A module label is a small table with consequences. Tradinor reads it as purchasing data for the inverter and the wire, not as a slogan. Use the datasheet coefficients when the label omits them. Do not invent a yield.
Five numbers, not one
Pmax is the power at standard test conditions. Vmp and Imp are the voltage and current at that power point. Voc is the voltage with the connector open. Isc is the current into a short circuit. Series strings add voltage. Parallel strings add current. The inverter maximum DC voltage must stay above the cold Voc of the string. The inverter MPPT window must cover the hot Vmp. Those are different checks.
Temperature coefficients say how Voc and Pmax move per degree. Ask for them. The mechanical rating, wind and snow, is a separate line from the electrical label and belongs on the RFQ if the site is exposed. Connector type has to match the rest of the string. A module that is electrically right and mechanically a different connector is still the wrong delivery.
- Pmax, Vmp, Imp, Voc, Isc, and the tolerance on power.
- Temperature coefficients for Voc and Pmax.
- Maximum system voltage and series-fuse rating.
- Connector and cable length on the module.
- Frame and the mechanical load if the mounting requires it.
| Number | Use it for | Do not use it for |
|---|---|---|
| Voc | Cold string voltage vs inverter max | Day-to-day operating voltage |
| Vmp | MPPT window | The safety limit of the string |
| Isc | Wire and fuse sizing | The expected daily energy |
| Pmax | Array power at STC | A promise of annual yield |
What to file with the PO
File the datasheet page that matches the label on the delivered pallet. Check one module’s label against the PO for Pmax and Voc. A different bin of the same family can have a different voltage. Confirm connectors before the crew is on the roof. Do not calculate annual energy on this page. That needs the site, the orientation, and losses the nameplate does not contain.
What to lock on the order
When you request a quote, ask for the datasheet page that lists STC electrical data and the temperature coefficients, and require the delivered label to match that page. String length is your calculation: cold Voc times modules in series, compared with the inverter maximum. Hot Vmp compared with the MPPT window is the second calculation. Put both results in the project file so purchasing does not shorten a string to save a connector. Specify the connector family so every module on the site mates. Power tolerance belongs on the PO if you are buying a named bin. At delivery, check one label per pallet for Pmax and Voc against the PO. Do not use this check as an energy forecast. The nameplate is a laboratory condition. The site yield depends on orientation, shade, temperature, and inverter limits that are outside the module line.
Questions buyers actually ask
Is wattage enough to buy a string inverter?
No. Open-circuit voltage at the coldest site temperature sets how many modules you may put in series. Power does not say that.
What is the difference between Vmp and Voc?
Vmp is the voltage at the power point while operating. Voc is the open-circuit voltage, higher, and it rises further in the cold. String limits use Voc.
Do I design from the nameplate at 25 C?
The nameplate is STC. Hot roofs reduce power. Cold mornings raise voltage. Ask for the temperature coefficients.