Japan's Tiny Spherical Solar Cells Bring Power to Glass, Fabrics and Sensors

Solar power in silicon beads just 1 to 2 millimeters wide

Japan's Sphelar solar cells measure just 1 to 2 millimeters in diameter, yet their developers see uses stretching from transparent building materials to electricity generating fabrics. Developed by Kyosemi Corporation and commercialized through Sphelar Power Corporation, the tiny silicon spheres collect light arriving from different directions, offering a different approach to the familiar flat solar panel.

As of January 18, 2026, the technology's product range includes modules for small electronic devices, glass blocks, photovoltaic yarn and outdoor lights. Its development reaches back to experiments associated with a former coal mining town in Hokkaido, where a research facility used a shaft extending deep underground to create brief periods of microgravity.

Sphelar's central idea is straightforward: sunlight moves, reflects and scatters, so a solar cell need not have just one flat face. A sphere exposes part of its surface to light arriving from almost any direction. Connected together, these miniature cells can form flexible or transparent structures that would be difficult to make from conventional rigid panels.

The approach challenges a design tradition stretching back more than 140 years. Charles Fritts created one of the earliest solar panels in 1883 as a rigid plate. Flat rectangles subsequently became the familiar form of photovoltaic technology, appearing on roofs and across large solar fields.

Sphelar is a registered trademark derived from Spherical Solar. Its developers describe it as the world's first commercially developed spherical solar cell. The practical attraction is its combination of small size, flexible placement and access to direct, reflected and scattered light.

Why Nakata questioned the flat panel

Shuji Nakata, Kyosemi's founder and the lead engineer behind the idea, had previously worked on solar panel development as a project member at Mitsubishi Electric. Years after founding Kyosemi, he began asking why photovoltaic cells should remain flat when the sun's position changes throughout the day.

A fixed laboratory light source presents a simpler problem than sunlight outdoors. Outside, the angle changes with the time and season. Clouds disperse incoming light, while water, glass and other surfaces reflect it. Buildings and trees also interrupt direct sunlight.

Flat panels work best when light strikes their surface directly, at a right angle. Their output falls as exposure becomes less favorable or shade reduces the light reaching them. Nakata's proposed answer was a curved cell that could receive illumination across its surface instead of relying on a single face pointed toward the sun.

Josuke Nakata, identified as founder and chairman of Sphelar Power Corporation, described that reasoning 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 engineering challenge was to translate this observation into a working semiconductor. A spherical shape had to be manufactured reliably, and the electricity generating structure had to be formed on its curved surface.

A former mining town supplied the experimental setting

Kyosemi was planning new factories in Hokkaido and an expansion of production capacity in the late 1980s. Kamisunagawa became the final candidate for a plant. The town's coal mine had closed as imports increased, leaving the community looking for industries that could replace lost employment.

JAMIC, the Japan Microgravity Center, emerged from that economic transition. It converted an abandoned mining tunnel into a scientific research site. In 1988, the year Kyosemi began operating its new Hokkaido plant, Nakata saw how the facility might help produce spherical silicon.

JAMIC's vertical tunnel extended 710 meters underground and included a drop shaft of 490 meters. Experiments placed inside a falling capsule could experience microgravity, a condition in which the effects of gravity within the experimental space become very small.

Molten silicon presented a difficult shaping problem under ordinary conditions. Gravity could distort the material as it cooled, while surface tension, the force that draws a liquid surface together, encouraged a rounded shape. The falling capsule offered a way to let surface tension play the leading role.

Kyosemi's team placed silicon in vacuum capsules and repeatedly attempted to melt and crystallize it during the brief free fall. Through successive experiments, the researchers produced the ball shaped grains needed for the cells. The mining site's unusual infrastructure became part of the route from an idea about sunlight to a usable material.

From a silicon sphere to an electrical circuit

Kyosemi then had to make the silicon balls generate electricity. The team drew on its experience producing opto-semiconductor chips to form a P-N junction on each curved surface. A P-N junction is the meeting point between two semiconductor regions with different electrical properties; it helps turn absorbed light into an electrical current.

Traditional silicon solar cells use the same basic principle, but applying it to a small sphere required a different manufacturing approach. The team eventually connected four cells in series and generated electricity when light struck them. Connecting cells in series combines their electrical contribution into a usable circuit.

The spherical shape also changes how a cell meets incoming light. A sphere presents the same projected area to a beam arriving from any direction. As the sun moves, another part of its surface can face the incoming beam without the whole device rotating.

Reflected light from water, buildings or glass can reach different parts of the sphere. Light scattered by clouds can do the same. This gives the design a way to collect illumination from several directions, including conditions in which a single flat surface has less favorable exposure.

For a user, the attraction is reduced dependence on precise positioning. A device containing Sphelar cells can sit on a horizontal or angled surface, or change position during use, while continuing to collect available light. Its electrical output still depends on how much light reaches the cells.

The milestones behind commercialization

Kyosemi intensified development after the first four connected cells produced electricity. The next steps included building its own research capability, giving the technology a name and supplying samples to potential commercial partners.

