Meta description:

TLS Energy delivered a 6 MW/6 MWh battery energy storage system in Sweden, configured for FFR, FCR-D, FCR-N and mFRR. Explore its system configuration and qualification testing milestones.

Project Overview

TLS Energy delivered a 6 MW/6 MWh battery energy storage system (BESS) for a major Swedish energy provider. The system was configured to support four ancillary services: Fast Frequency Reserve (FFR), Frequency Containment Reserve for Disturbances (FCR-D), Frequency Containment Reserve for Normal Operation (FCR-N), and Manual Frequency Restoration Reserve (mFRR).

The installation combined two DC battery container units using lithium iron phosphate (LFP) technology, two 4,000 kVA power stations and an energy management system (EMS). The project progressed through service-specific qualification testing, with test results submitted to Sweden’s transmission system operator, Svenska kraftnät, in early 2025.

Read TLS Energy’s project announcement.

1. The Project Requirement: One System, Four Grid Services

The customer needed a battery storage system capable of supporting different aspects of grid frequency management. These services do not all respond to the same operating conditions or serve the same purpose.

• FFR — Fast Frequency Reserve: Provides a rapid response when grid frequency changes sharply.
• FCR-D — Frequency Containment Reserve for Disturbances: Helps contain significant frequency deviations following a disturbance.
• FCR-N — Frequency Containment Reserve for Normal Operation: Supports frequency regulation during normal grid operation.
• mFRR — Manual Frequency Restoration Reserve: Supports the restoration of frequency balance through activated reserve capacity.

Supporting multiple services requires more than installing batteries with sufficient energy capacity. The system must also respond according to the relevant service requirements, while its power conversion and control functions work together.

For this Swedish project, the configuration brought together battery storage, power stations and EMS control to support the intended grid-service applications.

2. System Configuration: Battery Storage, Power Conversion and EMS

The published project configuration included three main elements.

DC battery containers

Two DC container units housed LFP battery technology. LFP chemistry is widely used in stationary energy storage because of its thermal stability and cycle-life characteristics. In this project, the battery containers formed the energy storage part of the wider installation.

Power stations

The system included two 4,000 kVA power stations designed for DC-coupled integration. Their role within the system was to support power conversion and grid interaction, connecting the battery storage capability with the wider electrical installation.

Energy management system (EMS)

The EMS provided system-level operating coordination. For a BESS serving multiple grid services, energy management and control are important because the system must operate within its available power and energy limits while following the requirements of the selected service.

These elements perform different but interdependent functions. Battery capacity alone does not determine whether a system can provide a particular ancillary service; power conversion, control behaviour and qualification requirements also matter.

3. Qualification Testing: From Configuration to Grid-Service Readiness

A BESS intended for ancillary services must demonstrate that it can meet the relevant technical requirements. The qualification process is therefore an important part of project delivery, beyond equipment supply and installation.

TLS Energy’s published project update records the following testing milestones:

The results were submitted to Svenska kraftnät, Sweden’s transmission system operator. These milestones document the project's progress through testing for all four named services.

The public project updates do not disclose detailed test curves, response-time measurements, acceptance thresholds or individual approval documents. Accordingly, the dates above describe the reported testing and submission milestones rather than independently verifying the formal qualification status of each service.

Read the qualification testing update.

4. Applicable Requirements and Project Outcome

For a BESS participating in Sweden’s ancillary-service market, the relevant technical requirements depend on the service being provided and the applicable qualification process administered by Svenska kraftnät.

The available TLS project reports identify the four services and document the testing submissions, but do not name specific IEC or EN standards or publish the complete project acceptance criteria. It would therefore be inaccurate to assign additional standard numbers to this project without confirmation from the approved technical documentation.

TLS Energy’s project announcement reports that the system was commissioned and deployed to support grid stabilisation and frequency regulation. The subsequent qualification update documents the testing milestones in early 2025.

The case illustrates an important distinction in BESS delivery: completing the physical installation is one milestone, while demonstrating suitability for the intended grid services is another. Both the equipment configuration and the service-specific qualification process matter to the final application.

5. Key Takeaways for BESS Project Developers

This Swedish project highlights three considerations when developing a battery energy storage system for grid services:

• Define the services early. FFR, FCR-D, FCR-N and mFRR serve different frequency-management purposes and should be considered during system planning.
• Assess the complete system. Battery containers, power conversion and EMS control must be considered as an integrated configuration rather than as independent products.
• Include qualification in the delivery plan. Testing and documentation for the intended services should be considered alongside equipment integration and commissioning.

For project developers, the key question is not simply how much energy a BESS can store, but whether the complete system is configured and qualified for its intended operating role.

FAQ

What was the capacity of TLS Energy’s Swedish BESS project?

TLS Energy’s published project overview identifies the system as a 6 MW/6 MWh battery energy storage system.

Which grid services was the system designed to support?

The project was configured for FFR, FCR-D, FCR-N and mFRR.

Can TLS Energy configure BESS solutions for other grid-service requirements?

TLS Energy can review a project’s intended application, power and energy requirements, battery configuration, power conversion and control architecture to assess a suitable containerised BESS solution.

