Key performance indicators

To facilitate monitoring of assets various key performance indicators are calculated at hourly, daily, monthly and yearly intervals. Following are the asset parameters and their computation

Active power

Active power received from the source

Table 1. Active power
Parameters and Source	Hierarchy	Aggregation Frequency	Computation Logic
Inverter Level Active Power (Direct Tag from source)	Inverter	Hourly	Average of Inverter Active power (kW) for that Hour
Plant Level Active Power (Direct Tag from source)	Plant	Hourly	Average of Plant Active power (kW) for that Hour

Table 2. Aggregation of active power for efficiency calculation
Parameters and Source	Hierarchy	Aggregation Frequency	Computation Logic
Inverter Level Active Power® (Direct Tag from source)	Inverter	Hourly	Sum of Active Power (kW)
		Daily	Sum of Active Power (kW)
		Monthly	Sum of Active Power (kW)
		YTD	Sum of Active Power (kW)
Plant Level Active Power (Direct Tag from source)	Plant	Hourly	Sum of Active Power (kW)
		Daily	Sum of Active Power (kW)
		Monthly	Sum of Active Power (kW)
		YTD	Sum of Active Power (kW)

Energy generation

Information on parameters that measure the energy generated.

Table 3. Measure of daily energy
Parameters and source	Hierarchy	Aggregation frequency	Computation logic
Inverter Level Daily Energy Note: Inverter level generation is a direct tag from Inverters.	Inverter	Hourly	Max. of Daily Energy (kWh)
Plant Level Daily Energy Note: Plant level generation is either a direct tag or aggregating all Inverters.	Plant	Hourly	Max. of Daily Energy (kWh)

Table 4. Calculation of energy generation
Parameters and Source	Hierarchy	Aggregation Frequency	Computation Logic
Inverter Level Generation Note: Inverter level generation is a direct tag from Inverters. If this tag is not available, system will fall back to active power.	Inverter	Hourly	Daily Energy(Current hour) - Daily Energy(Previous Hour) (kWh)
		Daily	Max. of Daily Energy (kWh)
		Monthly	$\sum_{i = 1}^{N} D_{i}$ where D_i = Daily Energy (kWh)
		YTD	$\sum_{i = 1}^{N} D_{i}$ where D_i = Daily Energy (kWh)
Plant Level Generation Note: Plant level generation is either a direct tag or aggregation of all Inverters.	Plant	Hourly	Daily Energy(Current hour) - Daily Energy(Previous Hour) (kWh)
		Daily	Max. of Daily Energy (kWh)
		Monthly	$\sum_{i = 1}^{N} D_{i}$ where D_i = Daily Energy (kWh)
		YTD	$\sum_{i = 1}^{N} D_{i}$ where D_i = Daily Energy (kWh)

Insolation

Amount of irradiance energy received per unit area

Table 5. Amount of cumulative irradiance energy received per unit area
Parameters and source	Hierarchy	Aggregation frequency	Computation logic
Insolation from WMS (Direct Tag from source)	Inverter	Hourly	Daily POA Energy(Current hour) - Daily POA Energy(Previous Hour)(Wh/m²)
Insolation from WMS (Direct Tag from source)	Plant	Hourly	Daily POA Energy(Current hour) - Daily POA Energy(Previous Hour)(Wh/m²)

Table 6. Amount of irradiance energy received per unit area
Parameters and Source	Hierarchy	Aggregation Frequency	Computation Logic
Insolation from WMS (Direct Tag from source)	Inverter	Hourly	Daily POA Energy(Current hour) - Daily POA Energy(Previous Hour) (Wh/m²)
		Daily	Max. of Daily POA Energy (Wh/m²)
		Monthly	$\sum_{i = 1}^{N} D_{i}$ where D_i = Daily POA Energy (Wh/m²)
		YTD	$\sum_{i = 1}^{N} D_{i}$ where D_i = Daily POA Energy (Wh/m²)
Insolation from WMS (Direct Tag from source)	Plant	Hourly	Daily POA Energy(Current hour) - Daily POA Energy(Previous Hour) (Wh/m²)
		Daily	Max. of Daily POA Energy (Wh/m²)
		Monthly	$\sum_{i = 1}^{N} D_{i}$ where D_i = Daily POA Energy (Wh/m²)
		YTD	$\sum_{i = 1}^{N} D_{i}$ where D_i = Daily POA Energy (Wh/m²)

Specific power

Specific power is a ratio of active power and DC capacity. It is used to benchmark relative performance of inverter

