Standard solar panels generate power from one side: the front face that faces the sun. The back of the panel is covered with an opaque white or black backsheet — protecting the cells but contributing nothing to energy output. Bifacial solar panels change this by replacing the opaque backsheet with a transparent material, allowing the rear cells to generate power from reflected light hitting the back of the panel.
The technology has moved from a niche specification to the mainstream very fast. In 2026, bifacial modules represent roughly 70% of new module production globally. Most major manufacturers — LONGi, JA Solar, Trina, Canadian Solar — have largely transitioned their product lines to bifacial. Understanding when the bifacial premium is justified, and when it isn't, is now a core competency for anyone specifying solar systems.
What you'll learn in this chapter
- The difference between bifacial and monofacial construction — what actually changes
- How front-side and rear-side generation work together
- The bifaciality factor: what it is and what to look for in specifications
- Albedo data for all common ground surface types
- Bifacial gain calculations by installation type
- Why height above ground matters for rear-side irradiance
- The SAT + bifacial combination and why it dominates utility solar
- How to simulate bifacial generation accurately in design software
What Are Bifacial Solar Panels?
Bifacial solar panels are modules designed to generate power from both the front face (receiving direct and diffuse irradiance from the sky) and the rear face (receiving reflected irradiance from the ground and surroundings). They differ from standard monofacial panels in one key structural element: the backsheet.
Monofacial vs Bifacial Construction
In a standard monofacial panel, the cell stack is: front glass → encapsulant → solar cells → encapsulant → opaque backsheet. The opaque backsheet is white or black polymer — it reflects light internally to the cells above it but blocks all light from entering through the rear. A bifacial panel replaces this with either a transparent backsheet or (more commonly for higher-end bifacial) a dual-glass construction: front glass → encapsulant → solar cells → encapsulant → rear glass. The rear glass is clear, allowing light to pass through to the cells from below.
Dual-glass bifacial panels (also called glass-glass) have additional advantages beyond bifacial generation: better resistance to potential-induced degradation (PID), lower long-term degradation rates (0.35–0.45%/year vs 0.5–0.6% for standard panels), and better durability in humid or harsh environments. They're heavier and slightly more expensive than transparent-backsheet bifacial, but they're the standard specification for utility-scale bifacial.
How Much Rear-Side Power?
The rear side of a bifacial panel doesn't generate as much power as the front. Cells are optimized for the front-side light spectrum and intensity. Reflected light from the ground is always less intense than direct irradiance — even very bright surfaces like white gravel reflect 35–45% of incident light, so the rear side receives at most 35–45% of front-side irradiance from the ground, plus some additional diffuse sky irradiance on the rear.
The resulting bifacial gain — additional energy from the rear side expressed as a percentage of front-side energy — ranges from as low as 3% on a rooftop with dark tiles to 30% or more on an elevated ground-mount with a high-albedo substrate. The median well-installed ground-mount bifacial system delivers 10–20% bifacial gain.
Market Adoption
Bifacial now represents approximately 70% of new module production globally. The transition has been driven by falling costs (the glass-glass premium has compressed significantly as scale has increased), clear yield advantages for ground-mount applications, and the lower long-term degradation rates of dual-glass construction. For utility-scale and large commercial ground-mount solar, bifacial is effectively the default specification. For residential rooftop, the picture is more nuanced — the gain is smaller and the premium is harder to justify without careful analysis.
Key Takeaway
Bifacial panels are now the dominant technology in new module production, but the bifacial gain varies enormously with installation conditions. On the right site (elevated ground-mount, high-albedo substrate), the yield gain is substantial. On the wrong site (close-mounted rooftop, dark tiles), you're paying a premium for minimal benefit. The installation context determines whether bifacial makes financial sense.
How Bifacial Generation Works
A bifacial panel generates power from two separate irradiance sources simultaneously. Understanding both helps explain why installation configuration affects bifacial gain so strongly.
Front-Side Generation
The front side works exactly like a standard monofacial panel. It receives global horizontal irradiance (GHI) — the sum of direct beam irradiance (from the sun disc itself) and diffuse sky irradiance (from the sky dome). In a well-sited installation, this front-side irradiance is the dominant source of power and behaves the same as any other solar panel. Front-side efficiency for bifacial panels is equivalent to equivalent monofacial technology — bifacial is an additive gain, not a trade-off.
