Shared Grid Connection for Solar and Storage: Owners, Metering and Contracts

A shared connection point can bring solar generation, energy storage and consumption together at one grid interface. However, a common cable does not make owners a single market participant and does not cancel metering requirements. Before designing, you need to distinguish between two situations: the equipment of one customer and the installations of different users. The documents, distribution of authorized power, responsibility and the method of determining the amount of electricity depend on this. Let's consider what decisions should be agreed upon before purchasing a storage system.

One owner and several users: different models

In the first model, the enterprise uses its own solar station, storage and production loads at one connection point. The design method is determined by the effect of the new installation on the current parameters. A connection service, a change in technical parameters or a prescribed procedure for installing ESS in internal networks without increasing the permitted capacity may be required.

In the second model, electrical installations of one user are connected to the internal network of another. Here, the shared power distribution or transmission point, abbreviated STRPP in Ukrainian, is used. There is a main user, a sub-user and an external network operator. Their roles cannot be determined only by the address of the object or who owns the land plot.

The adjacent placement of the solar plant and the battery in itself does not yet describe the legal model. First, the owners of electrical installations, the connection scheme and planned energy flows are established. A comparison of ESS usage models will help separate co-location from self-consumption or a separate market project.

For a preliminary check, make a list: who owns the solar plant, who owns the storage system, who owns the internal network and for whom the connection is registered. If the answers are different, do not use the abbreviated description "all ours". It hides exactly those relations for which the right to use the network and separate obligations of the parties need to be determined. This is a working method of data preparation, not an independent legal opinion.

What power is available through the common point

The sum of the installed capacities of the equipment may be greater than the permitted capacity at the connection point. However, actual import from and export to the external network must remain within the limits of the respective permitted values. These are two separate limitations. The existing permission to release does not automatically mean the same permission to charge the battery from the network.

Concurrent operation modes are required for testing. During the day, the solar plant can produce energy, the battery can be charged, and the enterprise can consume. At other times, the storage system will discharge energy together with the generation or will be charged simultaneously with the maximum production load. Evaluate the resulting flow at the boundary with the operator, not each device in isolation.

Technical conditions for shared connection points provide for control means, in particular automation, which reduces the load or disconnects installations when the permitted values are exceeded. Arrangements by dispatchers do not replace the necessary technical protection. If the selected modes require more contracted power, this issue is resolved through the appropriate procedure, and not by increasing the inverter settings.

For one owner, the order of installation of ESS at an existing enterprise also depends on other connection conditions. The very argument "we are not increasing capacity" is not enough to conclude that registration is not necessary.

Conditional situation to check. The solar plant exports surplus energy to the grid, and at this moment the battery also receives a discharge command. It is necessary to check their joint result on the outer boundary. If there is no free reserve of authorized power, the mode will have to be limited. This example does not specify numerical settings: they are determined by the project and the agreed conditions of the object.

Responsibilities at a shared connection point

The main user can be an electricity producer, an ESS operator or a non-household consumer whose internal networks are directly connected to the external network. The sub-user belongs to the respective categories, but its installations are connected exclusively to the main user's internal networks.

To the system operator, the main user is responsible for exceeding the permitted capacity of the common point in accordance with the contract. Therefore, the internal agreement should explain who switches modes, how schedules are coordinated, and what happens when both parties need available capacity at the same time.

A practical order of interaction is also needed: responsible persons, access to equipment and data, notification of repairs and interruption of power supply. Without these agreements, a formal joint joining can create a dependency on the decisions of the other party, which the investor did not take into account in the work model.

It is useful to analyze in advance the situation when the internal network of the main user needs repair. Who informs the subuser which installations are stopped and under what conditions their operation is resumed? The answer should be found in the agreed operational and contractual rules. It does not automatically follow from the fact that a cable is laid between users.

