply less capacity than if it were discharg ed to the reco mmended EOD cell voltage. 
 
8.3.3 Multicell unit considerations  
 
If the cell type selected is available only in multic ell units, it may be necessary to use a different 
number of cells than previously calculated. The conversion from maximum system voltage to number 
of multicell units is: 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008CD/K/04-4:2003  
© EAC 2008 — All rights reserved  9 Total number of multicell units = recharge   multicell   maximummaxV 
 
Fractional results are to be rounded down to the next lowe st whole number. It is necessary to review the 
voltage window calculation to ensure that  all system requirements are met. 
 
8.3.4 Optimization  
 
The calculation in 8.3.1 will provide the maximum number of allowable series-c onnected cells that 
should ensure proper system performance. It may be  possible to use fewer series-connected cells 
and yet maintain proper system per formance. See Clause 10 for the iterative process that can result 
in fewer series-connected cells. However, this could result in other problems, including thermal 
runaway, under certain conditions [see item a) of 9.5].  
 
NOTE Care should be taken to ensure that the chosen number of battery cells can be charged effectively by a commercially 
available photovoltaic charging system. Nonstandard equipment may be expensive and difficult to obtain. 
 
9 Battery size determination 
 
Battery size is determined by using the results of  Clause 7 and Clause 8 to select an appropriate 
battery that meets the l oad and site requirements. 
 
9.1 Cell size selection 
 
The cell size is selected by using the same manufac turer's data that was used in 7.2. Choose a cell 
that meets the capacity requirem ents of 7.3.3 when discharged at the functional-hour rate determined 
by 7.4 to an EOD voltage that is greater than or equal to the EOD voltage determined by 8.3. When 
the cell available from the manufacturer does not meet  the exact capacity requirement, the next larger 
capacity cell should be selected. If no single cell has t he necessary capacity or its use is not practical 
for the application, then refer to 9.2. A manufactu rer may list available capacities by one of the 
following: 
 
a) The capacity of the cell itself 
 
b) The capacity of an individual positive plate 
 
If the manufacturer lists capacity of positive plat es, the required number of positive plates may be 
determined by dividing the capacity requirement as found in 7.3.3 by the positive plate capacity. 
Fractional results are to be rounded up to the next higher whole number. 
 
9.2 Number of parallel strings 
 
Parallel strings are used in order to  meet design requirements such as: 
 
⎯ Increasing capacity of  an existing battery 
 
⎯ Providing redundancy 
 
⎯ Providing battery reserve while a string is disconnected for maintenance or testing 
 
If cells of sufficiently large capacity  are not available or practical, then two or more strings, of equal 
numbers of identical series-connected cells,  may (consistent with the manufacturer's 
recommendations) be connected in parallel to obtain the necessary capacity. 
 
The number of parallel strings is calculated by dividi ng the capacity found in 7. 3.3 by the selected cell 
capacity determined by 9.1 (rounded up). 
 
9.3 Final number of cells 
 
The total number of cells can then be calculated by multiplying the number of series cells determined 
by 8.3 by the number of parallel strings. PUBLIC REVIEW DRAFT, SEPTEMBER 2008CD/K/04-4:2003  
10 © EAC 2008 — All rights reserved  
9.4 Final battery capacity 
 
The final battery capacity is calculated by multiplying the selected cell capacity by the number of 
parallel strings.  
 
9.5 Checks and considerations 
 
There are other considerations with respect to the PV system design, which may affect battery 
performance. These are as follows: 
 
a) Excessive overcharging. Excessi ve overcharging may result from factors such as too high an end-
of-charge voltage, no high-limit cutoff voltage, or excessive ampere hours recharged for the 
ampere hours discharged. For vented batteries, overcharging will result in the generation and 
release of potentially hazardous quantities of hydrogen and oxygen, and will accelerate water 
loss. For valve-regulated batteries, overcharging also will result in the generation of potentially 
hazardous quantities of hydrogen and oxy gen that may be released. The quantity and 
composition depends on the rate and duration of the overcharge, the battery and its valve design, 
oxygen recombination efficiency (see A.2), thermal environment, and previous usage of the 
battery. Consequences of water loss are different for vented batteries, where the liquid can 
generally be replaced. In valve-regulated batteries , the water lost cannot be replaced and, 
therefore, life will be shortened. Overcharging  valve-regulated batteries can also cause a 
potentially hazardous condition kn own as thermal runaway. This results in excess heat, which 
enables the battery to draw ever more current, a co ndition that continues until the battery releases 
all its water and the battery is destroyed. For both vented and valve-regulated batteries, excessive 
overcharging will increase the rate of positive gr id corrosion and will shorten the battery's life. If 
any of the conditions that may lead to overch arging exist, discussion between the PV system 
designer and the battery manufacturer will be  necessary to determine the preventive and 
corrective actions. 
 
b) Undercharging. Insufficient time at the avail able charge rate or too low a charging voltage will 
result in an undercharged battery. If either of these conditions exist, discussion between the PV 
system designer and the battery manufacturer will be necessary to determine the corrective action. 
 
c) High-discharge rate. A momentary load, particula rly one occurring at or near the end of the days 
of battery reserve period, may cause the batte ry voltage to drop below the minimum system 
voltage. If such a momentary load is significantly larger than the average load, it is recommended 
that the battery capacity be sized in accordance  with the method of EAS 389-1 (considering the 
required days of battery reserve for the load profile diagram), or a reexamination of the worst case 
loads be made and discussed wi th the PV system designer. If th e method of EAS 389-1 is used, 
the resulting battery should be reevaluated according to the criteria given in this document. In 
most cases, if the momentary load is less than the 20 h discharge rate, then the discharge rate will not 
cause the battery voltage to drop below the minimum system voltage. 
 
d) Freezing of the electrolyte. Freezing a battery's electrolyte can cause damage and, therefore, should 
be prevented. The freezing point of the electrolyte (refer to the manufacturer's literature) should be 
less than the lowest anticipated operating temperature based on the battery's lowest design state of 
charge. If not, consider thermal insu lation for the battery or increasing the battery capacity and minimum 
system voltage. 
 
e) Self-discharge as a battery load. All batteries su ffer from an internal capacity loss mechanism known as 
self-discharge. The amount of self-discharge (A h/month) is a function of battery operating 
temperature, type, and age. The self-discharge for the battery type selected, within its operating 
environment, should be obtained and the resulti ng capacity loss calculated and added to the 
calculated battery capacity, if appropriate. 
 
10 Battery sizing worksheets 
 
Worksheet 1 may be used to organize the manual a pplications of the procedures outlined previously. 
Examples of its use are in Annex B. Instructions for use follow; the numbering system corresponds to that 
of the worksheet. 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008CD/K/04-4:2003  
© EAC 2008 — All rights reserved  11 1) Project name and description. Enter the necessary information. 
 
2) Nominal system voltage. Enter the nom inal system voltage (e.g., 12 V, 24 V). 
 
3) Days of battery reserve. Enter the number of days of battery reserve. 
 
4) Load data. Enter the necessary load information for each load device and calculate the daily load for 
each device. Worksheet 2 is to be used when the load duty cycle exceeds 1 day (24 hours). The 
following is an explanation of the terms used: 
 
a) DC load device: The identification of the dc loads.  
 
NOTE 1 If the load is an inverter, a separate calculation should be made of the loads run by the inverter plus inverter 
losses. 
 
NOTE 2 If the load device has a momentary current as well as  a running current, e.g., a moto r, the load device should he 
treated as two distinct loads, one of which has only a momentary current, the other of which has only a running current. 
 
b) Voltage window: The maximum and minimum voltage, Vmax and Vmin, acceptable to each load. ( Vmin 
includes wiring voltage drops.) 
 
c) Momentary currents: The inrush or peak current of each load, e.g., the inrush current required to 
start a motor. If the momentary current and the running current are the same, enter the running 
current only (column 4d). The two columns, Icoin and Inoncoin, refer to the coincident and noncoincident 
currents. The Inoncoin column is used only for loads that will never operate at the same time as other 
loads. 
 
d) Running currents: The normal running current of each load, Icoin and Inoncoin. The Inoncoin column is used 
only for loads that never operate at the same time as other loads. Parasitic currents are entered as 
running currents. 
 
e) Constituents of maximum running currents: The load s that can operate in coincidence to generate 
the maximum running current are identified, if known. If the loads are random, the sum of all 
coincident running currents is used. 
 
NOTE Columns 4f and 4g are provided to facilitate ca lculations when the load currents, and their duration per 
occurrence, are identical. Otherwise, enter the total run time in column 4h. 
 
f) Number of occurrences: The number of operational periods of each load for the day. 
 
g) Duration: The hours per operational occurrence for each load. 
 
h) Run time: The hours per day of operation of each load (line 4f times line 4g or the total time). If the 
run time varies from day to day, use Worksheet 2. 
 
i) Daily load: The ampere hour per day requirements for each load. It is the product of each load 
current and its respective run time. 
 
