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kWh/kWp - Specific yield (or simply “yield”) refers to how much energy (kWh) is produced for every kWp of module capacity over the course of a typical or actual year.

Performance Ratio (PR) of a plant for a period of time is energy measured(kWh)/(Irradiance(kWh/m2) on the panel x Active area of PV module(m2) x PV module efficiency). PR is a measure for the performance of a PV system taking into account environmental factors (temperature, irradiation, climate changes etc.). PR will take into account the availability of the grid, minimum level of irradiation needed to generate electrical energy, irradiation levels at a given period of time.

Annual energy production and energy yield assessment values of the plant are computed using the software.

Plane of array irradiance (POA) is a term used to quantify the incident irradiance on a given solar array. It is the parameter most directly related to the power output of a PV module and is used extensively in PV performance analysis and modeling of PV arrays.

The irradiance on a panel or Plane of Array (POA) is the irradiation coming directly from the sun multiplied by the cosine of the angle of incidence (the angle between the direction of the sun and a vector normal to the panel).

Energy yield of a solar panel is proportional to the covered area A, the energy received from the sun (insolation in W/m2) dependent on the solar irradiance and the angle at which the beam is captured, I, and a conversion efficiency rate that is dependent on the solar panel material ρ, Esolar=ρAI.

A project’s location determines the amount of sunlight, or irradiance, it will receive. Irradiance is usually the biggest driver of specific yield because irradiance can vary so much.

Weather file. There are a number of different ways of constructing a weather file, including ground-based measurements, satellite-based models and hybrid approaches. These different methodologies can result in weather files that differ by 10% or more for the same location and the same period of time.

P50 and P90

To quantify the economic risk with interannual solar resources the software calculates exceedance probabilities representing the amount of energy expected to be produced by a plant. P50 and P90 are values that represent the level of certainty. Software calculates P50 and P90 values of the annual energy output.

In P50 and P90, the “P” stands for Percentile. The P90 defines the point separating the top 90% of observed annual energy values from the lower 10%. Annual energy values are expected to have a 90% chance of exceeding the P90 value. The P50 defines the point where these future values will have a 50% probability of exceedance. These probabilities are often computed assuming a normal distribution, in which case the P50 is equal to the mean, and the P90 can be calculated using the standard deviation.