Table 7. Inverter and Plant Efficiency Computation
Parameters and source	Hierarchy	Aggregation frequency	Computation logic
Inverter DC Capacity Active Power	Inverter	Hourly	$\frac{Avg Inverter Active Power (kW)}{Inverter DC Capacity (kWp)}$
Plant DC Capacity Active Power	Plant	Hourly	$\frac{Avg Plant Active Power (kW)}{Plant DC Capacity (kWp)}$

Specific yield

Specific yield is the amount of energy generated per unit of installed capacity. It is a key performance indicator (KPI) used to compare the relative performance of an inverter or plant

Table 8. Inverter Efficiency Computation
Parameters and source	Hierarchy	Aggregation frequency	Computation logic
Inverter DC Capacity Inverter Level Generation	Inverter	Hourly	$\frac{Max. of Daily Energy (kWh)}{Inverter DC Capacity (kWp)}$
		Daily	$\frac{Max. of Daily Energy (kWh)}{Inverter DC Capacity (kWp)}$
		Monthly	$\frac{Sum(D₁ + D₂ + ... + Dₙ)(kWh)}{Inverter DC Capacity (kWp)}$
		YTD	$\frac{Sum(D₁ + D₂ + ... + Dₙ)(kWh)}{Inverter DC Capacity (kWp)}$ Where Dₙ = Daily Energy (kWh)
Plant DC Capacity Plant Level Generation	Plant	Hourly	$\frac{Max. of Daily Energy (kWh)}{Plant DC Capacity (kWp)}$ Where Dₙ = Daily Energy (kWh)
		Daily	$\frac{Max. of Daily Energy (kWh)}{Plant DC Capacity (kWp)}$
		Monthly	$\frac{Sum(D₁ + D₂ + ... + Dₙ)(kWh)}{Plant DC Capacity (kWp)}$ where Dₙ = Daily Energy (kWh)
		YTD	$\frac{Sum(D₁ + D₂ + ... + Dₙ)(kWh)}{Plant DC Capacity (kWp)}$ where Dₙ = Daily Energy (kWh)

Inverter efficiency

Inverter efficiency is the ratio of the active power (AC output) to the DC power input during normal operating conditions of the inverter

Table 9. Inverter Efficiency Parameters
Parameters and source	Hierarchy	Aggregation frequency	Computation logic
Inverter Active Power (kW) Inverter DC Power (kW)	Inverter	Hourly	$\frac{Avg Inverter Active Power (kW)}{Avg Inverter DC Power (kW)}$
		Daily	$\frac{Sum of (Inverter Active Power) (kW)}{Sum of (Inverter DC Power) (kW)}$ Note: Daily sum of parameters
		Monthly	$\frac{Sum of (Inverter Active Power) (kW)}{Sum of (Inverter DC Power) (kW)}$ Note: Monthly sum of parameters
		YTD	$\frac{Sum of (Inverter Active Power) (kW)}{Sum of (Inverter DC Power) (kW)}$ Note: YTD sum of parameters
	Plant	Hourly	$\frac{Avg of all Inverter Active Power (kW)}{Avg of all Inverter DC Power (kW)}$
		Daily	$\frac{Sum of (all Inverter Active Power) (kW)}{Sum of (allInverter DC Power) (kW)}$ Note: Daily sum of parameters
		Monthly	$\frac{Sum of (all Inverter Active Power) (kW)}{Sum of (all Inverter DC Power) (kW)}$ Note: Monthly sum of parameters
		YTD	$\frac{Sum of (all Inverter Active Power) (kW)}{Sum of (all Inverter DC Power) (kW)}$ Note: YTD sum of parameters

Capacity utilization factor (CUF)

Capacity utilization factor is the ratio of actual output to the maximum possible output under ideal conditions from an asset over a specified period of time. It is usually expressed in percentage and is a measure of asset's performance

Table 10. Calculation of capacity utilization factor
Parameters and source	Hierarchy	Aggregation frequency	Computation logic
Inverter Generation Inverter DC Capacity	Inverter	Hourly	$\frac{Inverter hourly Generation (kWh)}{Inverter DC Capacity (kWp) x 24 (h)}$
		Daily	$\frac{Inverter daily Generation (kWh)}{Inverter DC Capacity (kWp) x 24 (h)}$
		Monthly	$\frac{Inverter monthly Generation (kWh)}{Inverter DC Capacity (kWp) x 24 (h) x No. of days passed in the month}$
		YTD	$\frac{Inverter YTD Generation (kWh)}{Inverter DC Capacity (kWp) x 24 (h) x No. of days passed in the month}$
Plant Generation Plant DC Capacity	Plant	Hourly	$\frac{Plant hourly Generation (kWh)}{Plant DC Capacity (kWp) x 24 (h)}$
		Daily	$\frac{Plant daily Generation (kWh)}{Plant DC Capacity (kWp) x 24 (h)}$
		Monthly	$\frac{Plant monthly Generation (kWh)}{Plant DC Capacity (kWp) x 24 (h) x No. of days passed in the month}$
		YTD	$\frac{Plant YTD Generation (kWh)}{Plant DC Capacity (kWp) x 24 (h) x No. of days passed in the month}$