5) Load data summary (using the load data from 4, columns 4a through 4i) 
 
a) Enter the maximum coincident momentary current [refer to the load-profile diagram(s)]. 
 
b) Enter the maximum coincident running current [refer to the load-profile diagram(s)]. 
 
c) Enter the total from the daily load column of Worksheet 1 or the average daily ampere hours from 
Worksheet 3, if used. 
 
d) Enter the maximum daily load from Worksheets 2, if used. 
 
e) Enter the greatest of the va lues in the momentary currents Inoncoin column or from Worksheet 3, if 
used. PUBLIC REVIEW DRAFT, SEPTEMBER 2008CD/K/04-4:2003  
12 © EAC 2008 — All rights reserved  
f) Enter the greater of line 5a or line 5e. This val ue will be used later when checking the ability of the 
battery selected to provide the maximum momentary current. 
 
g) Enter the greatest of the values in the running currents Inoncoin column or from Worksheet 3, if used. 
 
h) Enter the greater of line 5b or line 5g. This will be used later to calculate the appropriate 
discharge rate for the battery. 
 
i) Enter the greater of line 5f or line 5h. 
 
j) Enter the lowest value from the voltage window Vmax column or from Worksheet 3, if used. 
 
k) Enter the highest value from the voltage window Vmin column or from Worksheet 3, if used. 
 
6) Battery capacity. To complete this section, it  is necessary to have the following information: 
 
⎯ Maximum allowable depth of discharge (MDOD), in percent 
 
⎯ Maximum allowable daily depth of  discharge (MDDOD), in percent 
 
⎯ End-of-life (EOL) capacity, in percent 
 
⎯ Minimum temperature at which battery is required to support the load, corresponding temperature 
correction factor from the manufa cturer's literature, in percent 
 
⎯ Design margin, in percent 
 
a) An unadjusted battery capacity is calculated. Enter the product of the days of battery reserve and 
the total daily load (line 3 times line 5c). 
 
b) Enter MDOD. 
 
c) Adjust the capacity for MDOD (line 6a divided by line 6b). 
 
d) Enter MDDOD. 
 
e) Adjust the capacity for MDDOD (line 5c divi ded by line 6d, or line 5d divided by line 6d if 
Worksheet 3 is used.) 
 
f) Enter EOL. 
 
g) Adjust the capacity for EOL (line 6a divided by line 6f).  
 
h) Enter the largest of the above three capacities,  
 
i) Enter the minimum operating temperature in degrees Celsius (°C).  
 
j) Enter the appropriate temperature correction factor from the manufacturer's literature.  
 
NOTE Adjustments for temperatures above 25 °C are not typically made. 
 
k) Adjust the capacity (line 6b) for temperature.  
I) Enter the design margin factor ( ≥1); e.g., for a 10 % oversize, enter the number 1.1.  
 
m) Adjust the capacity for the design margin (line 6k times line 6l). 
 
7) Functional-hour rate. Divide the adjusted capacity (line 6m) by the maximum running current from the 
battery (line 5h). The functional-hour rate may be greater than the period of battery reserve.  
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008CD/K/04-4:2003  
© EAC 2008 — All rights reserved  13 8) Voltage window adjustment. This section provides for any adjustment that may be necessary as a 
result of controller setpoints. The controller setpoints should determine the limits of the voltage window 
and provide as wide a voltage range as possible while protecting the loads and battery (see Note in 
8.2.) When temperature-compensated charge co ntrollers are used, the voltage window should 
correspond to the anticipated maximum an d minimum battery temperature extremes.  
 
a) Enter the setpoint of the low-voltage load disconnect of the controller, if used. The value 
should be greater than or equal to line 5k.  
 
b) If a charge controller is used, enter line 8a, otherwise enter line 5k.  
 
c) Enter the setpoint of the full-charge voltage cutout of the controller, if used. The value should be 
less than or equal to line 5j.  
 
d) If a charge controller is used, enter line 8c, otherwise enter line 5j.  
 
9) Number of series-connected cells. To complete th is section, the following information is required 
from the battery manufacturer:  
 
⎯ Cell's charge voltage: the manufacturer's recommended charging voltage for the type of battery  
 
⎯ End-of-discharge (EOD) voltage (at the functional-hour rate)  
 
⎯ Cell voltage when the fully available capacity to MDOD is reached  
 
a) Enter the cell's charge voltage.  
 
b) Calculate the maximum number of cells connected in series that can be charged within the battery 
voltage window; round down (line 8d divided by line 9a).  
 
c) Enter the manufacturer's recommended cell EOD voltage.  
 
d) Calculate the cell's EOD voltage that corresponds to Vmin (line 8b divided by line 9b). If equal to or 
greater than line 9c, proceed to step 9g; if less than line 9e, proceed to step 9e.  
 
e) Decrease the number of series cells by 1.  
 
f) Calculate the cell's charge voltage as dete rmined by the system voltage window (line 8d 
divided by line 9e). If the result is within the manufacturer's recommended cell charge voltage 
range, proceed to step 9g. If the result is outside the range, do one of the following:  
 
i) Repeat steps 9e and 9f.  
 
ii) Select a different type of cell, e.g. different plate composition or specific gravity (go back to 
step6b).  
 
iii) Adjust the full-charge voltage setpoint on the controller, if used, downward to prevent 
excessive overcharge (go back to step 8c).  
 
iv) Choose a different controller (go back to step 8a).  
 
g) Enter the selected number of series-connected cells (line 9b or line 9e, as appropriate).  
 
10) Cell selection  
 
a) An appropriate cell capacity, considering functional-hour rate and calculated EOD (line 9d), is 
found in the manufacturer's literature and entered.  
 
b) The number of parallel strings is determined by dividing the required capacity by the capacity of 
the selected cell (line 6m divided by line 1 0a). Round up to the next higher whole number.  PUBLIC REVIEW DRAFT, SEPTEMBER 2008CD/K/04-4:2003  
14 © EAC 2008 — All rights reserved  
c) The final capacity of the battery is the capacity  of the selected cell multiplied by the number of 
parallel strings (line 10a times line 10b).  
 
11) Checks and considerations. This section serves as a cross check between the selected battery and 
the other aspects of the PV system design (e.g., PV array/controller combination). As each check 
and consideration is resolved (a step that may require changes to the system design or the battery 
selection) the appropriate box is checked off. In order to complete this section, the following 
information is required:  
 
⎯ Maximum recommended charge current for the battery during recharge (line 11a, i)  
 
⎯ Maximum available charging current within the voltage window (line 11a, ii)  
 
⎯ Maximum recommended charging current for the battery after reaching the regulation voltage (line 
11b.1) (this current is highly dependent on the battery's operating temperature.)  
 
— Maximum available charging current at battery's regulation voltage (line 11b, ii)  
 
— Array-to-load ratio for the minimum design month (line lie)  
 
— Maximum discharge current (line 11d)  
 
— Electrolyte freezing temperature at the lowest state of charge (line 11e)  
 
— Battery's self-discharge rate (line 11f)  
 
— Electrolyte reserve capacity for vented cells (line 11g)  
 
— Battery's physical characteristics (individual uni t's weight and dimensions, handling restrictions, 
etc.). 
 
Considerations resolved  
 
a) Maximum charge rate. The available charging current should be checked against the battery's 
allowable charging current to ensure that the battery is not damaged from excessive current.  
 
b) Excessive overcharging. For systems without di sconnecting charge controllers, the array current 
equivalent to the battery's regulation voltage should be checked against the battery's 
allowable float current to assure that the battery is not damaged by overcharging [see item a) of 
9.5]. 
 
c) Array-to-load ratio. The ampere hour output of  the array over the load ampere hours for the 
minimum design month. The minimum design month array-to-load ratio value should be above 1.3 
to recharge the battery while the daily load is supplied. 
 
d) High-rate discharge. Momentary or short-duration loads occurring near the end of the days of 
battery reserve will cause voltage decay [refer to item  c) of 9.5 if (line 10c divided by line 5i) < 20 
hours]. 
 
e) Freezing of electrolyte. To prevent damage to the battery, the freezing point of the electrolyte at 
MDOD should be lower than the minimum operating temperature (line 11e should be less than line 
6i). 
 
f) Battery's self-discharge. The ba ttery self-discharge may be a significant part of the overall battery 
capacity, particularly for a large number of days of battery reserve, e.g., 10 or more days. This 
should be checked to determine if the battery size is affected. (Other parasitic loads such as 
wiring, charge controller consumption, and tare losses of inverters should be included in the load 
data.) 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008CD/K/04-4:2003  
© EAC 2008 — All rights reserved  15 g) Electrolyte reserve. If vented cells are used, they should be selected so  that the electrolyte 
reserve capacity is adequate to sustain the anticipated maintenance interval. 
 
h) Battery size and weight. The battery size and weight should be compatible with the application 
requirements and transportation modes. 
 
