How Futuristic Windows Will Generate Electricity with Invisible Solar Panels
There are not many issues around the world that take greater precedence than global warming. A carbon-free future is the future and in the five years since the Paris climate agreement there have been great steps made towards this goal. A big part of this effort is reducing the amount of fossil fuel that is consumed, and converting this to renewable sources of energy like wind, sun, wave and water.
Of these options, solar energy has always been the most popular choice, as it is the most reliable and consistent source of clean energy in the world right now. Solar energy has become more available and cheaper over time, but the current solar cells are opaque, which restricts their use to rooftops and solar farms.
There is a product, Building Integrated Photovoltaics (BIPV), a type of glazing that can generate power from solar energy and is used on Windows, skylights and sunshades. However, it is not transparent and therefore not suitable for the applications that transparent solar cells are. Similarly, Elon Musk has also created his product Solar Roof, and proves that solar panels located on a roof do not always have to be an eyesore. Again, they are specifically designed roof tiles and the technology does not have the flexibility that the transparent solar panels do.
Solar panels are usually restricted to the roofs of houses where they can receive the most sunlight possible.
This is where the research conducted by the Department of Electrical Engineering at Incheon National University in Korea comes in. Professor Joondong Kim and his colleagues have recently published a study where they outline their newest invention; solar cells that are completely transparent. The applications of such a technology are practically endless and open up the option to integrate renewable energy into anything that includes glass. Think buildings, Windows, and even the screen of your cell phone! Professor Kim stated that The unique features of transparent photovoltaic cells could have various applications in human technology.
The concept of transparent solar cells is not a brand new idea that has come to light, but to have a real-world application of this concept is a huge breakthrough. In current technology, the layers of semiconductor that make solar cells opaque. These are the components of the cells that collect light and convert it into electrical current.
Two new semiconductor materials were explored by Professor Kim’s team:
Titanium dioxide (TiO2) was already a well known semiconductor material in this field, as it had already been used on a large scale to create solar cells. It has great electrical properties, is non-toxic and is environmentally friendly; a perfect candidate for this new project. TiO2 absorbs UV light (which is a part of the light spectrum that is invisible to human eyes) and allows most of the visible parts of the light spectrum through.
Nickel oxide (NiO) was the other material that was considered by the team at Incheon National University, which is a semiconductor, also known for its high optical transparency. Nickel is one of the most plentiful substances on Earth and can be easily worked at low temperatures. This makes NiO a great candidate for the manufacture of transparent solar cells.
The new solar cell design was constructed from a metal oxide electrode and a glass substrate, each of the two aforementioned semiconductors were laid on top of one another in thin layers (first TiO2, then NiO). The final step was to coat the construction with silver nanowires, which act as the second electrode for the solar cell.
Windows of the future will be able to harness the energy of the sun and reduce our dependence on fossil fuels. Source: Unsplash
Several tests were then conducted to analyze the new device’s performance, its ability to transmit and absorb light, as well as the cell’s efficiency and effectiveness.
The results were another encouraging step in the right direction. The cells demonstrated a power conversion efficiency of 2.1%, compared to 15% to 22% efficiency of current solar panels. This is a good figure for the new cells when it is considered that these cells target a relatively small section of the light spectrum. Another important property that these new cells possessed was the ability to work in low-light situations. This is extremely important for solar cells, as it is a common misconception that they must be located in a sun-filled climate in order to work efficiently. It was also found that the cells were highly responsive, more that 57% of the visible light was able to pass through the layers, achieving a, somewhat transparent, effect.
The final stage of testing showed how these solar cells could be used to power small motors. Professor Kim stated that while this technology is still quite new, improvements can still be made to optimize the cells for transparent applications. This will be the aim of this team and many others.
There are several other prototypes being tested in different research facilities around the world with varying results. A team from the University of Michigan have created a carbon-based solar panel that allows 43.3% of light through, but has an impressive efficiency of 8%. These cells have a slight green tint to them, akin to the tint you may see in sunglasses and car Windows. They have also tested a model with a silver electrode, with 45.8% transparency and 10.8% efficiency. These however may not be suitable for most applications due to their slightly more prominent green tint.
Time will tell whether the invisible solar cells integrated into Windows will become a reality. If so, the solar energy industry will have taken a huge leap forward in pushing the world towards clean sources of energy.
So what do you think of this new technology? I would love to hear your thoughts on these futuristic solar panels in the Комментарии и мнения владельцев below!
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Near-invisible solar cell based on tungsten disulfide photoactive layer
Japanese scientists built a near-invisible solar cell based on indium tin oxide (ITO) and tungsten disulfide (WS2) as a transparent electrode and a photoactive layer, respectively. The cell has the potential to achieve a transparency of 79%.
