How the Back of a New Solar Panel Just Changed Everything

Imagine getting up to 30% more power from the same solar panel setup, without any fancy new chemistry or physics. It sounds wild, but it’s happening thanks to a simple change: putting solar cells on both sides of the panel. Now, one company has made a huge leap, with the back of their panels working at 91.7% efficiency compared to the front. What’s even more interesting is they achieved this using technology that was thought to be less effective and cheaper.

Why Bifacial Solar Panels Matter

Bifacial solar panels, or BPVs, work much like the standard ones you’re probably familiar with. At their core, solar cells are made of silicon. When sunlight hits the silicon, it knocks electrons loose. An electric field inside the cell then directs these electrons and the resulting holes to different contacts, creating electricity. If these electrons and holes recombine before reaching the contacts, the energy is lost as heat. This is why typical solar panels have an efficiency of around 22%.

Bifacial panels aim to capture more energy. You might wonder why you’d put cells on the back, facing away from the sun. Won’t they just be in shade? Not necessarily. This is where something called albedo comes into play. Albedo measures how much light bounces off a surface. Things like snow, sand, and even some white roofs have high albedo, meaning they reflect a lot of light.

This reflected light can still be captured by the back of a bifacial panel, even on cloudy days or in urban environments. Plus, solar panels are often angled, and the sun moves throughout the day. Bifacial panels can catch some of this indirect or reflected light, acting like extra players in the outfield catching fly balls.

Key Takeaways

• Bifacial solar panels capture sunlight on both sides, increasing overall energy output.
• Albedo, the measure of light reflection, is key to how bifacial panels work, especially with surfaces like snow or white roofs.
• New technologies like Topcon are improving bifacial efficiency while keeping costs lower than older, high-efficiency methods.
• While bifacial panels are more expensive upfront, they can offer significant long-term gains, especially in environments with high albedo.

How Tongwei Achieved Record Efficiency

Tongwei’s new panels hit an impressive 91.7% bifaciality. This figure tells us how well the back of the panel performs compared to the front. So, how did they do it?

It comes down to three main technological advancements:

1. Topcon Solar Cells: This stands for Tunnel Oxide Passivated Contact. These cells are known for being stable and efficient. The thin silicon oxide layer in Topcon cells acts as a special barrier. It lets electrons pass through to create electricity but stops holes from recombining with them, which prevents energy loss.
2. Inverse Pyramid Architecture: These tiny pyramids on the back of the cell help capture more light. Instead of light just bouncing off, the pyramids bounce photons around until they are absorbed.
3. Zebra Crossing Passivation Contact Layers: This is a bit more technical. The researchers found that the valleys of the pyramid structures could be areas where passivation (a way to reduce defects) wasn’t perfect. They used a laser to heat and fuse these areas, creating different passivation layers on the peaks and valleys. This likely resulted in a pattern that looks like zebra stripes, improving electron collection.

These advancements allow Topcon cells to reach about 80-85% bifaciality, which is better than the 70% typical for PERC cells. However, the highest efficiency has been with Heterojunction (HJT) cells, reaching 92-95% bifaciality. The catch? HJT manufacturing is much more expensive ($70 million per gigawatt) compared to Topcon ($40 million per gigawatt). Topcon also allows for upgrades to existing manufacturing lines, making it a more cost-effective path.

The Cost and Installation Considerations

Bifacial panels are generally more expensive than standard monofacial ones, often by 10-20% for installation. This higher upfront cost can extend the payback period for the investment. For a typical home, monofacial panels might pay for themselves in 7-10 years. Bifacial panels, due to their higher initial cost, could take a few years longer.

Beyond the price, there are other factors:

• Dirt and Debris: Light and dirt can get trapped between the ground and the panel, which might require more maintenance.
• Mounting Systems: Traditional mounting brackets might cover parts of the back of the panel. Upgrading to bifacial means needing new brackets and mounts.
• Panel Angle: Bifacial panels often need to be installed at a different angle than monofacial ones to maximize their performance, which can complicate retrofitting existing systems.

These factors mean that whether bifacial panels are the right choice depends heavily on your specific situation and location, especially how much reflective surface (albedo) is around them.

Real-World Impact and Future Outlook

While the 91.7% bifaciality is a lab measurement, real-world gains are still significant. Most installations see about 10-20% more power from bifacial panels. This can range from 5-10% with standard grass underneath, up to 15-20% on white rooftops, and even 30% with fresh snow. Ground-mounted farms with tracking systems typically see 10-15% gains.

The real breakthrough with Tongwei’s technology is achieving high performance without the premium cost. By using cheaper Topcon technology to reach 91.7% bifaciality, they’ve closed the gap with expensive HJT cells while cutting costs by 40%.

These panels also show improved current density, meaning more usable energy per square centimeter. This translates to enough extra power for things like running a refrigerator. The front panels have an efficiency of 25.67%, and the rear ones are at 24.21%, both well above industry standards.

While Tongwei’s panels are a strong prototype demonstration, they still need to be proven in mass production. However, Tongwei already has the infrastructure to scale up production, which is often the biggest hurdle for new technology. Bifacial panels are steadily becoming more popular as the technology matures and costs decrease. Despite the challenges, the future for bifacial solar panels looks promising.