Think Round: Japan’s Spherical Solar Cells Challenge 140 Years of Flat Panel Design

A Century-Old Design Gets a Radical Update

For more than 140 years, solar power has looked essentially the same. Since Charles Fritts created one of the first solar panels in 1883 as a rigid plate, photovoltaic technology has been defined by flat blue rectangles mounted on rooftops or arranged in vast fields. This design has become so ubiquitous that most people never question whether solar cells need to be flat at all. In Japan, however, engineers at Kyosemi Corporation decided to challenge this fundamental assumption, developing a revolutionary family of tiny spherical solar cells called Sphelar that could transform how we harness solar energy.

The conventional flat panel design works well under ideal conditions, when sunlight hits the surface directly at a perfect 90-degree angle. In the real world, however, conditions are rarely ideal. The sun moves across the sky throughout the day and changes angles with the seasons. Clouds scatter light. Buildings, trees, and other obstacles create shadows. Flat panels lose significant efficiency when light strikes them at an angle, and they essentially become useless when shaded. These limitations have constrained where and how solar power can be deployed effectively.

The Japanese team behind Sphelar recognized that nature does not deliver light in a uniform, direct manner. Light comes from different angles throughout the day and across seasons. It arrives as direct beams, but also as reflected light bouncing off water, glass, and other surfaces, and as diffuse light scattered by clouds and atmospheric particles. A spherical solar cell, they reasoned, would be better equipped to capture this multidimensional light field, potentially generating electricity more consistently throughout the day and in less-than-ideal weather conditions.

The result of this insight is Sphelar, a registered trademark representing the world’s first commercially developed spherical solar cell. Measuring just 1 to 2 millimeters in diameter, these tiny silicon beads represent a fundamental reimagining of photovoltaic technology. Rather than trying to make light hit a flat surface at the right angle, Sphelar cells accept light from any direction, essentially creating a three-dimensional light-capturing system that works more like the way natural organisms capture energy from their environment.

The Eureka Moment: Why Must Solar Be Flat?

The story of Sphelar begins with a simple but profound question from Shuji Nakata, the lead engineer and founder of Kyosemi Corporation. Years after launching Kyosemi, Nakata found himself contemplating how to make photovoltaic cells more efficient. Drawing on his previous experience developing solar panels as a project member at Mitsubishi Electric, he asked himself why solar panels need to be flat when the sun is constantly moving.

In laboratory environments, light sources are typically fixed and predictable. However, in reality, sunlight arrives from constantly changing angles. Nakata observed that there is not only direct incoming light but also reflected and diffused ambient light that conventional flat panels largely fail to capture. This realization led to his core question: if the surface of a photovoltaic cell were spherical, would this be the most efficient way to capture sunlight? This became the founding inspiration for Kyosemi’s spherical micro solar cell.

Mr. Josuke Nakata, Founder and Chairman of Sphelar Power Corporation, reflected on the company’s mission in a corporate statement:

“Sphelar, the spherical solar cells, was created in response to simple questions like this. Light does not fall in a uniform manner in the natural world. The position of the sun is constantly moving. Some of the sunlight are dispersed by clouds and others are reflected of glass and water.”

The timing of this insight proved fortuitous. In the late 1980s, Kyosemi was planning to build new plants in Hokkaido and expand production capacity. Kamisunagawa emerged as the final candidate for the site. This former coal mining town had seen its mine close due to increasing imports, and the community was actively seeking new industries to replace lost jobs. One result of this economic transition was the establishment of JAMIC, the Japan Microgravity Center, which renovated an abandoned mining tunnel as a scientific research site. In 1988, the same year Kyosemi began operations in its new Hokkaido plant, Mr. Nakata had a new inspiration about how JAMIC’s unique capabilities might help realize his vision of spherical solar cells.

