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Solar PV String Voltage & Temperature Calculator electrical
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Solar PV String Voltage & Temperature Calculator

Calculate maximum cold-weather string Voc per NEC 690.7 and summer hot Vmp to ensure strings never exceed inverter maximum DC voltage ratings.

PV Module STC Nameplate

Site Climate & Inverter Limits

String Voltage Compliance Results

Coldest Winter String Voc (NEC 690.7)
-- V
-- compliance
Max Allowed Modules
-- Modules
-- V margin to max limit
Summer Hot String Vmp
-- V
Within MPPT window
Cold Single Module Voc: -- V
STC Nominal String Voc: -- V (at 25°C)
Temperature Rise Voltage Loss: -- V drop in summer
NEC 690.7 mandates calculating maximum PV system voltage using the lowest expected ambient temperature to prevent destroying inverter input semiconductors.

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Frequently Asked Questions

Why does solar PV voltage increase when temperature drops?

Solar photovoltaic cells have a negative temperature coefficient of voltage. As temperature decreases, the semiconductor bandgap widens and thermal recombination of electron-hole pairs decreases, causing the open-circuit voltage (Voc) to rise by 0.25% to 0.35% for every degree Celsius below standard test conditions (25°C).

What is NEC 690.7 compliance for maximum photovoltaic system voltage?

National Electrical Code (NEC 690.7) requires calculating maximum PV string voltage using module manufacturer temperature coefficients and the lowest expected ambient temperature recorded at the installation site. For utility-scale installations, string voltage must strictly never exceed 1500 V DC.

What happens if a solar string exceeds the inverter maximum DC voltage rating?

If string Voc exceeds the inverter maximum DC input limit (even momentarily during a freezing clear morning before the inverter connects), input surge suppression MOVs and DC bridge IGBT capacitors can suffer permanent dielectric breakdown and catastrophic failure.