Bifacial solar modules are a type of photovoltaic (PV) panel designed to capture sunlight and generate electricity from both sides – the front and the back. This is in contrast to traditional monofacial solar modules, which only absorb light from their front surface.
Here's a more detailed breakdown:
Key Differences:
Monofacial:
Opaque back surface (typically a white or black backsheet).
Generates electricity only from direct sunlight hitting the front.
Bifacial:
Transparent back surface (usually glass or a clear backsheet).
Generates electricity from direct sunlight on the front and reflected light (albedo) on the back.
How They Work:
Front Side: Functions like a traditional solar panel, absorbing direct sunlight and converting it into electricity via the photovoltaic effect.
Back Side: Captures albedo light – sunlight that has reflected off the ground or surrounding surfaces. The amount of albedo light depends on the reflectivity (albedo) of the surface. Light-colored surfaces like snow, white gravel, or sand reflect more light than darker surfaces like grass or asphalt.
1. Increased Energy Yield:
The Problem: Traditional monofacial solar panels can only absorb sunlight from one side (the front). The back side is opaque and doesn't contribute to power generation.
The Bifacial Solution: Bifacial solar panels are designed to capture sunlight from both the front and the back sides. The back side is typically made of a transparent material (like glass or a clear backsheet) that allows sunlight reflected from the ground or surrounding surfaces (known as albedo) to be absorbed and converted into electricity.
Benefit: This ability to capture light from both sides results in a significant increase in energy yield compared to monofacial panels. The amount of additional energy gained depends on factors like the albedo of the ground surface, the mounting height, the tilt angle, and the geographic location.
2. Higher Energy Production in Certain Conditions:
Morning and Afternoon: Bifacial panels can be particularly effective in the morning and afternoon when the sun is at a lower angle and more light is reflected from the ground.
High Latitudes: In regions closer to the poles where the sun is lower in the sky for much of the year, bifacial panels can capture more diffuse and reflected light.
Snowy Environments: Snow has a very high albedo, meaning it reflects a large percentage of sunlight. Bifacial panels installed in snowy areas can see a substantial boost in energy production from the light reflected off the snow.
Overcast Days: Even on cloudy days, bifacial panels can capture diffuse light reflected from the ground, leading to higher energy yield than monofacial panels.
3. Optimized for Specific Applications:
Ground-Mounted Systems: Bifacial panels are ideal for ground-mounted systems, especially when installed over light-colored surfaces like sand, white gravel, or even specially designed reflective membranes.
Carports and Awnings: These structures often have open space underneath, allowing for significant light reflection onto the back of bifacial panels.
Vertical Installations: Bifacial panels can be installed vertically as fences or facades, capturing sunlight from both sides as the sun moves across the sky.
4. Reduced Levelized Cost of Energy (LCOE):
While bifacial panels may have a slightly higher upfront cost than monofacial panels, their increased energy yield can lead to a lower LCOE over the system's lifetime.
Benefit: This means that the electricity generated by a bifacial system can be more cost-competitive with other energy sources.
Factors Affecting Bifacial Gain:
Albedo: The reflectivity of the ground surface is a crucial factor. Higher albedo (lighter surfaces) results in greater bifacial gain.
Mounting Height: Increasing the mounting height allows more light to reach the back of the panels, but there are diminishing returns beyond a certain point.
Tilt Angle: The optimal tilt angle for bifacial panels may be slightly different than for monofacial panels to maximize both front and rear-side light capture.
Panel Design: The design of the bifacial panel itself, including the transparency of the backsheet/glass and the cell technology, also influences performance.
Geographic Location: Latitude, climate, and weather patterns all play a role in bifacial performance.
Summary:
Bifacial solar modules are an innovative technology that leverages reflected light to increase energy yield. They are becoming increasingly popular, particularly in utility-scale and commercial solar projects, and are often combined with other advanced technologies like PERC, multi-busbar, and half-cell designs to maximize performance. They represent a significant step towards more efficient and cost-effective solar energy generation.