Optical image of the highly transparent solar cell.
Image: Tohoku University, scientific reports, Creative Commons License CC BY 4.0
Scientists from the Tohoku University in Japan have fabricated a near-invisible solar cell based on indium tin oxide (ITO) and tungsten disulfide (WS2) as a transparent electrode and a photoactive layer, respectively.
In this kind of PV device, which is also known as Schottky junction solar cell, the Band necessary for charge separation is provided by an interface placed between a metal and a semiconductor. In the proposed device and ideal Band structure, the discrepancy in the work function (WF) between one of the electrodes and the semiconductor separates the photogenerated electron–hole pairs. “Once the generated carriers travel to the opposite electrode, power generation can be realized,” the scientists explained.
WS2 is a member of the family of materials known as transition metal dichalcogenides (TMDs), which the scientists said are ideal for near-invisible solar cells, due to their suitable Band gaps in the visible light range and highest absorption co-efficiency per thickness.
In the development of solar cells, the researchers sought to avoid interface impurity that they said may be the cause of undesired surface recombination, which would, in turn, reduce the separation efficiency of carriers at the interface barrier, thus affecting the device’s open-circuit voltage.
The ITO–WS2 junction was fabricated by sputtering ITO on quartz substrate and the WS2 monolayer was grown via chemical vapor deposition (CVD). ” The work function of the transparent ITO electrodes was modulated by a thin metal film coating without sacrificing the high transparency of ITO,” the group said.
The solar cell achieved a power conversion efficiency that is 1,000 times higher than that of a reference device using a normal ITO electrode. “Large-scale fabrication of the solar cell was also investigated, which revealed that a simple size expansion with large WS2 crystals and parallel long electrodes could not improve the total power (PT) obtained from the complete device even with an increase in the device area,” the academics said, noting that the cell has the potential to achieve transparency of 79%.
They presented the cell technology in the paper “Fabrication of near-invisible solar cell with monolayer WS2“, published in scientific reports. “These findings can contribute to the study of TMD-based near-invisible solar cells from fundamentals to truly industrialized stages,” they said.
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Emiliano joined pv magazine in March 2017. He has been reporting on solar and renewable energy since 2009.
Transparent Solar Panels: Reforming Future Energy Supply
New solar panel technologies are set to transform the global solar energy landscape. Some of these promising technologies are already in the advanced stages of development, and could hit the market fairly soon. With these innovations, solar is no longer going to require extensive land parcels or unsightly roof spaces. (Aesthetically appealing and highly efficient solar shingles, for example, are already creating attractive solar roofs.)
What are transparent solar panels?
Photovoltaic glass is probably the most cutting-edge new solar panel technology that promises to be a game-changer in expanding the scope of solar. These are transparent solar panels that can literally generate electricity from Windows—in offices, homes, car’s sunroof, or even smartphones. Blinds are another part of a building’s window that can generate electricity (we will discuss it in a later section).
Researchers at Michigan State University (MSU) originally created the first fully transparent solar concentrator in 2014. This clear solar panel could turn virtually any glass sheet or window into a PV cell. By 2020, the researchers in the U.S. and Europe have already achieved full transparency for the solar glass.
These transparent solar panels can be easily deployed in a variety of settings, ranging from skyscrapers with large Windows to a mobile device such as a phone, a laptop, or an e-reader. As these solar power Windows can simply replace the traditional glass Windows in offices and homes, the technology holds the potential to virtually turn every building in the United States and the world into a solar producer.
How do solar panel Windows work?
A transparent solar panel is essentially a counterintuitive idea because solar cells must absorb sunlight (photons) and convert them into power (electrons). When a solar glass is transparent, the sunlight will pass through the medium and defeat the purpose of utilizing sunlight. However, this new solar panel technology is changing the way solar cells absorb light.
The cell selectively harnesses a portion of the solar spectrum that is invisible to the naked eye, while allowing the normal visible light to pass through. To achieve this technological wonder, the researchers have developed the transparent luminescent solar concentrator (TLSC) rather than trying to do the impossible by creating a transparent photovoltaic glass cell.
The TLSC is composed of organic salts that are designed to absorb specific invisible UV and infrared light wavelengths, which then glow (luminesce) as another invisible wavelength. This new wavelength is then guided to the edge of the window plastic, which thin PV solar cell strips convert it into electricity.
Once the mass production begins for transparent solar panels, researchers estimate that the TLSC should be able to deliver an efficiency of about 10%. This may not appear to be an earth-shattering number, but on a national or global scale, when almost every window in a home or office building consists of clear solar panels, the results can be transformative.
