The Problem with Solar Panels

The solar energy industry face a potential Achilles' heel: its reliance on silver. As a precious and costly metal, silver plays a crucial role in nearly all types of solar panels. With global solar energy production surpassing the terawatt level, the sustainability of this growth is now threatened by the scarcity and expense of silver. A possible alternative exists in copper-based panels, breaking world efficiency records and showing promising potential. However, manufacturers hesitate to replace silver with copper. Can the solar energy industry overcome the challenges posed by copper resistors and provide us with more affordable and efficient solar panels? Let's explore this complex and intricate journey.

Screen printing

Since the 1970s, screen printing has been the traditional method for manufacturing silicon solar cells, constituting around 85% to 90% of production. Analogous to imprinting a logo on a T-shirt, this method involves placing a screen on the silicon wafer's back. The machine deposits a layer of silver paste onto the screen, and a scraper presses it through. The wafer undergoes drying, firing, and flipping, repeating the process on the other side. While cost-effective, the challenge lies in the materials used. Silver constitutes approximately 10% of manufacturing costs and uses about 15% of the world's mined silver. With the advancement of solar energy, the global demand for silver has surged. Various evolving technologies vie for silver, including 5G infrastructure, electric vehicles, and other consumer electronics saturating the market. Scientists raised concerns as early as 2013, noting that the rapid growth in demand for both solar energy and silver is poised to significantly escalate the cost of solar energy.

Although solar energy is getting cheaper,Silver prices are surging rapidly. The Silver Association revealed that global demand for silver in 2021 hit a record high since 2015, with prices soaring 22% year-on-year, reaching a nine-year high of $25.14 per troy ounce. In contrast, copper prices in 2021 were approximately $0.29 per troy ounce. While some may consider silver recycling, a December 2022 study suggests it's not yet feasible due to insufficient silver for retirement. The longevity of solar panels has both positive and negative aspects. Additionally, the recycling process is labor-intensive, requiring panel disassembly and chemical treatment for silver removal. While recycling is beneficial in the long run, it may not be feasible in the coming decades.

Now, let's consider copper—an alternative with comparable conductivity but significantly lower costs. Two pivotal conversion paths stand out: 1) replacing silver paste with copper paste in screen printing, and 2) embracing embedded contact solar cell design over screen printing. Shifting to copper brings benefits such as achieving world-record solar cell efficiency and utilizing more affordable, abundant materials. In recent years, several companies, inspired by Australian pioneers Stuart Wenham and Martin Green, have made notable strides. Their 1985 patent for buried contact solar cells marked a significant improvement. To grasp these enhancements, let's outline some key solar panel structures. The grid-like pattern on the panel's front is the top contact point, typically featuring silver. These metal wires collect electricity generated by the battery. The thinner horizontal lines, known as 'fingers,' transmit current to thicker vertical lines called 'busbars.' Ideally, photovoltaic fingers are tightly squeezed together and as narrow as possible.

Regrettably, the production of thin fingers involves substantial costs. As a result, wider fingers in screen printing have a significant drawback: a 10% to 15% decrease in power output due to masking loss. Embedded contacts offer an elegant solution with deeper fingers than their width. Laser-cut grooves on silicon are filled with copper, resulting in more metal in the fingers and less metal obstructing the surface. This innovation reduces shading loss to 2% to 3%. Ultimately, the efficiency of embedded contact solar panels surpasses that of screen-printed counterparts by 25%.

By 1991, Wenham and Green's experimental cells with embedded contacts achieved a record efficiency of 24.7%, and commercial cells reached 20% efficiency. However, their widespread adoption faced challenges. Enter the "Sun King" Shi Zhenrong, who founded Suntech Power in 2001. Despite achieving a world record efficiency of 20.3% for copper-metallized cells in 2012, Suntech faced bankruptcy in March the following year. This fate was not unique; BP Solar, using laser-trough buried contact cells in its Saturn components, also faced bankruptcy in 2011. The question remains: If copper is so promising, why did these companies go bankrupt?

A significant factor contributing to this challenge is cost. Silver solar panels are more cost-effective to manufacture. While copper is a cheaper raw material than silver, its poor adhesion to solar panels has been a persistent issue for scientists and practitioners. Solar panels are designed to last for 25 years or more, enduring various climate conditions. However, copper is prone to flaking, potentially compromising the reliability of copper-plated cells. This apprehension explains manufacturers' hesitancy in transitioning. Performance is another critical concern. Although narrower fingers in copper cells enhance efficiency by reducing shadowing, the risk of copper diffusion into the underlying silicon poses a threat. Copper diffusion can convert semiconducting silicon into a conductor, leading to short circuits within the panel. This introduces additional risks not typically associated with a well-established product. Establishing effective diffusion barriers is complex and may incur extra production costs. Furthermore, concerns exist regarding how copper oxidation can limit conductivity.

Addressing these challenges in engineering involves incorporating additional steps and allocating more resources in the manufacturing process. This complexity stands as a primary hurdle, contributing to copper's limited adoption and the struggles faced by BP and Suntech. While BP Solar successfully commercialized its Saturn panels, the decision to cease production stemmed from the competition with lower-cost screen-printed silver. As technology advanced, screen-printed silver became more affordable. Despite a 2014 study indicating the durability of BP's embedded contact design, economic factors influenced production choices.

The question arises: Can copper overcome these challenges, especially given the current heightened risks? Shi Zhenrong expresses optimism. Two years post-Suntech's bankruptcy, he spearheaded an investment in the newly established startup SunDrive. Headquartered in Sydney, the company focuses on copper plates. Supervisor Lennon, determined to expedite the project, forwent his doctoral course, dedicating his time to garage experiments. After numerous attempts, he devised a method to attach copper to solar cells. Co-founding SunDrive with his roommates, they applied for a patent in 2015. By September 2022, the company achieved a panel efficiency of 26.41%, breaking the world record for commercial silicon solar cells.

If the company achieves large-scale production, the prospect of utilizing scrap silver becomes viable, potentially leading to significant reductions in consumer prices. Whether history repeats itself, consigning copper to the sidelines, remains uncertain. The answer may not be far off, as the company plans to establish a pilot production line in 2023. The historical challenges of copper-based panels, addressing issues like oxidation and diffusion, suggest that it might not be a universal solution. The looming threat of surging silver prices could potentially compel manufacturers to take decisive action. What are your thoughts? Still contemplating? Is copper the evident solution? What sustainable solar alternatives are available?