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How ‘Silicon Ball’ Contributes to BIPV: Solar Facades & Windows

The building-integrated photovoltaics (BIPV) market is set for significant growth at a compound annual growth rate (CAGR) of around 20% from 2024 to 2032. 

Currently, while c-Si and thin-film panels are dominant technologies in this market, there are still challenges in their real-world applications that can potentially hinder the development of BIPV.

The emergence of ‘silicon ball’ presents a promising solution for BIPV, combining advantages that other technologies may lack. This article will walk you through ‘silicon ball’, along with a comparison with other BIPV solutions.

Silicon Ball-Based Transparent Solar Module
Source: SOFTPV

Background of Silicon Ball

Restricted Use of Traditional c-Si Technology

While well-established, traditional c-Si technology is largely confined to rooftop solar installations within the domain of BIPV. This restriction stems primarily from the fact that c-Si materials are relatively thick (150-200 μm), making them unsuitable for applications in building facades or windows where transparency is a crucial requirement.

Plus, good transparency cannot be achieved by merely reducing their thickness, as slicing these materials too thin would significantly compromise efficiency as well as make the panels more prone to cracking or shattering under mechanical stress or impact.

Limited Supply of CdTe Technology

Though we have concluded in this article that CdTe technology is a proven BIPV solution for building façades or windows, the supply of its raw materials is relatively limited compared to silicon. This could pose a challenge, particularly if there are plans for large-scale expansion.

The Team Behind Silicon Ball

As the BIPV market continues to grow, teams worldwide are actively seeking innovative solutions to overcome the challenges that arise during the development of BIPV projects.

The concept of ‘silicon ball’ was first proposed and implemented by the Korea-based solar technology startup SOFTPV.

Founded in 2017, this company is led by Dr. James Hyeonwoo Ahn who has over two decades of experience in the fields of solar and electronic materials. Since its establishment, the company has been dedicated to silicon-based solutions for BIPV. 

Under the support of a think tank comprising professors, researchers and professionals with PhDs in various fields including electrical engineering, materials science and more, SOFTPV keeps refining its silicon ball-based BIPV solutions and strives for their commercialization.

What Is a Silicon Ball? How Is It Manufactured?

As noted by the company, a silicon ball is a spherical solar particle made with polysilicon. 

Fabrication of Different Layers

The manufacturing process involves melting the boron-doped polysilicon material at high temperatures and then cooling it under controlled conditions to form balls of a specific size, ranging from 0.35 to 1.8mm in diameter. 

Next, the n-type semiconductor layer, formed by the diffusion of phosphorus oxychloride (POCl3), is added onto these balls. This addition, combined with the existing p-type material, creates the p-n junction.

Then, a passivation layer is applied to reduce charge carrier recombination, followed by the addition of an anti-reflection layer to maximize light absorption, similar to traditional c-Si panels.

Lastly, a transparent conductive oxide (TCO) layer is added to collect current, reduce series resistance and enhance the overall performance of these balls.

Formation of Electrodes

The formation of the electrodes of these silicon balls is a significantly more intricate process, as it involves manipulation on an object of only around 1mm in diameter!

Firstly, one side of the silicon ball is cut open and polished. The center of the polished surface, namely the p-type material area, is processed to be the anode (+) by printing conductive paste and conducting sophisticated thermal treatment, whereas the outer periphery becomes the cathode (-) using similar processing.

The schematic below illustrates the locations and structures of the electrodes.

Electrodes of A Silicon Solar Ball

What Is the Silicon Ball-Based BIPV Solution?

Following the fabrication of multiple layers and the formation of electrodes, a complete silicon ball is created. Essentially, such a ball serves as a solar cell equivalent to those found in traditional, flat c-Si panels.

Module Assembly

Just akin to traditional panels, these silicon solar balls must be connected together to form a complete system to deliver specific power outputs.

In BIPV applications, a panel when used in the facade or as a window glass should possess a certain amount of transparency. Otherwise, it wouldn’t make any sense.

These silicon solar balls are connected in a distinctive manner to provide flexibility in transparency.

