580W vs. 620W: The Difference Is More Than 40 Watts

In recent quotes, the question customers ask most: what's the price difference between 580 watts and 620 watts, and is it worth it?

Today I'll run the numbers for you.

Price first

It's October 2026 now.

For the 580W TOPCon bifacial dual-glass module, we quote 0.68 yuan per watt.

For the 620W TOPCon high-efficiency version, we quote 0.70 yuan per watt.

How much difference per panel?

The 580W panel: 580 × 0.68 = 394.4 yuan.

The 620W panel: 620 × 0.70 = 434.0 yuan.

A difference of 39.6 yuan per panel, for 40 watts more.

How much power do those 40 watts make

Depends where you are. Let me take three types of locations:

Class I solar resource, 1,600 equivalent full-load hours a year. Forty watts generates 64 kWh more per year.

Class II, 1,300 hours. Forty watts makes 52 kWh more.

Class III, 1,100 hours. Forty watts makes 44 kWh more.

At a commercial-industrial rate of 0.6 yuan per kWh, that's worth 38.4, 31.2, or 26.4 yuan more per year.

At the coal benchmark of 0.35 yuan, it's 22.4, 18.2, or 15.4 yuan.

In other words, spend 39.6 yuan more, earn 15 to 38 yuan more per year.

Payback: one year to two and a half.

The module lasts twenty-five years. However you run this math, the higher wattage wins.

Then why does anyone buy 580

Because that math leaves out three things.

First thing left out: area

The 620W panel measures 2382 × 1134 mm.

The 580W panel is also 2382 × 1134 mm.

Same size, different wattage. That's cell efficiency, not a bigger panel.

So if your roof area is fixed — say a factory roof that fits exactly one hundred panels — using 620W takes total capacity from 58 kW to 62 kW. Four extra kilowatts generate five to six thousand kWh more a year.

In that case, higher wattage is close to mandatory.

Second thing left out: racking and labor

Say your project is sized by capacity — one megawatt.

With 580W panels you need 1,724 of them.

With 620W panels you need 1,613.

That's 111 fewer panels — 111 fewer sets of racking, clamps, and installation labor.

At current labor rates, the all-in cost of installing one panel runs 18 to 25 yuan. Skipping 111 panels saves 2,000 to 2,800 yuan.

That's two to three tenths of a cent saved per watt.

And that doesn't count savings on cable and combiner boxes.

Third thing left out: inverter ratio

This is the easiest one to get wrong.

When module wattage goes up, the inverter DC/AC ratio has to be recalculated.

An inverter sized at a 1.15 ratio for the old panels may end up at 1.23 once you switch to 620W, because the DC side got bigger.

If your inverter allows up to 1.3, no problem. If it only allows 1.2, you either swap the inverter or derate.

Swapping inverters costs more than what you saved.

So on every quote we always ask: what inverter model do you have, and what's its maximum DC/AC ratio?

Measured data

In July this year, we installed two comparison rows on a factory roof in Foshan.

Same orientation, same tilt, two strings on the same inverter.

One row of 580W, twenty panels. One row of 620W, twenty panels.

July through September, three months of data:

The 580W row generated 3,214 kWh in total.

The 620W row generated 3,408 kWh.

A difference of 194 kWh over three months. Annualized, about 770 kWh.

Per panel, that annualizes to 38.5 kWh — basically matching the 40 kWh I calculated for Class II regions above.

We share this data openly in our customer groups; anyone can see the raw logs.

When to buy 580

Three situations:

First, your budget is hard-capped and not a cent over. The 580 is cheaper, with more stock and shorter lead times.

Second, your inverter's DC/AC ratio is already maxed out, and swapping inverters doesn't pay.

Third, your project sits in a Class III solar region and sells all power to the grid at a low tariff. There, the 40-watt gap takes over three years to pay back — better to keep the cash.

When to buy 620

Roof area is limited and you want more capacity in the same footprint.

Places with expensive labor — Europe, North America, Japan.

Places with strong sun — the Middle East, North Africa, Australia.

Our stock

Figures as of October 15:

580W: 1,840 panels in stock at the Foshan warehouse.

620W: 620 panels in stock at the Changzhou warehouse.

620W stock has always run thinner than 580W because the production lines schedule less of it. If your order exceeds a thousand panels, lead time is twenty-five days.

That lead time is the honest number. Don't believe anyone claiming five thousand panels in stock.

How you can verify

Ask for our EL test reports, for every batch.

Ask for power calibration certificates, from third-party labs.

Ask for the three months of measured data I described above.

If you're in China, come see the goods. Foshan and Changzhou warehouses, any time.