Rear-Side Generation
The rear side receives reflected irradiance — light that has first hit a surface below or around the panel and been reflected upward. The primary source is the ground directly beneath and behind the panel array (albedo reflection). Secondary sources include reflected light from other nearby structures, diffuse sky irradiance reaching the rear of the panel around the edges of the array, and in some configurations, reflected irradiance from adjacent panel rows.
The Bifaciality Factor
The bifaciality factor (also called bifaciality coefficient) is a panel-level specification: the ratio of rear-side efficiency to front-side efficiency under standard test conditions. A bifaciality factor of 0.75 means the rear side operates at 75% of the front side's efficiency given equal irradiance on both sides.
Most modern bifacial panels have bifaciality factors of 0.70–0.80. TOPCon and HJT bifacial panels tend to be at the higher end (0.75–0.80) because their rear-side cell design is more symmetric. PERC bifacial panels are typically 0.65–0.75. When comparing bifacial panels, the bifaciality factor matters: a panel with 0.80 bifaciality will produce 7% more rear-side power than a panel with 0.75 bifaciality given identical irradiance on the rear.
The bifaciality factor is a laboratory value measured under controlled conditions. Real-world rear-side output is always lower than this figure implies, because the rear side is never receiving equal irradiance to the front — the ground reflects less than 100% of incident light, and some rear-sky view is blocked by the mounting structure and adjacent rows.
Albedo: The Ground Surface Effect
Albedo is the single most important installation variable for bifacial performance. It determines how much light reaches the rear face — and since the rear face is the additional source of bifacial gain, albedo has a direct proportional impact on how much extra energy you get.
What Albedo Means
Albedo is the fraction of incident solar radiation that a surface reflects. It's dimensionless, expressed between 0 (perfect absorber — reflects nothing) and 1 (perfect reflector — reflects everything). Practical surfaces range from around 0.05 for dark asphalt to 0.90 for fresh snow. The albedo directly multiplies the irradiance reaching the ground to give the irradiance available for rear-side reflection.
| Surface Type | Albedo Range |
|---|---|
| Fresh snow | 0.80–0.90 |
| White gravel / crushed stone | 0.35–0.45 |
| Light concrete / white painted surface | 0.30–0.40 |
| Concrete (standard grey) | 0.25–0.35 |
| Dry grass / light brown soil | 0.18–0.25 |
| Green grass (irrigated) | 0.20–0.28 |
| Dark soil | 0.10–0.15 |
| Asphalt / dark roofing membrane | 0.05–0.10 |
| Dark roof tiles (clay/slate) | 0.07–0.12 |
Improving Albedo in Ground-Mount Arrays
White gravel is the most common method of intentionally boosting albedo under ground-mount bifacial arrays. It's inexpensive (typically €3–8/m² installed), durable, requires minimal maintenance, and raises albedo from a typical bare-soil value of 0.10–0.15 to 0.35–0.45. The incremental bifacial gain from this albedo improvement can be 8–15 percentage points — meaning the gravel pays back its installation cost many times over the system's life.
Some installations use light-colored geotextile ground covers or reflective membranes for even higher albedo. These are more expensive but can achieve albedo of 0.50–0.65. The incremental gain over white gravel is usually modest enough that white gravel represents the practical optimum for most projects.
Rooftop Bifacial: Why the Gain Is Small
On a typical residential rooftop with dark tiles (albedo 0.07–0.12), very little light reaches the rear face of a bifacial panel. Close-mounted rooftop panels also have limited rear-sky view factor — the roof surface is close to the rear of the panel and the mounting hardware further reduces the sky fraction that contributes diffuse irradiance to the rear. The result is bifacial gain of 3–8% in most rooftop configurations — enough to notice in a simulation but often too small to justify the module premium on a short payback calculation.
The exception is heavy snow events. When snow covers the ground and surroundings (albedo 0.80+), bifacial rooftop panels can produce meaningfully more energy for the duration of snow cover. In Nordic countries with significant winter snow, this seasonal boost can make bifacial economically worthwhile even on rooftops.