12) Summary. The selected battery and it s performance features are specified. 
 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008CD/K/04-4:2003  
16 © EAC 2008 — All rights reserved  
Worksheet 1 — Battery sizing 
 
 
1) Project name and description: 
 
  
   
 
2)  
Nominal system voltage:  
  
V 
3) Days of battery reserve: 
     days 
 
4 Load data 
  
 
 
4a  
DC load 
device 
 4d  
Voltage 
window 
 4c  
Momentary 
currents 
 4d  
Running 
currents a 
 4e  
Constituents 
of maximum 
running 
current 
 4f  
Number of 
occurrences
 4g  
Duration 
 4h  
Run 
time 
 4i  
Daily 
load 
 
 
 Vmax 
V 
 Vmin 
V 
 Icoin  Inoncoin , 
A  
 Icoin Inoncoin , 
A 
   Number/ day
 Hours/ 
occurrence 
 Hours/ 
day 
 Ah/day
 
 
                       
                        
 
                       
                        
 
                       
                        
                        
                        
                        
Total daily load           Ah
 
 
a Including parasitic currents. 
 
5) Load data summary 
 
a) Maximum momentary current Icoin from above table (or line 5a of Worksheet 3) (refer to load 
profile diagram):_______A 
 
b) Maximum running current Icoin from above table (or line 5b of Worksheet 3) (refer to load profile 
diagram):_______A 
 
c) Total daily load from above table (o r line 5c of Worksheet 3): ______Ah/day 
 
d) Maximum daily load from Worksheets 2 if used:____________ Ah/day 
 
e) Greatest value of Inoncoin momentary currents from above table (or line 5d of  
Worksheet 3):____________ A 
 
f) Maximum momentary current draw from ba ttery (greater of line 5a or line 5e):_______ A PUBLIC REVIEW DRAFT, SEPTEMBER 2008CD/K/04-4:2003  
© EAC 2008 — All rights reserved  17  
g) Greatest value of Inoncoin for running currents from above table (or line 5e of  
Worksheet 3):______ A 
 
h) Maximum running current draw from battery (greater of line 5b or line 5g): _______ A 
 
i) Maximum current draw from battery (g reater of line 5f or line 5h): ______ A 
 
j) Lowest value of Vmax from above table (or line 5f of Worksheet 3):_______V 
 
k) Greatest value of Vmin from above table (or line 5g of Worksheet 3):______V 
 
6) Battery capacity  
 
a) Unadjusted battery capaci ty (line 3 × line 5c):______Ah  
 
b) Maximum allowable depth of discharge (MDOD): _______%  
 
c) Capacity adjusted for MDOD (line 6a ÷ line 6b):______ Ah  
 
d) Maximum daily depth of discharge (MDDOD):_______%  
 
e) Capacity adjusted for MDDOD (line 5c ÷ line 6d) [or (line 5d ÷ line 6d) if Worksheet 3 is 
used]: _______Ah  
 
f) Percent of capacity at end of life:_______%  
 
g) Capacity adjusted for end of life (line 6a ÷ line 6f):______Ah  
 
h) Capacity adjusted for depths of discharge and end of life (greatest of line 6c, line 6e, or line 
6g):______Ah  
 
i) Minimum operating temperature: ________°C  
 
j) Associated temperature correction factor: ______  
 
k) Capacity adjusted for temperature: ______Ah  
 
I) Design margin factor (>1): _______  
 
m) Capacity adjusted for design margin (line 6k × 6l): ______Ah  
 
7) Functional-hour rate (line 6m ÷ line 5h): _____ h  
 
8) Voltage-window adjustment  
 
a) Controller low-voltage disconnect setpoint:______V  
 
b) Adjusted Vmin (greater of line 5k or line 8a):______V  
 
c) Controller full-charge voltage setpoint:_______V  
 
d) Adjusted Vmax (lesser of line 5j or line 8c) (at the lowest battery temperature when a 
temperature-compensated charge controller is used):______V  
 
9) Number of series-connected cells  
 
a) Recommended full-charge voltage for selected cell: (limited by line 8d): ______V  
 
b) Maximum number of cells in series, round down (line 8d ÷ line 9a): _______  PUBLIC REVIEW DRAFT, SEPTEMBER 2008CD/K/04-4:2003  
18 © EAC 2008 — All rights reserved  
c) Recommended EOD voltage for selected cell: _______ V  
 
d) Calculated EOD voltage for cell (line 8b ÷ line 9b): _______ V  
 
NOTE If 9d > 9c, proceed to 9g; otherwise continue with 9e. 
 
e) Decrement number of series cells (line 9b - 1): ______ 
 
f) Calculated cell charge voltage (line 8d ÷ line 9e): _______ V 
 
NOTE If line 9f is within charge voltage range specified by manuf acturer, proceed to line 9g; otherwise, at least one of the 
following has to be done: decrement number of series cells (repeat 9e and 9f); select different battery type, go to 6b; 
change controller full-charge voltage setpoint, go to 8c; select different controller, go to 8a. 
 
g) Enter the selected number of series cells (line 9b or line 9e, as appropriate): ______ 
 
10) Cell selection and final capacity determination 
 
a) Smallest practical cell capacity available of selected type greater than or equal to line 6m, or 
largest practical cell less than line 6m, when discharged to the calculated EOD voltage (line 
9d), at the functional-hour rate (line 7): ____ Ah 
 
b) Number of parallel strings, round up (line 6m ÷ line 10a): ______ 
 
c) Final battery capacity (line 10a × line 10b): ______ Ah 
 
11) Checks/considerations 
 
a) Maximum charge rate 
 
i) Recommended maximum charge current during recharge: ___ A 
 
ii) Maximum available charging current during recharge: ___ A 
 
NOTE If line 11a, ii > line 11a, i, the battery may be damaged. 
 
b) Excessive overcharging  
 
i) Recommended maximum charge cu rrent after reaching regulation voltage at the battery's 
average temperature of ___ °C: _______ A  
 
ii) Maximum available charging current a fter reaching regulation voltage: ______A  
 
NOTE If line 11b, ii > line 11b, i, the battery may be damaged.  
 
c) Undercharging — Array/load rati o for the minimum design month:_____  
 
NOTE It line 11c < 1.3, there may be insufficient array energy to recharge this battery. 
 
d) High-rate discharge — Maximum discharge current: _____A 
(This is the same value as line 5i) 
 
NOTE If line 10c ÷ line 11d < 20, the cell voltage may drop below the allowable EOD voltage when this condition 
occurs near the end of discharge of the battery. 
 
e) Freezing of electrolyte — Freezing temper ature of electrolyte at MDOD: _____ °C  
 
NOTE If line 6i < line 11 e, the battery may freeze  
 
 
f) Battery self discharge  PUBLIC REVIEW DRAFT, SEPTEMBER 2008CD/K/04-4:2003  
© EAC 2008 — All rights reserved  19  
i) Battery's self discharge: ________ Ah/day  
 
ii) Battery's capacity for each day of battery reserve (line 10c ÷ line 3): ____ Ah/day  
 
NOTE If 11f, i/11f, ii> 0.05 and self-discharge was not included in the load considerations, the battery may be 
undersized.  
 
g) Electrolyte reserve — Battery electrolyte reserve capacity estimated in days: ______days  
 
NOTE If line 11g < anticipated maintenance interval, the battery may be damaged.  
 
Considerations resolved:  
 
a) Maximum charge rate [   ]  
 
b) Excessive overcharging [   ]  
 
c) Undercharging [   ]  
 
d) High-rate discharge [   ]  
 
e) Freezing of electrolyte [    ] 
 
f) Battery self discharge [    ] 
 
g) Electrolyte reserve [    ] 
 
h) Battery's size and weight [    ] 
 
12) Summary 
 
Battery manufacturer and model: _______________________  
 
Final battery is _____ cells in series by _____ strings in parallel.  
 
Battery capacity is ______ Ah rated at the ______ h functional-hour rate.  
 
Battery full-charge voltage is ______ V.  
 
Battery end-of-discharge voltage is _____ V. PUBLIC REVIEW DRAFT, SEPTEMBER 2008CD/K/04-4:2003  
20 © EAC 2008 — All rights reserved  
Worksheet 2 — Supplemental battery sizing for duty cycle periods > 24 h 
 
Complete Worksheet 2 for each day (24 h period) for which a distinct daily load exists. Summarize 
the data in Worksheet 3 and transfer to Worksheet 1:  
 
Load data  
 
 
Day: ________ 
 
4a  
DC load 
device 
 4d  
Voltage 
window 
 4c  
Momentary 
currents 
 4d  
Running 
currents a 
 4e  
Constituents 
of maximum 
running 
current 4f  
Number of 
occurrences
 4g  
Duration 
 4h  
Run 
time 
 4i  
Daily 
load 
 
 
 Vmax 
V 
 Vmin 
V 
 Icoin  Inoncoin , 
A  
 Icoin Inoncoin , 
A 
   Number/ day
 Hours/ 
occurrence 
 Hours/ 
day 
 Ah/day
 
 
                       
                        
 
                       
                        
                        
                        
Total daily load           Ah
 
 
a Including parasitic currents. 
 