Manufacturing in Microgravity

Creating perfectly spherical silicon crystals presented significant engineering challenges. On Earth, surface tension and gravity cause molten silicon to form irregular shapes as it cools and solidifies. To achieve the near-perfect spheres needed for efficient solar cells, Kyosemi turned to JAMIC and its remarkable drop shaft facility. This vertical tunnel extends 710 meters into the earth, with a 490-meter drop shaft that enables experiments in microgravity conditions.

The manufacturing process involves placing silicon in a vacuum capsule and dropping it down the shaft. During free fall, the interior of the capsule enters a microgravity state, allowing molten silicon to form into perfect spheres through surface tension alone, without the distorting effects of gravity. The Kyosemi project team conducted numerous experiments, placing pieces of silicon in capsules and attempting to melt and crystallize them during the brief period of free fall. Through trial and error, they eventually succeeded in creating the desired ball-shaped grains.

According to reports from Phys.org, this innovative manufacturing approach offers significant advantages beyond just creating the right shape. The process of making Sphelar cells generates little to no waste of silicon, a valuable and relatively rare material in semiconductor manufacturing. Conventional flat solar cell production typically involves cutting silicon wafers from ingots, which creates substantial waste material as the cylindrical ingots are sliced into flat wafers. The spherical crystallization process essentially creates the final product shape directly from the molten material, eliminating the need for cutting and reducing silicon consumption.

Phys.org also reported that Kyosemi Corp. estimated production costs for Sphelar cells could be halved compared to conventional flat solar panel production. This cost advantage stems from reduced material waste and potentially simpler manufacturing processes. The environmental benefits extend beyond just efficient use of materials, as the production process itself is described as more environmentally friendly than traditional photovoltaic manufacturing.

How Spherical Cells Capture Light

The fundamental advantage of Sphelar cells lies in their geometry. A sphere presents the same surface area to light from any direction. Unlike flat panels that need to be angled toward the sun and lose efficiency when light arrives at oblique angles, Sphelar cells maintain their light-capture effectiveness regardless of the angle of incidence. This means they can capture direct sunlight throughout the day as the sun moves across the sky without requiring mechanical tracking systems.

More importantly, the spherical design enables efficient capture of indirect light sources. Reflected light from buildings, water, or other surfaces hits Sphelar cells at various angles but still finds an optimal surface for absorption. Diffuse light from cloudy days, which typically causes flat panel efficiency to plummet, is also captured effectively because the spherical shape accepts light from all directions. This characteristic makes Sphelar cells potentially more reliable in variable weather conditions and geographic regions with frequent cloud cover.

The technology works by creating a P-N junction within each silicon sphere, similar to how traditional solar cells function but applied to a curved surface. The Kyosemi team applied manufacturing know-how acquired from producing opto-semiconductor chips to form these junctions on spherical surfaces, a technical challenge that initially required significant innovation. When wired together, these microscopic spheres generate electrical current that can be harvested to power devices or feed into electrical systems.

From a user perspective, this means devices or structures incorporating Sphelar cells do not need careful orientation toward the sun. A Sphelar-powered device can be placed on a horizontal surface, angled surface, or even moved around, and it will continue to capture available light efficiently. This eliminates the need for mounting systems that angle panels toward the sun and removes constraints on where solar-powered devices can be deployed or used.

From Concept to Commercial Products

The journey from concept to commercial product took several years of development. After successfully creating the first four cells connected in series that generated electricity when exposed to light, the research team intensified their efforts. In 1998, Kyosemi established its own Microgravity Laboratory to continue development work. By 2004, the company had progressed enough to apply for trademark registration for the name “Sphelar,” an abbreviation of “Spherical Solar,” and began providing samples to potential partners.

In the early stages, even the developers struggled to imagine all the potential applications for this novel technology. However, as the innovative idea reached the market, it inspired other innovative ideas from partners and customers. This collaborative development approach helped identify practical uses that leveraged the unique properties of spherical solar cells.

