What Is Bifacial Solar Panel? Definition & Guide

Key Takeaways

Bifacial panels generate electricity from both their front and rear surfaces, capturing direct sunlight on top and ground-reflected light underneath
Glass-glass construction is the dominant design, offering better durability, lower degradation, and a 30-year warranty compared to 25 years for most monofacial panels
The bifaciality factor — the ratio of rear-side to front-side efficiency — typically ranges from 70% to 85% depending on cell technology
Ground-mount installations with high-albedo surfaces deliver the strongest bifacial gain, often 15–30% more energy than equivalent monofacial systems
Bifacial panels qualify for the U.S. federal ITC/IRA tax credit and are exempt from most solar module tariffs, giving them a cost advantage
Market share is growing rapidly — bifacial modules accounted for over 40% of global shipments in 2024, up from under 10% in 2019

What Is a Bifacial Solar Panel?

A bifacial solar panel is a photovoltaic module designed to generate electricity from both sides. The front face works like any standard panel, absorbing direct and diffuse sunlight. The rear face captures light reflected off the ground, nearby structures, and other surfaces — a contribution measured as albedo.

Bifacial modules achieve this dual-side capture through either a transparent backsheet or a second layer of glass in place of the opaque backsheet found on conventional monofacial panels. The solar cells themselves are designed with contacts and passivation on both surfaces, allowing photons entering from either direction to generate current.

Bifacial technology turns wasted reflected light into usable electricity. On high-albedo surfaces like white roofing membrane or light gravel, the rear side alone can contribute 20–30% of a panel’s total output — energy that monofacial panels leave on the table.

Types of Bifacial Solar Panels

Most Common

Glass-Glass Bifacial

Solar cells laminated between two sheets of tempered glass. No backsheet to degrade. Lowest annual degradation rate (0.4–0.5%/year), best moisture resistance, and typically warranted for 30 years. Heavier than backsheet designs (roughly 25–28 kg for a 72-cell module).

Lightweight

Glass-Transparent Backsheet

Front glass with a clear polymer backsheet on the rear. Lighter than glass-glass (roughly 21–23 kg) and compatible with more racking systems. Slightly higher degradation rate than glass-glass, but still outperforms opaque-backsheet monofacial modules. Common in rooftop applications where weight matters.

Budget Option

Bifacial PERC

Uses Passivated Emitter and Rear Cell technology. Bifaciality factor of 70–75%. The most affordable bifacial option and widely available. Front-side efficiency of 20–21%. Rear-side gain is moderate compared to newer cell architectures.

Premium

Bifacial HJT / TOPCon

Heterojunction (HJT) and Tunnel Oxide Passivated Contact (TOPCon) cells deliver bifaciality factors of 80–90%. Front-side efficiency of 22–24%. Better temperature coefficients than PERC, meaning less output loss in hot climates. Higher cost per watt, but lower LCOE on high-albedo sites.

Bifacial vs. Monofacial: Specification Comparison

Specification	Bifacial Panel	Monofacial Panel	Advantage
Energy capture	Front + rear surfaces	Front surface only	Bifacial: 5–30% more energy
Construction	Glass-glass or glass-clear backsheet	Glass-opaque backsheet	Bifacial: better durability
Bifaciality factor	70–90%	N/A	Bifacial: rear-side generation
Annual degradation	0.40–0.50%/year (glass-glass)	0.50–0.70%/year	Bifacial: longer effective life
Warranty	30 years (typical glass-glass)	25 years (typical)	Bifacial: 5 extra years
Weight (72-cell)	25–28 kg (glass-glass)	20–22 kg	Monofacial: lighter
Temperature coefficient	-0.29 to -0.34%/°C (HJT/TOPCon)	-0.35 to -0.40%/°C (PERC)	Bifacial: better in heat
Cost per watt	$0.18–0.28/W	$0.14–0.22/W	Monofacial: lower upfront
LCOE (ground-mount)	$0.025–0.04/kWh	$0.030–0.05/kWh	Bifacial: lower lifetime cost
Tariff status (U.S.)	Exempt from most tariffs	Subject to AD/CVD tariffs	Bifacial: cost advantage

Calculating Bifacial Energy Output

Total Energy from a Bifacial Panel

Total Energy = Front-Side Energy + (Front-Side Energy × Bifacial Gain %)

Where Bifacial Gain depends on:

Ground albedo — higher reflectivity means more rear-side irradiance (see albedo values by surface)
Module height — greater clearance from the ground allows more reflected light to reach the rear cells
Row spacing — wider spacing reduces self-shading of the rear surface by adjacent rows
Tilt angle — steeper tilts expose more rear surface to ground-reflected light
Bifaciality factor — the ratio of rear-side efficiency to front-side efficiency (typically 0.70–0.85)

Example: A bifacial panel rated at 580 W (front side) with a bifaciality factor of 0.80, installed over white gravel (albedo 0.35) at 1.5 m height, might achieve a bifacial gain of 12%. Total effective output: 580 + (580 × 0.12) = 649.6 W equivalent production.

