Performance Ratio

The performance ratio (PR) expresses the ratio between the actual and the expected energy production of a device or plant. This allows you to assess the efficiency and effectiveness of the conversion of solar energy under real operation conditions, compared to the theoretical potential of plants or devices.

The system can calculate the PR at every level of the portfolio, down to individual devices. It is also possible to calculate the combined PR of groups of plants or devices.

The PR is expressed as a percentage, and is calculated using the following formula:

$PR (%) = \frac{Produced Energy}{Expected Energy} = \frac{Energy}{P_{p} {Insolation}_{Corr}}$

Aggregation methods

At each level of the portfolio, GPM Horizon aggregates and ponders the data used for the calculation, to provide relevant metrics at each level while preserving accuracy and reliability.


Level	Aggregated variables
Device	Device-level data is used directly to apply the formula.
Site	Insolation value of each individual device is weighed by nominal DC power. Sum of device-level data is used as the variable for the equation.
Portfolio	Insolation value of each individual device is weighed by nominal DC power. Sum of device-level data is used as the variable for the equation.

Corrected Performance Ratio

You can apply corrections to improve the accuracy of the PR. This allows you to produce accurate KPIs that reflect the needs and realities of specific projects, plants or devices.

Corrections allow you to take into consideration three key variables:

Irradiance.
Panel degradation.
Temperature.

Important: The data granularity of the PR must be the equal or higher than the data granularity of all the data sources included in the calculation. For example, if you have data that is retrieved every 10 minutes, and other data that is retrieved every 15 minutes, the minimum data granularity for the PR calculation is 30 minutes, because 30 is an integer multiple of both 10 and 15.

Available options for corrections and exclusion


Category	Type	Subtype
Correction	Temperature
Correction	Panel degradation	Exponental degradation
Correction	Panel degradation	Linear degradation
Correction	Custom fixed coefficient
Automatic interval exclusion	Irradiance out of range
Automatic interval exclusion	Irradiance source not communicating
Automatic interval exclusion	Energy source not communicating
Automatic interval exclusion	Custom condition
Manual interval exclusion	Exception

Formulas

To obtain the PR, you must first define certain parameters:

Mandatory:
- Energy source (in kWh).
- Peak Power (in kWp).
- Irradiance Source (in W/m²).
Optional:
- Panel temperature (in degrees Celsius).
- Fixed coefficient (%).
- Custom exclusion condition.


Element	Description
PR	Performance ratio [%].
E	Produced energy [kWh].
P_p	Peak power [kWp].
I_Rea	Measured irradiance [W/m²].
I_STC	Irradiance in Standard Testing Conditions (STC), where: Temperature: 25 ºC. AM: 1.5. Irradiance: 1000 W/m²].
d	Coefficient of peak power loss due to panel aging [%/year].
n	Number of years, from the installation date, that a panel has been in service [years].
α	Coefficient of peak power correction based on panel temperature, as established by the manufacturer [%/ºC].
T_Panel	Panel temperature [ºC].
T_ref	Reference temperature [ºC]. This value can be fixed or dynamic.
Coeff	Fixed coefficient given by the user [%]. For example, a fixed correction due to known losses between an inverter and a meter.
Energy	Energy component for PR aggregation [kWh].
Insoltation_Corr	Insolation component for PR aggregations [kWh/m²]. This is the component that correction factors are applied to. P_p and Energy are not affected by any correction.

Aggregations

You can configure the system to aggregate the Corrected PR. This is done by aggregating its components.

Note: The system stores the aggregated PR values in the database up to the third decimal digit. However, these values are rounded to the second decimal digit when displayed in the application.

