What Truly Matters in BESS Acceptance

In one of our recent newsletters, we outlined why standardized BESS quality management is a fundamental prerequisite for the sustainable and economically successful operation of a battery energy storage system (BESS). Technical, documentary and organizational audits form the backbone of this approach.

In this follow-up, we take the discussion one step further:Which standards are particularly relevant during acceptance? What practical challenges arise in technical inspections? And why are structured performance tests indispensable for a reliable evaluation?

1. Standards as the Foundation of Comparability and Legal Certainty

BESS acceptance must not rely solely on manufacturer specifications. It must be based on normatively defined parameters and testing procedures. A brief excerpt illustrates this principle:

DIN EN IEC 62933-2-1 – Uniform Parameters and Test Methods

The standard DIN EN IEC 62933-2-1 “Electrical Energy Storage (EES) Systems – Part 2-1: Unit parameters and testing methods” defines:

• standardized performance parameters (e.g., capacity, power, efficiency, lifetime),

• voltage and frequency ranges,

• harmonized terminology,

• testing procedures for evaluating electrical energy storage systems.

Its central value proposition:Storage systems become technology-neutral, comparable, and objectively testable. Without a normative foundation, any performance assessment remains open to interpretation.

Cybersecurity: The Underestimated Test Segment

One area that continues to receive insufficient attention in practice is cybersecurity. As system interconnectivity, remote access capabilities, and market integration increase, its relevance rises significantly.

IEC 62443 – Industrial Cybersecurity

The IEC 62443 series defines requirements for industrial automation and control systems, including:

• technical security requirements,

• organizational safeguards,

• process requirements for planning, operation and maintenance.

For BESS projects, this means that not only hardware and performance require validation, but also system architecture, access control concepts and security mechanisms.

EN 18031 – New Testing Requirements

From 1 August 2025 onwards, the EN 18031 series will become mandatory for affected devices. It provides manufacturers with standardized test procedures to demonstrate conformity with new cybersecurity requirements.

The regulation applies, among others, to “radio equipment” connected to the internet or other networks that must ensure they do not cause network harm or service disruption. Whether a specific battery storage system falls under this category depends on its technical implementation.

For operators, the implication is clear: Cybersecurity is no longer an optional add-on. It is part of regulatory compliance.

2. Challenges in Technical Acceptance Testing

In practice, success depends not only on what is tested, but equally on when and how.

Quality assurance is not a one-off action but a continuous process—from target specification through construction and into operation.

For formal acceptance testing at the end of the implementation phase, the following prerequisites should be met:

• Initial commissioning must have been completed.

• Full documentation (measurement, testing and commissioning reports) must be available.

• Major defects should already have been remedied.

At the same time, timing must not be chosen so late that effective remediation is no longer feasible.

The EPC contractor must still be available, and contractual safeguard mechanisms should remain in effect. An acceptance test that is conducted too early or too late can significantly reduce enforceability of corrective measures.

Technically sound testing requires suitable framework conditions:

• Accessibility and safety: Secure access to the installation is mandatory.

• Operationally realistic ambient conditions: Testing should, wherever possible, reflect realistic operating scenarios.

A performance test conducted at sub-zero temperatures allows only limited conclusions regarding system behavior under peak summer conditions.

If necessary, seasonal follow-up measurements should be scheduled. Only then can reliable conclusions be drawn regarding thermal behavior and performance stability.

Comprehensive access to system data is a decisive success factor:

• Log and runtime data from all relevant components (BESS, inverters, metering equipment),

• straightforward data export capability,

• uniform data formats,

• high temporal resolution (ideally 1-second values).

Without precise data, it is impossible to reliably assess system efficiency, control response behavior or performance under dynamic load changes.

3. The Relevance of Structured Performance Testing

As outlined in Part I, structured quality management is not administrative formalism—it is risk mitigation.

Practical experience demonstrates:The more systematically acceptance testing is conducted, the higher the probability of identifying latent defects, such as:

• deviations in performance indicators,

• thermal irregularities,

• inadequately configured protection mechanisms,

• inconsistencies in documentation.

Many of these issues would otherwise only become apparent during operation—often after economic damage has already occurred.

Conclusion: Standards Provide Structure – Structured Testing Provides Certainty

BESS acceptance is not merely a formal project milestone. It marks the transition into an economically relevant operational phase. Standards such as DIN EN IEC 62933-2-1, IEC 62443 and, in the near future, EN 18031 provide the regulatory framework. Decisive, however, is their practical implementation.

Strategic timing of acceptance testing, appropriate testing conditions and structured performance validation reduce not only technical risks but also economic and liability-related uncertainties.

Standardized BESS quality management is therefore not optional. It is an integral component of professional project governance.

Note: This article reflects our practical experience and is not a substitute for legal advice.

Feel free to contact us if you're planning a project—we’ll support you with hands-on expertise.