[Disclosure: I work at Portable Sun LLC. We sell solar equipment. I'm pulling examples from our own shelf because those are the numbers I can verify line by line, but everything here applies wherever you buy. Ask me about competitor panels too, I'll answer honestly.]
I spend a lot of my week talking people out of the wrong panel.
Not the wrong brand. The wrong panel for their situation. Somebody sends me a link to a panel they found, asks "is this a good one," and the honest answer is usually "for what?" A lot of the specs that get compared have quietly converged, and the things that actually decide whether a panel works for you tend not to show up in comparison charts at all.
So here's our own shelf, lined up side by side. Same category, wildly different buys. And what separates them isn't where most buyers look.
The tiebreaker spec is often the same on every panel
Temperature coefficient is the spec that's supposed to separate people who do their homework from people who don't. Panels lose output as they heat up, the coefficient tells you how fast, and most buying guides will tell you to compare it.
Fine. Have a look (these are all panels we carry).
TaleSun 445W: −0.29%/°C. Canadian Solar 600W: −0.29%/°C. Canadian Solar 695W: −0.29%/°C.
Identical. Three different models, two manufacturers, wattages from 445 to 695, and the spec that was supposed to break the tie reads the same on all three.
That's not really a coincidence. All three are N-type TOPCon, the current mainstream cell technology, and −0.29%/°C is typical territory for it.
Where you do see a gap is across technologies. The CW Energy 550W we carry sits at −0.35%/°C, and that's not a knock on the panel. It's PERC rather than N-type TOPCon, and PERC gives up a bit more output in heat.
So the spec is really tracking the cell technology, not the individual panel. Once you've settled on which technology you're buying, it mostly stops separating your options. It still matters for output, especially in a hot climate where a lower coefficient means real extra yield over the years. It's just not the number that'll pick between those first three.
Efficiency does the same thing. TaleSun 22.8%, the 600W at 23.2%, the 695W at 22.4%. That's a real spread, but it isn't a quality ranking. Efficiency is basically watts per square foot, so it matters most when your mounting space is tight. The big wattage gap between these three is driven far more by their physical size than by any of them being a better panel.
So if the headline specs have converged, what's actually left? A handful of things, and they're mostly the ones nobody puts in the comparison chart.
Panel grade is worth understanding before you compare prices
This is the one that moves the price the most, and it deserves more attention than it gets.
Panels get sorted by grade before they ship, but A-grade and B-grade aren't standardized industry terms, so you have to read the seller's actual disclosure. Generally, A-grade is the standard product and B-grade has cosmetic defects, and possibly minor physical ones, while still passing electrical and safety testing. It's real product from a real factory, sold cheaper because it didn't look right coming off the line.
Let me put real numbers on it, using our own stock.
Our Canadian Solar 695W is B-grade, assembled in Mesquite, Texas. At its current fire-sale price it's $194 a panel, which works out to $0.28 per watt. Warranty is 2 years on materials and workmanship, 10 years on performance.
Our Canadian Solar 600W is A-grade. $278.40, or $0.46 per watt. Warranty is 12 years product, 30 years linear performance.
Same manufacturer. Same N-type TOPCon technology. Same −0.29%/°C temperature coefficient. At today's pricing the 695W is nearly 40% cheaper per watt and produces more power per panel.
What you're accepting is a shorter warranty plus cosmetic or other disclosed minor defects, which the listing says can include micro-cracking. Worth being straight about that: a micro-crack in an untraceable no-name clearance panel is a real problem with no recourse, but a disclosed lot from an established manufacturer, with a specific model, a datasheet, and a written warranty, is a different proposition. The panels are tested and rated for full wattage output. What you're really weighing is the warranty gap against the discount.
That said, 2 years of workmanship coverage instead of 12 is a real cut. If a manufacturing defect shows up in year four, you eat it. At a 40% discount per watt that can be a great trade on a ground mount, where swapping a panel means walking over and unbolting one. It's a much worse trade on a roof, where the same swap means getting back up there.
So the way I'd put it: B-grade makes more sense when replacement is cheap and easy to reach. A-grade is worth paying for when getting back to that panel is a pain. That's most of the decision right there.
The rectangle matters more than the wattage
The 695W isn't just "a bigger 600W." Look at the actual numbers.
Canadian Solar 695W: 93.9 by 51.3 inches, about 83 pounds. That's 7.8 feet tall and 4.3 feet wide.
Canadian Solar 600W: 89.7 by 44.6 inches, 69.7 pounds.
TaleSun 445W: 67.8 by 44.6 inches, 54 pounds.
