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Project Specifications Definitions
- Module Manufacturer: The manufacturer name of the module to be used in the project.
- Module Model #: This number designates the type of module to be used in the project. The module specifications are used in calculations that determine the array configuration and inverter selection.
- Mounting Type (Ground/Pole/Roof): How the array is mounted affects the calculations that determine the eventual production of the system. A ground or pole mounted array may operate at a cooler temperature than a roof mounted one. This would result in a de-rating of the roof mounted system.
- Inverter Type: This allows the user to check system specifications for newer or prospective inverters and legacy inverters that are no longer manufactured.
- Temperature Scale (Fahrenheit/Celsius): The unit of measure used to calculate the open circuit and maximum power point voltages. Temperature affects the output of the modules.
- Correction Factor: This temperature compensation factor is determined by the NEC. This factor is used in calculations to compensate for temperature affects on the voltage output for Crystalline and Multi-crystalline Silicon Modules. Due to the fact that all states do not operate under the current NEC codes, the previous temperature compensation factors from 2005 is provided as an option.
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Local Temperature Range:
The temperature range is critical for the following reasons to determine the PV systems operational properties both at very low and high temperatures.
- The lower temperature should be the record lowest for your area.
- The higher temperature should be at least the average high, with perhaps a small safety factor added on for margin.
Module Specifications Definitions
- STC Watts: Standard Test Conditions. Laboratory testing standard for modules. 1000 W/M2, 25°C Cell Temp. “Nameplate Rating” of Module or Array. Manufacturers advertise and sell modules based on this value.
- PTC Watts: PV USA Test Conditions. Testing standard for modules that was developed to more closely represent conditions likely to be found in the field 1000 W/M2, 20°C ambient Temp.
- VOC: Open Circuit Voltage at STC.
- VMP: Voltage at Maximum Power Point at STC.
- IMP: Amperage at Maximum Power Point at STC.
- ISC: Short Circuit Current (Amps) at STC.
- VOC Temperature Coefficient: Coefficient used to determine effect of temperature on a PV panels output voltage. This coefficient is important when sizing a PV array for an inverter to ensure that the PV array is within the minimum and maximum DC input voltage limits. This is specific to each different module type.
- Maximum Power Temperature Coefficient: Coefficient used to determine effect of temperature on a PV panel's power output. This is specific to each different module type.
- Coldest Day VOC: This is the open circuit voltage determined by the prescribed record coldest day for the location of the installation.
- Warmest Day VMP: This is the open circuit voltage determined by the prescribed average warmest day for the location of the installation.
Inverter Specifications Definitions
- DC ISC Maximum Current: This value is the maximum allowable current that can be input in to the DC side of the inverter without an additional fusing requirement. The value is derived from taking the number of parallel series of PV Modules multiplied time the PV Module’s DC ISC.
- DC IMP Nominal Current: This value is the maximum DC current value that the inverter will continuously operate under the MPPT operation.
- Maximum STC DC Input Power: The maximum recommended STC wattage for prudent system design. One should note this is not a hard specification, only a recommendation. No harm to the inverter will occur if this value is exceeded.
- Continuous Power Output: This is the maximum rated continuous power output of the selected inverter.
- Weighted CEC Efficiency: The ratio of output power (or energy) to input power (or energy). Expressed in percent as determined by the California Energy Commission.
- Maximum DC Input Voltage: This is the maximum allowable open circuit voltage. Exceeding this value would damage the inverter.
- DC Peak Power Tracking Range (Commercial Inverters): This is the DC voltage range at which the maximum power point tracking is the most efficient.
- DC Voltage Operating Range (Residential Inverters): This is the DC voltage range which the inverter will operate.
- AC Nominal Voltage: This value is the default value of the AC voltage. There is an associated range stated in the AC Operating Range definition.
- AC Operating Range: This is the AC voltage range in which the designated inverter will operate. If the voltage deviates outside of this range the inverter will shut itself down per UL 1741 requirements.
- AC Frequency: This is AC frequency in which the designated inverter will operate. If the frequency deviates outside of 59.3 or 60.5 the inverter will shut itself down per UL 1741.
- AC Maximum Continuous Current: This is the maximum continuous amperage in which the designated inverter is intended to operate.
Recommendations Definitions
- Print System Designs to PDF: To print a PDF containing a table of system designs: First, select from the system designs by checking their corresponding check box. Then click on the "Print Selected Designs to PDF" button. Note that the Selected Configurations table will only appear on the PDF if at least one system design check box is checked.
- Parallel Strings: This value is the number of parallel series of PV Modules.
- Series Modules: This value is the number of PV Modules in series.
- Inverter AC Watts: This value is defined as the PTC watts multiplied times the inverter efficiency and provides further realistic guidance for maximum AC output of the PV system.
- STC Watts: Standard Test Conditions. Laboratory testing standard for modules. 1000 W/M2, 25°C Cell Temp. “Nameplate Rating” of Module or Array. Manufacturers advertise and sell modules based on this value.
- PTC Watts: PV USA Test Conditions. Testing standard for modules that was developed to more closely represent conditions likely to be found in the field 1000 W/M2, 20°C ambient Temp.
- CEC Watts: This value is defined as the PTC watts multiplied times the inverter efficiency and provides further realistic guidance for maximum output of the PV system.
- STC VOC: This value is the VOC of the PV system under STC conditions. The value is defined by taking the number of PV Modules in series and multiplying that value time the VOC of the STC.
- Coldest Day VOC: This values can be derived through several methods, the NEC 2005, the NEC 2008, and the mfg specifications of the PV Modules. The value applies the lowest temperature and determines what the PV Modules VOC will be. Next, the adjusted PV VOC will be multiplied times the number PV Modules in series.
- STC VMP: The maximum VMP that the inverter will operate efficiently.
- Warmest Day VMP: The minimum Vmp that the PV system will operate assuming no wire losses, taking into affect warmest day temperatures, and the temperature offset of the mounting schema.
- STC IMP: This value is the Imp of the PV system under STC conditions. The value is defined by taking the number of PV Modules in parallel and multiplying that value time the Imp of the STC.