23 September 2026
Every TOPCon bifacial solar panel datasheet promises extra energy from the back side. Some brochures say "up to 30% more power." Field results are usually far lower, often in the 3 to 12% range. Both numbers can be true. The gap depends on the ground under the panels, how high they are mounted, and how the rows are spaced.
This guide explains the three numbers that decide real bifacial gain: the module's bifaciality factor, the albedo of the surface below, and the rear irradiance your layout actually delivers. We also cover why n-type TOPCon has become the default cell for bifacial modules, and when a bifacial panel is not worth the premium.
The name combines two separate ideas.
TOPCon (Tunnel Oxide Passivated Contact) is a cell technology. A very thin oxide layer and a doped polysilicon layer on the back of an n-type silicon cell cut the electrical losses that happen where the metal contact meets the silicon. The result is higher efficiency, lower light-induced degradation and a better temperature coefficient than older p-type PERC cells. Our complete guide to TOPCon solar panels covers the cell structure in detail.
Bifacial describes how the module is built. Instead of an opaque backsheet, the rear is transparent glass (glass-to-glass) or a clear backsheet, so light reflected from the ground reaches the back of the cells and produces extra current.
TOPCon cells are naturally well suited to bifacial use because both faces of the cell can collect light efficiently. That is why most new utility-scale modules in 2026 are n-type TOPCon, glass-to-glass and bifacial. The Credence Quasar N, rated at 745 Wp and over 23.5% efficiency, is one example.
The bifaciality factor tells you how well the back of the module performs compared with the front. It is measured by testing each side separately under the same light, as defined in the international standard IEC TS 60904-1-2. For background on how bifacial solar cells work, Wikipedia has a good overview.
If a module makes 100 W from the front under a given light and 80 W from the back under the same light, its bifaciality is 80%.
| Cell technology | Typical bifaciality | Typical power temperature coefficient |
|---|---|---|
| p-type Mono PERC | About 70% (± 5%) | -0.34 to -0.36 %/°C |
| n-type TOPCon | About 80% (± 5%), up to 85% | -0.29 to -0.30 %/°C |
| n-type HJT | About 85 to 90% | About -0.24 to -0.26 %/°C |
Credence's TOPCon modules, the Quasar N and Hyper Nova N, carry a bifaciality factor of 80 ± 5%.
Bifaciality is not the same as bifacial gain. An 80% bifaciality factor does not mean 80% extra energy. It only says how well the back side converts whatever light reaches it. How much light reaches it depends on the site.
Many datasheets list extra power ratings at "bifacial nameplate irradiance" (BNPI). This is a standard test condition of 1,000 W/m² on the front plus 135 W/m² on the back. It lets you compare modules fairly, but 135 W/m² of rear light is a fairly generous assumption for most Indian sites with ordinary soil below the panels.
Albedo is the share of sunlight a surface reflects. A value of 0.2 means the ground reflects 20% of the light that hits it. For bifacial modules, albedo is the single biggest driver of rear-side energy.
| Surface | Typical albedo | Bifacial potential |
|---|---|---|
| Dry asphalt | 0.09 to 0.15 | Low |
| Green grass | 0.15 to 0.26 | Low to moderate |
| Bare soil (varies with colour and moisture) | About 0.17 to 0.30 | Moderate |
| Concrete | 0.25 to 0.35 (new concrete higher) | Moderate |
| Light desert sand | About 0.40 | Good |
| White membrane or white-painted roof | About 0.60 to 0.80 when clean | High |
| Fresh snow | About 0.80 | Very high |
Sources: PVsyst's albedo coefficient reference and the Wikipedia albedo overview. Where possible, measure albedo on your own site with an albedometer for a few weeks. Soil changes colour when wet, and white roofs lose reflectivity as dust builds up.
For most Indian ground-mounted plants on natural soil, a design albedo of 0.2 to 0.3 is realistic. Plants in the Thar region with light sand can see higher values.
A simple rule of thumb gets you close:
Bifacial gain ≈ Bifaciality × (Rear irradiance ÷ Front irradiance)
The rear-to-front irradiance ratio depends on albedo, mounting height, row spacing and shading. Some examples:
Field studies back these ranges. NREL's global study of bifacial single-axis trackers found bifacial gains of about 4 to 15%, averaging around 9%, on top of the gain from tracking itself. Fixed-tilt plants on ordinary ground usually sit in the lower half of that range. The IEA-PVPS report on bifacial PV systems is a good reference if you want the full modelling detail.
So what about "up to 30% more power"? That figure is reachable on very bright surfaces, such as snow or white gravel, with high mounting. It is not a sensible planning number for a typical Indian site. For a design, use PVsyst or a similar tool with your measured albedo and actual structure geometry.
The higher the lower edge of the module sits above the ground, the more evenly reflected light spreads across the back. Raising a fixed-tilt array from about 0.5 m to 1 to 1.5 m clearance usually improves rear gain noticeably. The trade-off is a taller, costlier structure and higher wind loads.