What contracts and documents are needed

In the distribution system, the future sub-user applies to the distribution system operator (DSO). The service is executed by a tripartite contract with the participation of the operator, the main user and the sub-user. The technical conditions determine the necessary measures, the project undergoes approval, and before the procedure is completed, the distribution point records are drawn up or changed.

The main user and the sub-user separately conclude a contract for the use of internal networks. It confirms the access arrangements, but does not replace the joining procedure and the relationship with the operator. The transmission system uses its own procedure, so distribution requirements should not automatically be applied to the transmission system operator (TSO).

In the contract between the users, it is important to agree on the distribution of the import and export capacity, work schedules, energy balance, responsibility for the quality of electricity, termination of power supply and termination of cooperation. The set also includes documents on the network ownership boundaries and operational responsibility, a single-line diagram, information on metering and the procedure for determining losses.

The owner of the finished cable cannot guarantee in advance the absence of additional work. A new installation can change the characteristic mode of the network, and this needs to be checked by the operator and reflected in the project. The material about documents and cost of joining ESS will help to divide the costs of connection, design and metering.

The completion of cooperation is especially carefully checked. If a sub-user loses access to the common point, it will affect the ability to operate his installation in the planned model. Therefore, the term and grounds for termination of the contract must be compared with the project work plan, and the order of disconnection and responsibility for unjustified termination of power supply should be prescribed before the start of investments.

Why one shared meter is not enough

A shared connection point does not mean a common undivided record of all activity. For an ESS, it is necessary to determine the energy that enters during charging and exits during discharge. At a site with solar generation and consumption, it is necessary to distinguish the flows between the installations and the external network, in particular the origin of the energy that the storage unit returns to the outside.

Separate commercial metering sites are established for different owners at the shared connection point. Their commercial boundary is set at a common point, and the volumes of each site are determined separately, taking into account the losses between the measurement point and this boundary. Therefore, the physical location of the meter and the place to which the calculated volume leads may differ.

Measuring locations and the method of calculating the balance are laid together with a single-line diagram. For a complex commercial metering site, if it is technically impossible to equip individual metering points, the calculation method can be used under the conditions stipulated by the rules. The contract algorithm must correspond to the actual scheme, demarcate flows and allow for verification of calculations.

This option does not cancel the requirements for separate metering of electrical installations of different owners at the shared connection point. Such installations require separate platforms and metering nodes. The calculation of the balance is not a permission to replace them with one common meter.

Don't confuse equipment monitoring with commercial metering. An application can show useful performance indicators, but the calculations require properly organized points, measurement tools and data transmission. The cost of these works should be included in the budget even before choosing the final configuration.

The check must correspond to a specific billing period. One summary for a month does not explain when the battery was charged from solar generation, when it received energy from the grid, and to whom the subsequent exported energy belonged. That is why the measurement scheme, the time data and the flow separation algorithm must work together. Otherwise, participants will receive numbers, but not enough explanation for mutual calculations.

What to prepare for the project discussion

A single set of input data is useful for the first meeting. It will allow you to check whether the desired mode of operation, network restrictions and rights of participants are mutually agreed upon.

• Owners and roles: list of installations, responsible legal entities, primary user and future subuser, if any.
• Valid joining: technical conditions, contracts, passports of points and permitted values for both directions.
• Operating modes: graphs of generation, charging, discharging and consumption, including simultaneous peaks.
• Scheme and metering: internal networks, limits of responsibility, existing measurements and additional points required.
• Terms of cooperation: access, distribution of capacity and losses, management of restrictions, repair and withdrawal procedure.

If the task is to work together with a solar station and storage, you can discuss hybrid solar system for business. Backup during a grid failure requires a separate configuration check. For the solar part of the project, a solar power plant design service is provided; the composition of works related to ESS, metering and approvals are specified separately for a specific object.

It is worth bringing up-to-date versions of the documents to the discussion and indicating which parameters have not yet been agreed upon. A separate list of open questions will help distribute checks between the designer, accountant and lawyer. The decision to purchase equipment should be based on the agreed configuration, and not only on the available area of the site.