Pro Tip
When specifying bifacial for ground-mount, include white gravel in the BOM. The gravel cost is small compared to the additional energy revenue it generates over 25 years. Make sure your simulation uses the actual measured albedo of the gravel material — supplier datasheets for solar-grade white gravel typically specify albedo values you can use directly in your design tool.
Calculating Bifacial Gain
Bifacial gain is calculated from three inputs: the bifaciality factor of the specific panel, the irradiance reaching the rear face, and the irradiance reaching the front face. The formula is:
Bifacial Gain Formula
Bifacial gain (%) = Bifaciality factor × (Rear irradiance / Front irradiance) × 100
Example: Bifaciality factor 0.75, front irradiance 800 W/m², rear irradiance 200 W/m²:
Bifacial gain = 0.75 × (200/800) × 100 = 18.75%
In practice, rear irradiance depends on albedo, mounting height, row spacing, sky view factor, and tracker position (if applicable). This is why accurate bifacial simulation requires more inputs than standard monofacial simulation — and why simple percentage estimates can be significantly wrong for specific installations.
Typical Bifacial Gains by Installation Type
| Installation Type | Typical Bifacial Gain |
|---|---|
| Ground-mount, white gravel substrate, elevated >1m | 20–30% |
| Ground-mount, grass / standard soil, standard height (0.5m) | 10–18% |
| SAT tracker + white gravel substrate | 25–35% |
| Carport structure (open, elevated) | 15–25% |
| Agrivoltaic (elevated, crop albedo varies) | 12–22% |
| Rooftop, light concrete / white membrane | 8–14% |
| Rooftop, standard grey tiles | 5–9% |
| Rooftop, dark tiles / asphalt membrane | 3–7% |
Why Height Above Ground Matters
The higher a bifacial panel is mounted above the ground, the more of the sky dome is visible to the rear face — the "rear sky view factor" increases. This matters for two reasons. First, a larger sky view factor means more diffuse sky irradiance reaches the rear directly (contributing to rear generation independent of albedo). Second, the panel can "see" a larger area of ground surface for albedo reflection, increasing the total reflected irradiance reaching the rear face.
Panels mounted at 0.3m above ground see a much smaller sky view factor on the rear side than panels at 1.0m. Studies have shown that increasing mounting height from 0.5m to 1.0m can increase bifacial gain by 3–6 percentage points on a typical ground-mount installation. This is why elevated agrivoltaic and carport structures often show strong bifacial performance even with moderate-albedo substrates.
Best Installation Configurations for Bifacial
Bifacial panels perform differently across installation types. The configurations below range from maximum bifacial benefit to essentially none.
Ground-Mount Elevated (the Best Case)
A ground-mount system with at least 0.5m clearance between the bottom of the panels and the ground surface, over a high-albedo substrate, delivers maximum bifacial gain. Typical specification: panels at 0.8–1.2m bottom edge height, white crushed stone (albedo 0.40) beneath the array, standard 30–35° fixed tilt or SAT tracking. This configuration consistently achieves 15–30% bifacial gain and is the standard utility-scale bifacial deployment.
Single-Axis Trackers + Bifacial (the Highest-Performing Combination)
SAT + bifacial is now the standard configuration for utility-scale solar on suitable terrain. Trackers contribute 20–28% yield gain vs fixed. Bifacial adds 15–30% (with good substrate). The two effects are partially multiplicative — a tracker-mounted bifacial panel in the right position gets more rear irradiance than a fixed bifacial panel at the same moment, because tracker positioning changes the sky view factor and ground illumination angle on the rear face throughout the day. Well-designed SAT + bifacial + white gravel systems can achieve total yield premiums of 35–50% over fixed-tilt monofacial — a very substantial advantage.
Carport Structures
Solar carports are an excellent bifacial application. The elevated structure with open sides provides good rear sky view factor on all sides of the panel, and the ground below is often concrete or asphalt (albedo 0.10–0.35). Even with moderate-albedo asphalt, carport bifacial systems typically achieve 15–20% bifacial gain — better than most rooftop applications, because of the improved mounting height and open rear exposure.
