Bifacial panels are no longer a technological curiosity — today they are a standard option in most N-type TOPCon module offerings. The question is no longer "does bifaciality work" but "when does it actually pay to upgrade to a double-sided module".
What bifacial modules are
Standard bifacial panels use a glass-glass construction with N-type TOPCon cells that also generate power from the rear side of the module — from light reflected off the ground and diffuse radiation. Manufacturers state a bifaciality factor, typically 70-85% — meaning that under identical illumination, the rear side generates 70-85% of the front side's power.
In practice the rear side never receives as much light as the front, so the actual extra energy gain of the whole module is much lower than the bifaciality factor itself — a key point when planning an investment.
Ground albedo is decisive
The amount of light reflected from the ground to the rear side depends on the albedo of the surface beneath the structure:
| Ground surface | Albedo (light reflection) |
|---|---|
| Grass (green, moist) | 20-25% |
| Light gravel | 25-30% |
| Light concrete / light paving | 30-40% |
| Fresh snow | 60-80% |
| Dark roofing membrane / asphalt | 5-10% |
A bifacial installation over grass will yield noticeably less than the same installation over light gravel or concrete. Some investors deliberately change the surface under the structure (light gravel instead of grass) precisely to raise the albedo and capture the potential of bifacial modules. The cost of such a surface change — a few euros per square metre for gravel — is usually small compared to the total budget of a ground-mount system, so it's worth planning at the design stage rather than adding later.
Real gain: 5-15%, not 20-30%
Despite a bifaciality factor of 70-85%, the actual extra energy yield of a whole ground-mount installation typically falls within 5-15% compared to an identical monofacial module of the same front-side power. The upper end of this range applies to installations with light ground surfaces, adequate mounting height and wide row spacing. In winter, with snow cover, the momentary gain can be higher, but this doesn't significantly change the annual balance.
It's worth remembering that manufacturers' datasheets often quote "bifacial" power assuming an additional 10-30% from the rear side — these are lab values at full albedo of 1.0 (a white, perfectly reflective surface). Such a scenario practically never occurs in real field conditions, so when designing an installation it's better to rely on conservative PVsyst simulations accounting for the actual site albedo rather than on the maximum datasheet figures.
Mounting height and row spacing
Two mechanical parameters determine how much of the bifacial potential can actually be captured:
At a typical tilt angle of 20-30° and structure height of about 1-1.2 m, the row spacing needed to fully exploit bifaciality is usually 1.3-1.5 times the row height — more than would follow from simply avoiding winter front-side shading. This means installations designed only to minimise front shading may unknowingly lose part of the rear bifacial potential.
Trackers and bifaciality
Single-axis tracking systems pair well with bifacial modules — the changing tilt angle throughout the day improves exposure of both the front and rear side to diffuse and reflected light. In large-scale ground-mount installations, combining tracker + bifacial + light ground surface has become standard practice, as the marginal cost of the extra output is relatively low there. In Poland's climate, with a large share of diffuse radiation due to significant cloud cover for much of the year, bifaciality combined with tracking gives a more stable daily production profile than a fixed structure.
When bifaciality does NOT make sense
Cost per Wp vs. return
Glass-glass bifacial modules are typically 5-10% more expensive per Wp than standard glass-backsheet modules. With a real gain of 5-15% on a well-designed ground-mount system, the extra cost pays back within a reasonable time. On a roof installation, the same extra spend essentially never pays back — the budget is better spent on extra capacity in monofacial modules.
For example: a 100 kWp ground-mount system with monofacial modules generating about 105,000-110,000 kWh per year could, after switching to bifacial modules with good albedo (light gravel, 1.2 m mounting height), generate an extra 6,000-15,000 kWh per year — with a module cost difference of a few thousand euros for the whole system, the simple payback of the bifacial upgrade itself typically falls within 3-6 years.
Warranties and degradation
Glass-glass modules with N-type TOPCon cells typically have longer product and performance warranties than classic P-type modules — usually 30-year performance warranties, with annual degradation around 0.4-0.5% (compared to 0.5-0.7% per year for classic P-type PERC modules). The glass-glass construction is also more resistant to microcracks and moisture, which matters over the 25-30-year lifetime of a ground-mount system. In practice this means that after 25 years, a bifacial glass-glass module typically retains 87-89% of its initial power, while a classic P-type PERC module retains 80-83%, further widening the bifacial advantage over the long investment horizon.
Row orientation and layout
In ground-mount installations, east-west row orientation in a double-tilt layout combined with bifaciality is sometimes considered as an alternative to the classic south-facing layout — it allows tighter row packing without losing morning and afternoon production, while the rear side benefits from reflections on both sides of the structure. This solution mainly suits large farms where maximising installed power per hectare matters, and less often smaller commercial installations up to 1 MW.
Summary
Bifacial panels on ground-mount systems make sense when: the ground has high albedo (light gravel, concrete), the structure is mounted high enough, row spacing is adequate, and the investment horizon is long. In other cases — especially on roofs — a higher-power monofacial module at the same price is usually the better choice.
Check current module options at FNC photovoltaics and estimate the profitability of a ground-mount system with our calculator.
