Which power class is cheapest per watt

In short: In Poland a watt costs a median 0.157 EUR/W before tax in the 400 to 449 W class and 0.134 EUR/W at 600 W and up, where the middle half of offers runs from 0.128 to 0.144 EUR/W. Inside the same shop, 39 of 46 shops listing both 450 to 499 W and 600 W and up price the bigger class lower per watt. Hold each median against its class's spread before you pick a size: where the spreads overlap, the offer you pick matters more than the class.

A shop's module prices rise with the watts. The question is how fast. If a 600 W module costs less than one and a half times a 400 W module, its watt is cheaper, and the offers shops list today show whether it does.

Does a watt get cheaper on a bigger module?

Two checks decide it. Does the median price per watt before tax fall from one 50 W power class to the next? And is that fall larger than the spread of prices inside each class? If it isn't, two offers picked from neighbouring classes can go either way, and the class tells you little.

The prices are for modules only. Mounting, inverter, cabling and labour aren't in them, and some of those costs follow the number of modules rather than the watts.

How the offers are split into power classes

The pool is the one from solar panel price per watt by market: 2,685 single rooftop module offers from 117 shops, priced before tax and converted to euro. The watt is the rated power the shop printed, which is the module's power at standard test conditions: 1000 W/m², 25 °C cell temperature, AM1.5 spectrum.

Each offer goes into one of five classes by that rating. Every class is 50 W wide, except the last, which takes everything from 600 W up. The exact filters are in Figures and denominators below the article.

Two views: Poland, and every market but the United States

Price levels differ between markets. Mix them freely and you mostly measure which markets sell which sizes, not what size does to price.

The first view is Poland on its own. I picked it because every class there held offers from at least 20 shops when this article was written; the Shops column gives today's count.

The second is every market in the pool except the United States. I left US shops out because their price level sits above the European one (the market article shows it) and because they hold a large share of the smallest class: 132 of its offers across all markets, against the total in Figures and denominators. Left in, they would make the 400 to 449 W class look dear for a reason unrelated to its size.

That view isn't a European figure. The pool covers 18 markets, and every one outside Europe other than the United States stays in.

Price per watt by power class

Read each table two ways. Down the Median column, see how far the price moves from one class to the next. Along each row, see how wide the middle half is: the band from the 25th to the 75th percentile, where half of a class's offers sit.

Poland:

Every market but the United States:

Where the step between two medians is smaller than either class's middle half, the class barely separates the offers: pick one from each and either could be cheaper. Where one class's middle half sits wholly below the next one's, the gap is real.

A class whose middle half is much wider than its neighbours' holds very different offers under one size. One reason the classes differ in more than size is further down.

The same shop, two classes

Medians mix shops. A shop that sells mostly big modules may simply be a cheap shop, which would make big modules look cheap for the wrong reason. So each shop outside the United States gets its own median price per watt per class, and two classes are compared only where a shop lists both.

Read the third column against the second. A count near half of the shops listing both means the size makes no consistent difference inside a shop; a count near all of them means it does. A negative median difference means the bigger class is cheaper per watt.

Bigger classes, longer modules, different cells

Some offers name a module precisely enough for us to match it to our catalogue, and its datasheet then shows what else changes with the class. PERC is an older cell technology than TOPCon and the other n-type cells.

The table sets the smallest Polish class against the largest. Read the length for roof fit, and the PERC count against the matched offers for how much of each class is the older cell type.

Where the two rows differ in length and in cell mix, the price gap between the classes is partly a gap between module generations. The extra watts are only part of it.

Two modules, real offers

The rows behind the medians look like this. I picked the two modules by one rule: the module with the most shop offers in our catalogue in the 450 to 499 W class when this was written, and the same for 600 W and up. Nobody paid for a place here.

The most-offered module in the 450 to 499 W class when this was written:

Cheapest current offers for JA Solar JAM54D40-470/LR, prices read 9 Oct 2026.

Each price is the figure the shop printed, on its own side of VAT.

The most-offered module from 600 W up when this was written:

Cheapest current offers for Jinko Solar JKM620N-66HL4M-BDV, prices read 9 Oct 2026.

Each price is the figure the shop printed, on its own side of VAT.

Each row prints the shop's own price, in its own currency and on its own side of VAT. For a price per watt, take the price without VAT and divide it by the rated power in the module name. The rows are ordered by the price before VAT in a common currency, so a net price can sit between two higher prices that include VAT; gross or net shop prices explains why.

What this means when you buy

Pick the size for the roof, then shop inside it

If the class medians sit closer together than the width of one class's middle half, choosing the offer does more than choosing the class. That's how I would shop: settle the module size the roof suits, then compare offers hard inside that size.

A cheaper watt only helps if the module fits

Bigger modules are longer; the length table above gives the medians. On a small or broken-up roof, fewer large modules can leave more of it empty than more small ones would. You end up with fewer watts at a lower price per watt, which saves nothing.

The roof-fit selector counts how many modules of each size fit a roof, tells you which size gives the most kWp, and prints the cheapest offer we hold for each size.

Mounting and labour are paid per module

Clamps and the time spent lifting and fixing each module are paid per module. Fewer, larger modules for the same array spread those costs over more watts. This data doesn't measure that, because the prices here are for modules alone.

The effect grows with the job. On a large flat roof the module count runs into the hundreds, and every module brings its own share of racking and handling.

Compare per watt, on the same tax basis

A cheap listing with a lower rating can cost more per watt than a dearer one with a higher rating. Take a 420 W module at 80 EUR net: 80 / 420 = 0.190 EUR/W. A 500 W module at 90 EUR net works out at 90 / 500 = 0.180 EUR/W. The dearer listing buys the cheaper watt.

Check whether the shop printed its price with or without VAT before you divide; our offers list marks it next to every price. Type in the offers you are weighing and the figure below ranks them the same way, against the market median before tax.

The rated watts are a nameplate figure with a power tolerance around them, so two modules on the same label won't necessarily deliver exactly the same.

Watts per square metre are a separate question

A larger module isn't necessarily a more efficient one, since extra area adds watts by itself. If roof area is your limit, compare module efficiency instead. The solar payback calculator turns a price into a payback time, and the levelized cost of electricity prices the watt over the system's life.

Limits of this data

These are asking prices. A shop may sell below its listed price to installers or on bigger orders, and shipping isn't included. Pallets and multipacks are out of the pool, so for a full pallet the gap between classes may look different; pallet or single module compares the two.

The class comes from the power the shop printed. Length and cell technology come from the manufacturers' datasheets in our catalogue, so they rest on matched offers only: compare the Matched offers column with the class's Offers count before you lean on them.

The pool counts offers, not shops, so a shop with a long list of one size weighs more in that class's median. The same-shop comparison checks for that, but it rests only on the shops that list both classes.

Prices are converted at the ECB reference rate of the day each offer was read. An exchange rate move can shift a non-euro market's figures without any shop changing a price.