Glossary · Panels · Intermediate · Pakistan 2026
Voc is the dangerous number on a cold January morning.
Voc is the voltage of a module with no current — the highest DC voltage it will make. Strings add Voc. Cold weather raises Voc.
People also search open circuit voltage string voltage pv max
Key takeaways
- String Voc_cold = n × Voc_stc × (1 + γ_voc × (Tmin − 25)).
- Example Voc STC: ~45–50 V — 645 W N-type class.
- House PV max: ~500 V class — Read the carton, not WhatsApp.
- Cold add: Several volts per module — Hills and GB.
- Before you buy plates, read inverter Vmax and module Voc + temperature coefficient.
What it is
String Voc_cold = n × Voc_stc × (1 + γ_voc × (Tmin − 25)). γ_voc is about −0.25 %/°C (the coefficient is negative; colder means higher Voc). Ten 45.5 V modules are 455 V at 25 °C and higher in Quetta at 5 °C.
In Pakistan 2026
House hybrids in Pakistan are often 500 V class on PV. Shops count modules until the MPPT “looks full” and skip the cold morning. That is how a January inverter locks on PV overvoltage.
How we spec it
Before you buy plates, read inverter Vmax and module Voc + temperature coefficient. Count the longest string. Write the January math on the quote.
Numbers you can actually use
Street ranges, not a quotation. Confirm the carton the week you book.
| Thing | 2026 number | How to use it |
|---|---|---|
| Example Voc STC | ~45–50 V | 645 W N-type class |
| House PV max | ~500 V class | Read the carton, not WhatsApp |
| Cold add | Several volts per module | Hills and GB |
Do this in order
- Read module Voc and Voc temperature coefficient on the datasheet.
- Pick the coldest morning you will actually see (not STC 25 °C).
- Multiply modules in series × corrected Voc.
- Compare to inverter maximum input voltage with margin.
- Only then pick how many plates per MPPT.
Voc vs MPPT window
Startup voltage is the bottom of the window — too few modules and the box wakes late. Vmax is the top — too many and it faults. Pakistani roofs want strings that sit in the window in January and in June. That is two seasons, one string count.
Worked example — Peshawar
Take a 3.6 kW-class hybrid in Peshawar (PESCO, ~4.9 PSH). 6 × 645 W is 3.87 kW DC. Derated yield ≈ 3.87 × 4.9 × 0.78 ≈ 14.8 kWh on a clean day — then weaker winter sun and variable waits. This page (Voc (open-circuit voltage)) is the piece of that plant people skip on WhatsApp. If your quote cannot survive this Peshawar sentence, it will not survive May. Open the calculator with city set to Peshawar, and the lookup map for a stocking dealer — not a green-meter SKU.
Keywords this lesson actually answers
People land here asking open circuit voltage, string voltage, pv max. The honest 2026 answers still collapse to: N-type plates with flash, IP65 hybrid with GRID vs LOAD, 51.2 V LFP on CAN, 14 SWG, XLPO, derate 0.78, and net-billing at ~Rs 11 export if you file with PESCO. Everything else on this page is how not to get robbed while buying those things.
Internal links worth clicking before you pay
Size: system sizing · Policy: net-billing · Battery: LFP · Buy: checklist · Shops: near you · City climate: Peshawar · Numbers: calculators.
How shops fail this
12 modules on a 500 V box because “it worked in
12 modules on a 500 V box because “it worked in June”
Ignoring temperature coefficient
Ignoring temperature coefficient
Mixing Voc bins on one string
Mixing Voc bins on one string
FAQ — Voc (open-circuit voltage)
Can I add one more plate later?
Only if the cold Voc still fits. Leave a module of headroom on day one.
Is Vmp the same as Voc?
No. Vmp is operating voltage. Voc is open. MPPT lives near Vmp. Protection cares about Voc.
What about Karachi winters?
Milder than Quetta, still colder than STC. Do the math anyway.
Read next
Vmp (voltage at max power)
Vmp is where the MPPT is trying to sit.
glossaryIsc (short-circuit current)
Isc is how you cook an MPPT if you parallel too much.
guideHow to size PV strings
Cold Voc under Vmax. Hot Vmp over MPPTmin. Current under Imax.
glossaryMPPT
MPPT is the tracker that chases watts while the roof cooks.
glossarySTC (standard test conditions)
STC is a laboratory noon that your roof will never be.
glossaryNOCT
NOCT is the less-fake wattage on a warm roof.
Open the calculators Shops near you All lessons
Educational page, September 2026. Not a DISCO filing, not a live quotation, not medical or bank advice. SRO 251(I)/2026 net-billing for new files after 9 Feb 2026.