The Callsun 200W TOPCon N-Type bifacial panel is one of the most affordable 200W panels on the market at 78 cents per watt but does it deliver in real-world testing? I ran a series of tests covering output, bifacial gain, and shade performance to find out. here is the video:
Price and Packaging
Click here for current pricing on Amazon
At the time of recording, two panels cost $310, or 78 cents per watt. For comparison, the Renogy ShadowFlux 200W comes in at around 95 cents per watt. The Callsun ships in a protective box with foam inserts, better packaging than what I received with the Renogy ShadowFlux.
One of my clients received a broken panel. He contacted Callsun customer service and received a replacement without issue, which is good to see from a smaller brand.
Output Tests
The panel had been in the sun for about an hour before testing. This matters. Cold panels produce more power, which is why some reviewers show readings above 200W straight out of the box. That’s not real-world. On a warm sunny day at the end of March the panel was producing 190W. Great performance for a 200W rated panel under real conditions.
Callsun vs Two 100W Panels in Series
I wired two 100W panels in series on one MPPT input and the Callsun on a separate MPPT, both feeding the same battery. Under identical conditions:
- Callsun: 184W
- Two 100W panels in series: 177W
The Callsun wins on output. Worth noting that the 100W panels produced a higher voltage something to consider when sizing your charge controller. The reason the Callsun performs better is because of Topcon cells which have a better temperature coefficient.
Bifacial Gain Test 1 — Back Contribution
With both panels side by side on their own MPPT inputs, both were producing identically 193W and 192W. I then covered the back of one panel with cardboard.
- Uncovered back: 192W
- Covered back: 180W
- Bifacial gain from rear reflection: approximately 12W
With a mostly green and stone background, the rear contribution was modest but measurable.
Bifacial Gain Test 2 — Front vs Back Facing the Sun
One panel faced the sun normally with its front, the other faced it with its back.
- Front facing: 180W
- Back facing: 137W
- Difference: approximately 40W
A 40W difference between front and back is actually very good for vertical solar installations. Solar fences, east-west setups, or any application where one face catches the morning sun and the other catches the evening sun. You get a longer, flatter production curve across the day compared to a single south-facing panel.
How This Panel Works — Half Cut Cells Explained
Before getting into shade testing it’s worth understanding what makes this panel different.
Standard solar cells are square. In a half-cut panel each cell is laser-cut in two. This keeps the voltage the same at 0.5V per cell but halves the current. Lower current means less resistive loss, less heat, and thinner busbars which also means more cell surface exposed to sunlight.
The two halves are placed on opposite sides of the panel and wired in parallel. Each half contains two sections in series at 12V and 4.2A each, giving 24V at 4.2A = 100W per half. The two halves combine in parallel for 24V at 8.4A = 200W total.
The practical result: the top half and bottom half of the panel are completely independent of each other.
Shade Test 1 — Single Panel, One Section Shaded
Starting at 185W unshaded. Shading one quarter of the panel:
- Output dropped to approximately 110W
The shaded half loses its contribution while the unshaded half continues producing at full power. The same result occurs whether you shade a top section, bottom section, or the entire top half you consistently lose around half the panel output, not all of it. This is the key advantage of half-cut cells over standard full-cell panels.
Shade Test 2 — Single Panel, Both Halves Shaded
When both halves are shaded simultaneously on a single panel, output dropped to zero and the bypass diodes did not activate. Here is why.
If a bypass diode fires on a single 24V panel, the panel voltage drops to 12V. A 12V battery requires at least 17-19V to charge. With only 12V available the MPPT shuts down. The bypass diodes firing would make things worse, not better. On a single panel the bypass diodes serve no useful purpose.
Shade Test 3 — Two Panels in Series, One Section Shaded
With two panels in series producing 365W at approximately 50V and 8A, I shaded one section.
Immediate result: 227W at 50V and 4.5A no bypass diode triggered yet. The shaded section reduced current but the voltage remained the same, confirming the bypass diode had not yet fired.
Then the MPPT started searching for a new maximum power point. After approximately four minutes it found it:
- New output: 266W at 34V and 7.8A
- Voltage drop: 12V (from 46V to 34V)
The 12V voltage drop confirms exactly one bypass diode activated, removing one 12V section from the circuit. The IV curve shifted left to a new maximum power point and the MPPT eventually found it.
The delay nearly four minutes has nothing to do with the panels themselves. It is determined by how frequently the charge controller sweeps the full IV curve to find the global maximum power point. The victron scans the voltage-current curve every 10 minutes to find a new potential maximum power point.
Key Takeaways
Output: 184W under real-world warm conditions against 177W for two 100W panels in series the Callsun wins.
Bifacial gain: Around 10W from reflected light off typical ground surfaces. Up to 40W difference between front and back facing direct sun making this panel genuinely useful for vertical east-west installations.
Shade performance: Half-cut cell design limits shade losses to the affected half only. The unaffected half continues at full power regardless.
Bypass diodes: Confirmed working in a series string triggered by shading two or more cells, dropping string voltage by exactly 12V. On a single panel they cannot activate usefully due to insufficient voltage headroom.
Price: At 78 cents per watt with N-Type TOPCon cells, bifacial design, IP68 junction box, and positive-only power tolerance, this panel offers strong value against more established brands.
I’m an off-grid enthusiast. I created this website to give clear and straight-to-the-point advice about solar power. I’m also the author of the book ‘Off-grid solar power simplified‘. Read more about me on my about page, check out my Youtube channel, or send me a message.