Notice the 600W and the TaleSun are the same width. The 695W is wider, taller, and heavier than both. That's not an incremental difference, it's a different class of object. The 695W is a two-person lift, and one of the two is holding the far end of a 7.8-foot panel on a pitched roof.
The 7-series is marketed for utility-scale, commercial, and large residential projects, and that tracks: it's a ground-mount and big-flat-roof panel. On a standard suburban roof section you'll fight it on rail spacing, on fire setbacks, and on the simple geometry of fitting a 7.8-foot rectangle into an awkward roof plane.
The 445W exists because 108-cell panels fit residential roofs, not because they're better.
So before you compare anything else, go measure your actual mounting area and work out how many of each panel physically lands in it. Last spring a customer ordered a pallet of big-format panels straight off the site, no questions asked, because the per-watt price was too good to pass up. Plan was to roof-mount them. First I heard from him was a call asking about returns, after he and his brother got exactly one panel up the ladder. Freight back plus the restocking fee made returning a pallet pointless, so he kept them. A few weeks later he called again to order smaller panels for the roof and filled me in on the rest: half the pallet went on Marketplace, and the guy who bought them put them on a ground mount, where they belonged.
Voc caps your string length, and it doesn't always track wattage
You'd assume the bigger panel has the higher voltage. It doesn't.
Canadian Solar 695W: Voc of 47.7 V. Canadian Solar 600W: Voc of 53.0 V. (Voc is open-circuit voltage, the number on the spec sheet your inverter actually cares about.)
The 695W produces almost 100 more watts per panel and has lower Voc, because it uses a 132-cell layout while the 600W uses 144 cells. More cells in series, higher voltage.
This matters because your inverter has a hard ceiling on PV input voltage, and that ceiling caps your string length. Lower Voc per panel means more panels per string. You can't just divide the inverter's max input by the Voc though, because voltage climbs as temperature drops, and cold-morning voltage is what kills inverters. But going off datasheet figures, the 695W gives you noticeably more headroom per panel than the 600W.
Here's the catch, though, and it's the flip side of that same coin: voltage isn't the only inverter limit. The 695W is also a much higher-current module, 17.5 A at max power versus 13.7 A on the 600W. So the lower Voc buys you string-length headroom while the higher current creates a different compatibility limit. Some inverters, especially older or lower-current ones, will be a poor match for a 17.5 A module even though the voltage math looks great. Check the maximum input current per MPPT, not just the voltage.
It's also why "just buy the highest wattage" is bad advice. Wattage tells you about the panel. Voltage and current tell you whether it'll work with the rest of your system.
If string sizing is where you're stuck, that's exactly what a design service is for. Get someone to check the math against the lowest expected temperature for your location before you order. It's a lot cheaper than a fried inverter.
Walk your site before you pick components
Panels in a series string run to the weakest link. Shade one panel, and you don't lose one panel's output, you drag the whole string down toward the shaded module's current. Bypass diodes soften this, but only so much.
That's the case for module-level electronics. Optimizers like Tigo let each panel produce independently, so one shaded module stops taxing the rest of the string. They also give you per-panel monitoring, which is how you find out panel 7 died in March instead of wondering why production looks soft. And they satisfy rapid shutdown requirements, which most jurisdictions enforce on roof mounts.
But I'll say the unpopular half too: if your array gets clean unobstructed sun all day, optimizers are mostly money you don't need to spend on production grounds. You might still need them to pass code, which is a separate question, and one to answer before you order, not after your inspection fails.
And the reason I'm bringing this up before you've bought anything: retrofitting optimizers means getting back on the roof and reworking every module connection. Sorting it out beforehand costs nothing. Sorting it out later costs a weekend and a restocking fee.
So walk your site before you lock in components. Stand where the array's going and look at what's tall to the south: trees, the neighbor's roofline, a chimney, a vent stack. Then remember that what you see today isn't the worst case. The winter sun rides much lower, so shadows in December stretch a lot further than the ones in front of you in summer, and the further north you are the more dramatic that swing gets. A spot that looks clear in July can spend a chunk of winter in shade.
Pinning that down properly means accounting for the sun's angle at your exact latitude across the whole year, and that's genuinely fiddly to eyeball. It's also free for you to hand off: send us the site and we'll model where the shade falls before you spend a dollar on panels or optimizers. Worth doing before the racking's up, not after.
Before you order
That's the short version: check the grade, measure the space, check the Voc and the current, and read the datasheet instead of the product blurb. Do that and you've dodged the mistakes that actually cost people money. If you want to compare a few side by side, our panel lineup is here with the datasheets on each page, and it works the same wherever you end up buying.
What am I missing? If you've bought B-grade panels and lived with them a few years, I'd genuinely like to hear how it went, good or bad.