The principal dates trace a development process lasting decades:

• 1883: Charles Fritts created one of the earliest rigid solar panels.
• 1988: Kyosemi began operations at its new Hokkaido plant, and Nakata identified a possible role for JAMIC's microgravity facility.
• 1998: Kyosemi established its own Microgravity Laboratory.
• 2004: The company applied to register the Sphelar trademark and began providing samples to potential partners.
• 2012: Sphelar Power Corporation was established as a spin-off from Kyosemi to concentrate on spherical solar cells and their applications.

The developers initially struggled to identify every possible use. Samples and collaboration with customers helped turn the unusual cell shape into proposals for building materials, electronics and everyday products.

Ikuo Inagawa, representative director and president of Sphelar Power Corporation, described the company's commercialization and environmental aims:

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!'

Sphelar Power's strategy centers on applied products and partnerships. Instead of relying on one standard rectangular module, it uses the small cells as components that can be arranged around the requirements of another object.

Less cutting, with a claimed cost advantage

Kyosemi's spherical crystallization process creates the intended silicon shape directly from molten material. Conventional wafer production involves slicing silicon ingots into thin pieces, producing waste during cutting. Making spheres directly removes that slicing step and is described as generating little to no silicon waste.

Kyosemi estimated that production costs could be halved compared with conventional flat solar panel production. The claimed saving rests on reduced material loss and potentially simpler manufacturing, rather than on the spherical shape alone.

Silicon prepared for semiconductor manufacturing is a valuable material, and producing it involves energy intensive processes and chemicals. Using more of that material in finished cells could reduce the resources consumed during production. The spherical process is also described as more environmentally friendly than traditional photovoltaic manufacturing.

The cost estimate is a prospective production advantage, while the laboratory history explains how the spheres were developed. Current manufacturing volumes, independently verified cost comparisons, detailed performance tests and dates for wider deployment were not given as of January 18, 2026.

Windows and walls that also generate electricity

Sphelar's building product line places solar cells inside materials that serve another purpose. Building integrated photovoltaics, often shortened to BIPV, means making electricity generation part of the building itself rather than adding separate panels above a roof.

Sphelar BIPV products include glass blocks enclosing solar modules. The transparent elements can be incorporated into walls, windows and other architectural features, allowing some light to pass through while collecting some for electricity generation.

Transparency ranges from 50% to 80%, depending on the density of the cells and the application. More widely spaced cells leave more space for light to pass between them. Designers can adjust the arrangement to suit the desired balance between transparency and power generation.

Sphelar Glass Blocks similarly enclose compact modules in transparent glass. Potential uses include windows, skylights and decorative building elements. The cells' small size also allows arrangements following curved surfaces and more complex architectural forms.

Urban buildings provide a particular reason to explore this approach. Roof space may be limited or shaded by neighboring structures, while visible panels can conflict with appearance or historic preservation requirements. Walls and facades provide other surfaces where reflected and scattered light may be available.

Electricity generating glass could contribute to buildings designed to produce as much energy as they consume. The role described for Sphelar is to add generation to surfaces with other architectural functions, including those where a rigid, opaque panel would be impractical.

Small sensors are another target

Sphelar's EIPV Series consists of compact solar modules intended for devices that need relatively little power. The applications include sensors, smart wireless electronics and other equipment that can collect energy from surrounding light.

Energy harvesting, also called energy scavenging, means gathering small amounts of energy already present in a device's environment. For a solar module, that energy comes from available light. The approach is particularly relevant to the Internet of Things, or IoT, networks of connected devices that collect and exchange information.

Large networks of sensors create a practical power problem. Replacing batteries across many scattered devices can be difficult, while installing electrical wiring can be expensive. Small solar modules offer a way to reduce dependence on those repeated visits or wired connections.

The proposed applications include environmental sensors, agricultural monitoring and smart building systems. Sphelar's acceptance of light from different directions is intended to help where devices have varied positions, move during use, or receive indirect illumination indoors or between buildings.

Cells measuring only 1 to 2 millimeters can also fit into objects too small for conventional panels. Their developers see possibilities in wearable electronics and monitors embedded in infrastructure, with the power source incorporated into the device rather than mounted separately.

Solar yarn moves the cells into fabric

Sphelar Power has developed a filament shaped yarn that generates electricity from sunlight while remaining flexible. The Sphelar TEXTILE product is described as light, thin, flexible and stretchable, with wearable electronic textiles among its intended uses.

The development came through joint research involving industry, government and academia. The participating organizations included Japan's Ministry of Economy, Trade and Industry, Sphelar Power Co., Ltd., and the Fukui Prefectural Industrial Technology Center.

Electricity generating yarn could be woven into clothing, bags and other fabric products. Wearable electronics face a familiar constraint: batteries add weight and bulk, while repeated charging makes continuous use less convenient. Fabric that collects light could supply energy to embedded sensors, communications equipment or health monitors.

The proposed uses extend beyond garments to tents, awnings, sailcloth and vehicle covers. Each would place solar generation in a flexible surface already exposed to light.

