Sighten‘s production model incorporates key aspects of the industry’s most sophisticated models while maintaining simplicity of user inputs.
Highlights
Simple and non-assumptive user inputs required: module and inverter quantities/models, pitch, azimuth, and shading
Hourly production calculations with granular weather data
Module and inverter-level electrical behavior modeled
Overview
User inputs | Irradiation | Module output | Array output |
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Sighten vs PVWatts
| Component | Sighten | PVWatts |
|---|---|---|
Weather data | NREL TMY Stations | NREL TMY Stations |
Shading | SAM2 shading model | User input |
Module production | DeSoto 5-parameter | User derate input |
Inverter clipping | Sandia MPPT Tracking | None |
Inverter efficiency | SAM CEC Efficiency | User input |
Full description of Sighten's production calculation
- Production is simulated for each array on an hourly basis
- Primary sources of input:
- TMY weather data (8760 hours) based on system location
- PV module electrical specifications per manufacturer spec sheet
- includes parameters we calculate to construct IV curve (DeSoto)
- Inverter electrical specifications per manufacturer spec sheets
- Array details (e.g. tilt, azimuth, string size, shading, etc)
- For each hour of a TMY dataset:
- Determine the solar radiation incident on the tilted surface
- "unshaded" radiation includes beam radiation component
- "shaded" radiation assumes no beam radiation
- Determine solar cell temperature based on PV model specifications in both shaded and unshaded conditions
- Construct I-V curve of solar cell based on IV curve parameters calculated as functions of solar cell temperature for both shaded and unshaded conditions (Desoto)
- Determine the AC power generated from the array:
- NOTE: the percentage shading implies the percentage of PV modules IN EACH STRING that receive "unshaded" radiation versus "shaded" radiation
- If the array uses a string inverter:
- The string voltage is calculated as a composite of the unshaded and shaded PV modules
- Find array max power (DC) by calculating string voltage as a function of a universally-applied string current
- Find module voltage on the I-V curve for unshaded module
- Find module voltage on the I-V curve for shaded module
- String voltage is the sum of voltages generated by unshaded and shaded modules in their respective proportion
- Iterate until maximum of product of string voltage and array current is found
- Convert array power (DC) into array power (AC) based on inverter efficiency specifications (per spec sheet) and derate assumptions applied to all string inverters:
- wiring_dc = 0.980
- mismatch = 0.980
- diodes = 0.995
- soiling = 0.950
- wiring_ac = 0.990
- If the array uses microinverters:
- Find array max power (DC) by calculating unshaded and shaded module voltages as functions of a individually-managed current
- Find module max power (DC) on the I-V curve for unshaded module
- Find module max power (DC) on the I-V curve for shaded module
- Convert module power (DC) into module power (AC) for unshaded and shaded modules based on inverter efficiency specifications (per spec sheet) and derate assumptions applied to all microinverters:
- wiring_dc = 0.995
- mismatch = 1.000
- diodes = 0.995
- soiling = 0.950
- wiring_ac = 0.990
- Array power (AC) is the sum of power (AC) generated by unshaded and shaded modules in their respective proportion of the array
- Find array max power (DC) by calculating unshaded and shaded module voltages as functions of a individually-managed current
- If the array uses string inverters with optimizers:
- Same methodology as for microinverters, but using the following derate factors:
- wiring dc = 0.980
- mismatch = 1.000
- diodes = 0.995
- soiling = 0.950
- wiring ac = 0.990
- Same methodology as for microinverters, but using the following derate factors:
- Determine the solar radiation incident on the tilted surface