Open-circuit voltage, abbreviated Voc, is the voltage across a PV module or string's terminals when no current flows. Module datasheets and design guides list Voc as a key electrical rating. During commissioning, the Voc of each source circuit is measured before the DC disconnects are closed. The reading is compared with the expected value, and the same test confirms polarity. Identical strings measured under the same conditions should read about the same Voc, usually within 5% of each other. A reading lower than expected can mean wiring errors, failed modules or shorted bypass diodes. Voc goes down as module temperature goes up. With measured cell temperature and the temperature coefficient, readings can be corrected to a reference temperature. String Voc must stay inside the DC voltage limits of the inverter, charge controller or other DC equipment. Module-level rapid shutdown devices change the expected string Voc, so check the manufacturer's guidance when testing these systems.
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related_toc1 verified · fact Open-circuit voltage measurement
Voc of each PV source circuit is measured before the array DC disconnects are closed, to confirm correct installation and polarity.
sec=5.3.1 h=5dce7dfc896dtbl=2.r3 h=4a9dff1fba77sec=7.1 h=8d8044e267c7verified by: review-workflowverified on: 2026-10-24
c2 drafted · lead Temperature coefficient
If cell temperature is also measured, a voltage-temperature coefficient can translate Voc readings to a reference temperature.
sec=5.3.1 h=5dce7dfc896dc3 verified · fact Low open-circuit voltage
Voc below expectation can point to improper array wiring, failed modules or shorted bypass diodes.
sec=5.3.1 h=5dce7dfc896dverified by: review-workflowverified on: 2026-10-24
c4 drafted · lead Crystalline silicon PV
The guide gives a standard voltage-temperature coefficient for crystalline silicon modules.
sec=5.3.1 h=5dce7dfc896dc5 drafted · lead PV rapid shutdown
The expected string Voc changes when SunSpec rapid shutdown devices are installed.
fig=3 h=7b9f7a9f1da3review note: support check: partial - u15 only shows a figure of expected Voc for a string with SunSpec rapid shutdown devices; it implies but doesn't explicitly state that expected Voc changes.; review: partial - The SMA passage is only a figure caption showing example expected Voc for a string with SunSpec rapid shutdown devices; it does not say the expected Voc changes.
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