Military uniforms are another possible application, with electricity directed toward communication or navigation equipment. Civilian outdoor gear could supply GPS devices, emergency beacons or mobile phones. These are potential uses of the yarn rather than a list of confirmed deployments.

Flexibility is central to the idea. Clothing and equipment must bend as people move or as fabric is folded. Integrating tiny cells into yarn offers a different route from attaching rigid panels to a garment, with the aim of preserving comfort and movement.

Garden and tree lights show the everyday use

The Sphelar Garden Light combines solar cells mounted on top with an LED lighting element. It stores electricity gathered during daylight and uses that energy to illuminate gardens, parks or walking paths at night.

The product's design aims to fit into a landscape without a conspicuous electrical installation. It requires no wiring work or external electricity supply, making it suitable for locations where connecting a light to electrical infrastructure would be inconvenient.

Sphelar Illumination uses modules that can be hung on trees. They collect energy during the day and switch on LEDs at night, with the modules themselves glowing softly. The design is intended to avoid damaging trees or disrupting their natural appearance.

Both products turn the geometry into a practical design feature: the small cells can be incorporated into decorative objects without presenting a large flat panel. Different placement angles and some access to indirect light provide more flexibility in positioning, including partially shaded settings.

Nighttime operation uses energy collected earlier and stored in the product. The absence of an external electricity connection removes electricity bills for operating the lights, while the compact modules aim to keep the technical components visually unobtrusive.

How to understand the efficiency claims

Kyosemi's flexible panels have been described as offering close to 20% higher efficiency than most commercial photovoltaic cells. The explanation given is their ability to collect light from different angles and use both direct and indirect illumination.

Efficiency and energy production answer different questions. Efficiency describes how much incoming light energy becomes electricity under specified conditions. Energy yield describes how much electricity a device produces over a period, such as a day, as the angle and strength of sunlight change.

Conventional panels are commonly evaluated under controlled conditions with light directed toward their surface. Sphelar's proposed advantage concerns performance across changing angles and surroundings. Its cells may collect useful light for longer portions of the day even when a flat panel has a less favorable position.

Mechanical tracking systems provide another comparison. Some large solar installations use motors to keep panels facing the sun. Such equipment adds maintenance, complexity and energy consumption. Sphelar's geometry offers a passive way to receive light as its direction changes, without those moving parts.

Clouds, early mornings and late afternoons also change the amount and direction of available light. The spherical design is intended to make better use of scattered illumination in such conditions. That characteristic is relevant to locations with frequent cloud cover and devices whose orientation cannot be carefully controlled.

The commercial argument therefore combines several considerations: conversion efficiency, useful operating time, positioning, installation requirements and maintenance. For sensors or transparent glass, fitting generation into the object can matter alongside the electricity produced by each cell.

More places for solar power, with practical limits

Sphelar Power connects its work to the Sustainable Development Goals, reducing fossil fuel depletion and addressing global warming. The proposed environmental benefits include lower silicon waste, potentially cheaper production and generation built into objects or structures already in use.

Embedding small cells in protective materials could also help durability. Their size and packaging may reduce vulnerability to wind, hail or debris compared with exposed, larger components. Longer service life would reduce replacement needs and the associated manufacturing and disposal demands.

Conventional flat panels are expected to remain the main technology for large electricity generating installations in the near term. Sphelar's strongest proposed role is expanding the places where solar generation can be installed, including curved surfaces, fabric, transparent building elements and miniature devices.

Distributed generation means producing electricity close to where it is used. Windows, walls and wearable items could contribute small amounts locally rather than relying entirely on remote power stations and long transmission routes. The proposed benefits include lower transmission losses and greater resilience through more dispersed sources.

Connected buildings and smart city devices provide a related opportunity. Ambient light could help power sensors without extensive wiring, while architectural surfaces could contribute electricity beyond the roof. Those applications depend on matching each device's energy needs to the light available where it is installed.

Sphelar's history joins an engineering question, an unusual research facility and decades of commercialization. Partnerships helped move the idea from four connected cells to glass, yarn and lighting products. Its contribution is a broader choice of shapes and settings for solar power, built around silicon spheres small enough to become part of another object.

The Bottom Line

• Sphelar cells developed by Kyosemi measure 1 to 2 millimeters in diameter and collect direct, reflected and scattered light from different directions.
• Experiments used JAMIC's facility in Kamisunagawa, with a tunnel extending 710 meters underground and a drop shaft of 490 meters.
• Kyosemi established its Microgravity Laboratory in 1998, sought the Sphelar trademark in 2004 and created Sphelar Power Corporation as a spin-off in 2012.
• The company estimated that production costs could be halved through reduced silicon waste and changes to manufacturing.
• Applications include transparent glass, sensor modules, electricity generating yarn, garden lights and illumination hung on trees.
• Building installations are described as offering transparency of 50% to 80%, depending on cell spacing and application.
• A claimed efficiency advantage of close to 20% accompanies a broader focus on changing light angles, flexible placement and avoiding mechanical tracking.
• As of January 18, 2026, the development centers on adding solar generation to objects and surfaces beyond conventional flat panels.