In 2012, Sphelar Power Corporation was established as a spin-off from Kyosemi Corporation to focus specifically on developing and commercializing the spherical solar cell business. Ikuo Inagawa, Representative Director and President of Sphelar Power Corporation, described the company’s vision:

“Sphelar Power Corporation has commercialized the world’s first small diameter spherical solar cell, Sphelar, and provides its applied products. We have been promoting the use of Sphelar as a familiar solar cell to help reduce major change in the global environment and contribute to the Sustainable Development (SDGs), and working to spread the use of our applied products under the slogan ‘Sphelar always by your side!'”

Today, the company offers several product lines that showcase the versatility of spherical solar technology. These applications demonstrate how moving beyond flat panels enables entirely new approaches to integrating solar energy into our built environment and daily lives.

Building Integration and Transparent Surfaces

One of the most promising application areas for Sphelar technology is building-integrated photovoltaics (BIPV). Traditional solar panels are typically mounted on top of roofs as separate systems, visible and sometimes considered aesthetically unappealing. Sphelar cells, however, can be embedded directly into building materials, creating surfaces that generate electricity while maintaining other functions like transparency or architectural design.

The Sphelar BIPV product line includes glass blocks that enclose Sphelar modules. These transparent building elements can be used in walls, windows, and other architectural features, allowing light to pass through while simultaneously generating electricity. The transparency of Sphelar installations can range from 50% to 80%, depending on the density of cell placement and the specific application requirements.

This capability addresses a significant limitation of conventional solar panels in urban environments. In densely populated cities, roof space is often limited or shaded by surrounding buildings. Traditional panels may block views or conflict with historic preservation requirements. Sphelar cells, however, can be integrated into facades, windows, and other vertical surfaces that receive indirect light throughout the day. They can be incorporated into curved surfaces and complex architectural forms that would be impossible or impractical with rigid flat panels.

The company has also developed Sphelar Glass Blocks, small compact solar modules enclosed in transparent glass. These can serve as both building materials and power generators, potentially transforming ordinary windows, skylights, or decorative elements into energy-producing surfaces. The ability to maintain transparency while generating power opens possibilities for energy-positive buildings that produce as much electricity as they consume without compromising architectural aesthetics.

Energy Harvesting for the Internet of Things

As the world moves toward greater connectivity with the Internet of Things (IoT), powering vast networks of sensors and small devices presents a significant challenge. Battery replacement is impractical for distributed sensor networks, and wiring costs can be prohibitive. Sphelar cells offer a solution through energy harvesting, also known as energy scavenging, where devices collect the small amounts of ambient energy available in their environment.

The Sphelar EIPV Series provides compact solar modules designed specifically for low-power applications. These modules can harvest energy from available light to power sensor devices, smart wireless applications, and other small electronics. Because Sphelar cells capture light from all directions and work well with diffuse light, they are particularly suitable for indoor or urban environments where traditional solar cells might struggle.

Applications for these energy harvesting modules include environmental sensors, smart building systems, agricultural monitoring, and any application where small, distributed devices need power without battery replacement or wired connections. The ability to work without precise orientation toward the sun makes these cells ideal for devices that may be placed in various positions or moved during their operational lifetime.

The compact nature of Sphelar cells, measuring just 1 to 2 millimeters in diameter, allows them to be integrated into very small devices where traditional solar cells simply would not fit. This miniaturization capability could enable entirely new categories of self-powered smart devices, from wearable technology to environmental monitors embedded in infrastructure.

Wearable Technology and Solar Fabrics

Perhaps the most futuristic application of Sphelar technology is in the realm of wearable electronics and smart textiles. The company has developed a filament-shaped solar power generation yarn that generates electricity with sunlight while maintaining excellent flexibility. This photovoltaic yarn enables the manufacture of textiles that generate electricity, effectively turning clothing, bags, or other fabric items into solar power generators.

The development of solar power generation yarn was conducted through an industry-academia-government joint research project involving the Ministry of Economy, Trade and Industry, Sphelar Power Co., Ltd., and the Fukui Prefectural Industrial Technology Center. The resulting Sphelar TEXTILE product is described as light, thin, flexible, and stretchable, making it suitable for wearable e-textile power supply applications.

