Six power ratings, one panel
A manufacturer offers the same series at 555, 560, 565, 570, 575 and 580 W. These are not six designs. They are one panel, built on one line, sorted afterwards by how efficient its cells turned out to be.
That sorting step is called binning, and understanding it answers most of the questions a datasheet raises: why the higher rating costs more per watt, why it is harder to get, and why mixing two of them in one string is a bad idea.
Why one series has six ratings
Browse any manufacturer's range and the same series appears several times over. JA Solar's JAM72D40-GB is sold at 555, 560, 565, 570, 575 and 580 W.
All of them are the same panel. Same dimensions, same 144 half-cells, same frame, same glass, same encapsulant, same warranty, same certifications. What differs is the grade of cell that went into them, and the electrical figures that follow from it.
Think of sorting fruit
Apples from one orchard grew on the same trees in the same weather, and still come off the tree in different sizes. The best go to one grade, the rest to another. Cells are graded the same way, for the same reason: mass production has variance, and variance has to be sorted rather than wished away.
- Identical: dimensions, 144 cells, cell technology, frame and glass, warranty, certifications.
- Moves: peak power, module efficiency, Voc and Vmp, Isc and Imp.
Where the variance comes from
The process starts with silicon refined to 99.9999% purity. It is melted at around 1,400 °C and pulled slowly into a cylindrical monocrystalline ingot by the Czochralski method.
The ingot is sliced into wafers 150 to 180 micrometres thick with a diamond wire saw. The first differences appear here: no two wafers have quite the same crystal structure.
Each wafer is then textured to trap light in microscopic pyramids, doped with phosphorus and boron to form the p-n junction, passivated under anti-reflective layers, and printed with its conductive fingers and busbars.
Every one of those steps adds a little spread. Passivation thickness, metallisation quality, crystal defects - none of it is controllable to the last percent, and the finished cells come off the line a few percent apart in efficiency from best to worst.
Every finished cell passes through a flash tester, which measures its full electrical behaviour in a fraction of a second under standard test conditions: 1,000 W/m² irradiance, 25 °C cell temperature, AM1.5G spectrum.
The tester records maximum power (the parameter cells are sorted on), short-circuit current, open-circuit voltage and fill factor - which is the one that says how good the cell actually is rather than how big.
Why sorting matters
Cells are wired in series, and a series string is limited by its weakest member. Mixing efficiencies inside one panel would waste the good cells. Grouping cells of like performance is what makes each panel deliver the power its label claims.
Bins are usually 5 W wide, though 2 to 10 W is all seen. The cells that make a 580 W panel come from the top bin - the best of that batch.
Cell efficiency follows a bell curve, so the top bin is the smallest. That is why the highest rating in a series is the hardest to source and usually the dearest per watt.
One datasheet, six columns
The JAM72D40-GB series as its datasheet prints it. Power, efficiency, voltage and current all step together, because they are all consequences of the same cell grade.
| Parameter | 555/GB | 560/GB | 565/GB | 570/GB | 575/GB | 580/GB |
|---|---|---|---|---|---|---|
| Maximum power, Pmax | 555 W | 560 W | 565 W | 570 W | 575 W | 580 W |
| Open-circuit voltage, Voc | 50.55 V | 50.70 V | 50.85 V | 51.00 V | 51.15 V | 51.30 V |
| MPP voltage, Vmp | 42.24 V | 42.40 V | 42.55 V | 42.70 V | 42.85 V | 43.03 V |
| Short-circuit current, Isc | 14.02 A | 14.09 A | 14.16 A | 14.23 A | 14.30 A | 14.36 A |
| MPP current, Imp | 13.14 A | 13.21 A | 13.28 A | 13.35 A | 13.42 A | 13.48 A |
| Module efficiency | 21.5% | 21.7% | 21.9% | 22.1% | 22.3% | 22.5% |
Depending on production date, JAM72D40-GB modules may be built on TOPCon (newer batches) or PERC (older ones). The 25 W between the ends of the ladder is 4.5%: on a 10 kWp array at 1,050 kWh/kWp, roughly 470 kWh a year from the same roof area.
Power tolerance
Every datasheet states a power tolerance. On a modern premium panel it reads 0 ~ +5 W.
That is a one-sided tolerance, and the direction is the whole point. A module labelled 560 W will measure between 560 and 565 W under standard test conditions. It cannot measure less than its label. You always get at least what you paid for.
This has not always been true, and it is still not true everywhere. A cheaper panel may carry +/-3% or +/-5%, which means a "400 W" module is allowed to be a 380 W module. Check the tolerance before you compare two prices per watt.
| Period | Tolerance | A 300 W panel |
|---|---|---|
| around 2010 | +/-5% | 285-315 W |
| around 2015 | +/-3% | 291-309 W |
| around 2018 | 0 to +3% | 300-309 W |
| today | 0 to +5 W | 300-305 W |
Some manufacturers quote 0 to +3 W rather than +5 W. Either way, a one-sided tolerance is the sign of a modern line.
What it means when you buy
- Tight roof: take the highest rating in the series. More kWp on the same area is the only thing that helps.
- Space to spare: the lower ratings are usually cheaper per watt. Same system size, less money.
- Output scales with the rating. A 580 W module makes about 4.5% more than a 555 W one, not dramatically more.
- The top rating is the scarcest, because the top bin is the smallest. Order early.
Panels from one series share almost the same voltages, so they can be combined - carefully.
- Not in one string. The currents differ, and a series string runs at its weakest member's current. Whatever you gain from the stronger panel, you give back.
- On separate strings, yes. Two strings of one rating each, into the same inverter, is fine.
- With microinverters or optimisers, freely. Per-module electronics is exactly the case mixed ratings are safe in.
Either way, check Voc and Vmp for the specific rating against the inverter's window. They step with the power, and a string sized on the wrong column is a string that clips or fails to start.
In short
- Panels in one series share dimensions and construction exactly.
- The power differences come from unavoidable variance in cell efficiency.
- Binning is the sorting of cells into groups of like performance.
- A 0 to +5 W tolerance means the panel never measures under its label.
- Higher ratings cost more per watt and save roof area. Which matters is your roof's answer, not the panel's.
- Energy produced scales with the rating - about 4 to 5% across this ladder.