Agrivoltaic Applications
Agrivoltaic systems — panels elevated over active cropland — combine high mounting height with variable crop albedo. Green crops typically have albedo of 0.18–0.28, which is moderate. However, the elevated structure (often 2–4m clearance for machinery access) provides excellent sky view factor. Agrivoltaic bifacial systems typically achieve 12–22% bifacial gain depending on crop type and season. In harvested or fallow periods when bare soil is exposed, albedo can drop, reducing the gain temporarily.
What NOT to Do with Bifacial
The single worst use of bifacial panels is a low-mounted rooftop installation with dark tiles. Close-mounted panels over dark roofing have near-zero rear-side irradiance — the roof blocks almost all reflected light, and what little makes it to the rear face comes from diffuse sky light around the edges. You're paying a 3–8% module premium for a 3–5% yield improvement at best. Run the numbers before specifying bifacial for any close-mounted rooftop project.
Pro Tip
For borderline rooftop bifacial decisions, calculate the additional annual energy from the bifacial gain, multiply by the system's electricity value or feed-in rate, and compare to the module cost premium. If the simple payback on the bifacial premium exceeds 5 years, monofacial is likely the better financial choice for that specific site.
Bifacial vs Monofacial: Cost and Value
The economics of bifacial have become much clearer as the technology has matured and the premium has compressed. Here's how to frame the decision.
Current Cost Premium (2026)
In 2026, bifacial panels (glass-glass dual-glass construction) command a premium of approximately 3–8% over equivalent monofacial panels from the same manufacturer and technology generation. For a 500 kWp ground-mount project using €0.22/Wp modules, a 5% bifacial premium represents €5,500 in additional module cost — relatively small against total project cost.
This premium has declined significantly from 20–30% premiums common in 2018–2020, when bifacial production volumes were lower. As bifacial has become the mainstream production technology, the cost gap has mostly closed.
NPV Calculation: When Bifacial Is Worth It
Consider a 500 kWp ground-mount system in southern France (1,100 kWh/kWp fixed yield, 15% bifacial gain, electricity value €0.09/kWh):
- Additional annual energy: 500 kWp × 1,100 × 0.15 = 82,500 kWh
- Additional annual revenue: 82,500 × €0.09 = €7,425/year
- Bifacial module premium: 500,000 Wp × €0.22 × 5% = €5,500
- Simple payback on bifacial premium: €5,500 / €7,425 = 0.74 years
Under 1 year payback on the bifacial premium, with the system running for 25 years. The bifacial choice is obvious. This is why bifacial is the default for ground-mount: the economics are compelling whenever the installation delivers meaningful bifacial gain.
When Monofacial Is the Right Choice
The monofacial decision is right when:
- Rooftop installation with dark roof covering (albedo below 0.10) and limited panel clearance
- Any installation where bifacial gain will be under 5% and the module premium is above 5%
- Weight-constrained rooftops where dual-glass bifacial is too heavy and lighter transparent-backsheet bifacial isn't available in the target panel specification
- Small residential systems where the complexity of specifying and simulating bifacial accurately exceeds the benefit
Key Takeaway
At current premiums, bifacial is almost always worth it for ground-mount solar with controlled substrate and adequate panel clearance. For rooftop solar, the gain is often too small to justify the premium without site-specific simulation. The decision should always be based on modeled bifacial gain for the specific installation, not rule-of-thumb assumptions.
Mono PERC Bifacial vs N-Type Bifacial: Which to Specify
Not all bifacial panels are made with the same cell technology. The two dominant categories — mono PERC bifacial and N-type bifacial (which includes TOPCon and HJT) — have different performance profiles, bifaciality factors, and price points. Choosing between them affects your project's energy yield and financial returns.
Mono PERC Bifacial
PERC (Passivated Emitter and Rear Cell) adds a passivating oxide layer to the rear of a standard p-type silicon cell, reducing recombination and improving efficiency. When combined with a transparent rear sheet, PERC becomes bifacial. Mono PERC bifacial panels were the first generation of commercially successful bifacial modules, and they remain widely deployed.
