BESS FAT and SAT: Define Acceptance Before Shipment

Before ordering a containerized battery energy storage system (BESS), agree what evidence permits shipment, what must be demonstrated at the site, and who signs off the completed scope. A factory acceptance test (FAT) report covers an identified configuration and test scope. Site acceptance testing (SAT) must address the installed system and its agreed duties. Keep those decisions explicit in the purchase specification.

For a HUA-X PowerFac-5M enquiry, start with the published DC-side product and identify the wider system to be supplied. Then request an acceptance plan covering the battery container, power conversion, controls and site interfaces in the offered scope. Agree the test scope, services and acceptance criteria with the project parties before ordering.

1. Separate three acceptance decisions

EPRI's May 2023 commissioning guidance explains that FAT commonly concerns equipment tested before shipment, and that the factory's test capability limits what can be demonstrated. It also records a lesson in which battery and power-conversion subsystems passed separate factory tests but failed to operate when integrated. Its guidance supports checking integration evidence as well as individual equipment reports (printed pages 5-2 to 5-3). [2]

2. Turn the PowerFac-5M specification into acceptance questions

A DC-side energy rating does not by itself define the energy delivered at a site's AC connection. Ask the proposal to identify the tested equipment, included auxiliaries and measurement point before comparing any energy result. Request the current controlled specification, interface documents and acceptance limits for the offered configuration. Agree project-specific FAT and SAT pass thresholds with the responsible project parties.

The factory test scope should also identify any site equipment that is absent or represented by a simulator. Ask which results are transferable to the delivered configuration and which demonstrations remain for the installed system. Record these as open scope decisions before agreeing shipment release.

3. Make each result traceable to a configuration

A report marked “pass” is useful only when the buyer can identify what passed. Ask for a concise record that connects the requirement, the configuration and the result.

Keep a version change visible even when the equipment model name stays the same. A changed controller, firmware release or approved setting should trigger a documented decision about the validity of earlier results. Agree the decision owner and the handling of unresolved retesting before a shipment or site milestone is reached.

4. A utility case shows why the revision matters

Southern California Edison's Tehachapi project report, revised February 12, 2016, describes a laboratory mini-system used to support full-system startup and commissioning. Initial phase-one testing ran through 11 rounds over nine months, from November 2013 to August 2014. Each round except the final one generated software or firmware updates; the team repeated the phase-one tests because updates could introduce new issues (PDF page 62). [3]

This historical third-party utility project in California illustrates why acceptance evidence must identify the tested revision. Agree a test plan and timetable for the proposed PowerFac-5M configuration.

5. Zero-export SAT must capture the transient

Zero-export site acceptance testing needs to show net power at the point of common coupling (PCC) while the site changes operating state. A steady reading near zero cannot reveal the peak export or recovery time after a sudden change. Intertek’s UL 3141 testing overview identifies load steps, generation steps, export/import limiting and loss of control circuits as relevant test categories, depending on the control function. These certification categories help identify questions for the site plan; a project SAT report is a separate deliverable. [6]

The reason is a changing power balance. If site load falls while generation or battery discharge remains unchanged, the surplus can flow toward the grid until the controls respond. Battery charging can absorb surplus only within its available charging power and operating limits. When that capacity is unavailable, the system needs another response, such as reducing generation or battery discharge. The installed control design determines which response is possible.

The measurement boundary matters as much as the setpoint. A battery inverter reading describes one branch; the PCC reading includes the combined effect of the site’s generation, storage and loads. A time-aligned PCC power trace shows the excursion and recovery. Its sampling interval and sign convention must be clear enough to assess the agreed response limit; a long-period energy total cannot establish a seconds-scale response.

A specific example is PG&E’s California Rule 21, Option 8, sheet 266, effective August 29, 2025. It requires a certified power control system with an open-loop response time of no more than two seconds, configured for zero export. It specifies reducing export to zero or below within two seconds of commencing export. It also states that certified open-loop response of no more than two seconds, together with a steady-state time of no more than ten seconds, meets this requirement. Response time and settling time are distinct; this path does not create a universal SAT threshold. Here, “power control system” means the export-control function, not simply the battery’s power converter. [7]

For PowerFac-5M, the published 5016 kWh nominal DC-side energy rating does not establish the export-control response of the complete installation. The relevant scope includes the selected power conversion equipment, controller, PCC metering and any generation controls. Include the zero-export duty and connection requirements with a PowerFac-5M project enquiry, so the proposed system and its site acceptance scope can be assessed together.

6. Define the site and handover responsibilities

U.S. Department of Energy guidance for federal distributed-energy projects connects commissioning to the design intent and its evaluation protocol. Before acceptance, it calls for reviewed test and inspection reports, resolved discrepancies, staff training, operating manuals and as-built drawings. Use these document categories to agree the handover requirements for the destination and contract. [4]

For the proposed BESS, name who supplies the battery container, power conversion system, supervisory controls and site work. Ask who coordinates evidence across those parties, who witnesses the agreed tests and who may accept a deviation. Specify which open items prevent the relevant milestone and how any permitted outstanding work will be closed. A signature should identify the accepted scope and the remaining responsibilities.

Extend the handover discussion to the operating period. U.S. DOE guidance for federal distributed-energy projects says site staff need operational knowledge even when a contractor performs O&M. Its customizable lithium-ion battery procurement template, Section 2.19, provides for a named maintainer and O&M reports covering downtime, causes, maintenance and repairs. [4][5]

Confirm these responsibilities for the proposed PowerFac-5M supply split. Request the proposed roles and record access with your PowerFac-5M technical documents. The after-sales guide helps identify evidence to include when reporting an operating issue.

7. Include the acceptance scope in the enquiry

Send the intended application, site country, connection arrangement, operating duties and proposed supply split with your PowerFac-5M enquiry. Identify the required measurement boundary and any buyer or independent witness requirements. Request the proposed FAT scope, site acceptance responsibilities, deliverable records and treatment of changes before accepting a quotation.

Use the product page and procurement brief below for the published baseline. The related site-planning guide covers access and physical project inputs; this article adds the evidence needed to decide when the agreed equipment and integrated system are acceptable. Final test methods and acceptance limits require the project parties' engineering and contractual agreement.