Modeling Bifacial in Design Software

Do not simply add the bifacial gain percentage to the panel’s nameplate wattage. Rear-side production varies by hour, season, and weather — it is not a fixed uplift. Accurate modeling requires ray-tracing or view-factor calculations that account for ground albedo, module height, row geometry, and structural shading of the rear surface. Use solar design software that handles rear-side irradiance as a separate simulation layer rather than a flat percentage adder.

Practical Guidance

Model rear-side irradiance separately. Use solar design software that calculates rear-side energy based on actual albedo, module height, and row geometry — not a flat bifacial gain percentage. This matters most for ground-mount systems where rear-side contribution is highest.
Increase row spacing for bifacial arrays. Bifacial systems benefit from wider row spacing (ground coverage ratio of 0.3–0.4) to reduce rear-side shading from adjacent rows. The extra land use is often offset by 10–15% higher energy yield per module.
Specify minimum mounting height. The rear side needs at least 0.5 m clearance for rooftop and 1.0 m for ground-mount installations. Higher mounting (1.5–2.0 m) increases bifacial gain but adds structural cost — model the tradeoff.
Run shading analysis on the rear surface. Junction boxes, racking crossbars, and cable trays can shade the rear cells. Use shadow analysis tools to check for rear-side obstructions that reduce bifacial gain.

Use clamps and racking rated for glass-glass modules. Glass-glass bifacial panels are heavier and have different clamping zones than standard modules. Verify that racking hardware is certified for the specific module’s weight and dimensions. Edge clamps must grip the glass without over-tightening.
Keep the rear surface clean and unobstructed. Route cables and conduit away from the rear glass. Avoid attaching labels, stickers, or monitoring devices to the back of bifacial panels. Any obstruction reduces rear-side light capture.
Prepare ground surfaces per design spec. If the system design assumes a specific albedo (e.g., white gravel), install the ground cover material before commissioning. Incomplete or uneven coverage will cause production to fall short of projections.
Handle with care — glass on both sides. Unlike monofacial panels with a flexible backsheet, bifacial glass-glass panels can crack on both faces. Use proper lifting equipment, store vertically, and never set panels face-down on uneven surfaces.

Pitch bifacial on high-albedo sites. White membrane commercial roofs, concrete pads, and light-colored gravel make the strongest business case. Use the generation and financial tool to show the customer the production gain and faster payback period compared to monofacial options.
Lead with the 30-year warranty. Glass-glass bifacial panels typically carry a 30-year product warranty and slower degradation. Over 30 years, a bifacial system produces 8–12% more lifetime energy than a monofacial system with identical front-side ratings — even before counting rear-side gain.
Highlight the tariff exemption (U.S. market). Bifacial panels are exempt from Section 201 safeguard tariffs and most AD/CVD duties. This can make bifacial modules cost-competitive or even cheaper than monofacial alternatives after tariffs are applied.
Use conservative bifacial gain in proposals. Quote 8–12% gain for ground-mount and 3–8% for rooftop. If the system over-delivers, the customer is delighted. Over-promising bifacial gain is a common source of production guarantee disputes.

Design Bifacial Solar Systems with Accurate Rear-Side Modeling

SurgePV simulates rear-side irradiance using actual site albedo, module height, and row geometry — so your bifacial production estimates match real-world performance.

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Sources & References

Frequently Asked Questions

Are bifacial solar panels worth it?

For ground-mount systems and commercial rooftops with light-colored surfaces, yes. The 5–30% energy gain, 30-year warranty, lower degradation rate, and U.S. tariff exemption often make bifacial panels the better financial choice despite a higher upfront cost per watt. For residential rooftops with dark shingles and limited tilt, the bifacial gain is typically only 3–5%, which may not justify the price premium. Run the numbers for each project using accurate albedo and mounting height inputs in your solar design software.

How much more energy do bifacial panels produce?

Bifacial gain — the percentage increase in energy production compared to an identical monofacial panel — ranges from 5% to 30% depending on installation conditions. Ground-mount systems over high-albedo surfaces (white gravel, concrete, snow) achieve the highest gains (15–30%). Rooftop systems on dark surfaces see more modest gains (3–8%). The main drivers are ground albedo, module mounting height, row spacing, and the panel’s bifaciality factor.

Can bifacial panels be used on rooftops?

Yes, but the bifacial advantage is smaller on rooftops than on ground-mount systems. Flat commercial roofs with white TPO or PVC membrane (albedo 0.60–0.80) and tilted racking can deliver 8–15% bifacial gain. Residential pitched roofs with dark shingles and flush-mounted panels offer minimal rear-side exposure and low albedo, limiting gain to 2–5%. The glass-glass construction still provides durability and degradation benefits even when rear-side energy gain is modest. Check the roof’s structural capacity — glass-glass bifacial panels weigh 3–6 kg more per module than standard panels.