As the transparent solar panels cost comes down with their mass production and deployment, this non-intrusive technology can be scaled right from commercial and industrial applications to handheld consumer devices, while remaining very affordable.
Types of transparent solar panels
Just the way solar roof panels are currently produced using different technologies (Tesla’s solar shingles and other technologies), solar Windows are also being developed using different techniques. The two major types of transparent solar panels include partial and full transparent panels.
Partially transparent solar panels
A German manufacturer, Heliatek Gmb, has developed this partially clear solar panel, which can absorb about 60 percent of the sunlight it receives. Compared to the conventional solar PV cells, the partially transparent solar panels have a lower efficiency at 7.2%. However, solar power generation can be increased by adjusting the balance between the sunlight that is transmitted and absorbed.
For instance, in south-facing glass buildings, it is often important to reduce the transmitted light (many such office buildings already use tinted glass). In these locations, the partially transparent solar panel can work very well.
Fully transparent solar panels
As described in the beginning of this report, researchers at MSU have already achieved a breakthrough to produce fully transparent photovoltaic glass panels that resemble regular glass. Researchers estimate the efficiency of these fully transparent solar panels to be as high as 10% once their commercial production commences.
It’s vital to understand here that when it comes to solar panel Windows, efficiency of the panel is not the be all and end all. In practical terms, a less efficient solar window only means that the window has to be larger in size compared to the more efficient panel in order to generate the same amount of electricity.
Once fully transparent solar panels get integrated into large Windows in buildings, their lower efficiency is bound to be overcompensated by their potential scale of deployment.
Solar panel blinds: An easy-to-implement solar window technology
Solar panel blinds are a supplement to transparent solar glass/panels when using the window to generate electricity. Solar power panels are designed to harvest sunlight to produce energy, while the essential function of window blinds is to block direct sun’s rays from entering inside.
Solar panel blinds are cleverly combining these two divergent functions. An innovative startup called SolarGaps has introduced solar panel blinds, which it claims can cut down energy costs by up to 70 percent. For every 10 sq. ft. of window space, these solar window blinds can generate 100 watts of power (you could roughly power three laptops with this much electricity).
These solar blinds can be installed either inside or outside, and you can control their angle and positioning using an app that will also inform you of the energy generation figures. It includes a setting to automatically optimize the angle of the blinds according to the position of the sun.
Pioneers in transparent solar panel research and manufacturing
Researchers at Michigan State University and MIT as well as manufacturers such as Ubiquitous Energy, Physee, and Brite Solar are pioneers in promoting this new solar panel technology.
Ubiquitous Energy, in partnership with a leading glass manufacturer NSG Group, is developing Ubiquitous’s unique ClearView Power technology to integrate transparent solar panels into architectural glass Windows. ClearView Power’s transparent solar coating can be directly applied to building Windows at the time of the normal glass making process.
The technology also enhances energy efficiency of the buildings through blocking of infrared solar heat. When combined with solar energy generation through clear solar panels, it can lead to net-zero energy buildings. The company has already announced that ClearView Power’s transparent solar cells have reached an electricity conversion efficiency of 9.8%.
Physee is a European manufacturer that has introduced an advanced product called PowerWindow. In fact, it is the only currently installed transparent solar panel in the world right now (covering 300 sq. ft. in a Dutch bank building).
Physee’s PowerWindow makes use of small solar panels that are installed along the window pane edges to generate power. While these solar Windows are unable to be a standalone power source for buildings yet, the company is confident of Rapid improvements in the scale and efficiency of its transparent panels.
PowerWindows serve as the building blocks for “SmartSkin,” the clear photovoltaic glass that the company is promoting as the “future-proof glass façade for next-generation sustainable buildings.” SmartSkin can work autonomously to sense, power, and regulate the climate inside the building using intelligent systems.
The future of transparent solar technology
According to Richard Lunt, the Johansen Crosby Endowed Associate Professor of Chemical Engineering and Materials Science at MSU, highly transparent solar cells represent the “wave of the future” for new solar panel technologies.
Lunt says that these clear solar panels have a similar power-generation potential as rooftop solar, along with additional applications to improve the efficiency of buildings, cars and mobile devices. Lunt and his team estimate that the U.S. alone has about 5 to 7 billion square meters of glass surface at present. (Just in the last 10 years, as much as 682 million sq. ft. of office space has been added in the U.S.).