Maximum momentary current Icoin (refer to load profile diagram):_______A  
 
Maximum running current Icoin (refer to load profile diagram):_______A  
 
Number of repetitions:______ 
 
Worksheet 3 — Summary 
 
5) Load data summary 
 
a) Greatest value of the maximum momentary Icoin currents: _____ A 
 
b) Greatest value of the maximum running Icoin currents: ____ A 
 
c) Average daily load: 
 
i) Determine the series of repetitions that is going to result in the greatest load, over the 
period of days of battery reserve. 
 
ii) Total the load over the period of days of ba ttery reserve and divide by the number of days 
of battery reserve: ______ Ah/day 
 
d) Greatest value of Inoncoin  for momentary currents for any of the above load devices: ______ A  
 
e) Greatest value of Inoncoin  for running current for any of the above load devices: ________ A 
 
f) Lowest value of Vmax for any of the above load devices: __ __________ V  
 
g) Greatest value of Vmin for any of the above load devices: __________ V PUBLIC REVIEW DRAFT, SEPTEMBER 2008CD/K/04-4:2003  
© EAC 2008 — All rights reserved  21  
Annex A 
(informative) 
 
Battery characteristics 
 
This annex summarizes some factors that should be considered in selecting a battery design for a 
terrestrial photovoltaic (PV) application. 
 
A.1 Capacity  
 
The ampere hour capacity of a battery depends on the size and number of plates of the cells, the amount 
and concentration of electrolyte (particularly in valve-regulated cells), and the number of parallel strings of 
cells used. The conditions under which a battery is used  can change the available capacity of the battery, as 
illustrated in the following examples: 
 
a) Low temperatures reduce capacity. 
 
b) High discharge rates reduce capacity. 
 
c) High end-of-discharge voltages reduce capacity. 
 
d) Limitations on the depth of  discharge reduce capacity. 
 
e) Failure to properly recharge a battery limits its capacity. 
 
f) Excessive periods of high temperature and/or ov ercharge may result in the loss of electrolyte and 
limit capacity of batteries. 
 
A.2 Type  
 
The two generic types of lead-acid batteries are: 
 
a) Vented. Vented batteries are characterized by plat es immersed in liquid electrolyte. The volume of 
electrolyte is sufficient to allow for a reasonable loss of water by evaporation and by the electrolysis 
associated with overcharging. A vent in the cell's cover allows a free exchange of the resulting gases 
with the atmosphere. Catalytic recombiners may be incorporated in each cell vent to reduce water 
loss. In most of these types of batteries, the lost water can be replaced. 
 
b) Valve-regulated. Valve-regulated level acid batteries (VRLA) are characterized by plates in contact 
with a limited amount of immobilized electrolyt e. Water loss is minimized during overcharge by 
oxygen recombination. As long as the cell's recombination rate is not exceeded, the evolved oxygen is 
recombined at the cell's negative plates to reform water. However, other mechanisms, such as grid 
corrosion, consume oxygen and lead to water loss and hydrogen evolution. The cell or multi-cell 
container is sealed with the exception of a pres sure-relief valve ("valve- regulated") that allows 
excess pressure (mostly hydrogen) resulting from overcharging to be released. In these types of 
batteries, the lost water generally cannot be replaced. 
 
A.3 Cyclability  
 
Lead-acid batteries for PV applications are genera lly categorized as deep-cycle and shallow-cycle. 
 
A.3.1 Deep-cycle batteries  
 
Deep-cycle batteries may be discharged up to 80 % of  their rated capacity on a daily basis. Typical 
deep-cycle-battery PV applications are those that have a low number of days of battery reserve, or are 
connected to a backup power  source or a utility grid. 
 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008CD/K/04-4:2003  
22 © EAC 2008 — All rights reserved A.3.2 Shallow-cycle batteries  
 
Usually, shallow-cycle batteries are discharged less than 25 % of their rated capacity on a daily basis 
(MDDOD), and up to 80 % over the period of battery  reserve (MDOD). Manufacturers can supply the 
maximum number of permissible 80 % discharges per year . Typical shallow-cycle-battery PV applications 
are those with larger numbers of days of battery reserve where neither a utility grid nor an emergency 
backup power source is available. 
 
A.4 Cycle life  
 
The life of a battery can be measured by the number of times it can be cycled before it is no longer able 
to deliver sufficient energy to satisfy the load requiremen ts of the system. The number of cycles of operation 
a battery will provide depends on  the following th ree factors: 
 
a) Cell design 
 
b) Use 
 
c) Operating temperature 
 
A.4.1 Design factors  
 
Some of the design factors that affect cycle life are: 
 
a) Plate thickness 
 
b) Grid alloy and construction 
 
c) Active material density 
 
d) Active material retention systems 
 
e) Electrolyte density and amount 
 
f) Type of separator 
 
g) Pressure setting of valve (valve-regulated batteries) 
 
A.4.2 Use factors  
 
How a battery is used has an effect on its cycle life. Some of the considerations are listed below: 
 
a) Depth of discharge 
 
b) Stratification of electrolyte 
 
c) Excessive over charge (see A.4.3) 
 
d) Insufficient recharge 
 
e) End-of-discharge voltage 
 
f) Higher-than-rated operating temperatures (>25 °C) 
 
A.4.3 Operating temperature  
 
High temperatures decrease cycle life, while low temperatures decrease available capacity. A battery 
should be sized for operation at its coldest expected oper ating temperature, which, in effect, oversizes the 
battery for normal warmer operation, resulting in a reduced depth of discharge, which increases cycle life. 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008CD/K/04-4:2003  
© EAC 2008 — All rights reserved  23 The VRLA battery's oxygen recombination cycle is exothermic (generating heat on charging). Thus this 
type of battery is more sensitive to conditions t hat can lead to thermal runaway, wherein the battery 
generates heat at a rate faster than it can be dissipat ed. Thermal runaway can result in deformation of 
the battery case and significant emission of gases. When thermal runaway occurs, it is typically the 
result of extended overcharging, which can be the result of shorted cells, coupled with an elevated 
temperature of the battery environment and an inadeq uately ventilated battery en closure. Thermal runaway 
can be prevented or arrested by appropriate charging control including temperature compensation, spacing 
of the individual cells or units of the battery to allow for adequate air circulation, adequate ventilation of the 
battery enclosure, and appropriate periodic maintenance . To arrest thermal runaway, circuitry can be 
included to disconnect the battery from its charging source s hould the battery temperature rise 
significantly above the ambient temperature. 
 
A.5 Economic considerations  
 
The optimum battery will be the battery with lowest life-cycle cost. The life-cycle cost, expressed in dollars 
per kilowatt hour ($/kWh) of energy delivered, is a function of a number of variables. These include the 
following: 
 
a) Initial cost 
 
b) Cycle life 
 
c) Maintenance costs 
 
d) Battery/system reliability 
 
e) Economic impact on PV system design including: 
 
1) Charge controller 
 
2) Structural design including battery support structure and enclosure 
 
3) Heating, ventilation, and cooling 
 
f) Replacement costs 
 
g) Salvage value/disposal costs 
 
h) Energy efficiency 
 
i) Accessory systems such as those for electrolyte agitation and water addition 
 
A.6 Physical characteristics  
 
Physical characteristics that may be important are: 
 
a) Size and weight of the smallest transportable unit 
 
b) Cell access requirements for maintenance, such as addition of water 
 
c) Strength of cell containers for safety and if electrolyte freezing is a possibility 
 
d) Terminal connection configuration 
 
e) Accessory requirements 
 
f) Vent fittings to attach tubing for external venting 
 
g) Available enclosure space 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008CD/K/04-4:2003  
24 © EAC 2008 — All rights reserved h) Container flammability 
 
A.7 Maintenance  
 
The required maintenance of  batteries depends on the batteries' design and use. Refer to EAS 363-2. 
 
A.8 Safety  
 
Batteries are potentially hazardous for a number  of reasons, including generation and release of 
explosive gasses (see 9.5), stored el ectrical energy, and presence of corrosive liquids. Installation and 
maintenance personnel should be qualified in battery operating and safety procedures. Refer to EAS 363-2 
for safety details. PUBLIC REVIEW DRAFT, SEPTEMBER 2008CD/K/04-4:2003  
© EAC 2008 — All rights reserved  25  
Annex B 
(informative) 
 
Examples 
 
The following examples, including the parameters used, show the application of this sizing method. They 
are illustrative only and are not intended to cover all possible sizing features. 
 
