KPI calculation

This page introduces the main KPI used for the Solar O&M Dashboard. The main reference used for the definition of the solar specific KPI is the Solar Best Practices from SolarPower Europe. The terminology and basic principles used here are based on this guidelines (further called guidelines for simplicity reason).

Performance Ratio (PR)

The performance ratio displayed on the Novasense portal corresponds to the temperature-corrected performance ratio according to the equation defined in the guidelines. The equation involves different variables that can come from different sources. The Novasense portal relies on the following sources:

• Irradiance on the inclined plane (GPOA): Meteorological data based on satellites and ground stations, obtained from an external provider. Geometric transposition on the inclined plane carried out by Novasense.
• Panel temperature: Calculation based on the ambient temperature from external meteorological data and the thermal insulation of the solar panels according to the type of mounting. The coefficients used are oriented towards the default values of the PVSyst software.
• Thermal coefficient: The thermal coefficient $\gamma_{Pmpp}$ used comes from the technical data sheet of the solar panel in question.

Energy Performance Index (EPI)

The Energy Performance Index displayed on the Novasense portal is calculated according to the guidelines. The calculation of the EPI involves the theoretical performance of the plant, which can be calculated in several ways. The calculation of the theoretical performance used by Novasense can be done in two different ways:

1. Standard model based on a simulation of a generic plant with average loss factors.
2. Machine learning model based on the historical performance of the plant in question.

The choice of the appropriate model is made on a case-by-case basis. The standard simulation model is used by default in most situations. The machine learning model is activated in situations that require it, for example, in the case of a strong impact from nearby shading sources.

Availability at inverter level

Technical time based availability

General equation according to the guidelines:

$$A_t = \dfrac{T_{\text{useful}} - T_{\text{down}}}{T_{\text{useful}}} \cdot 100$$

The variable $T_{\text{useful}}$ is determined using a Minimum Irradiance Threshold (MIT) of 60 W/m², applied to the irradiance in the plane of array (GPOA). For inverters with multiple MPPTs connected to different fields, the weighted average GPOA is calculated, where the weight factor is the installed power per MPPT. This threshold can be configured at the plant level. For customized settings, please contact support.

The variable $T_{\text{down}}$ is the part of $T_{\text{useful}}$ with total inverter downtime. Underperformance with an unavailable power below the installed power of the corresponding inverter doesn't count as downtime.

Technical energy based availability

General equation according to the guidelines:

$$A_e = \dfrac{E}{E + E_{\text{loss}}} \cdot 100$$

The variable $E$ is the total inverter energy production during the considered period.

The variable $E_{\text{loss}}$ are the presumed energy losses due to any kind of issue (underperformance, missing data, total outage), during the time where the irradiance in the plane of array (GPOA) is above the defined MIT threshold. Since the definition of missing data or total outage is self-evident, the definition of underperformance is not. Following general definition for underperformance can be done: an inverter is underperforming if its measured electrical values at inverter or MPPT level deviates significantly from its expected values according to the Novasense model.

Contractual availability

A contractual time based or energy based availability with the definition of exclusion factors according to the guidelines chap. 10.5.1 is not implemented yet.