This technology addresses a fundamental challenge in wearable electronics: power. Batteries add weight and bulk to wearable devices, and frequent recharging reduces their convenience. Solar-integrated fabrics could harvest energy throughout the day from ambient light, continuously powering embedded sensors, communications devices, or health monitors without requiring user intervention or adding significant weight.

The potential applications extend beyond clothing to include tents, awnings, sailcloth, vehicle covers, and any other fabric surface exposed to light. Military applications could include uniforms that power communication equipment or navigation devices. In civilian use, outdoor gear could generate power for GPS devices, emergency beacons, or mobile phones. The flexibility of the material means it can be integrated into garments without compromising comfort or movement, unlike rigid solar panels that would be impractical for wearable applications.

Consumer Products and Illumination

Beyond specialized industrial applications, Sphelar Power Corporation has developed consumer-facing products that demonstrate the practical benefits of spherical solar technology in everyday contexts. These products showcase how the unique characteristics of Sphelar cells enable designs that would be difficult or impossible with traditional flat solar panels.

The Sphelar Garden Light features a stylish design with the spherical Sphelar solar cell mounted on top and an LED light element. During daylight hours, electricity is stored from sunlight, and at night, the stored energy powers the LED to illuminate gardens, parks, and walking paths. The design prioritizes aesthetics, aiming to provide lighting without disrupting the landscape. Installation is simple, requiring no electricity bills or wiring work, making it suitable for remote locations or areas where electrical infrastructure is unavailable.

Similarly, the Sphelar Illumination product features Sphelar modules that can be hung on trees. These modules collect electricity during daylight hours and turn on LEDs at night, with the Sphelar module itself glowing softly. The product is designed to provide safe and attractive illumination without damaging trees during installation or destroying their natural appearance. Like the garden light, these illumination products require no electrical connection or ongoing energy costs.

These consumer products demonstrate practical advantages of Sphelar technology that stem from its omnidirectional light capture. Garden ornaments and tree lights can be placed in various orientations without concern for optimal sun exposure. They can be located in partially shaded areas where flat panels might not receive enough direct light. The aesthetic appeal of the design is enhanced by the compact, unobtrusive nature of the spherical cells, which can be integrated into decorative elements without appearing as technical add-ons.

Efficiency and Performance Considerations

When evaluating any solar technology, efficiency remains a critical metric. Reports from TheFutureOfThings indicate that Kyosemi has developed flexible solar panels with close to 20% higher efficiency than most commercial photovoltaic cells available today. This significant improvement stems from the ability to capture light from all angles and utilize both direct and indirect light sources.

However, comparing Sphelar cells directly to traditional flat panels requires careful consideration of different performance metrics. Flat panels are typically rated based on their peak efficiency under ideal laboratory conditions with direct, perpendicular light. Sphelar cells, by contrast, maintain more consistent performance across varying light conditions and angles. While they may not exceed flat panels in peak efficiency tests under perfect conditions, their overall energy yield across a full day in real-world conditions may be superior.

The elimination of tracking systems represents another efficiency advantage. Large-scale solar installations often use motors and tracking systems to keep flat panels oriented toward the sun throughout the day. These systems consume energy, require maintenance, and add complexity to installations. Sphelar cells achieve similar benefits through their inherent geometry, capturing optimal light from dawn through dusk without mechanical assistance. This passive operation increases system reliability and reduces maintenance requirements.

Performance in low-light conditions represents another differentiator. On cloudy days or during early morning and late afternoon hours when light intensity is low, flat panels see dramatic drops in output. Sphelar cells, designed specifically to capture diffuse and scattered light, maintain relatively better performance under these challenging conditions. This characteristic makes them particularly suitable for geographic regions with frequent cloud cover or for applications where consistent operation across varying weather conditions is essential.