Tightly packed rows shade the ground between them, so less light bounces up. Wider spacing raises rear irradiance, but you fit fewer modules on the same land. Modelling studies show bifacial gain rising steadily as row spacing increases. Designers usually settle on a balance between land cost and energy.
Purlins, rails, torque tubes and junction boxes all cast shadows on the back of the module. Structures designed for bifacial modules keep rails away from cell areas. Uneven rear light across cells can also cause small mismatch losses, which half-cut cell designs help reduce.
Steeper tilts let the back see more of the sky and ground. Most Indian fixed-tilt plants use a tilt close to the site latitude, which works well for bifacial modules too.
| Factor | PERC bifacial | TOPCon bifacial | HJT bifacial |
|---|---|---|---|
| Bifaciality | ~70% | ~80 to 85% | ~85 to 90% |
| Heat performance | Weakest | Good | Best |
| Light-induced degradation | Higher (p-type) | Low (n-type) | Low (n-type) |
| Cost per watt | Lowest | Slightly higher than PERC | Highest |
| Availability in India | Wide | Wide, growing fastest | Limited |
The temperature coefficient matters a lot in India. On a hot day, cells in the field can reach 65°C, which is 40°C above test conditions. A TOPCon module at -0.29%/°C loses about 11.6% of its power at that point. A PERC module at -0.35%/°C loses about 14%. That 2.4-point difference repeats through every hot afternoon for 25 years.
If budget rules out TOPCon, Mono PERC bifacial modules like the Quasar Bi 685 W still capture rear-side energy at a lower upfront cost. Our guide to glass-to-glass bifacial solar panels covers construction and handling in more detail.
In these cases, a good monofacial module often gives a lower cost per unit of energy. That said, glass-to-glass bifacial modules also bring durability benefits, such as better moisture resistance, so some buyers pick them even when rear gain is small.
1. Using the brochure maximum in the financial model. Plan with site-specific simulation, not "up to 30%".
2. Assuming a default albedo. The PVsyst default of 0.2 may be too high or too low for your site. Measure it.
3. Ignoring soiling on the ground and roof. Dust and moss reduce albedo over time. A white roof that starts at 0.7 can fall much lower after a year without cleaning.
4. Using monofacial structures. Rails running directly behind cells cut rear gain.
5. Sizing inverters on front-side power only. Bifacial modules can produce more current than the front rating suggests. Check inverter input current limits.
Credence Solar manufactures n-type TOPCon glass-to-glass bifacial modules, including the Quasar N (745 Wp, 18BB) and Hyper Nova N (650 W, 16BB), at our 2.2 GW plant in Rajkot. Learn about our R&D work, download datasheets from the download page, or share your site details on our contact page for a technical recommendation. Call +91 90330 72969 or email info@credencesolar.com.
A TOPCon bifacial solar panel combines two strengths: an efficient n-type cell with good heat tolerance, and a transparent back that turns reflected light into extra energy. With 80% bifaciality, the realistic gain on a typical Indian ground-mounted plant is around 5 to 7%, and more on bright surfaces with higher mounting. Get the albedo, height and spacing right, and bifacial TOPCon is one of the most cost-effective ways to raise energy per acre in 2026.
It is a solar module that uses n-type TOPCon (Tunnel Oxide Passivated Contact) cells in a bifacial build, usually glass-to-glass. The front captures direct sunlight, and the transparent back captures light reflected from the ground, adding extra energy. TOPCon cells offer higher efficiency and better heat performance than PERC cells.
Real gains depend on the site. On typical Indian ground-mounted plants over soil, expect about 5 to 7% more energy. Elevated arrays over bright sand or white roofs can reach 10 to 15%. Claims of 30% apply only to very high-albedo surfaces such as snow with high mounting.
Most TOPCon modules have a bifaciality factor of about 80%, with a tolerance of plus or minus 5%. Some reach 85%. This compares with about 70% for PERC and 85 to 90% for HJT. Credence's Quasar N and Hyper Nova N TOPCon modules are rated at 80 ± 5%.
Albedo is the share of sunlight a surface reflects, on a scale from 0 to 1. Grass reflects about 0.15 to 0.26, concrete about 0.25 to 0.35, light sand about 0.40, and a clean white roof up to 0.80. Higher albedo means more light reaches the back of bifacial panels.
They work well on flat commercial roofs where modules are raised on elevated structures, especially over white or light-coloured roofing. On flush-mounted residential roofs with dark surfaces, rear gain is small, so a monofacial module may give better value.
Yes, in most cases. TOPCon has higher bifaciality (about 80% versus 70%), a better temperature coefficient, and lower light-induced degradation. It costs slightly more per watt, but usually produces more energy over the plant's life, especially in hot Indian conditions.