B.1 Refrigerator/freezer for vaccine storage 
 
Example B.1 describes the battery sizing for a va ccine storage refrigerator intended for remote use. 
The refrigerator is to be located near the equator in a tropical climate. Vaccines are delivered quarterly. At 
the same time deliveries are made, a technician is avai lable for system maintenance. There is a constraint 
on the physical size of the battery that can be installe d in the refrigerator's battery box. Figure B.1 shows 
a typical load profile diagram for this application. 
 
 
 
Figure B.1 — Simulated load-profile diagram for vaccine storage refrigerator/freezer 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008CD/K/04-4:2003  
26 © EAC 2008 — All rights reserved  
Example B.1: Worksheet 1 — Battery sizing 
 
1) Project name and description: 
 
Remote refrigerator/freezer. Brazilian village, tropic al climate. High availa bility required, quarterly 
maintenance, four starts each 24 h peri od (including one for ice pack freezing)  
 
2) Nominal system voltage:       12       V 
 
3) Days of battery reserve:      6     days 
 
4) Load data: 
 
4a  
DC load 
device 
 4d  
Voltage 
window 
 4c  
Momentary 
currents 
 4d  
Running 
currents a 
 4e  
Constituents 
of maximum 
running 
current 4f  
Number of 
occurrences
 4g  
Duration 
 4h  
Run 
time 
 4i  
Daily 
load 
 
 
 Vmax 
V 
 Vmin 
V 
 Icoin  Inoncoin , 
A  
 Icoin Inoncoin ,
A 
   Number/ day
 Hours/ 
occurrence 
 Hours/ 
day 
 Ah/day
 
Run 1 
compressor 
 15.0 
 10.5      6    √ 
 3  1  3  18  
 
  
           or          
Run 2b 
compressor 
 15.0 
 10.5      6    √ 1 
 5  5  30  
 
  
                     
Start 
compressor  15.0 
 10.5  15          4  0.0167    1  
 
  
                     
Parasitics 
  
       0.1    √  
   2.4  2.4  
 
                       
                        
Total daily load                                                        51.4Ah
 
 
a) Including parasitic currents.  
 
b For ice pack freezing. 
 
5) Load data summary 
 
a) Maximum momentary current Icoin from above table (or line 5a of Worksheet 3) (refer to load 
profile diagram):__ 15.1___A 
 
b) Maximum running current Icoin from above table (or line 5b of Worksheet 3) (refer to load profile 
diagram):__  6.1__A 
 
c) Total daily load from above tabl e (or line 5c of Worksheet 3): __ 51.4__Ah/day 
 
d) Maximum daily load from Worksheets 2 if used:____ —_____ Ah/day 
 
e) Greatest value of Inoncoin momentary currents from above table (or line 5d of  
Worksheet 3):____  0____ A 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008CD/K/04-4:2003  
© EAC 2008 — All rights reserved  27 f) Maximum momentary current draw from ba ttery (greater of line 5a or line 5e):__  15.1__ A 
 
g) Greatest value of Inoncoin for running currents from above table (or line 5e of  
Worksheet 3):__  0__ A 
 
h) Maximum running current draw from battery (greater of line 5b or line 5g): __ 6.1__ A 
 
i) Maximum current draw from battery  (greater of line 5f or line 5h): __ 15.1_ A 
 
j) Lowest value of Vmax from above table (or line 5f of Worksheet 3):__ 15.0__V 
 
k) Greatest value of Vmin from above table (or line 5g of Worksheet 3):__ 10.5__V 
 
6) Battery capacity  
 
a) Unadjusted battery capa city (line 3 × line 5c):__  308__Ah  
 
b) Maximum allowable depth of discharge (MDOD): __ 80___%  
 
c) Capacity adjusted for MDOD (line 6a ÷ line 6b):__  385__ Ah  
 
d) Maximum daily depth of discharge (MDDOD):___  20___%  
 
e) Capacity adjusted for MDDOD (line 5c ÷ line 6d) [or (line 5d ÷ line 6d) if Worksheet 3 is 
used]: __ 257___Ah  
 
f) Percent of capacity at end of life: ___  80___%  
 
g) Capacity adjusted for end of life (line 6a ÷ line 6f): __  385__Ah  
 
h) Capacity adjusted for depths of discharge and end of life (greatest of line 6c, line 6e, or line 
6g): __  385__Ah  
 
i) Minimum operating temperature: ___ 25___°C  
 
j) Associated temperature correction factor: __ 1__  
 
k) Capacity adjusted for temperature: __ 385__Ah  
 
I) Design margin factor (>1): ___ 1.1__  
 
m) Capacity adjusted for design margin (line 6k × 6l): __ 424__Ah  
 
7) Functional-hour rate (line 6m ÷ line 5h): __ 70__ h 
 
8) Voltage-window adjustment  
 
a) Controller low-voltage disconnect setpoint: __ 10.8__V 
 
b) Adjusted Vmin (greater of line 5k or line 8a):__ 10.8___V  
 
c) Controller full-charge voltage setpoint: ___ 14.7__V 
 
d) Adjusted Vmax (lesser of line 5j or line 8c) (at the lowest battery temperature when a 
temperature-compensated charge controller is used): __ 14.7__V 
 
9) Number of series-connected cells  
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008CD/K/04-4:2003  
28 © EAC 2008 — All rights reserved a) Recommended full-charge voltage for selected cell: (limited by line 8d): ___ 2.45__V 
 
b) Maximum number of cells in series, round down (line 8d ÷ line 9a): ___ 6__ 
 
c) Recommended EOD voltage for selected cell: __ 1.80___ V  
 
d) Calculated EOD voltage for cell (line 8b ÷ line 9b): ___ 1.80___ V  
 
NOTE If 9d > 9c, proceed to 9g; otherwise continue with 9e. 
 
e) Decrement number of series cells (line 9b - 1): __ —__ 
 
f) Calculated cell charge voltage (line 8d ÷ line 9e): __ —___ V 
 
NOTE If line 9f is within charge voltage range specified by manuf acturer, proceed to line 9g; otherwise, at least one of the 
following has to be done: decrement number of series cells (repeat 9e and 9f); select different battery type, go to 6b; 
change controller full-charge voltage setpoint, go to 8c; select different controller, go to 8a. 
 
g) Enter the selected number of series cells (line 9b or line 9e, as appropriate): __ 6___ 
 
10) Cell selection and final capacity determination 
 
a) Smallest practical cell capacity available of selected type greater than or equal to line 6m, or 
largest practical cell less than line 6m, when discharged to the calculated EOD voltage (line 
9d), at the functional-hour rate (line 7): _ 110__ Ah 
 
b) Number of parallel strings, round up (line 6m ÷ line 10a): ___ 4___ 
 
c) Final battery capacity (line 10a × line 10b): ___ 440___ Ah 
 
11) Checks/considerations 
 
a) Maximum charge rate 
 
i) Recommended maximum charge current during recharge: _ 80__ A 
 
ii) Maximum available charging current during recharge: _ 35__ A 
 
NOTE If line 11a, ii > line 11a, i, the battery may be damaged. 
 
b) Excessive overcharging  
 
i) Recommended maximum charge cu rrent after reaching regulation voltage at the battery's 
average temperature of _ 40.6__ °C: ___ 1*____ A  
 
*4A for the four parallel strings. 
 
ii) Maximum available charging current after reaching regulation voltage: ___ 0*__A  
 
*Disconnecting charge controller is used. 
 
NOTE If line 11b, ii > line 11b, i, the battery may be damaged.  
 
c) Undercharging — Array/load rati o for the minimum design month: __ 1.5___ 
 
NOTE It line 11c < 1.3, there may be insufficient array energy to recharge this battery. 
 
d) High-rate discharge — Maximum discharge current: __ 15.1___A 
 
(This is the same value as line 5i) PUBLIC REVIEW DRAFT, SEPTEMBER 2008CD/K/04-4:2003  
© EAC 2008 — All rights reserved  29  
NOTE If line 10c ÷ line 11d < 20, the cell voltage may drop below the allowable EOD voltage when this condition 
occurs near the end of discharge of the battery. 
 
e) Freezing of electrolyte — Freezing te mperature of electrolyte at MDOD: __ 6.7___ °C  
 
NOTE If line 6i < line 11 e, the battery may freeze  
 
f) Battery self discharge  
 
i) Battery's self discharge: ___ 0.5_____ Ah/day  
 
ii) Battery's capacity for each day of battery reserve (line 10c ÷ line 3): __ 73__ Ah/day  
 
NOTE If 11f, i/11f, ii> 0.05 and self-discharge was not included in the load considerations, the battery may be 
undersized.  
 
g) Electrolyte reserve — Battery electrol yte reserve capacity estimated in days: _ 120_days*  
 
*Cells with extra head space selected. 
 
