Yield loss calculation

When your PV system experiences disruptions, technical failures, or curtailment measures, you want to know how much it is going to cost you – quickly. Yield loss data can help you prioritize O&M service interventions, report to relevant stakeholders, and file claims for lost revenue. Since disruptions are often linked to loss of revenue, yield loss data is integrated into the VCOM ticket system. Depending on the cause, the loss of earnings can be calculated using different models. Likewise, the duration can vary between hours or days. Depending on the case, the available data may also vary, for example, if the local irradiation measurement is also affected by the failure.

In addition to the view in the ticket system, yield losses can also be visualized in the Power control tab.

Integration in the ticket system

The yield loss calculation is closely linked to the ticketing system. As a rule, a loss of revenue must 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. A ticket must be available to calculate a loss of revenue. You can convert an existing alarm into a ticket, add a calculation, or manually create a ticket to calculate the loss. You can navigate to the Yield loss tab via the ticket details:

Steps

1. At the individual system level, go to the Cockpit > Tickets portlet.

2. Right-click on a ticket and select Edit.

3. Select the desired calculation model under Yield loss.

Calculation models

All of our calculation models are based on the measurement of local irradiance and energy with a typical resolution of 5 or 15 minutes. For systems using power control, curtailment information may also be required. The following calculation models are described in more detail below as well as in the API documentation:

• Reference system

• Reference component

• Linear equation

• Flat-rate billing (specific to Germany)

• Peak billing

• Simplified peak billing

If your desired method is not visible in your system, see Yield loss calculation method not available

Reference system

The reference system uses the data of another system to calculate yield loss. In this case, the calculation takes the irradiance of the reference system and its performance ratio into account. This model is suitable for calculating the yield loss for the entire system if no irradiance data is available.

Reference component

The reference component model assumes that only a part of the PV system, such as an inverter, is disrupted, and uses the data from a nearby component to calculate the loss. The calculation uses a reference component and a defined period to determine the difference between the energy generated by the reference inverter and the energy actually generated. The normalizing factors of the inverters are used for this. This method is not suitable for calculating the loss of income due to curtailment by the grid operator or energy trader.

Linear equation

The linear equation model uses a linear regression for a specific reference period and irradiance to calculate a simulated target yield. To determine yield loss, the target yield is then compared with the actual yield. This model is suitable for calculating the overall cost of a failure.

Prerequisites:

• Irradiance sensor

• The system must have irradiation data available for the reference period.

Calculation models specific to Germany

We’ve updated our yield loss calculation models for peak billing and flat-rate billing to correctly reflect the newest requirements of the German Federal Network Agency (Bundesnetzagentur). To ensure a smooth transition for you, the previous calculation methods are still available with the suffix “<2021”. Choose the most suitable method for your needs.

When selecting the peak or flat-rate calculation models, choose the source of curtailment: grid operator or energy trader. This information is then saved in the ticket. If your system can be curtailed by both a grid operator and an energy trader, choose either model and VCOM will automatically select the lower setpoint value.

Flat-rate billing

The flat-rate billing model is based on the “Pauschalabrechnungsverfahren” and is intended for systems using power control. The model uses the last measured values before power curtailment within a defined period as illustrated in the table below:

The power of the last fully measured quarter of an hour before the regulation is used as a reference value. If the curtailment was made outside the valid period, the value from the previous day will be determined. If a curtailment occurs outside of the valid period, the previous day must be used. This does not happen automatically: you must select the period manually to include the reference value. 

Prerequisites

For the model to be selected, the following data must be available:

• Grid operator or energy trader's relative active power setpoint value

• Time stamps correspond to the table

To calculate the loss of earnings, two conditions must be met:

• The reduced power during active power control must be lower than the reference value

• The measured power when power control is applied must be lower than the reference value

Peak billing

The peak billing model is intended for systems using power control. The model is based on the irradiation measured at the PV system site at the time of curtailment. The formula is based on the German “Spitzabrechnungsverfahren”, but can be applied in any situation which meets the prerequisites:

Prerequisites

• Irradiation data: the system must have an irradiance sensor

• Grid operator's relative active power setpoint value

• The derated power must be lower than the expected power

• The measured power must be lower than the expected power

Formula

Simplified peak billing

The simplified peak billing model is similar to peak billing but uses data from external weather services rather than data measured on-site. It is based on the German "vereinfachte Spitzabrechnung”, but can be applied in any situation which meets the prerequisites:

Prerequisites:

• Irradiation data from an external weather provider

• Grid operator's relative active power setpoint value

• The derated power must be lower than the expected power

• The measured power must be lower than the expected power

Set up revenue and currency

You can set up the remuneration per kWh and currency for each system at the system level: Settings (wrench icon) > Administration > Solar account > Settings. For more information, see System revenue.

Integration into reporting

Yield loss is linked to a ticket and can, in turn, be shown in reports with the values “Lost yield” and “Lost yield (euros)”. The yield loss is recorded in the error protocol both in kWh and in the respective national currency you have set up in the system administration. For more information, see Portfolio reports (under Reporting).

Troubleshooting: Yield loss calculation method not available

Problem

Some of the yield loss calculation methods are grayed out or not visible. Possible reasons:

• You need to configure variables.

Solution

1. At the individual system level, go to the Cockpit > Evaluations tab.

2. Ensure that Power control and Active power are available in the variables list.

3. Under Diagram creator, select all variables.

4. Go to your Tickets portlet.

5. Right-click on a ticket and select Edit.

6. Under the Yield loss tab, check whether your desired calculation model is now available.