Before a battery energy storage system reaches site, buyers want evidence that the delivered package matches the approved design. For a BESS container supplied as an empty enclosure, inspection can verify the structure, finish, doors and specified interface provisions. It cannot verify battery operation, electrical protection, cooling performance or control logic when those systems are outside the supply scope.

Recent TLS content discusses factory acceptance testing (FAT) for integrated BESS. The same quality-planning principle applies to enclosure-only orders: define the checks and acceptance criteria before production, and make sure the inspection plan reflects what is being purchased.

Separate enclosure inspection from system FAT

FAT is often used to describe checks performed at the factory before shipment. Its scope varies by contract. An integrated BESS FAT may include mechanical, electrical, thermal, control, communication and safety tests when those systems are supplied and available for testing.

An enclosure-only order has a narrower boundary. The inspection can confirm the physical product against its drawings and specification. It should not be described as a complete BESS FAT if the container ships without batteries, PCS, BMS, cooling equipment, fire systems and controls. The buyer, enclosure manufacturer and system integrator should assign each test to the party that supplies or installs the relevant equipment.

Build an inspection plan from the approved drawings

The approved drawing set should identify dimensions, openings, doors, structural interfaces, lifting points, finish requirements and any project-specific accessories within scope. A practical inspection plan then turns those requirements into observable checks, with an agreed method and acceptance criterion for each one.

For example, the plan may specify which overall dimensions are measured, how door operation is checked, what finish documentation is required and how cable openings are compared with the approved interface drawing. Inspection points should be selected to suit the order and any applicable standards or customer specifications. There is no single universal checklist for all container projects.

Typical checks for an enclosure-only package

 Dimensions and configuration

Confirm the external dimensions, door locations, equipment openings and overall configuration against the latest approved drawings. If the buyer has specified internal clearances or mounting interfaces, record how these will be checked and which drawing revision governs acceptance.

 Structure and lifting provisions

Review the structural features and lifting points included in the design. The project documents should state the applicable design basis and any required inspection or test evidence. Do not assume a lifting certification, offshore classification or a particular load rating unless it is expressly included and documented for that unit.

 Doors, access and sealing details

Operate doors and access panels to confirm that they open and close as intended. Check the installed hardware and sealing details against the approved scope. If the project requires a water-ingress or other performance test, define the method and acceptance level in the specification; a visual inspection alone does not prove a particular ingress-protection rating.

 Cable openings and customer interfaces

Compare the number, location and size of the agreed cable openings with the interface schedule. Verify frames, blanking arrangements or sealing components only when these are part of the order. Cable glands, cable trays and electrical terminations should not be presumed included.

 Coating and corrosion protection

Where specified, review coating records and carry out agreed visual or thickness checks. The inspection standard, sampling plan, measurement locations and acceptance limits should be agreed in advance. Required performance depends on the site environment and the selected coating system.

 Documentation to request at handover

The purchase order can list the records required for release. Depending on the project, these may include approved as-built drawings, material or weld documentation, coating records, dimensional inspection results, non-conformance closeout and a final inspection report. Only request records relevant to the supplied scope and applicable specification.

The handover package should make clear what the buyer or integrator must complete after delivery. Site installation, final grounding, customer cabling, equipment installation and integrated system commissioning may sit outside the enclosure supplier’s work.

 Plan tests that require integrated equipment separately

If the project expects checks of BMS communication, PCS functions, battery alarms, thermal controls or fire-system responses, identify which supplier provides the equipment and who leads the test. Those functions require an agreed system configuration, test procedure, inputs, expected responses and acceptance criteria. An enclosure supplier cannot demonstrate functions of equipment it does not provide.

For a multi-party project, a responsibility matrix can help connect enclosure inspection, equipment FAT, site acceptance testing and commissioning. The goal is to avoid both gaps and duplicate tests while keeping each result traceable to the responsible party.

 FAQ

 1.Is enclosure inspection the same as BESS FAT?

 No. Enclosure inspection covers the contracted container structure and interfaces. A system FAT may cover electrical, battery, thermal, controls and safety functions if those systems are included and available for testing.

 2.Can an empty container be certified as IP55 through a visual check?

A visual check alone does not establish an IP rating. Any required ingress-protection rating and verification method must be specified and assessed for the completed design under the applicable test or certification process.

 3.Should lifting tests be included in every container order?

The required lifting design basis and verification depend on the application, governing requirements and contract. The buyer should state the intended transport and lifting conditions and request the applicable evidence in the specification.

 4.Who tests the BMS, PCS and cooling system?

The suppliers or integrator responsible for those systems should define and perform the relevant tests. The project should document responsibilities and interfaces before the factory test stage.

Conclusion

TLS conducts Factory Acceptance Testing according to its established FAT standards and the requirements applicable to the supplied package. For an enclosure-only order, FAT focuses on the container structure, dimensions, doors, finish and specified interfaces. When batteries, PCS, BMS or other systems are included in TLS’s supply, the applicable tests can also cover those integrated systems.