Typical mono PERC bifacial specs: front-side efficiency 20–21.5%, bifaciality factor 0.65–0.75, temperature coefficient around -0.35%/°C, and rated power in the 430–550 Wp range. They represent a solid, cost-effective option for ground-mount and carport applications where the front-side efficiency doesn't need to be maximized.
N-Type Bifacial (TOPCon and HJT)
N-type cells use a phosphorus-doped silicon base rather than the boron-doped base used in p-type PERC cells. N-type silicon has lower bulk recombination, which translates to better efficiency and lower annual degradation rates. TOPCon (Tunnel Oxide Passivated Contact) and HJT (Heterojunction Technology) are the two main N-type bifacial technologies now available at commercial scale.
N-type bifacial panels offer higher bifaciality factors (0.75–0.85 for TOPCon, up to 0.90 for some HJT products), lower temperature coefficients (HJT at -0.26%/°C vs -0.35%/°C for PERC), and lower annual degradation rates (0.35–0.45%/year vs 0.5–0.6% for PERC). They cost 8–20% more per watt than PERC bifacial, but for utility-scale ground-mount with good albedo, the additional bifacial gain and lower degradation often justify the premium.
| Specification | Mono PERC Bifacial | TOPCon Bifacial | HJT Bifacial |
|---|---|---|---|
| Front efficiency | 20–21.5% | 22–23.5% | 23–24.5% |
| Bifaciality factor | 0.65–0.75 | 0.75–0.82 | 0.80–0.90 |
| Temp. coefficient (Pmax) | -0.35%/°C | -0.30%/°C | -0.26%/°C |
| Annual degradation | 0.50–0.60%/yr | 0.40–0.50%/yr | 0.35–0.45%/yr |
| Relative cost (per Wp) | Baseline | +8–15% | +15–25% |
| Best use cases | Standard ground-mount, cost-sensitive | Ground-mount, utility scale | Hot climates, space-constrained, premium residential |
Top Bifacial Panel Specs (2026)
| Panel Model | Technology | Rated Power | Efficiency | Bifaciality Factor |
|---|---|---|---|---|
| LONGi Hi-MO X6 | N-type HPBC (Back-Contact) | up to 625 Wp | 23.3% | 0.85 |
| Canadian Solar HiKu7 | Mono PERC bifacial | up to 670 Wp | 21.5% | 0.70 |
| Trina Vertex S+ (NEG9R.28) | N-type TOPCon bifacial | up to 435 Wp | 22.3% | 0.80 |
| JA Solar DeepBlue 4.0 Pro | N-type TOPCon bifacial | up to 620 Wp | 22.8% | 0.80 |
| REC Alpha Pure-R | N-type HJT IBC bifacial | up to 430 Wp | 22.3% | 0.82 |
For ground-mount utility-scale projects, N-type TOPCon bifacial (Trina, JA Solar, LONGi) represents the current price-performance optimum. For space-constrained or hot-climate commercial projects, HJT panels from REC or Panasonic command a premium that the lower temperature coefficient and higher efficiency often justify in an accurate energy yield model. Always simulate both options with your site's specific irradiance and albedo data before selecting — the financial margin between choices is sometimes narrower than the spec sheet suggests.
Compare Bifacial Panel Technologies in Your Project
SurgePV lets you simulate PERC, TOPCon, and HJT bifacial panels side by side with your site's real irradiance, albedo, and shading data — so you can make the selection with actual yield and financial data, not assumptions.
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Simulating Bifacial Systems Accurately
Standard solar simulation tools built for monofacial panels often underestimate bifacial performance — or get the numbers right for the wrong reasons. Accurate bifacial simulation requires several inputs that don't appear in monofacial workflows.
Why Standard Tools Fall Short
Most basic simulation tools model bifacial by applying a fixed percentage gain to the monofacial energy output (for example, "add 10% for bifacial"). This is fast but imprecise — it doesn't account for how the actual installation geometry affects rear irradiance. A simulation that applies a flat 10% bifacial gain to both a close-mounted dark rooftop and an elevated ground-mount with white gravel will be significantly wrong for at least one of them.