Environmental Impact and Sustainability

Environmental considerations play an increasingly important role in energy technology selection, and Sphelar cells offer several potential advantages from a sustainability perspective. The reduced silicon waste in manufacturing represents a significant environmental benefit. Silicon production is energy-intensive and involves chemical processes with environmental impacts. Using this valuable material more efficiently reduces the overall environmental footprint of solar cell production.

The potential reduction in production costs, estimated at half that of conventional panels according to Phys.org, could make solar power more economically accessible. Lower costs accelerate adoption, which in turn displaces more fossil fuel generation and reduces greenhouse gas emissions. The ability to integrate solar cells into existing structures and products without requiring additional materials or modifications further reduces the environmental impact of deployment.

The durability and longevity of Sphelar technology contribute to its environmental profile. Spherical cells may be less susceptible to damage from environmental factors like wind, hail, or debris compared to large, fragile flat panels. Their compact size and ability to be embedded in protective materials could extend operational lifespan, reducing the need for replacement and the associated environmental costs of manufacturing and disposal.

Sphelar Power Corporation explicitly connects their technology to broader environmental goals, including contributions to Sustainable Development Goals (SDGs). The company’s mission includes helping to prevent the depletion of fossil fuel resources and combat global warming through the expanded use of solar energy. By making solar power possible in applications and locations where it was previously impractical, Sphelar technology could significantly increase the overall contribution of solar energy to the global energy mix.

The Future of Solar Energy

While flat solar panels will likely remain the dominant technology for large-scale utility installations in the near future, Sphelar cells represent an important diversification of solar technology. Rather than competing directly with traditional panels, spherical cells open entirely new application spaces that flat panels cannot address. This expansion of where and how solar energy can be harvested could accelerate the overall adoption of solar power and bring it closer to ubiquitous integration into our daily environment.

The concept of “energy everywhere” becomes more feasible with technologies like Sphelar. Instead of thinking of solar power as something generated at remote farms and transmitted over long distances, we can imagine a world where every surface exposed to light becomes a potential power source. Windows generate electricity while letting in light. Clothing powers wearable devices. Buildings produce energy from their walls as well as their roofs. This distributed generation model reduces transmission losses and increases energy system resilience.

As the Internet of Things expands and smart cities become reality, the need for distributed power sources will grow. Sphelar cells, with their suitability for energy harvesting and integration into diverse materials and form factors, could become a key enabling technology for this connected future. The ability to power sensors and devices using ambient light eliminates infrastructure costs and deployment barriers for smart city applications.

The development of Sphelar technology also demonstrates how challenging fundamental assumptions can lead to breakthrough innovations. For more than a century, the flat solar panel design remained largely unquestioned. By asking why solar cells must be flat, Japanese engineers opened a path to entirely new approaches to light capture and energy generation. This spirit of questioning conventional wisdom will likely drive further innovations in solar technology and renewable energy more broadly.

As Sphelar Power Corporation continues to develop original products and applications with their partners worldwide, the impact of spherical solar cells continues to grow. From specialized industrial applications to consumer products, from building materials to wearable technology, these tiny spheres are proving that sometimes the best way to move forward is to think in circles rather than rectangles.

The Bottom Line

• Sphelar spherical solar cells, developed by Kyosemi Corporation in Japan, measure just 1 to 2 millimeters in diameter and capture light from all directions.
• The technology originated from founder Shuji Nakata’s question about why solar panels need to be flat when the sun is constantly moving.
• Manufacturing uses Japan’s Microgravity Center’s 710-meter drop shaft to create perfect silicon spheres in microgravity conditions.
• Production generates little silicon waste and costs approximately half that of conventional flat solar panel manufacturing.
• Spherical cells maintain efficiency across varying light angles and capture both direct and indirect light, performing better in cloudy conditions.
• Applications include transparent building materials, energy harvesting for IoT devices, solar-generating textiles, and consumer lighting products.
• Sphelar Power Corporation was spun off from Kyosemi in 2012 to focus exclusively on developing spherical solar cell applications.
• The technology enables solar integration into curved surfaces, wearable items, and architectural elements where traditional flat panels cannot be used.