The FAT scope follows what is included in the project delivery. This gives the customer a clear record of what TLS has inspected and tested before shipment, while identifying any equipment or site checks handled by other suppliers or the system integrator.

Renewable-energy projects often face the same problem: electricity is generated when the sun is shining or the wind is strong, but demand does not always occur at the same time. Grid connection delays, peak demand charges, power fluctuations and renewable-energy curtailment can make the project harder to operate and less profitable.

A Battery Energy Storage System can store electricity when it is available and release it when the project needs it. TLS Energy provides BESS containers in three integration levels: container enclosures, semi-integrated systems and fully integrated energy storage solutions. TLS BESS Container Solutions

Why Are More Projects Adding BESS?

A renewable-energy project does not always produce electricity at the right time.

Solar generation usually increases during the day, while electricity demand may reach its highest level in the morning or evening. Wind generation can also change quickly according to weather conditions.

A BESS can help the project:

• Store surplus renewable energy.
• Reduce peak electricity demand.
• Smooth rapid power changes.
• Support grid-frequency control.
• Provide backup power.
• Improve the use of on-site renewable generation.
• Reduce the effect of short-term power fluctuations.
• Support microgrid operation.

The best application depends on the project’s electricity profile. A battery for peak shaving may need several hours of discharge. A battery for frequency response may need fast power changes but a shorter operating duration.

What Does a BESS Container Include?

A BESS container may include several systems working together:

• Battery racks.
• Battery Management System.
• Power Conversion System.
• Thermal management.
• Electrical protection.
• Fire detection and protection.
• Control and monitoring systems.
• Cable-management systems.
• External power and communication interfaces.

The container itself provides the protected structure and installation environment. The final system can be supplied at different levels of integration depending on what the customer already has and what TLS is expected to provide.

This is important because a “BESS container” does not always mean a complete turnkey system. The quotation should clearly state whether batteries, PCS, cooling, controls and fire-protection systems are included.

Which BESS Integration Level Is Right for the Project?

TLS offers three general integration options.

Container Enclosure

The container enclosure is suitable for customers that already have their own battery racks, PCS and control systems.

TLS can provide the structure, internal arrangement, equipment supports, cable routes and required environmental provisions. The customer or another system integrator then completes the equipment installation.

This option gives the customer greater control over the selected battery and electrical systems.

Semi-Integrated BESS

A semi-integrated system can include battery racks and selected auxiliary equipment while leaving other parts of the system open for customer integration.

This option can reduce some installation work while allowing the customer to retain control over specific battery, PCS or control-system selections.

Fully Integrated BESS

A fully integrated BESS can combine battery systems, thermal management, protection and electrical integration in one coordinated package.

This option is suitable for customers looking for a more complete solution with fewer separate equipment interfaces. The exact system scope still depends on the project specifications and selected equipment.

How Much Energy Can a TLS BESS Container Store?

TLS’s published BESS platform lists an energy-capacity range of approximately 3.73–6.26 MWh.

The final usable energy depends on the battery system, operating conditions, control strategy and project requirements.

The customer should define both:

• Power output in MW.
• Stored energy in MWh.

MW describes how much power the system can deliver at one time. MWh describes how much energy the system can store.

Can BESS Support More Than Backup Power?

Yes. A BESS can provide several services depending on the electrical architecture and control system.

TLS identifies possible applications including:

• Energy shifting.
• Peak-load shaving.
• Power smoothing.
• Voltage control.
• Frequency response.
• Active power reserve.
• Custom power schedules.
• Reverse-power protection.
• Renewable-energy integration.

These functions are not automatically included in every BESS project. They depend on the PCS, BMS, energy-management system, grid connection and project control requirements.

The customer should define the required operating modes before the system is designed.

Why Is TLS Suitable for Customized BESS Projects?

TLS Energy’s BESS Scope covers engineering, structural integration, electrical integration, thermal management, fire protection, manufacturing and project testing.

TLS can also work with customer-specified battery systems, BMS, PCS, cooling technologies and control architectures, subject to the agreed project requirements.

This is useful for energy-storage companies and EPC contractors that already have their own technology but need a reliable manufacturing and container-integration partner.

FAQ

1.Can a BESS reduce peak electricity demand?

Yes. Peak-load shaving is one of the applications identified for TLS BESS solutions. The actual result depends on the load profile, battery capacity and control strategy.

2.Can BESS work together with solar panels or wind turbines?

Yes. BESS can store excess renewable energy and release it later, subject to the complete electrical and control-system design.

3.What should be sent to TLS first?

Send the required power, energy capacity, discharge duration, operating profile, site conditions, cooling preference and preferred level of integration. Contact TLS Energy

Conclusion

BESS is no longer limited to emergency backup. For renewable-energy developers, utilities, microgrids and commercial users, a properly configured battery container can help manage peak demand, smooth power changes, store renewable electricity and support grid operation.

TLS provides BESS containers from basic enclosures to semi-integrated and fully integrated systems. The right solution depends on the project’s power requirement, energy capacity, operating profile, cooling method and integration scope. Explore TLS Energy Storage Solutions