The substrate used to assemble these silicon balls features electrical circuit patterns via printing, regardless of whether it's a rigid laminate or a flexible film.

The solar balls are then mounted onto the substrate using the surface mount technology (SMT) process. The electricity generated by the silicon balls flows through the printed circuit which is configured in series and/or parallel connections to supply the required voltage and current.

Advanced Features

The film used as the substrate is transparent by itself. Further, the overall transparency of such a type of solar module can be adjusted by controlling the size and spacing of the silicon balls. In other words, larger balls and smaller spacing will lead to higher energy yield but lower transparency; and vice versa.

Notably, unlike traditional rigid, flat substrates, the film substrate utilized in these silicon ball solar modules is bendable and can be fashioned into tailored shape and dyed with color. These properties unlock vast possibilities in BIPV applications.

Additionally, the substrate printed with PCB circuit also serves as a platform and can be equipped with electronic components like LEDs, sensors, chips and micro-batteries to create a smart BIPV solar module. This versatility definitely takes imagination to new heights in BIPV.

Silicon Ball-Based BIPV vs. Other Solutions

Undoubtedly, this silicon ball-based BIPV solution presents a unique departure from other available BIPV solutions.

For one thing, this silicon ball module presents a unique approach to make silicon-based modules transparent enough for adoption in building facades and windows. The three-dimensional sphere shape design realizes minimum visual obstruction while offering a maximum amount of surface area for absorption.

This approach stands in stark contrast to the approach utilized in CdTe BIPV panels. The latter adjusts transparency by controlling the thickness or density of its continuous photovoltaic materials. 

And unlike silicon ball panels, these transparent CdTe solar panels typically have their photovoltaic layer and associated layers sandwiched between two tempered glass to form a complete module. They are generally installed for new facades or windows, or used to replace current materials.

While they can be technically assembled and installed like transparent CdTe BIPV panels, these silicon ball solar panels offer a more streamlined solution, allowing for simple attachment to the interior surfaces of facades and windows. This advantage enables a remarkably seamless process for retrofitting or 'solarifying' existing building facades and windows.

The Pros & Cons of This BIPV Solution

In summary, when compared to existing solutions, silicon ball panels present a mixed bag of advantages and disadvantages for BIPV applications.

Pros of Silicon Ball Solar Modules

  • Abundant Material Supply: In contrast to the cadmium and tellurium used in CdTe panels, silicon for these silicon ball panels is plentiful in supply, laying the groundwork for future mass production.
  • Versatility: The transparency and power output of these panels can be tailored by adjusting the size and spacing of the silicon solar balls. By leveraging advanced circuit printing technology and flexible film substrates, these panels can be readily tailored to meet the unique requirements of various BIPV projects.
  • Easy Installation: They can be assembled and installed with ease, just like transparent CdTe panels, but they take it to the next level by enabling the conversion of existing building envelopes into solar generators by simply attaching themselves to the surfaces.
  • Smart Upgrade: By integrating smart electronics on their substrate, they become an all-in-one multi-functional module that works for any specific application, such as data collection, monitoring, IoT communication and signaling.

Cons of Silicon Ball Solar Modules

  • Reliability to Be Proven: By and large, this silicon ball solar technology is still being refined and awaiting a catalyst to propel its commercialization forward. Any manipulation of these balls with a diameter of 0.35 to 1.8mm necessitates extremely precise work. Compared to existing established transparent CdTe panel technology, its reliability still requires validation through extended testing and diverse real-world applications.
  • Cost: Even when commercially available, these silicon ball modules would be pricey initially. During that period, they may be better suited for flagship or demonstrative projects, rather than typical buildings or structures.

Final Words

In spite of the challenges, the prospects of silicon ball BIPV panel technology remain promising.

This technology displays an innovative way to utilize the abundant photovoltaic material. To repeat for emphasis, its super handy installation similar to applying a glass film is an unparalleled advantage so far in the realm of BIPV panel solutions.

However, its reliability is a major concern.

If you're looking for a reliable, proven technology that offers great flexibility to integrate solar power into your facades or windows, transparent CdTe panels are worth your consideration.

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