General
Determining a loss of earnings caused by any cause is of great importance for reporting to operators/investors or energy suppliers. Depending on the cause, the loss of earnings can be calculated using different models.
It may be necessary to determine a loss of yield for an entire system or just for sub-components such as an inverter. Likewise, the duration can vary between hours or days. Depending on the case, the available data basis can also vary, for example if the local measurement of the irradiation is also affected by the failure.
Integration in the ticket system
The requirement to calculate a loss of revenue is closely linked to the ticketing system. As a rule, a loss of earnings is to be calculated when a disruption has occurred. The alarm may have been generated by the data logger or the portal, or a manual ticket was created.
In any case, a ticket must be available for the calculation of the loss of earnings. This can be created manually or an existing alarm can be converted into a ticket or added to a ticket. You can recognize tickets by the fact that they start with a "T". Alarms, on the other hand, are displayed with an "A".
The “Lost production” tab appears in the ticket details (right-click on ticket -> Edit). The desired calculation model can be selected there.
Calculation models
When determining the lost production, the respective calculation model must be selected by the user. Depending on the model, additional user inputs may be required (selection of reference system/inverter, selection of periods). The following calculation models are available:
- Reference system
- Linear equation
- Reference component
- Billing procedure based on the Eligible period
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Billing procedure based on measured values
A prerequisite for all models is that the selected reference objects/periods have previously been checked by the processor for their suitability. The calculation models do not carry out a suitability test of the reference data.
Reference system
This method is based on the fact that there are other systems, located nearly to the system, whose data can be used to calculate a failure. In this case, the lost production is calculated taking into account the irradiation of the reference system and the PR. When determining the reference system, any load management or disturbances must be taken into account. The decision as to which plant is selected as the reference plant must be made manually.
This method is suitable for calculating the lost production for the entire system if no irradiation data is available for the controlled system and the "Linear equation" method can therefore not be carried out.
Linear equation
Assuming that irradiation values are available for the system, a target yield can be determined via a system characteristic at a specific time and a specific irradiation using the characteristic. By comparing the target yield with the yield actually generated, the lost production is determined. It must be possible to access the system's own irradiation data for the period under consideration.
Reference component
Dieses Verfahren setzt voraus, dass vom Ertragsausfall nur Teile einer Anlage betroffen sind. Die Ermittlung des Ertragsausfalls wird dann anhand von Referenzkomponenten und dem angenommenen Zeitraum berechnet. Für die Referenzkomponente wird 100% Leistung angenommen (keine Störung an der Referenzkomponente) und die Energie für den Zeitraum übertragen.
Beispiel:
Outage |
Reference |
Lost production |
INV1 (100 kWp) |
INV2 (600 kWp) |
3 kWh/kWp * 100 kWp = 300 kWh |
1 kWh/kWp |
4 kWh/kWp |
Thus, for example, the defect of certain components can be calculated. The method is not suitable for calculating the loss of income due to a regulation by the grid operator or direct marketer.
Billing procedure based on the Eligible period
The model (relevant for Germany) determines the energy lost in a photovoltaic system during a power-curtailment. According to the guidelines of the German Federal Network Agency, the calculation is carried out on the basis of the last quarter-hour value before the power-curtailment.
According to the guidelines of the German Federal Network Agency, only time stamps in the period from 7 a.m. to 8 p.m. CEST may be taken into account. The power of the last fully measured quarter of an hour before the regulation is used as a reference value. If the regulation was made outside the valid period, the performance from the previous day will be determined. If a regulation takes place outside of the valid period, the previous day must be used. This does not happen automatically, the time period must be selected manually so that the reference value is included.
In order for the model to be selected, the following data must be available:
- Grid operator's relative active power target value
In order for the loss of earnings to be calculated, two conditions must be met:
- The reduced power during active power control must be lower than the reference value
- The actually measured power during active power control must be lower than the reference value
Billing procedure based on measured values
This model (relevant for Germany) determines the lost energy of a photovoltaic system during a power-curtailment. According to the guidelines of the German Federal Network Agency, the calculation is carried out on the basis of the radiation power measured at the system location.
In order for the procedure to be selected, the following data must be available:
- Irradiation data
- Grid operator's relative active power target value
In order for the loss of earnings to be calculated, two conditions must be met:
- The derated power must be lower than the expected power
- The measured power must be lower than the expected power
Integration into reporting
The lost production is linked to the ticket and can therefore be shown in reports. The lost production is made available as an additional value in the reporting. This makes it possible to use it in tabular form. The lost production is recorded in the error protocol both in kWh and in the respective national currency issued.