NOTE If line 11g < anticipated maintenance interval, the battery may be damaged.  
 
Considerations resolved:  
 
a) Maximum charge rate [ √ ] 
 
b) Excessive overcharging [ √ ] 
 
c) Undercharging [ √ ] 
 
d) High-rate discharge [ √ ] 
 
e) Freezing of electrolyte [ √ ] 
 
f) Battery self discharge [ √ ] 
 
g) Electrolyte reserve [ √ ] 
 
h) Battery's size and weight [ √ ] 
 
12) Summary 
 
Battery manufacturer and model: ________ XYK Co Ltd _______________  
 
Final battery is __ 6___ cells in series by __ 4___ strings in parallel.  
 
Battery capacity is __ 440___ Ah rated at the __ 70___ h functional-hour rate.  
 
Battery full-charge voltage is __ 14.7____ V.  
 
Battery end-of-discharge voltage is __ 10.8__ V. 
 
NOTE Because of this application's enclosed container and hi gh ambient temperature, caution should be exercised if a 
valve-regulated battery is selected. The potential for thermal runaway exists for these conditions. 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008CD/K/04-4:2003  
30 © EAC 2008 — All rights reserved  
B.2 Remote communications system 
 
The following worksheet (Example B.2) describes the battery sizing for a 48 V (nominal) simplex 
communications system (single-mode operation). A battery reserve of 15 days was selected to ensure 
high system reliability. The system is not accessible during six months of the year. There is a weight 
limitation on battery transportation. Figure B.2 shows a simulated load-profile diagram for this application. 
 
 
 
Figure B.2 — Simulated load-profile diagram for remote communications repeater PUBLIC REVIEW DRAFT, SEPTEMBER 2008CD/K/04-4:2003  
© EAC 2008 — All rights reserved  31  
Example B.2: Worksheet 1 — Battery sizing  
 
1) Project name and description: 
 
Communications system. High reliability required. 6 mont h interval between servicin g, mountain top location, 
thermally insulated battery.  
 
2) Nominal system voltage:       48      V 
 
3) Days of battery reserve:       15       days 
 
4) Load data: 
 
4a  
DC load 
device 
 4d  
Voltage 
window 
 4c  
Momentary 
currents 
 4d  
Running 
currents a 
 4e  
Constituents 
of maximum 
running 
current 4f  
Number of 
occurrences
 4g  
Duration 
 4h  
Run 
time 
 4i  
Daily 
load 
 
 
 Vmax 
V 
 Vmin 
V 
 Icoin  Inoncoin , 
A  
 Icoin Inoncoin ,
A 
   Number/ day
 Hours/ 
occurrence 
 Hours/ 
day 
 Ah/day
 
Transmitter  
 64 
 40 
  
  
  
 10 
 ' 
 b
  
 0.5 
 5 
 
Recover  
 64 
 40 
  
  
  
 1 
  
  
  
 2.0 
 2 
 
Standby  
 64 
 40 
  
  
  
 0.5 
  
  
  
 21.5 
 10.8 
 
Note — All loads include parasitics.  
 
 
  
  
  
  
  
  
  
  
  
  
  
 
 
  
  
  
  
  
  
  
  
  
  
  
 
 
  
  
  
  
  
  
  
  
  
  
  
 
 
  
  
  
  
  
  
  
  
  
  
  
 
Total daily load    17.8 Ah
 
 
a Including parasitic currents. 
 
b Since individual durations depend on usage, columns 4f and 4g have not been used. The hours/day have been obtained from the 
customer's requirements.  
 
5) Load data summary 
 
a) Maximum momentary current Icoin from above table (or line 5a of Worksheet 3) (refer to load 
profile diagram):__ 0___A 
 
b) Maximum running current Icoin from above table (or line 5b of Worksheet 3) (refer to load profile 
diagram):__  0__A 
 
c) Total daily load from above tabl e (or line 5c of Worksheet 3): __ 17.8__Ah/day 
 
d) Maximum daily load from Worksheets 2 if used: ____ —_____ Ah/day 
 
e) Greatest value of Inoncoin momentary currents from above table (or line 5d of  
Worksheet 3):____  0____ A 
 
f) Maximum momentary current draw from ba ttery (greater of line 5a or line 5e):__  0__ A 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008CD/K/04-4:2003  
32 © EAC 2008 — All rights reserved g) Greatest value of Inoncoin for running currents from above table (or line 5e of  
Worksheet 3):__  10__ A 
 
h) Maximum running current draw from battery (greater of line 5b or line 5g): __ 10__ A 
 
i) Maximum current draw from battery  (greater of line 5f or line 5h): __ 10_ A 
 
j) Lowest value of Vmax from above table (or line 5f of Worksheet 3):__ 64__V 
 
k) Greatest value of Vmin from above table (or line 5g of Worksheet 3):__ 40__V 
 
6) Battery capacity  
 
a) Unadjusted battery capa city (line 3 × line 5c):__  267__Ah  
 
b) Maximum allowable depth of discharge (MDOD): __ 80___%  
 
c) Capacity adjusted for MDOD (line 6a ÷ line 6b):__  334__ Ah  
 
d) Maximum daily depth of discharge (MDDOD):___  20___%  
 
e) Capacity adjusted for MDDOD (line 5c ÷ line 6d) [or (line 5d ÷ line 6d) if Worksheet 3 is 
used]: __ 89___Ah  
 
f) Percent of capacity at end of life:___  80___%  
 
g) Capacity adjusted for end of life (line 6a ÷ line 6f):__  334__Ah  
 
h) Capacity adjusted for depths of discharge and end of life (greatest of line 6c, line 6e, or line 
6g):__  334__Ah  
 
i) Minimum operating temperature: ___ 7.2___°C  
 
j) Associated temperature correction factor: __ 1.2__  
 
k) Capacity adjusted for temperature: __ 401__Ah  
 
I) Design margin factor (>1): ___ 1.1__  
 
m) Capacity adjusted for design margin (line 6k × 6l): __ 441__Ah  
 
7) Functional-hour rate (line 6m ÷ line 5h): __ 44__ h 
 
8) Voltage-window adjustment  
 
a) Controller low-voltage disconnect setpoint: __ 42__V 
 
b) Adjusted Vmin (greater of line 5k or line 8a):__ 42___V  
 
c) Controller full-charge voltage setpoint: ___ 58__V 
 
d) Adjusted Vmax (lesser of line 5j or line 8c) (at the lowest battery temperature when a 
temperature-compensated charge controller is used):__ 58__V 
 
9) Number of series-connected cells  
 
a) Recommended full-charge voltage for selected cell: (limited by line 8d): ___ 2.40__V 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008CD/K/04-4:2003  
© EAC 2008 — All rights reserved  33 b) Maximum number of cells in series, round down (line 8d ÷ line 9a): ___ 24__ 
 
c) Recommended EOD voltage for selected cell: __ 1.75___ V  
 
d) Calculated EOD voltage for cell (line 8b ÷ line 9b): ___ 1.75___ V  
 
NOTE If 9d > 9c, proceed to 9g; otherwise continue with 9e. 
 
e) Decrement number of series cells (line 9b - 1): __ —__ 
 
f) Calculated cell charge voltage (line 8d ÷ line 9e): __ —___ V 
 
NOTE If line 9f is within charge voltage range specified by manuf acturer, proceed to line 9g; otherwise, at least one of the 
following has to be done: decrement number of series cells (repeat 9e and 9f); select different battery type, go to 6b; 
change controller full-charge voltage setpoint, go to 8c; select different controller, go to 8a. 
 
g) Enter the selected number of series cells (line 9b or line 9e, as appropriate): __ 24___ 
 
10) Cell selection and final capacity determination 
 
a) Smallest practical cell capacity available of selected type greater than or equal to line 6m, or 
largest practical cell less than line 6m, when discharged to the calculated EOD voltage (line 
9d), at the functional-hour rate (line 7): _ 242__ Ah 
 
b) Number of parallel strings, round up (line 6m ÷ line 10a): ___ 2___ 
 
c) Final battery capacity (line 10a × line 10b): ___ 484___ Ah 
 
11) Checks/considerations 
 
a) Maximum charge rate 
 
i) Recommended maximum charge current during recharge: _ 97__ A 
 
ii) Maximum available charging current during recharge: _ 40__ A 
 
NOTE If line 11a, ii > line 11a, i, the battery may be damaged. 
 
b) Excessive overcharging  
 
i) Recommended maximum charge cu rrent after reaching regulation voltage at the battery's 
average temperature of _ 15.6__ °C: ___ 2____ A  
 
ii) Maximum available charging current after reaching regulation voltage: ___ 2__A  
 