There are three types of aggregation, combining devices and time periods:

Single device:
- Multiple periods:
  
  $PR (%) = \frac{\sum_{D {ay}_{i = 1}}^{D {ay}_{i = n}} E_{{Day}_{i}}}{\frac{(\sum_{D {ay}_{i = 1}}^{D {ay}_{i = n}} P_{p_{{Day}_{i}}} \times {Insolation}_{Corr . {Day}_{i}})}{\sum_{D {ay}_{i = 1}}^{D {ay}_{i = n}} {Insolation}_{Corr . {Day}_{i}}} * \sum_{D {ay}_{i = 1}}^{D a y_{i = n}} {Insolation}_{Corr . {Day}_{i}}} * 100$
Multiple devices:
- Daily aggregation:
  
  $PR (%) = \frac{\sum_{{PR}_{j = 1}}^{{PR}_{j = m}} E_{{PR}_{j}}}{\sum_{{PR}_{j = 1}}^{{PR}_{j = m}} P_{p_{{PR}_{j}}} * \frac{(\sum_{{PR}_{j = 1}}^{{PR}_{j = m}} P_{p_{{PR}_{j}}} * {Insolation}_{Corr . {PR}_{j}})}{\sum_{{PR}_{j = 1}}^{{PR}_{j = m}} P_{p_{{PR}_{j}}}}} * 100$
- Multiple periods:
  
  $PR (%) = \frac{\sum_{D {ay}_{i = 1}}^{D {ay}_{i = n}} Total Energy {Agg}_{{Day}_{i}}}{\frac{(\sum_{D {ay}_{i = 1}}^{D {ay}_{i = n}} Total P_{p} {Agg}_{{Day}_{i}} * Total Insolation {Agg}_{{Day}_{i}})}{\sum_{D {ay}_{i = 1}}^{D {ay}_{i = n}} Total Insolation {Agg}_{{Day}_{i}}} * \sum_{D {ay}_{i = 1}}^{D {ay}_{i = n}} Total Insolation {Agg}_{{Day}_{i}}} * 100$

Automatic Period Exclusion

You can configure the Corrected PR to automatically exclude periods from the calculation when specific conditions are met.

These conditions include:

Irradiance values are above or below your custom range.
No data can be retrieved from the devices that provide the reference values for:
- Irradiance.
- Energy
Energy values are empty or below 0.
A custom condition is met (for example, the inverter power setpoint is below the inverter peak power).

Exceptions

You can manually enter exceptions to correct the PR. Exceptions allow you to retrospectively exclude a period from the Corrected PR calculations when you need to account for production downtimes caused by external events (for example, curtailment requests from the grid operator).

Note: For more information, see the Exceptions section.

Panel degradation

Solar panels to lose output power as they age over time. When correcting the PR by panel degradation, the correction is calculated based on the panel's years of service. To calculate the number of years, you must enter the installation date in the system.

There are two types of panel degradation:

Linear:

$PR (%) = \frac{Produced Energy}{Expected Energy} = \frac{Energy}{P_{p} {Insolation}_{Corr}} = \frac{E}{P_{p} \int \frac{I_{Real}}{I_{STC}} (1 - \frac{d * n}{100}) [1 + \frac{α}{100} (T_{Panel} - T_{ref})] \frac{Coeff}{100}} * 100$
Exponential:

$PR (%) = \frac{Produced Energy}{Expected Energy} = \frac{Energy}{P_{p} {Insolation}_{Corr}} = \frac{E}{P_{p} \int \frac{I_{Real}}{I_{STC}} {(1 - \frac{d}{100})}^{n} [1 + \frac{α}{100} (T_{Panel} - T_{ref})] \frac{Coeff}{100}} * 100$

Example of panel degradation reducing expected energy over 15 years. — Figure 1. Example: panel degradation factor reducing expected energy over 15 years

Temperature correction

The Peak Power of the solar panels is established by the manufacturer under Standard Testing Conditions (STC).

These conditions are:

Temperature: 25 ºC.
AM: 1.5.
Irradiance: 1000 W/m²].

Correcting the PR the by temperature provides stable values through the year. To do this, you can apply the real-time panel temperature to its expected energy.

Figure 2. Sample PR plot with temperature correction

You can skip the temperature correction, regardless of the feature being enabled, in the following cases:

Temperature is above or below your custom range.
No data can be retrieved from the device that provides the reference value for Temperature.