What Is a Factory Acceptance Test (FAT) in BESS?

A factory acceptance test is a formal verification that equipment has been manufactured correctly — built and tested against the manufacturer’s defined quality and acceptance criteria before it leaves the factory. In BESS, the most substantial FAT is on the DC block, though other equipment such as the PCS, transformers, and power plant controllers also goes through factory acceptance testing.

FAT is a contractual milestone. It marks the point where the buyer — or their representative — confirms that the equipment is ready for delivery. The results feed into the project’s quality documentation and provide a reference point if quality or performance issues arise after the equipment reaches site.

What a DC Block FAT Covers

A DC block FAT follows a standardised testing protocol defined by the equipment manufacturer. The scope covers several categories of verification.

Electrical testing. Insulation resistance, hi-pot testing, continuity checks, and earthing verification across all electrical systems within the DC block.

Functional verification. Charge and discharge testing, BMS communication checks, cooling system operation, and protection system response. This confirms that the DC block operates as designed under controlled conditions.

Safety checks. Fire suppression system verification, emergency stop functionality, gas detection, and arc flash protection. These are critical safety systems that must be confirmed before the equipment ships.

Quality inspection. Physical inspection of the enclosure, internal component installation, cable routing and termination quality, labelling, and general workmanship.

Energy capacity testing. Usually one of the final steps — a full charge and discharge cycle to verify the DC block’s energy capacity against the product specification.

How FAT Is Conducted

The procedure follows a standardised document defined by the equipment manufacturer. There may be a window for buyer-requested additions, but in most cases the manufacturer’s standard protocol is what gets used.

The process is thorough. Expect a full day or more per unit, moving between the factory floor and a review room, working through checkpoints, examining the physical product, and discussing findings with the manufacturer’s testing engineers.

FAT attendance is typically a buyer requirement. When attended, the buyer or their appointed representative reviews the results and makes the acceptance decision.

Common Findings

FAT commonly surfaces practical findings rather than fundamental failures. The equipment has already been through the manufacturer’s production quality process before it reaches the FAT stage.

Cosmetic and appearance issues. Scratches on enclosure panels. Paint inconsistencies between units. Welding points that are not fully aligned. These signal manufacturing discipline and are visible to everyone who walks past the equipment once it is installed on site.

Cable routing and workmanship. Internal cabling that is not straight, bend radii that are too tight, cable ties that are inconsistent. Rarely functional failures, but they indicate whether the production team is maintaining attention to detail across a high-volume run.

Labelling and documentation. Labels in the wrong language for the destination market. Nameplate data that does not match the project specification. Logos placed incorrectly. Easy to correct, but should not pass FAT.

IP testing failures. Ingress protection tests that fail because a gasket on a container door is not properly seated or aligned.

Firmware and Parametrisation

A DC block coming off the production line is commonly loaded with the manufacturer’s standard testing firmware. This firmware is configured for the manufacturer’s internal testing process and may not reflect the specific requirements of the project it is destined for.

Project-specific parametrisation — voltage limits, alarm thresholds, operational setpoints, and protection settings — may need to be applied either as a final production step or during commissioning on site. The distinction matters. A DC block can pass FAT with testing firmware and still not be configured for its intended operational environment.

Verifying which firmware version is loaded, when the project-specific parametrisation will be applied, and whether the correct settings have been defined is part of a thorough FAT review.

The Broader Quality Chain

FAT is one stage in a broader manufacturing quality process. Understanding where it sits provides context for what has already been verified and what happens after.

Manufacturing procedure. The full production sequence — assembly steps, component integration, and quality checkpoints at each stage. This captures process steps that a standalone FAT document does not show. The manufacturing procedure is where the product is actually built and progressively verified.

Factory acceptance test. The formal testing stage where the completed DC block is verified against the manufacturer’s acceptance criteria. This is the stage where the buyer has visibility and the opportunity to review the product and its test results.

End-of-line process. The final stage before the unit ships. Cosmetic corrections, cleaning, protective wrapping for transportation, and installation of printed documentation inside the enclosure. None of this is part of the FAT, but it directly affects what arrives on site.

Why FAT Matters

FAT is the last point of visibility into equipment quality before it leaves the factory. Once the DC block ships, the next opportunity to verify what was built is on site during commissioning — where resolving issues is slower, more expensive, and directly affects the project timeline. A well-executed FAT catches what needs to be caught while correction is still straightforward.