Key Simulation Parameters for Accurate Bifacial Modeling
- Bifaciality factor: Use the value from the specific panel's datasheet — not a generic assumption
- Albedo: Use the measured or specified albedo for the actual ground surface, not a default value
- Mounting height: Input the actual clearance from the bottom panel edge to the ground surface
- Row spacing and GCR: These affect how much ground between rows contributes to rear irradiance
- Sky view factor: Some tools calculate this automatically from geometry; others require an input
IEC 62670-3
IEC 62670-3 is the emerging standard for bifacial PV module performance measurement. It defines testing conditions and reporting requirements for bifacial panels, making it possible to compare bifaciality factor and rated power between panels from different manufacturers on a consistent basis. When specifying bifacial panels, require test data in compliance with IEC 62670-3 from the manufacturer — this ensures the quoted bifaciality factor is measured consistently and not optimistically estimated.
For accurate bifacial modeling in your design workflow, use solar design software that models rear-side irradiance from first principles — including sky view factor, albedo, and row geometry — rather than applying a flat percentage adjustment. The difference can be 5–10 percentage points in predicted bifacial gain, which has a meaningful impact on project financial projections.
Model Bifacial Gain Accurately in Your Designs
SurgePV's simulation engine models bifacial generation including albedo, height, sky view factor, and row spacing — giving you accurate energy predictions before specifying bifacial panels.
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The shadow analysis component of your simulation is particularly important for bifacial — inter-row shading affects not just front-side output but also the ground illumination pattern that determines rear irradiance. A row that's shaded on the front side also casts a shadow on the ground beneath it, reducing the reflected irradiance available to the rear of the row behind it.
Frequently Asked Questions
How much more electricity do bifacial solar panels produce?
It depends heavily on installation conditions. On an elevated ground-mount with a light-colored substrate (white gravel or concrete), bifacial panels can produce 15–30% more than a comparable monofacial panel. On a typical rooftop with dark tiles, the gain drops to 3–8% — barely worth the premium. The bifacial gain is maximized when the rear of the panel receives significant reflected light, which requires adequate clearance from the ground and a high-albedo substrate beneath.
Are bifacial solar panels more expensive?
The premium for bifacial over monofacial has narrowed significantly as bifacial technology has become mainstream. In 2026, bifacial panels command a 3–8% price premium over equivalent monofacial panels from the same manufacturer. Given that bifacial panels can produce 15–30% more energy in ideal ground-mount conditions, the premium typically pays back in less than 2 years for well-designed ground-mount systems.
Do bifacial solar panels work on rooftops?
Yes, but the bifacial gain is much lower on rooftops — typically 3–8% depending on roof color and panel clearance. The rear side receives very little reflected light when mounted close to a dark roof surface. Bifacial panels on rooftops do offer a meaningful advantage in snow conditions, where snow on the ground reflects significant light onto the rear surface temporarily. For most residential rooftop applications, the additional cost of bifacial panels may not justify the marginal gain.
What is albedo and why does it matter for bifacial solar?
Albedo is the reflectivity of a surface — the fraction of incident light that the surface reflects back. For bifacial solar panels, the albedo of the ground beneath the panel determines how much light reaches the rear face. Fresh snow has albedo of 0.80–0.90 (reflects 80–90% of light), while dark asphalt reflects only 5–10%. Installing white gravel under a bifacial ground-mount array can increase bifacial gain by 8–15 percentage points compared to dark soil, at a low installation cost.
Can bifacial panels be used with solar trackers?
Yes — and this is one of the highest-performing combinations in utility solar. Single-axis trackers with bifacial panels achieve bifacial gains of 25–35% because the elevated, dynamic positioning of the panel exposes the rear side to more reflected and diffuse light throughout the day. Utility-scale solar projects increasingly combine SAT trackers, bifacial modules, and white gravel substrate as the standard configuration for maximum energy yield per acre.
About the Contributors
CEO & Co-Founder · SurgePV
Keyur Rakholiya is CEO & Co-Founder of SurgePV and Founder of Heaven Green Energy Limited, where he has delivered over 1 GW of solar projects across commercial, utility, and rooftop sectors in India. With 10+ years in the solar industry, he has managed 800+ project deliveries, evaluated 20+ solar design platforms firsthand, and led engineering teams of 50+ people.