In this article
A flexible connection allows part of an energy storage system’s capacity to be used subject to agreed limits. It can be an alternative to performing individual network works before gaining access to the entire ordered capacity. For businesses, the main question is: will the storage system be able to perform the required work during hours when the network will limit charging or discharging? The answer depends on the technical conditions, automation and schedule of use of the installation.
What guaranteed and non-guaranteed capacity mean
Guaranteed capacity defines the portion of access that the network can provide continuously, except for cases provided by the rules of network operation. Non-guaranteed capacity is available with possible interruptions or limitations. Its use is related to the availability of a suitable reserve at the network node and the operation of automation. Both values must be documented.
For the storage device, electricity withdrawal from the network and supply to the network are considered separately. Sufficient reserve for discharge does not confirm the possibility of charging with the same power. In each direction, the guaranteed and non-guaranteed parts together must correspond to the ordered capacity of that direction.
| Parameter | Practical content | What to check |
|---|---|---|
| Guaranteed import | Agreed guaranteed share of grid import capacity. | Is it sufficient for the required charging regime. |
| Non-guaranteed import | Additional import capacity that may be restricted. | When charging needs to be reduced or transferred. |
| Guaranteed export | Agreed guaranteed share of grid export capacity. | What work can be planned within this access. |
| Non-guaranteed export | Export capacity subject to possible restrictions. | How reduced export affects the schedule and revenue. |
These parameters describe network access. Battery energy reserve is calculated separately. The difference between them is explained in the material on the selection of ESS power and capacity.
In the original task, it is convenient to specify the required maximum power, hours of operation and the minimum acceptable mode for each direction. Then the technical team will check the specific task: how much energy needs to be accumulated by the specified time and how much power needs to be given in the planned window.
When to consider a flexible connection
For the distribution system, this procedure is provided for the customer of a non-standard connection with a capacity of more than 1 MW at a voltage at the connection point of 20 kV or higher. This is the case when the customer performs design, construction, installation and commissioning works for generating capacity. Applications are submitted after the entry into force of technical conditions and preparation of project documentation.
The following condition applies to the network itself: the ordered non-guaranteed power must fit within the non-guaranteed reserve of the relevant network node. Therefore, the characteristics of the battery or free space at the substation do not in themselves confirm the availability of the service. Operator data and technical solution verification required.
There is a separate procedure for the transmission system. It also provides for the ordered capacity of more than 1 MW, the current technical conditions, the developed project and the corresponding reserve. In addition, established operational security requirements are taken into account. The 20 kV voltage criterion given for distribution should not be mechanically transferred to this procedure.
If the facility does not meet these prerequisites, it is worth checking the general ESS joining procedure, available capacity and other acceptable options. The flexible mode does not replace the initial registration of the connection.
The power threshold is checked according to the connection order, and the voltage is checked according to the corresponding point. The power designation in the equipment catalog or the voltage inside the battery cabinet are not sufficient data for such a conclusion. For a preliminary check, prepare valid documents for the point and parameters of the future installation.
Permanent and temporary non-guaranteed capacity
For a permanent flexible connection, the non-guaranteed part remains so under the conditions specified in the documents. It should not automatically be considered as future guaranteed power. The financial model should be checked taking into account possible limitations during the relevant period of operation.
The temporary option is used until technical measures are taken to access the entire ordered capacity as guaranteed. These measures and terms should be defined in the technical conditions. If the necessary works are foreseen in the network development plan, the expected access is linked to their implementation. In the absence of such measures in the plan, they are foreseen in the technical conditions in the prescribed manner.
For the customer, this means the need to check a specific list of works, performers and dependencies between stages. The wording "temporary" by itself does not give a calendar date for full access. In the schedule of the project, it is advisable to separately show the work with restrictions and the subsequent transition to the agreed guaranteed regime.
If the economic feasibility depends on the completion of a certain reconstruction, this dependence must be made visible to the investor. Keep confirmation of terms and update the financial scenario when they change. The preliminary discussion of the expected date should not replace the agreed terms and confirmation of the implementation of the necessary technical measures.
