E.S.M. completed a detailed Reliability, Availability, and Maintainability (RAM) study for a 400 MWh Battery Energy Storage System (BESS) plant developed by a major renewable energy company.

With the project facing significant penalties for not meeting contracted performance requirements, the RAM study played a critical role in assuring stakeholders that the complex plant design could reliably deliver its required energy capacity.

System Overview

The BESS plant featured a highly branched architecture, distributing capacity from a high‑voltage substation through:

  • 2 switch rooms
  • 60 RMUs and inverters
  • Nearly 100 battery systems housing a total of 4,600 battery packs

To achieve the contracted 400 MWh storage capacity, the plant was intentionally over‑designed by approximately 10%, resulting in a total installed capacity of around 440 MWh.

Because the system could continue operating at partial capacity even when elements failed, a traditional binary (available/unavailable) assessment was insufficient. Instead, the study needed to determine how much capacity remained available under a wide range of failure scenarios.

Availability Measures

The RAM study defined two key system availability metrics:

  • Capacity Availability – The total accumulated available storage capacity over time, expressed as a proportion of theoretical perfect performance.
  • Performance Availability – The proportion of time during which the plant’s available capacity meets or exceeds the contractual performance requirement.

Quantitative Modelling Approach

Reliability Block Diagrams (RBDs) were used to calculate capacity availability. This allowed E.S.M. to accurately model the plant’s complex architecture and determine the reduction in energy capacity associated with the failure of any individual component.

To determine performance availability, E.S.M. applied a novel Event Tree Analysis (ETA) approach. This mathematically intensive method evaluated:

  • Every possible combination of multiple component failures
  • The likelihood of each combination occurring
  • The resulting loss of storage capacity

The results were then combined to generate a continuous function describing BESS capacity availability across all failure scenarios. The ETA approach was also extended to determine the plant’s Mean Time Between Failures (MTBF).

Supporting Qualitative Assessment

A complementary Failure Modes and Effects Analysis (FMEA) was undertaken to explore potential failure modes for each system element and their impact on overall plant performance. The FMEA grounded the quantitative results in practical engineering insight and generated recommendations related to:

  • Design improvements
  • Spare parts strategies
  • Maintenance requirements

Outcome

The RAM study delivered calculated reliability and availability metrics that demonstrated the plant’s ability to meet its contracted obligations. In addition, E.S.M. provided actionable recommendations for design refinements, spares provision, and maintenance strategies to support reliable long‑term operation.