The Confusion Around Pmax
The harmonization of national regulations with European guidelines (GL – Guidelines) and network codes (NC – Network Codes) has led to a change in the way the operation of the National Power System (KSE) is planned concerning reference capacity (power)—from gross (or gross-like) values to verified net values. This change has been reflected in the new IRiESP (TSO Grid Code) [3] and should once and for all close the discussion on the significant parameters characterizing Power Generating Modules [2]. However, as is often the case, every change is accompanied by resistance resulting from the inertia of habits, and shaking up the entrenched interpretation practices in Poland still seems to be a matter of more or less successful interpretations. Unfortunately, all parties involved in the connection process interpret these changes, which inevitably results in the accumulation of errors from the stage of applying for connection conditions to the final stage of obtaining an operation permit.
Definition of Maximum Capacity (Pmax)
This parameter is defined in Article 2, item 16 of NC RfG [2] and referenced in [1][3][4], as well as many other documents (including applications and forms), in its original form:
Maximum Capacity (Pmax): The maximum active power that a generating module is capable of continuously generating, reduced by any demand exclusively related to the operation of this generating module and not fed into the grid, as specified in the connection agreement or as agreed by the relevant system operator and the energy generation plant owner.
To avoid any doubts, IRiESP additionally states that the maximum capacity of a PGM is determined at the connection point, i.e., at the point where the connection meets the grid.
It is worth noting that the term “connection agreement” in the Pmax definition may be an unfortunate translation of “connection agreement,” which refers to a broader category encompassing both the connection agreement and the contract for the provision of distribution or transmission services for electricity. This is supported by the definition from the Procedure for Utilizing Operational Permits for Type D Generating Modules in the Connection Process to the Transmission Network [4]:
Connection agreement – an agreement between the relevant system operator and the owner of the power generation facility, the owner of the receiving installation, the distribution system operator, or the HVDC system owner, which includes relevant and detailed technical requirements concerning the power generation plant, receiving installation, distribution system, connection of the distribution system, or HVDC system, including the connection agreement and the contract for the provision of transmission or distribution services for electricity as defined in the Energy Law Act;
and the scheme of the procedure for obtaining an operation permit, which provides for the possibility of amending the contract for the provision of services (…) signed after completing the subject of the connection agreement.
The definition of Pmax also requires an understanding of the somewhat abstract definition of the Power Generating Module (PGM), which needs to be distilled from the definitions of the Energy Park Module and the Synchronous Power Generating Module. Below is a definition that serves as such a “distillate,” deliberately referencing the definition of a Generating Unit from the Energy Law Act [5]:
PGM can be defined as:
A distinct set of devices and networks and installations used for the generation of electricity and power output, connected to the Relevant Operator’s network at a single point.
At this stage, it is also worth providing the basic criterion for distinguishing the above-mentioned set, which directly results from the procedures for confirming PGM compliance with NC RfG [2]. The technical requirements apply to the PGM as a whole; thus, there must also be a comprehensive method for verifying them. A good example can be a single communication interface, a single control interface, and a single security system. In conclusion—if a given set of devices operates dependently on each other, can generate electricity, and can feed it into the grid at a single point, such a set should be treated as one PGM. Attempts to separate PGMs according to other criteria may be justified but should result from an agreement between the owner of the power generation facility and the system operator. Imposing separation criteria by creating definitions for entities such as Wind Farm or Photovoltaic Farm demonstrates a misunderstanding of the criteria for establishing significance [2], which neglect the type of primary energy of the PGM. More on this topic in the Article.
What is Maximum Capacity (Pmax) for a PGM?
It is the maximum value of active power fed into the operator’s grid at the PGM connection point (or at an agreed reference point for net active power of the PGM), for which continuity criteria are met.
Maximum capacity is determined for a specific availability of primary energy, above which net active power does not change within certain tolerance limits.
Pmax is the reference value for the vast majority of technical capabilities of PGMs derived from NC RfG [2] (Pref), and its determination allows for the actual load level of the connection and the impact on the connection point and the immediate environment to be assessed.
Pmax allows for determining the full range of active power regulation within any defined period of significance (e.g., the period for balancing energy settlement).
What is the confusion with Pmax?
