Bifacial solar panels are increasingly popular for UK solar farms and commercial installations. But are they worth the extra cost? This guide explains how bifacial panels work, when they make sense, and what to consider for your project.

What Are Bifacial Solar Panels?

Traditional solar panels (monofacial) have an opaque backsheet and only generate electricity from the front surface. Bifacial panels have a transparent or semi-transparent back, allowing them to capture light from both sides.

The rear side captures:

• Reflected light (albedo) from the ground, roof, or nearby surfaces
• Diffuse light scattered by clouds and atmosphere
• Edge effects from light entering at angles

This dual-sided generation can increase total energy output by 5-30% compared to equivalent monofacial panels - without using any additional space.

How Do Bifacial Panels Work?

Bifacial panels use the same photovoltaic cell technology as standard panels - typically monocrystalline silicon. The key differences are:

• Transparent backsheet: Glass or clear polymer replaces the opaque white backsheet
• Cell design: Cells are optimised to capture light from both directions
• Frame design: Often frameless or thin-framed to minimise shading on the rear

When sunlight hits the ground beneath the panels, some is reflected back up. The transparent back allows this reflected light to hit the rear of the cells and generate additional electricity.

The Albedo Effect

Albedo refers to how much light a surface reflects. Different surfaces provide different benefits for bifacial panels:

Bifacial vs Monofacial: Which Should You Choose?

When Bifacial Makes Sense

• Solar farms - Ground mounting with reflective surfaces delivers maximum benefit
• Trackers - Single-axis trackers elevate panels, improving rear-side irradiance
• Carports - Elevated installation with light-coloured ground surfaces
• White/light roofs - TPO or white-coated commercial roofs
• Areas with snow - Winter snow provides excellent reflection

When Monofacial Makes More Sense

• Dark rooftops - Limited benefit from low albedo surfaces
• Flush-mounted systems - No gap for light to reach rear
• Budget constraints - Lower upfront cost may be priority
• Residential installations - Typically lower ROI due to roof type

Bifacial Panels in UK Conditions

The UK's climate actually has some advantages for bifacial panels:

• High diffuse light: Cloudy UK skies scatter light effectively, improving rear-side capture. The UK receives 50-60% of its annual irradiance as diffuse light, compared to 30-40% in southern Europe — and diffuse light reaches the rear of panels more effectively than direct beam
• Lower temperatures: Cooler UK temperatures improve panel efficiency by 0.3-0.4% per degree below STC (25°C). Average UK cell temperatures are 10-15°C lower than southern Spain, giving a 3-6% efficiency advantage
• Long summer days: UK summer days are 16-17 hours — more generation time than southern European locations despite lower irradiance intensity
• Occasional snow: Winter snow events provide excellent temporary albedo boost (80-90% reflectivity)

UK Regional Yield Comparison: Bifacial vs Monofacial

Bifacial gains vary by UK region due to differences in irradiance, weather patterns, and typical ground conditions:

Note: Bifacial yields above assume grass/vegetation ground cover (20-25% albedo). With white gravel or concrete (50-70% albedo), gains increase by an additional 5-15 percentage points. All figures assume south-facing, 20-25° tilt, ground-mounted installation.

For UK solar farms on agricultural land, laying white stone or gravel between panel rows can significantly boost bifacial gains — a common practice that also helps with drainage and maintenance access. The cost of gravel (approximately £3-£5 per m²) is typically recovered within 2-3 years from the additional generation.

Durability and Warranty: Glass-Glass vs Glass-Backsheet

Bifacial panels come in two main constructions, and the durability difference is significant:

Glass-Glass Bifacial (Recommended for Solar Farms)

• Warranty: 30-year product warranty and 30-year performance warranty (typically guaranteeing 87.4% output at year 30) — vs 25-year warranties for monofacial
• Degradation rate: 0.4-0.45% per year — lower than the 0.5-0.55% typical of monofacial panels
• PID resistance: Glass-glass construction provides superior resistance to Potential Induced Degradation, a failure mode that can cause 10-30% output loss in affected panels
• Mechanical strength: Higher wind load and snow load ratings. IEC 61215 tested to 5,400 Pa front load
• Fire rating: Glass-glass panels achieve Class A fire rating without modification — important for insurance and planning on commercial rooftops

Glass-Backsheet Bifacial (Lower Cost Option)

• Warranty: 25-year product warranty — same as monofacial
• Lighter weight: 20-25% lighter than glass-glass, easier for rooftop installation
• Lower cost: 5-10% cheaper than glass-glass bifacial
• Reduced rear-side gain: Backsheet transmittance is lower than glass, resulting in 2-5% less rear-side generation compared to glass-glass

Cost vs Benefit Analysis

Let's look at a typical UK solar farm comparison:

For solar farms with good albedo conditions, bifacial panels typically deliver strong ROI. For commercial rooftop installations on dark surfaces, the decision is less clear-cut and depends on specific project economics.

Frequently Asked Questions