NOTE If line 11b, ii > line 11b, i, the battery may be damaged.  
 
c) Undercharging — Array/load rati o for the minimum design month: __ 1.5___ 
 
NOTE It line 11c < 1.3, there may be insufficient array energy to recharge this battery. 
 
d) High-rate discharge — Maximum discharge current: __ 10___A 
 
(This is the same value as line 5i) 
 
NOTE If line 10c ÷ line 11d < 20, the cell voltage may drop below the allowable EOD voltage when this condition 
occurs near the end of discharge of the battery. 
 
e) Freezing of electrolyte — Freezing te mperature of electrolyte at MDOD: __ -12.2 ___ °C  
 
NOTE If line 6i < line 11 e, the battery may freeze  PUBLIC REVIEW DRAFT, SEPTEMBER 2008CD/K/04-4:2003  
34 © EAC 2008 — All rights reserved  
f) Battery self discharge  
 
i) Battery's self discharge: ___ 1.0_____ Ah/day  
 
ii) Battery's capacity for each day of battery reserve (line 10c ÷ line 3): __ 32__ Ah/day  
 
NOTE If 11f, i/11f, ii> 0.05 and self-discharge was not included in the load considerations, the battery may be 
undersized.  
 
g) Electrolyte reserve — Battery electrol yte reserve capacity estimated in days: _ —_days*  
 
*Valve regulated battery  selected. 
 
NOTE If line 11g < anticipated maintenance interval, the battery may be damaged.  
 
Considerations resolved:  
 
a) Maximum charge rate [ √ ] 
 
b) Excessive overcharging [ √ ] 
 
c) Undercharging [ √ ] 
 
d) High-rate discharge [ √ ] 
 
e) Freezing of electrolyte [ √ ] 
 
f) Battery self discharge [ √ ] 
 
g) Electrolyte reserve [ √ ] 
 
h) Battery's size and weight [ √ ] 
 
12) Summary 
 
Battery manufacturer and model: ________ PDZ Co Ltd _______________  
 
Final battery is __ 24___ cells in series by __ 2___ strings in parallel.  
 
Battery capacity is __ 484___ Ah rated at the __ 44___ h functional-hour rate.  
 
Battery full-charge voltage is __ 58____ V.  
 
Battery end-of-discharge voltage is __ 42__ V. 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008CD/K/04-4:2003  
© EAC 2008 — All rights reserved  35  
B.3 Remote residence 
 
Example B.3 describe the battery sizing for a remote cabin, used only on the weekends. Seven days of 
battery reserve are sought. Although the major load is  present on weekends only, the security system 
operates at all times. Figure B.3 is a typical load profile diagram. 
 
 
 
 
Figure B.3—Simulated partial load profile diagram for remote residence (4-1/2 days) 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008CD/K/04-4:2003  
36 © EAC 2008 — All rights reserved  
Example B.3: Worksheet 1 —Battery sizing  
 
1) Project name and description: 
 
Weekend cabin on an island off the coast of Maine. Artist occupied—heavy loads are for equipment used in 
his work.  
 
2) Nominal system voltage:       24      V 
 
3) Days of battery reserve:       7       days 
 
4) Load data: 
 
4a  
DC load 
device 
 4d  
Voltage 
window 
 4c  
Momentary 
currents 
 4d  
Running 
currents a 
 4e  
Constituents 
of maximum 
running 
current 4f  
Number of 
occurrences
 4g  
Duration 
 4h  
Run 
time 
 4i  
Daily 
load 
 
 
 Vmax 
V 
 Vmin 
V 
 Icoin  Inoncoin , 
A  
 Icoin Inoncoin ,
A 
   Number/ day
 Hours/ 
occurrence 
 Hours/ 
day 
 Ah/day
 
            
            
            
            
            
SEE WORKSHEET 2 
            
            
            
            
Total daily load 
 
 
a) Including parasitic currents.  
 
5) Load data summary 
 
a) Maximum momentary current Icoin from above table (or line 5a of Worksheet 3) (refer to load 
profile diagram):__ 36.1___A 
 
b) Maximum running current Icoin from above table (or line 5b of Worksheet 3) (refer to load profile 
diagram):__  35.15 __A 
 
c) Total daily load from above tabl e (or line 5c of Worksheet 3): __ 54.1__Ah/day 
 
d) Maximum daily load from Worksheets 2 if used:____ 153_____ Ah/day 
 
e) Greatest value of Inoncoin momentary currents from above table (or line 5d of  
Worksheet 3):____  0____ A 
 
f) Maximum momentary current draw from ba ttery (greater of line 5a or line 5e):__  36.1__ A 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008CD/K/04-4:2003  
© EAC 2008 — All rights reserved  37 g) Greatest value of Inoncoin for running currents from above table (or line 5e of  
Worksheet 3):__  0__ A 
 
h) Maximum running current draw from battery (greater of line 5b or line 5g): __ 35.15 __ A 
 
i) Maximum current draw from battery  (greater of line 5f or line 5h): __ 36.1_ A 
 
j) Lowest value of Vmax from above table (or line 5f of Worksheet 3):__ 30__V 
 
k) Greatest value of Vmin from above table (or line 5g of Worksheet 3):__ 23__V 
 
6) Battery capacity  
 
a) Unadjusted battery capa city (line 3 × line 5c):__  417__Ah  
 
b) Maximum allowable depth of discharge (MDOD): __ 50___%  
 
c) Capacity adjusted for MDOD (line 6a ÷ line 6b):__  834__ Ah  
 
d) Maximum daily depth of discharge (MDDOD):___  20___%  
 
e) Capacity adjusted for MDDOD (line 5c ÷ line 6d) [or (line 5d ÷ line 6d) if Worksheet 3 is 
used]: __ 772___Ah  
 
f) Percent of capacity at end of life:___  80___%  
 
g) Capacity adjusted for end of life (line 6a ÷ line 6f):__  521__Ah  
 
h) Capacity adjusted for depths of discharge and end of life (greatest of line 6c, line 6e, or line 
6g):__  834__Ah  
 
i) Minimum operating temperature: ___ 0___°C  
 
j) Associated temperature correction factor: __ 1.35__  
 
k) Capacity adjusted for temperature: __ 1126__Ah  
 
I) Design margin factor (>1): ___ 1.1__  
 
m) Capacity adjusted for design margin (line 6k × 6l): __ 1239__Ah  
 
7) Functional-hour rate (line 6m ÷ line 5h): __ 35__ h 
 
8) Voltage-window adjustment  
 
a) Controller low-voltage disconnect setpoint: __ 24.5__V 
 
b) Adjusted Vmin (greater of line 5k or line 8a):__ 24.5___V  
 
c) Controller full-charge voltage setpoint: ___ 28.8__V 
 
d) Adjusted Vmax (lesser of line 5j or line 8c) (at the lowest battery temperature when a 
temperature-compensated charge controller is used):__ 28.8__V 
 
9) Number of series-connected cells  
 
a) Recommended full-charge voltage for selected cell: (limited by line 8d): ___ 2.40__V 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008CD/K/04-4:2003  
38 © EAC 2008 — All rights reserved b) Maximum number of cells in series, round down (line 8d ÷ line 9a): ___ 12__ 
 
c) Recommended EOD voltage for selected cell: __ 2.0___ V  
 
d) Calculated EOD voltage for cell (line 8b ÷ line 9b): ___ 2.04___ V  
 
NOTE If 9d > 9c, proceed to 9g; otherwise continue with 9e. 
 
e) Decrement number of series cells (line 9b - 1): __ —__ 
 
f) Calculated cell charge voltage (line 8d ÷ line 9e): __ —___ V 
 
NOTE If line 9f is within charge voltage range specified by manuf acturer, proceed to line 9g; otherwise, at least one of the 
following has to be done: decrement number of series cells (repeat 9e and 9f); select different battery type, go to 6b; 
change controller full-charge voltage setpoint, go to 8c; select different controller, go to 8a. 
 
g) Enter the selected number of series cells (line 9b or line 9e, as appropriate): __ 12___ 
 
10) Cell selection and final capacity determination 
 
a) Smallest practical cell capacity available of selected type greater than or equal to line 6m, or 
largest practical cell less than line 6m, when discharged to the calculated EOD voltage (line 
9d), at the functional-hour rate (line 7): _ 1240__ Ah 
 
b) Number of parallel strings, round up (line 6m ÷ line 10a): ___ 1___ 
 
c) Final battery capacity (line 10a × line 10b): ___ 1240___ Ah 
 
11) Checks/considerations 
 
a) Maximum charge rate 
 
i) Recommended maximum charge current during recharge: _ 150__ A 
 
ii) Maximum available charging current during recharge: _ 12__ A 
 
NOTE If line 11a, ii > line 11a, i, the battery may be damaged. 
 
