This case study examines a distributed energy storage retrofit project carried out at an existing 2MW grid-connected power generation facility. The project involved the installation of 12 units of 150kW power conversion systems (PCS) alongside a 5MWh containerized battery energy storage system (BESS), transforming the conventional power plant into a hybrid generation-storage asset capable of delivering enhanced grid services, peak load shaving, and improved operational economics.
The project adopts an integrated energy storage cabin solution, with the BESS container connected to the grid via the low-voltage bus of the plant’s distribution system. This configuration enables the facility to store excess energy during periods of low demand and discharge it during peak pricing periods, capturing the value of time-of-use electricity tariffs while simultaneously reducing demand charges.
Background and Rationale
The Retrofitting Opportunity
Retrofitting existing power generation assets with battery storage has emerged as one of the most cost-effective strategies for improving asset utilization and unlocking new revenue streams. For the 2MW plant in question, the addition of storage capacity offered multiple value propositions:
Peak shaving: Reducing maximum demand charges by flattening load peaks;
Energy arbitrage: Charging during off-peak periods (low electricity prices) and discharging during peak periods (high prices);
Grid stability support: Providing frequency regulation and voltage support services;
Renewable integration: Smoothing the output of intermittent generation sources.
Why AC Coupling
For existing grid-connected plants, AC coupling is the preferred retrofit architecture as it enables storage expansion without altering the original power generation system. In this configuration, the battery system connects via a dedicated AC/DC converter on the load side of the existing inverters, eliminating the need to redesign the DC side of the plant. This approach offers:
Compatibility: Works with any brand or vintage of existing inverters;
Installation simplicity: Minimal disruption to existing operations;
Future flexibility: Easy to expand or modify the storage capacity.
System Configuration
The 5MWh BESS is deployed in a containerized format, which provides significant advantages in terms of installation speed, transportation, and scalability. A 40-foot container can typically accommodate 3 to 6 MWh of storage capacity, making it well-suited for this 5MWh requirement.
The system comprises the following key components:
Battery System
Lithium iron phosphate (LiFePO₄) battery cells, known for their thermal stability and long cycle life;
Battery management system (BMS) for cell-level monitoring and protection;
Modular battery racks arranged for optimal space utilization and thermal management.
Power Conversion System
12 units of 150 kW PCS (total 1.8 MW power conversion capacity);
Bi-directional inverters supporting both charging and discharging modes;
Grid synchronization and anti-islanding protection.
Energy Management System
Centralized EMS coordinating charge/discharge strategies;
Real-time monitoring of state of charge (SoC) and state of health (SoH);
Integration with grid operators for demand response and ancillary services.
Thermal Management
Liquid cooling or forced-air cooling depending on ambient conditions;
Temperature control ensuring optimal battery performance and longevity.
Safety Systems
Multi-level fire suppression (pack-level and container-level);
IP55-rated enclosure for environmental protection;
Ground fault detection and isolation.
Integration with Existing Plant
The BESS container is connected to the plant’s low-voltage distribution bus, allowing seamless integration with the existing 2MW generation infrastructure. The system operates in parallel with the plant’s existing inverters, with the EMS orchestrating optimal dispatch based on:
Real-time electricity prices;
Plant generation output;
Grid conditions and operator signals;
Battery state of charge.
Grid and Operational Benefits
Beyond direct economic returns, the storage system provides critical grid services:
Load leveling: Reducing peak demand on the grid during high-consumption periods;
Grid stability: Providing fast-response frequency regulation;
Renewable integration: Smoothing variability and reducing curtailment;
Resilience: Supporting the grid during disturbances or unexpected demand spikes.
Environmental Benefits
The project contributes to sustainability goals by:
Enabling greater utilization of renewable generation;
Reducing reliance on peaking plants (typically fossil-fuel based);
Extending the useful life of existing generation assets;
Supporting the transition to a lower-carbon grid.
Lessons Learned and Best Practices
Key Success Factors
AC coupling for retrofit applications minimizes disruption and maximizes compatibility;
Containerized deployment dramatically reduces installation time and site works;
Pre-commissioning at the factory ensures smooth on-site acceptance;
Integrated EMS is essential for optimizing dispatch and maximizing economic returns;
Modular design enables future expansion and scalability.
Technical Considerations
Thermal management: Critical for battery performance and longevity, particularly in high-ambient-temperature environments;
Safety systems: Multi-level fire protection and robust enclosure design are essential;
Grid compliance: Inverter selection must meet local grid code requirements;
Communication integration: Seamless integration with existing plant controls and grid operator systems.
Conclusion
The retrofit of a 2MW grid-connected power plant with 12 × 150kW PCS units and a 5MWh containerized BESS represents a compelling model for upgrading existing generation assets. The project demonstrates that:
AC-coupled containerized storage offers a practical, cost-effective path to adding storage capability to existing plants;
Multiple value streams – from energy arbitrage to grid services – can be captured simultaneously;
Modular, containerized deployment enables rapid installation with minimal disruption;
The 2MW/5MWh configuration has become a globally adopted standard for distributed storage applications.
As the energy transition accelerates, retrofitting existing grid-connected assets with battery storage will play an increasingly vital role in grid modernization, renewable integration, and the decarbonization of power systems. This project serves as a practical reference for asset owners and operators considering similar upgrades, demonstrating both the technical feasibility and the commercial viability of containerized BESS retrofits.