Battery storage for a Bangladeshi factory: sizing to the critical load, not the plant

By Vvon Engineering Team | Published 2026-02-13 | Updated 2026-09-13

Size storage from critical-load power, interruption limits and autonomy, then check environmental conditions, safety, lifetime cost and alternatives.

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Size factory storage from the services that need support, their power and duration, and the operating objective. The PV array rating alone cannot determine battery capacity.

Start with the load that cannot stop

A 575 kWp array, such as the published Ahad Jute Mills project, does not imply a 575 kW battery. Establish which circuits must operate, their running and starting demand, the allowed interruption and required autonomy.

Possible critical loads include controls, communications, treatment-process equipment, cold rooms and ventilation. The process owner must identify the consequence of interruption. Fire alarms, emergency lighting and fire pumps require their applicable life-safety design and approved supply arrangements, not casual addition to a general battery board.

Compare a battery, UPS, generator and coordinated combination against the actual interruption tolerance and operating cost. A production-line supply and a brief control-system ride-through are different projects.

• Have critical sub-board demand logged under a safe measurement plan covering representative operating conditions.
• Select autonomy from risk, required service duration, outage scenarios and recovery strategy; historical longest outage alone is insufficient.
• Check starting current, overload duration, transfer time and power quality as well as running kW.

Three numbers, not one

A battery system has a power rating and an energy rating, and they are bought separately even when they arrive as one line on a quotation.

• Power. Confirm continuous kW/kVA, starting and overload duty, cell discharge limits and the required transfer response.
• Energy. Integrate the critical-load profile over the required autonomy and include conversion losses, auxiliaries, permitted usable capacity, temperature and end-of-life reserve.
• Duty and life. State daily cycling, standby reserve and operating conditions; obtain model-specific capacity retention, throughput and warranty terms.

A brief ride-through and several hours of operation have different power, energy and cost requirements. Value avoided interruption using the site's actual process consequences and compare alternatives; neither duty guarantees a payback.

A sizing sequence that works

• List the supported circuits and their service requirements.
• Log representative demand and starting events.
• Agree autonomy, reserve and failure scenarios with the process and safety owners.
• Select equipment against power, energy, transfer-time and environmental requirements.
• Include losses, auxiliary demand and end-of-life capacity.
• Check generator failure-to-start and maintenance scenarios as well as its normal start time.

Chemistry, and how each behaves in the heat here

Heat is the deciding variable in Bangladesh, and it is not the outdoor temperature that decides it. It is the temperature inside an unventilated plant room on the top floor of a factory in May, which is a good deal higher than anything the weather report shows.

Chemistry	Checks before selection	Duty comparison
Flooded lead-acid	Ventilation, electrolyte maintenance, containment, temperature and discharge limits.	Compare documented life and maintenance cost for the intended duty.
VRLA / gel lead-acid	Model-specific standby/cycle ratings, temperature limits and charging profile.	Do not assume all sealed lead-acid products are suitable only for shallow discharge.
LFP lithium-ion	Cell and complete-system safety evidence, BMS, thermal management, installation and emergency plan.	Compare power, throughput, usable capacity and warranty at the proposed duty.
Other lithium-ion including NMC	Exact chemistry, complete-system tests, cooling, siting and incident controls.	Energy density alone does not establish suitability or safety.

Obtain capacity and power limits at the proposed temperatures and operating duty. Confirm BMS alarms, protective actions, monitoring and restart procedures. Design the room or enclosure to meet the specified limits rather than assuming continuous derating is acceptable.

Where the battery room goes

The battery room decision is usually made too late, after the modules are already on the roof and the only space left is a store cupboard beside the inverters.

• Assess structure, flood exposure, fire access, escape routes and separation when choosing the location.
• Verify equipment and rack reactions against the supporting structure.
• Design cooling, ventilation and their backup requirements for the chosen chemistry and enclosure.
• Have fire protection, clearances, doors and emergency procedures approved for the actual system and applicable requirements.
• Compare cable routes and replacement access before fixing the layout.

AC-coupled or DC-coupled

AC coupling may allow an existing PV plant to remain in place, but requires a compatible control, protection, metering and islanding design. Confirm with the utility whether the modification affects the existing approval.

DC coupling can avoid some conversion stages for particular energy paths, but its efficiency and suitability depend on architecture and duty. Compare retrofit cost, usable PV power during outages, approvals and equipment compatibility rather than treating one coupling method as universally better.

When storage is not worth buying

This is the part suppliers skip. There are sites where the correct recommendation is to spend the money somewhere else.

• Compare interruption tolerance with the performance and cost of existing backup.
• If there is little surplus PV, test any other value case such as resilience or permitted demand management rather than assuming storage has no possible purpose.
• Model low-use long-outage duty against alternatives and the value of lost production.
• Reject a location that cannot meet the equipment and fire-safety requirements.
• Assign inspection, monitoring and service responsibility and include it in lifecycle cost.

The defensible scope is the one that meets an explicit service requirement and survives the site-specific technical and financial comparison. It may be small, large or no battery at all.

Sources and project checks

Consult the relevant edition and the documents for the exact equipment and site: US Department of Energy: battery energy storage procurement checklist; NREL: photovoltaic and energy storage operation and maintenance; SREDA: Net Metering Guidelines and current application documents.

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