Highest temperature ever recorded (most conservative) There are three different options for Tmax, all are acceptable for design best practices:Ģ% ASHRAE high temperature (most commonly used)Ġ.4% ASHRAE high temperature (required for ETO incentives, slightly more conservative)
#Sma string sizer for free
Find ASHRAE site temperature data for free on Solar ABCs. The industry standard for site temperature data is provided by the American Society of Heating, Refrigerating and Air-Conditioning Engineers ( ASHRAE ). Tmax = the ambient high temperature for the installation site. Module Vmp_min = minimum module voltage expected at site high temperature. The module minimum voltage is calculated using the high temperature for the installation site when the modules would produce the lowest expected voltage. This is because as a PV module gets hotter it is less efficient and produces less voltage. Then take the inverter minimum voltage and divide by the calculated module minimum voltage to get the minimum number of modules. In order to calculate the minimum string size we first have to calculate the minimum output voltage, Module Vmp_min, that each module will produce for the specific installation site. However, our customers care whether the system we design is operating during the summertime when their return on investment is highest. The National Electrical Code (NEC) doesn’t address the effects of high temperatures on module voltages because that is considered a performance issue, not a safety issue. The minimum string size is the minimum number of PV modules, connected in series, required to keep the inverter running during hot summer months.