What to agree on in the technical conditions and contract
Start document verification with four dimensions: guaranteed and non-guaranteed import, guaranteed and non-guaranteed export. Next, specify the permanent or temporary nature of the non-guaranteed part, the requirements for automation, the phasing of technical measures and the procedure for exchanging information.
- 01. Determine the needAgree on capacity directions, ESS work schedule and business-acceptable limitations.
- 02. Check the possibilityCompare the project and current technical conditions with the reserve at the network node and the requirements of the operator.
- 03. Establish conditionsMake changes to the contract and technical conditions, define automation, work and inspections.
10 calendar days are provided for consideration of an application regarding the application of flexible joining. The result is a supplemental agreement, modified terms and conditions, adjusted fee calculation and invoice as needed, or a written reasoned refusal. This is a deadline for responding to a change in conditions, not a promise to build or run a plant in ten days.
Before agreeing to changes, check the kit against the short list:
- In the application, technical conditions and the contract, the power values for both directions are agreed.
- For the temporary part, it is clear which works give access to the full guaranteed capacity.
- Automation requirements allow you to determine the equipment, communication channels, responsible persons and the inspection program.
- The calculation of the fee corresponds to the proposed option and the agreed division of works.
- The operational team understands the order of receiving commands, recording events and actions in the event of a malfunction.
Save written responses, project versions, and agreed changes. In more detail, the verification of the kit is considered in the material documents and cost of joining ESS. For a solar plant with storage solar power plant design refers to the solar part; the scope of work on ESS and network automation must be agreed separately.
How automation implements restrictions
Automation of flexible connection controls the mode of the power node and affects import or export within the limits of non-guaranteed capacity. It should provide information about approaching operational safety limits, power regulation, necessary automatic shutdown and exchange of information with the operator.
The ability to manage the battery through a normal application does not confirm that these requirements are met. Comprehensive tests of automation and communication channels are required before the service is completed. The result is drawn up in a report with the participation of representatives of the operator and the customer. Information about modes, commands and their execution must be kept for a calendar year.
The user has no right to interfere with the agreed operation of automation. If the user's equipment does not work properly, the operator issues a request to eliminate the deficiencies. Failure to comply with this requirement within the prescribed period may result in the restriction of access to the level of guaranteed capacity.
For the operations team, it is useful to determine in advance who is responsible for communication with the operator, checking the command log and restoring good operation. The settings, ownership and maintenance of automation elements are checked separately on both sides of the network ownership boundary.
The threshold of 90% or more specified for automation concerns network-node parameters relative to operational safety limits during overload. This is not the battery level. For several users of flexible connection, the sequence of restrictions by the date of the contract, starting from the latest, is also defined. It must be taken into account in the assessment of the facility regime.
How restrictions affect project economics
It is worth comparing the options according to the full budget and the possible mode of operation. The evaluation includes connections, network operations, automation, communication channels, testing and maintenance. The fee calculation depends on the applicable procedure and agreed parameters. The total percentage of savings without calculating a specific object does not show a real benefit.
In the hourly model, you need to check whether the restrictions coincide with the favorable charging or discharging hours. The same number of hours of restriction can have different consequences depending on the moment of their occurrence, the charge level and the planned energy use. For the temporary scheme, the delay of the transition to the full guaranteed capacity is evaluated separately.
Conditional situation. The storage has enough energy for the planned evening discharge, but that is when the available non-guaranteed capacity is limited. It will not be possible to export the entire planned volume in this window. On another day, limiting the charge may leave the battery undercharged. These are two different risks that need to be modeled separately.
Start with three scenarios: expected usage, more frequent restrictions, and operating mostly within guaranteed access. Do not invent the frequency and duration of restrictions: ask the operator for available data, and mark unconfirmed assumptions in the model. Separately check the result under less favorable assumptions before choosing equipment.
In the absence of sufficient history of network operation, use ranges of assumptions and show at which mode the project ceases to fulfill the financial task. The presence of a regulatory procedure does not prove that a specific network node already has a confirmed practice of working with such installations.
Do not assume automatic compensation for lost income from restrictions on non-guaranteed capacity: the operator is not responsible for limiting it within the prescribed limits. The flexible mode must correspond to the risk acceptable to the owner, and the income forecast needs separate verification.