Performance ratio measured (actual)

Performance ratio is the amount of energy generation achieved given the ambient irradiation and inverter capacity

Table 11. Calculation of actual performance ratio
Parameters and source	Hierarchy	Aggregation frequency	Computation logic
Inverter Generation Inverter DC Capacity Insolation	Inverter	Hourly	$\frac{Inverter Daily Energy (kWh) x 100}{Inverter DC Capacity (kWp) x (Daily POA Energy (Wh/m²)/1000)}$
		Daily	$\frac{Inverter Daily Energy (kWh) x 100}{Inverter DC Capacity (kWp) x (Daily Insolation (Wh/m²)/1000)}$
		Monthly	$\frac{Inverter Monthly Energy (kWh) x 100}{Inverter DC Capacity (kWp) x (Monthly Insolation (Wh/m²)/1000)}$
		YTD	$\frac{Inverter YTD Energy (kWh) x 100}{Inverter DC Capacity (kWp) x (YTD Insolation (Wh/m²)/1000)}$
Plant Generation Plant DC Capacity Insolation	Plant	Hourly	$\frac{Plant Daily Energy (kWh) x 100}{Plant DC Capacity (kWp) x (Daily POA Energy (Wh/m²)/1000)}$
		Daily	$\frac{Plant Daily Energy (kWh) x 100}{Plant DC Capacity (kWp) x (Daily Insolation (Wh/m²)/1000)}$
		Monthly	$\frac{Plant Monthly Energy (kWh) x 100}{Plant DC Capacity (kWp) x (Monthly Insolation (Wh/m²)/1000)}$
		YTD	$\frac{Plant YTD Energy (kWh) x 100}{Plant DC Capacity (kWp) x (YTD Insolation (Wh/m²)/1000)}$

Temperature corrected performance ratio

The measured performance ratio is temperature corrected to 25°C® using the temperature coefficient. This allows for comparison of asset performance across different time periods

Table 12. Inverter Performance Ratio (PR) Computation
Parameters and source	Hierarchy	Aggregation frequency	Computation logic
Inverter PR	Inverter	Hourly	$\frac{Inverter Hourly PR (%)}{1 + [γ × (Δt)]}$
		Daily	$\frac{Inverter Daily PR (%)}{1 + [γ × (Δt)]}$
		Monthly	$\frac{Inverter Monthly PR (%)}{1 + [γ × (Δt)]}$
		YTD	$\frac{Inverter YTD PR (%)}{1 + [γ × (Δt)]}$
Plant PR	Plant	Hourly	$\frac{Plant Hourly PR (%)}{1 + [γ × (Δt)]}$
		Daily	$\frac{Plant Daily PR (%)}{1 + [γ × (Δt)]}$
		Monthly	$\frac{Plant Monthly PR (%)}{1 + [γ × (Δt)]}$
		YTD	$\frac{Plant YTD PR (%)}{1 + [γ × (Δt)]}$

Note:

γ = Temp coefficient of PV module
Δt = Avg. Module temp - 25°C

Time based availability

The ratio of time the inverter was generating power to the duration of sufficient irradiance (> 20 W/m²) expressed in percentage

Table 13. Time based availability
Parameters and source	Hierarchy	Aggregation frequency	Computation logic
Active Power Irradiance	Inverter	Hourly	$\frac{Generation hours x 100}{Available hours}$
		Daily	$\frac{Daily Generation hours x 100}{Daily Available hours}$
		Monthly	$\frac{Monthly Generation hours x 100}{Monthly Available hours}$
		YTD	$\frac{YTD Generation hours x 100}{YTD Available hours}$
Active Power Irradiance	Plant	Hourly	$\frac{Sum (Inverter Generation hours) x 100}{Sum (Inverter Available hours)}$
		Daily	$\frac{Sum (Inverter Daily Generation hours x 100}{Sum (Inverter Daily Available hours}$
		Monthly	$\frac{Sum (Inverter Monthly Generation hours x 100}{Sum (Inverter Monthly Available hours}$
		YTD	$\frac{Sum (Inverter YTD Generation hours x 100}{Sum (Inverter YTD Available hours}$

Note: Generation hours = hours where Active Power Available hours = hours where irradiance > 20 W/m²

Capacity based availability

The percentage of time duration for which the overall capacity of the Plant was available during the generation hours. This is similar to Time based availability but factors the capacity of the Inverter to derive the availability.

