Which numbers on a solar panel’s spec sheet actually matter?
Solar basics Updated 2026-08-10
A solar panel’s label usually prints four numbers under “Electrical Data”: open-circuit voltage (Voc), voltage at maximum power (Vmp), short-circuit current (Isc) and current at maximum power (Imp), all measured at the same standard test conditions. Our matching engine checks three of them against a real limit on your power station. The fourth only feeds an estimate of how many watts will flow — change it and the estimate moves, but no pass-or-fail answer does.
The number that decides the most is not on that four-number line at all: without a panel’s temperature coefficient, published separately under “Thermal Characteristics,” this engine will not evaluate the panel against any station, on any pairing.
The four numbers on the label
Jackery SolarSaga 100 Air — Electrical Data
The four figures a spec sheet usually groups together, all measured at the same standard test conditions. Printed together does not mean checked the same way, which the next section is about.
Feeds the one check that can damage a station’s input stage.
See how it is checked →Feeds two separate checks — the top of the tracking window and, separately, the bottom.
Feeds the input-current limit, summed across every panel wired in parallel.
Feeds no pass-or-fail check at all.
Official specverified 2026-08-01Jackery SolarSaga 100 Air · US record
Three numbers, three limits — and each one can be the reason
Voc, corrected for the coldest morning the array will see, is checked against the station’s voltage ceiling — the one failure mode that can damage the machine rather than simply waste output. Vmp is checked against the tracking window from both ends: too high and the tracker cannot hold the peak; too low and it never finds one. Isc, summed across every parallel string, is checked against the port’s input-current limit. Three numbers, three separate limits, and on a real pairing any one of them can be the reason a panel is refused.
Jackery Explorer 300 Plus — three panels, three different reasons
Every panel this site holds a full electrical picture for, run single-panel against the same charging port. All three are refused, and not for the same reason twice.
Cold-corrected Voc reaches 32.3 V against this port’s 27 V ceiling. Its Vmp and Isc both clear their own limits comfortably — this panel is refused on one number only.
Run it yourself →Isc reaches 5.3 A against this port’s 5 A limit — no cold correction involved, this comparison holds at room temperature already. Its Voc and Vmp both clear their own limits.
Cold-corrected Voc reaches 40.8 V against the same 27 V ceiling, and Isc reaches 6.9 A against the same 5 A limit. Both numbers miss at once.
Derived by WattPairverified 2026-08-09Jackery Explorer 300 Plus · US record
The fourth number: Imp decides nothing
Imp is a real, published measurement and it is not wasted — it feeds this site’s estimate of how many watts will actually flow, alongside Vmp. What it never does is move a pass-or-fail answer. Run the same single panel on the same port three times, changing only its Imp, and every one of the six checks returns byte-for-byte the same result each time.
BLUETTI Elite 100 V2 — one arrangement, three values of Imp
The same panel, the same port, the same arrangement. Only the current-at-max-power figure changes between rows.
Every one of the six checks on this arrangement passes. This is the number on the label.
The same six checks return the same six results — the estimate moves, the verdict does not.
Even here, every check still returns exactly what it returned above. Imp is not one of the numbers this engine checks against anything.
Derived by WattPairverified 2026-08-01solar engine · live run
The fifth number is not on that line at all
A panel’s voltage temperature coefficient — how much Voc rises as the cells get cold — is printed separately, usually under “Thermal Characteristics” rather than beside Voc, Vmp, Isc and Imp. It decides the most of any number on the sheet: without it, verified, this engine will not correct Voc for cold at all, and refuses to evaluate the panel against any station rather than assume a typical figure.
What to actually pull off the sheet
Five numbers, not four
The calculator below runs all three limits live, on your own panel and your own station.
All three are usually on one line, at standard test conditions. Isc is sometimes mislabelled “short-circuit voltage” on a spec sheet — the unit column, not the label, tells you which it actually is.
Look for “Temperature Coefficient of Voc,” not the power coefficient printed beside it — the two are different numbers and only one corrects voltage. Some sheets print a single, unlabelled “Voltage Temperature Coefficient” without saying whether it means Voc or Vmp; when that happens, this library records the ambiguity rather than guessing which.
Every station record in this library publishes both, next to the panels this article checked against them.
Open the source →