The problem is multi-layered and begins with the application for connection conditions. The applicant must declare the maximum capacity (net achievable power), which may be interpreted as a real technical obligation, whereas, at this stage, it may only have a planned character. This is obvious, considering the range of factors affecting the actual performance of the PGM, such as the connection location, connection route, power output system parameters, actual operating conditions of generators, reserves for reactive power compensation, etc. Such a declaration is, at best, an estimate (calculations using the nominal parameters of individual devices). In this situation, one might ask whether declaring Pmax at the stage of applying for connection conditions is justified, given that the same application already provides the planned net achievable power. If someone is surprised—let me clarify by providing the definition of connection power according to the so-called System Regulation [1]:
Connection Power (generation): The active power planned to be fed into the grid, specified in the connection agreement as the maximum value determined within each hour of the settlement period from the average values of this power in 15-minute periods, used to design the connection.
Connection power is thus the planned net achievable power (fed into the grid) determined (or rather estimated) for a given period of significance.
Does this mean that Maximum Capacity (Pmax) equals Connection Power?
No. The maximum capacity of the PGM (Pmax) is an actual value, and its close equivalent is contractual power, as defined in [1] (unified):
Contractual Power (generation): The active power fed into the grid, specified in the contract for the provision of transmission or distribution services for electricity (…) as a value not less than the maximum value determined as the average value of power over a 15-minute period, taking into account factors reflecting the specifics of the recipient’s power system.
Conclusion – In practice, this transition moves from a planned value (connection conditions) to an actual value (contract for distribution or transmission services) during the verification of the PGM’s actual performance. The ability to amend the distribution/transmission contract should serve, among other things, to indicate maximum capacity different from connection power. Connection power can serve as an initial classification criterion for PGM types (A, B, C, D), as the applicant for connection conditions is aware of the technical obligations arising from the PGM’s significance (impact on the National Power System) on the date of submitting the application.
Problematic Interpretations of Simulation Results and Compliance Tests
The entity performing the PGM simulation analyses (ION application) should not directly refer to the declared net achievable power and connection power. The purpose of the analysis is to indicate the maximum capcity for which the required technical capabilities can be achieved. However, there is often a reversal of this logic, where simulations are performed for predefined (unrealistic) Pmax values based on presumed correlations with connection power or the nominal power of devices. In simpler terms, the analysis is tailored to fit fictional compliance with a fictional Pmax, moving away from the basic reality in which physical laws cannot be bypassed.
Let us assume, however, that someone would like to conduct a reliable analysis and propose an optimal solution from both technical and economic perspectives. Here arises the problem of the risk of the operator not accepting a suitably corrected simulation analysis. The operator treats the declaration in the application (planned/estimated value) as a binding commitment transferred to the connection agreement without any tolerance (or with an arbitrarily defined tolerance). Failure to achieve the declared maximum capacity (or connection capacity) during simulations or compliance tests would allegedly result in the need to change the connection conditions and the connection agreement.
This suggests unilateral responsibility for the applicant for something they could not have known when signing the connection agreement. The question arises: Should the investor lose the right to utilize the technical potential of an already built connection due to their “reckless” declarations? Certainly, this cannot be inferred directly from the NC RfG [2] network code. I also do not find a basis for such an interpretation in other sources [1-5].
In Defense of Operators…
The obligation to achieve the declared maximum capacity is not entirely devoid of logic. Connection power is a “scarce resource” and should be allocated with respect to the actual performance of PGMs (criterion of efficiency). However, the end does not justify the means. First, operators should, colloquially speaking, “get their own house in order,” simplify the applications for connection conditions, standardize definitions, and transparently present the obligations arising from the connection agreement.
For example:
- Obligation to confirm Pmax within the range of 0.9–1.0 of the connection power.
- Obligation not to exceed the connection power.
Subsequent steps should include:
- Recording actual Pmax in agreements for the provision of distribution and transmission services.
- Correcting network impact studies in relation to the actual performance of PGMs at the connection point and the immediate surroundings.
In summary: fewer nameplates, more common sense.
[1] Rozporządzenie Ministra Klimatu i Środowiska z dnia 22 marca 2023 r. w sprawie szczegółowych warunków funkcjonowania systemu elektroenergetycznego
[2] Rozporządzenie Komisji (UE) 2016/631 z dnia 14 kwietnia 2016 r. ustanawiające kodeks sieci dotyczący wymogów w zakresie przyłączenia jednostek wytwórczych do sieci (Tekst mający znaczenie dla EOG)
[3] Instrukcja Ruchu i Eksploatacji Sieci Przesyłowej (dalej „IRiESP”), zatwierdzona DRR.WRE.4320.4.2023.LK z dnia 19 stycznia 2024 r.
[4] Procedury wykorzystywania pozwoleń na użytkowanie dla modułów wytwarzania energii typu D w procesie ich przyłączania do sieci przesyłowej.
[5] Ustawa z dnia 10 kwietnia 1997 – Prawo energetyczne (Dz. U. 1997 Nr 54 poz. 348)