Energy Storage at an Existing Facility: When Is a New Connection Needed?

An energy storage system at a business does not always require a new grid connection service. If the system is installed within the business’s own internal network, check whether it can operate within permitted import and export limits, meet applicable technical conditions and be properly registered. The mere presence of free space near the transformer or its power reserve is not enough.

For the owner of the existing facility, the main question sounds like this: what will change at the border with the external network after the battery starts up? The answer requires a scheme, documents and calculation of the simultaneous operation of consumers and generation. Below we will consider how to prepare this data, distinguish possible routes and avoid purchasing equipment under unconfirmed conditions.

Start with existing point documents

Physically, one territory can contain networks of different owners. Therefore, first establish who owns the cables, the transformer and the place of the future connection. Compare the current one-line diagram with the connection point record and documents on the network ownership boundaries. For the rented site, specify the rights to use electrical installations separately.

Installation after the network ownership boundary in own networks and connecting another user through the enterprise network have different organizational prerequisites. Do not determine the route based only on where the battery will be. The owner of the installation, the party to the contract with the operator and the actual power supply scheme are important.

Write out the permitted import power and permitted export power separately. If a permitted value cannot be found, do not substitute the inverter or transformer rating. This is an undefined condition that needs to be clarified with the documents and with the operator before finalizing the design decision.

If flexible connection is applied, separate the guaranteed and non-guaranteed parts of the capacity. The storage system’s operating mode must take into account the possible limitations of the non-guaranteed part. One common indicator in the vendor's presentation does not reflect this.

Calculate flows for different business operating modes

The rated power of the ESS describes the equipment, and the allowed values describe the exchange with the network. These are different limits. A large rating in itself does not prove the need to increase the connected power, but a smaller rating does not guarantee the absence of excesses either.

Check at least work shift, process pause, night charging and solar generation change. After production stops, local consumption decreases, so the same battery discharge can generate greater export. The battery capacity in kWh does not answer this question: you need the balance of kW at a specific moment. The difference is revealed in the material on power and capacity of ESS.

For comparison, take consumption and generation for the same time intervals. The monthly energy total does not show whether charging and peak load coincide. Mark downtime, weekends, seasonal shifts and planned new production lines. If data is missing, determine the measurement program first, rather than replacing an unknown graph with an average value.

Check the charging and discharging capabilities of a specific kit separately: do not assume that they are the same in all conditions. The calculation must take into account the available energy reserve and when it can be restored. Operating within the connection power limit does not by itself establish that the required operating duration can be achieved.

Illustrative example of three operating modes

For an educational calculation, let's assume: the permitted import is 400 kW and permitted export is 100 kW. All capacities are on the AC side; losses and additional auxiliary consumption are not taken into account. Charging and discharging in one line do not occur at the same time.

Exchange with the network = load + charging - generation - discharge. A positive result means import; a negative result means export.

The second mode requires a change in management or design of other parameters. A simple discharge reduction may be one option to check, but is not a complete set-up guide. The real calculation takes into account own needs, losses, speed of load change and characteristics of the entire system.

Distinguish internal installation from a new connection

A distribution-system user may install storage in its internal network without obtaining a new connection service, provided applicable requirements are met. Permitted flows must be respected, technical requirements fulfilled, metering arranged and required registration completed with the distribution system operator (DSO).

The transmission system user works with the transmission system operator, or TSO, in a separate order. The scope of interaction depends, in particular, on the total power of the installations and the status of the user. The form of the application, the need for approvals and the sequence of actions are determined before implementation. A DSO document package cannot be assumed to apply to a transmission-system facility without verification.

If an increase in the permitted capacity of at least one direction is required, this issue is resolved through the relevant connection service. A new point, voltage change, power circuit or reliability requirement also needs a separate assessment. Not every document change means the same amount of network work.

The page connecting ESS to power grids describes the general procedure from the initial data to the completion of the work. Here, the main task is to check the already existing point and the changes made by the storage system.

Check control, protection and failure behavior

Keeping flows within permitted values requires an engineered solution. The design task specifies the location of flow measurement, control devices, command execution and protection. The very entry of "export restrictions" in the commercial offer does not yet describe the operation of the entire facility.

Ask the designer to analyze loss of meter communication, part load tripping, generation change and control restart. Each situation requires a specific response and method of verification. Reaction time and settings are chosen according to the project and equipment documentation, not according to the universal advice from the article.

Flow control, electrical protection and backup are separate functions. An export limit does not establish the ability to operate without the external grid. For backup, check designated loads, switching, isolation from the grid and the capabilities of the specific configuration.

If the main goal is to support the technological area, go to backup power for production. The initial data will be a list of equipment and a permissible pause, not a promise to power the entire enterprise from any battery.

Agree on metering and confirmation of completed work

Storage monitoring and commercial metering have different purposes. The metering scheme should correspond to the role of the user and energy operations. For the producer and the active consumer, it is necessary to take into account the requirements for separate metering of flows to and from the ESS.

For the DSO route, check the application, the necessary attachments, access for the stipulated technical checks and sealing, updating the connection point record and relevant acts. This is a list of questions for preparation, not a replacement for the current application form. For the TSO route, the composition of the notification, tests and approvals is specified separately.

Save the agreed scheme, parameters of installed equipment, test results and settings. They must correspond to the actual configuration. Replacing a converter or adding another cabinet after approval requires re-checking the impact on modes and documents.

For acceptance, match "requirement, verification, document". For example, for flow limiting, record which mode was tested, where the power was measured, and what result was obtained. Confirmation of equipment delivery does not replace such a record. Leave uncompleted checks open with the responsible executor, and do not close with a general mark of completion of installation.

At the equipment comparison stage, you can view the Sungrow PowerStack 255CS-2H card. The final version, compatibility and available functions are checked against the documentation of the specific kit. The presence of a product page does not confirm the suitability of a model for your attachment point.

Prepare a project discussion package

Add the actual facility data to the supplier request. This will help you compare offers with the same prerequisites and see which works are not yet included in the estimate.

For active production, it is also useful to prepare an organizational plan of work. Agree on a possible shutdown window, access to electrical installations responsible for the enterprise and the procedure for resuming work. These are working issues for planning, not a universal regulation of switching: specific operations are determined by the responsible technical team.

• Valid scheme, connection point record and permitted values of both directions.
• Network Owners, Point User and ESS Planned Role.
• Consumption and generation profiles for matching time intervals.
• Calculation of extreme modes and list of undefined parameters.
• Control, protection, metering and inspection requirements.
• List of works, responsible performers and completion documents.

If a new solar part is planned at the same time, a solar power plant site audit can be discussed for its assessment. Storage network issues and the scope of special checks are agreed separately. Do not replace them with the standard service description for a solar station.

When comparing estimates, separate equipment, project work, internal networks, protection, metering, testing and registration. For each position, specify whether it is included, who performs it and under what conditions. The absence of a new connection service does not mean the absence of storage integration costs.