Table 14. Calculation of capacity based availability
Parameters and source	Hierarchy	Aggregation frequency	Computation logic
Available Hours Generation Hours Capacity of inverter from configuration Plant capacity = Sum of inverter capacity	Plant	Hourly	$\frac{Sum(Inverter DC Capacity (kWp)) × Sum(Inverter Generation Hours) x 100}{Sum(Inverter DC Capacity (kWp)) × Sum(Inverter Available Hours)}$
		Daily	$\frac{Sum(Inverter DC Capacity (kWp)) × Sum(Inverter Daily Generation Hours) x 100}{Sum(Inverter DC Capacity (kWp)) × Sum(Inverter Daily Available Hours)}$
		Monthly	$\frac{Sum(Inverter DC Capacity (kWp)) × Sum(Inverter Monthly Generation Hours) x 100}{Sum(Inverter DC Capacity (kWp)) × Sum(Inverter Monthly Available Hours)}$
		YTD	$\frac{Sum(Inverter DC Capacity (kWp)) × Sum(Inverter YTD Generation Hours) x 100}{Sum(Inverter DC Capacity (kWp)) × Sum(Inverter YTD Available Hours)}$

Note:

Generation hours = hours where Active Power > 0
Available hours = hours where irradiance > 20 W/m²

Investment performance ratio (IPR)

The percentage of actual generation relative to the target generation.

Table 15. Calculation of investment performance ratio
Parameters and source	Hierarchy	Aggregation frequency	Computation logic
Plant Daily Generation Target Generation	Plant	Daily	$\frac{Max. of Daily Energy (kWh) x 100}{Target Generation (Prorated for One day) (kWh)}$
		Monthly	$\frac{Sum of Generation (kWh) x 100}{Target Generation of that Month (kWh)}$
		YTD	$\frac{Sum of Generation (kWh) x 100}{Target Generation of that Year (kWh)}$

Weather performance ratio (WPR)

The percentage of actual irradiance relative to the target irradiance.

Table 16. Calculation of weather performance ratio
Parameters and source	Hierarchy	Aggregation frequency	Computation logic
Plant Daily POA energy Target irradiance	Plant	Daily	$\frac{Max. of Daily POA Energy (Wh/m²) x 100}{Target Generation (Prorated for One day) (Wh/m²)}$
		Monthly	$\frac{Sum of Insolation (Wh/m²) x 100}{Target Insolation of that Month (Wh/m²)}$
		YTD	$\frac{Sum of Insolation (Wh/m²) x 100}{Target Insolation of that Year (Wh/m²)}$

Operating performance ratio (OPR)

The ratio of Investment performance ratio (IPR) to weather performance ration (WPR), in other words the ratio of Actual PR and Target PR..

Table 17. Calculation of operating performance ratio
Parameters and source	Hierarchy	Aggregation frequency	Computation logic
Plant Daily generation Budget from forecast	Plant	Daily	$\frac{IPR (%)}{WPR (%)}$
		Monthly	$\frac{IPR (%)}{WPR (%)}$
		YTD	$\frac{IPR (%)}{WPR (%)}$

Expected generation

Expected generation is the amount of generation expected for the given irradiation with respect to assumed PR

Table 18. Calculation of expected generation
Parameters and source	Hierarchy	Aggregation frequency	Computation logic
Irradiance Inverter DC capacity Assumed PR from plant configuration or plant forecast Note: The assumed PR is at plant level and we need to refer the same for all inverters in the plant	Inverter	Hourly	$Assumed PR (%) \times Inverter DC Capacity (kWp) \times Insolation (Wh/m²)$
		Daily	$Assumed PR (%) \times Inverter DC Capacity (kWp) \times Insolation (Wh/m²)$
		Monthly	$Assumed PR (%) \times Inverter DC Capacity (kWp) \times Insolation (Wh/m²)$
		YTD	$Assumed PR (%) \times Inverter DC Capacity (kWp) \times Insolation (Wh/m²)$
Irradiance Plant DC capacity Assumed PR from plant configuration or plant forecast	Plant	Hourly	$Assumed PR (%) \times Plant DC Capacity (kWp) \times Insolation (Wh/m²)$
		Daily	$Assumed PR (%) \times Plant DC Capacity (kWp) \times Insolation (Wh/m²)$
		Monthly	$Assumed PR (%) \times Plant DC Capacity (kWp) \times Insolation (Wh/m²)$
		YTD	$Assumed PR (%) \times Plant DC Capacity (kWp) \times Insolation (Wh/m²)$