Introduction

Harmonization of the approach in determining the key quantities resulting from the process of connecting generation units to the power grid is a prerequisite for harmonization of national regulations and European Network Codes (CNC – Connection Network Codes). This text attempts to identify objective criteria for assessing the impact of connected sources on the network of the Relevant System Operators, in the context of the technical requirements arising from the basic categorization of Generation Modules resulting from Commission Regulation (EU) 2016/631 and the Implementation Guides of the Network Codes published by ENTSO-E (European Network of Transmission System Operators for Electricity).

What is being connected?

In the process of issuing Conditions of Connection, a point-of-connection site is determined, with respect to which the technical requirements for the connected facility and the formal obligations between the Generator and the Relevant System Operator are defined. The facility to be connected is therefore a single Power Generation Module (PGM) within the meaning of the NC RfG, which is further categorized based on four parameters: maximum power, voltage at the point of connection, mode of operation in the grid (SPGM or PPM), and location of the basic infrastructure and point of connection (offshore or onshore). The National System Operators properly recognized this fact in the model documents, but did not take advantage of the opportunity to move the comprehensive technical assessment to the stage of confirming compliance of the Generation Module with the NC RfG. As a result, the application templates, instead of shrinking to the necessary minimum, have grown to include a section resulting from the Grid Codes.

Is a detailed characterization of the PGM in the application for WP necessary?

First of all, let’s consider what information load the following sentence carries for the System Operator: “I apply for the determination of connection conditions for a new Power Park Module (PPM), located in (…) with a planned maximum power (Pmax) equal to 6.5 MW (±5%), as a place of connection I propose the X SN/110 KV substation”. Let’s break it down – the type, type and place of connection of the Power Generation Module has been specified, so the criteria for evaluating the possibility of connection to the OS grid and the technical requirements specified for PPM B in the Grid Code, General Requirements and Instructions for Operation and Maintenance apply. The planned net achievable power is also known, along with the tolerance, the upper limit of which allows the determination of the connection power. PPM B’s minimum technical commitments allow the determination of controllability ranges for active and reactive power in relation to the planned maximum power. Such information is sufficient to assess connectivity and issue connection conditions, which do not need to be updated due to changes in components that do not affect the net achievable power. Detailed information can be supplemented at the stage of connection agreements.

Does installed electrical capacity matter?

The connection process applies to Power Generation Modules, the characteristics of which do not include the type of primary energy and the ratings of the primary generating facilities (including generating equipment), as well as the components of the generating units (PGU – Power Generating Unit and in detail SPGU or NPGU). The relevant equipment certificates are applicable only at the stage of confirmation of compliance, and their expectation at the stage of the application for Conditions of Connection is unnecessary, given the high probability of changing equipment before the project is implemented. The legitimacy of declaring the total size of the installed electrical capacity is basically only due to the provisions [1] specifying the simplification of the connection process for renewable sources. Therefore, it is practical to specify the total installed electrical capacity, without specifying the detailed characteristics of the generating equipment (manufacturer, number, unit power, voltages, currents, etc.).

Expert report on the impact on the power grid

The connection process imposes on the Relevant System Operator a conditional (i.e., taking into account exceptions) obligation to prepare expert opinions on the impact on the grid (distribution and/or transmission) of equipment, installations and networks directly connected to it. This formulation gives rise to a separate assessment of the components of the Generation Module, while the actual assessment of compliance is subject to the PGM as a whole. The creation of an obligation to perform an expert opinion depending on the value of the installed electrical capacity further adds to the ambiguity of interpretation. The technical criteria for assessing the connectivity of sources refer to the impact at the point of connection (PCC), while the equipment (or sets of equipment) under analysis may be connected deep inside the generator’s grid and indirectly affect its operation (e.g., power electronic converters, compensation systems, filters). Such an approach may result in an inadequate representation of the PGM’s impact in the PCC, depending on the calculation method adopted, thus limiting the possibility of its connection and verification of the real impact during testing.

The assumed level of power injected into the grid, which allows the System Operator to take into account correction factors that characterize the operation (of the sources) and their type of primary energy, also has a not insignificant impact on the way expert opinions are performed. The use of such an approach is seemingly reasonable, translating into a more adequate modeling of system operating conditions, but may result in limitations to the Generator’s rights in connection with:

1. A non-transparent way of ensuring (guaranteed) energy offtake,
2. The non-transparent way of determining and updating correction factors,
3. Estimating the availability of primary energy when calculating correction factors.

It is worth pointing out the main implications of this approach in the way the “level of power injected” is determined [3].The ability of the PGM to derive power to the grid of the Relevant OS is determined in the course of testing by confirming the minimum and maximum power at the point of connection (PCC).
These quantities limit the power output bandwidth, and thus allow determining the maximum value of power injected into the OS grid (Pmax) and the control range from minimum power to instantaneous power [Pmin – P, where P≤Pmax]. It is worth noting that the net achievable power in the PCC (Pmax) must be less than or equal to the connection power, a condition that can be met by selecting equipment that is part of the power derivation system or by their appropriate parameterization. Imposing a correction factor derived from the availability of primary energy on the regulatory range defined in this way will result in constraints that narrow the power derivation capacity temporarily (P<P(t)_oze). Thus, there may be a limitation of the Generator’s entitlement to receive energy in terms of guaranteed connection capacity [1] in the case of modernization, expansion or modification of the primary energy source, which will not result in the need to change the connection capacity. Examples of such modifications include, but are not limited to: expansion of the PGM with a dependent energy storage facility (PGM component), increase of the installed capacity of the generating equipment (so-called overcapacity) and/or their type (co-location), installation of dependent reception (e.g., electrolyzer – component).

An alternative method of estimating the power injected into the OS network can be indicated, which, instead of the available primary energy, takes into account the Operator’s statistical ability to regulate PGM power. This capability is directly derived from the confirmed range of PGM active power regulation [Pmin-P where P≤Pmax] and can be used to assess the fulfillment (condition) of the power reserve in the WN/SN node in the operating state (n-1) of the GPZ/RPZ. In order to reduce the statistical risk, the temporary uncontrollability (failure) of the parts of the PGM affecting a given network node, such capacity can be adjusted by an appropriate factor k (e.g., Pmin + k[%] Pmax). This approach makes it possible to analyze loads for power bands below Pmax resulting from the controllability of new PGMs, while for existing (non-controllable) PGMs, correction factors resulting from the statistical availability of primary energy may apply.

[1] Law of April 10, 1997, Energy Law (Journal of Laws 1997 No. 54 item 348).

[2] Decree of March 22, 2023, on detailed conditions for the operation of the electric power system

[3] Criteria for assessing the possibility of connecting generation units to the medium-voltage distribution network of TAURON Dystrybucja S.A. (Poznań, 27.12.2023).