b) Excessive overcharging  
 
i) Recommended maximum charge cu rrent after reaching regulation voltage at the battery's 
average temperature of _ 15__ °C: ___ 11____ A  
 
ii) Maximum available charging current after reaching regulation voltage: ___ 2__A  
 
NOTE If line 11b, ii > line 11b, i, the battery may be damaged.  
 
c) Undercharging — Array/load rati o for the minimum design month: __ 1.3___ 
 
NOTE It line 11c < 1.3, there may be insufficient array energy to recharge this battery. 
 
d) High-rate discharge — Maximum discharge current: __ 36.1___A 
 
(This is the same value as line 5i) 
 
NOTE If line 10c ÷ line 11d < 20, the cell voltage may drop below the allowable EOD voltage when this condition 
occurs near the end of discharge of the battery. 
 
e) Freezing of electrolyte — Freezing te mperature of electrolyte at MDOD: __ -20___ °C  
 
NOTE If line 6i < line 11 e, the battery may freeze  PUBLIC REVIEW DRAFT, SEPTEMBER 2008CD/K/04-4:2003  
© EAC 2008 — All rights reserved  39  
f) Battery self discharge  
 
i) Battery's self discharge: ___ 1.5_____ Ah/day  
 
ii) Battery's capacity for each day of battery reserve (line 10c ÷ line 3): __ 177__ Ah/day  
 
NOTE If 11f, i/11f, ii> 0.05 and self-discharge was not included in the load considerations, the battery may be 
undersized.  
 
g) Electrolyte reserve — Battery electrol yte reserve capacity estimated in days: _ 30_days  
 
NOTE If line 11g < anticipated maintenance interval, the battery may be damaged.  
 
Considerations resolved:  
 
a) Maximum charge rate [ √ ] 
 
b) Excessive overcharging [ √ ] 
 
c) Undercharging [ √ ] 
 
d) High-rate discharge [ √ ] 
 
e) Freezing of electrolyte [ √ ] 
 
f) Battery self discharge [ √ ] 
 
g) Electrolyte reserve [ √ ] 
 
h) Battery's size and weight [ √ ] 
 
12) Summary 
 
Battery manufacturer and model: ________ ABC Battery Co Ltd _______________  
 
Final battery is __ 12___ cells in series by __ 1___ strings in parallel.  
 
Battery capacity is __ 1240___ Ah rated at the __ 35___ h functional-hour rate.  
 
Battery full-charge voltage is __ 28.8____ V.  
 
Battery end-of-discharge voltage is __ 24.5__ V. 
 
 
 
 
 
 
 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008CD/K/04-4:2003  
40 © EAC 2008 — All rights reserved  
Worksheet 2 — Supplemental battery sizing for duty cycle periods > 24 h  
 
Complete Worksheet 2 for each day (24 h period) for which a distinct daily load exists. Summarize the 
data in Worksheet 3 and transfer to Worksheet 1: 
 
Load data 
 
Day:      unoccupied days _ 
 
4a  
DC load 
device 
 4d  
Voltage 
window 
 4c  
Momentary 
currents 
 4d  
Running 
currents a 
 4e  
Constituents 
of maximum 
running 
current 4f  
Number of 
occurrences
 4g  
Duration 
 4h  
Run 
time 
 4i  
Daily 
load 
 
 
 Vmax 
V 
 Vmin 
V 
 Icoin  Inoncoin , 
A  
 Icoin Inoncoin ,
A 
   Number/ day
 Hours/ 
occurrence 
 Hours/ 
day 
 Ah/day
 
Security 
  
  
  
  
  
  
  
  
  
  
  
 
Lights 
 30 
 21 
  
  
 1.0 
  
 V 
  
 12 
 12 
 12.0 
 
Security 
Systems 
 30 
 21 
  
  
 0.3 
  
 V 
  
  
 24 
 7.2 
 
Parasitics 
  
  
  
  
 0.1 
  
 V 
  
  
 24 
 24 
 
 
  
  
  
  
  
  
  
  
  
  
  
 
 
  
  
  
  
  
  
  
  
  
  
  
 
 
  
  
  
  
  
  
  
  
  
  
  
 
Total daily load      21.6 Ah
 
 
a Including parasitic currents. 
 
Maximum momentary current Icoin (refer to load profile diagram): ___ 0_____ A 
 
Maximum running current Icoin (refer to load profile diagram): _____ 1.4_____  A 
 
Number of repetitions: __ 5_ 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008CD/K/04-4:2003  
© EAC 2008 — All rights reserved  41  
Worksheet 2 — Supplemental battery sizing for duty cycle periods > 24 hours  
 
Complete Worksheet 2 for each day (24 h period) for which a distinct daily load exists. Summarize the 
data in Worksheet 3 and transfer to Worksheet 1: 
 
Load data 
 
Day:      occupied days  
 
4a  
DC load 
device 
 4d  
Voltage 
window 
 4c  
Momentary 
currents 
 4d  
Running 
currents a 
 4e  
Constituents 
of maximum 
running 
current 4f  
Number of 
occurrences
 4g  
Duration 
 4h  
Run 
time 
 4i  
Daily 
load 
 
 
 Vmax 
V 
 Vmin 
V 
 Icoin  Inoncoin , 
A  
 Icoin Inoncoin ,
A 
   Number/ day
 Hours/ 
occurrence 
 Hours/ 
day 
 Ah/day
 
Security 
Lights  
 30 
 21 
  
  
 1.0 
  
 √  
 12 
 12 
 12.0 
 
Security 
System  
 30 
 21 
  
  
 0.3 
  
 √ 
  
  
 24 
 7.2 
 
Lights am  
 30 
 23 
  
  
 1.5 
  
  
  
 1 
 1 
 1.5 
 
Lights pm 1  
 30 
 23 
  
  
 10.0
  
  
  
  
 2 
 20.0 
 
Lights pm 2  
 30 
 23 
  
  
 3.0 
  
 √ 
  
  
 2 
 6.0 
 
Water pump  
 30 
 15 
 15 
  
 10.0 
  
  
 4 
 0.0675  
 0.27 
 3.7 
 
TV 
 30 
 23 
  
  
 0.75
  
 √ 
  
  
 2 
 1.5 
 
Projector  
 30 
 22 
 36 
  
 18.0
  
  
  
  
 5 
 90.6 
 
Appliance 1  
 30 
 22 
  
  
 30 
  
  
 4 
 0.0175  
 0.07 
 2.1 
 
Appliance 2  
 30 
 22 
  
  
 30 
  
 √ 
  
  
 0.25 
 7.5 
 
 
  
  
  
  
  
  
  
  
  
  
  
 
Parasitics  
  
  
  
  
 0.1 
  
  
  
  
 24 
 2.4 
 
 
  
  
  
  
  
  
  
  
  
  
  
 
 
  
  
  
  
  
  
  
  
  
  
  
 
 
  
  
  
  
  
  
  
  
  
  
  
 
Total daily load   1545 Ah 
 
 
a Including parasitic currents. 
 
Maximum momentary current Icoin (refer to load profile diagram): ___ 36.1_____ A 
 
Maximum running current Icoin (refer to load profile diagram): _____ 35.15 _____  A 
 
Number of repetitions: __ 2_ 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008CD/K/04-4:2003  
42 © EAC 2008 — All rights reserved  
Worksheet 3 — Summary  
 
5) Load data summary 
 
a) Greatest value of the maximum momentary Icoin currents: __ 36.1__ A 
 
b) Greatest value of the maximum running Icoin currents: __ 35.15 __ A 
 
c) Average daily load: 
 
i) Determine the series of repetitions that is going to result in the greatest load, over the 
period of days of battery reserve. 
 
ii) Total the load over the period of days of ba ttery reserve and divide by the number of days 
of battery reserve: __ 59.6____ Ah/day 
 
d) Greatest value of Inoncoin  for momentary currents for any of the above load devices: __ 0____ A  
 
e) Greatest value of Inoncoin  for running current for any of the above load devices: ___ 0_____ A 
 
f) Lowest value of Vmax for any of the above load devices: __ ___ 30____ V  
 
g) Greatest value of Vmin for any of the above load devices: ____ 23___ V 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008CD/K/04-4:2003  
© EAC 2008 — All rights reserved  43  
Annex C 
(informative) 
 
Bibliography 
 
[B1] IEC 60050-482, International Electrotechnical Vocabulary (IEV) — Part 482: Primary and 
secondary cells and batteries  
 
[B2] EAS 366:2005, Characteristic parameters of sta nd-alone photovoltaic (PV) systems  
 
 
|B3] IEC 61727:2004, Photovoltaic (PV) systems — Charac teristics of the utility interface  
  
  
 
  
 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008PUBLIC REVIEW DRAFT, SEPTEMBER 2008CD/K/04-4:2003  
© EAC 2008 — All rights reserved