With this much of glass surface to cover, transparent solar panel technology has the potential to meet about 40 percent of the country’s annual energy demand. This potential is nearly the same as that of rooftop solar. When both these technologies are deployed complimentarily, it could help meet nearly 100 percent of the U.S. electricity needs if we also improve energy storage. comment
Transparent Solar Windows: You Ain’t Seen Nothing Yet
See-through, truly transparent solar Windows could open the door to a whole new clean power revolution while conserving farmland and natural habitats, too.
The idea of transparent solar Windows almost sounds too good to be true, and it is, but not entirely. Researchers have been hammering away at the challenge of harnessing sunlight to generate electricity from see-through Windows for years. The prize is acres upon acres of new sites for solar panels on buildings, without losing the energy-saving advantages of daylighting. Just look at any glass building and you can practically feel the blooming of the possibilities. The obstacles are many but it looks like a real breakthrough is finally at hand, so to speak.
Transparent Solar Windows, For Real
See-through solar cells have been bouncing around the CleanTechnica radar since at least 2010, when the possibility of creating a transparent solar window was beginning to emerge alongside thin film solar technology.
Thin film solar technology is just what it sounds like. Instead of a stiff, bulky solar panel that nobody can see through, the thin film platform involves fabricating flexible solar cells in the form of a solution that can be literally painted onto various surfaces, allowing sunlight to trickle through.
One early obstacle between fully transparent solar cells and the commercial market is scaling up from laboratory specimens to a marketable size.
That problem has begun to fade out of the picture, but researchers are still fiddling around with graphene and other high-tech tweaks to tackle the real meat of the matter, which is how to formulate a truly transparent solar window that works effectively enough to justify the cost.
MSU Plunges Into Transparent Solar Cell Territory
The latest buzz over transparent solar cells was sparked last August, when Michigan State University announced a makeover of its Biomedical and Physical Sciences Building with fully transparent solar Windows.
To be clear, the MSU project is more of a toe-dipping than a plunge. Still, it appears more ambitious than other transparency projects to surface this year. The new MSU solar array consists of a 100-square-foot installation of transparent panels above the main entrance to the building. If all goes according to plan, which presumably it has, the idea is to harvest enough sunlight to light up the atrium.
See-Through Windows That Generate Electricity
The company behind the project is Ubiquitous Energy, which was co-founded by MSU Professor Richard Lunt, who holds the Johansen Crosby Endowed Professor of Chemical Engineering and Materials Science at the school’s College of Engineering.
Got all that? Good! Lunt’s contribution to the field of transparent solar cells is a window that looks exactly like conventional glass, but it sorts out visible light from the invisible light at both ends of the spectrum, meaning ultraviolet and infrared light. The visible light passes through and the rest is put to work generating electricity.
That’s an interesting twist, because normally one would think that visible sunlight does all the heavy lifting in a solar cell. Maybe it does, but researchers like Lunt have also discovered that invisible light can generate a significant share of electricity, too.
Back in 2017 MSU profiled Lunt’s work and explained that he and his team “pioneered the development of a transparent luminescent solar concentrator that when placed on a window creates solar energy without disrupting the view. The thin, plastic-like material can be used on buildings, car Windows, cell phones or other devices with a clear surface.”
“The solar-harvesting system uses organic molecules developed by Lunt and his team to absorb invisible wavelengths of sunlight. The researchers can ‘tune’ these materials to pick up just the ultraviolet and the near-infrared wavelengths that then convert this energy into electricity,” MSU adds.
Of course, transparent solar cells do not rank as high on the solar conversion efficiency chart as their conventional counterparts, since they don’t take full advantage of all the sunlight that hits them. Still, Ubiquitous Energy’s technology offers a respectable 10% conversion efficiency at a relatively low cost, due to the use of abundant, inexpensive materials.
The location of the MSU installation also suggests that solar installers can help trim costs by placing arrays of transparent solar cells at or near their end use, which would help reduce expenses related to wiring and other electrical systems.
Onward Upward For Windows That Work
As for next steps, that’s an interesting question. Our friends over at EnergySage recently took a look at the market, and so far it looks like Ubiquitous Energy is the first to come up with a truly transparent form of photovoltaic technology that looks like a regular window.
EnergySage does take note of another approach, which is to treat only the edges of a window pane as solar cells, leaving most of the surface as standard glass. That approach has been adopted by the solar cell company Physee, marketed under the name POWER.
“POWER is our power generating glass coating. It directs sunlight onto integrated solar cells in PowerWindows. Without impacting the transparency of its glass, Windows will produce the same energy as 1/5 of a solar panel placed on a building’s roof,” Physee explains.
The High Tech Window Of The Future
Physee is also applying it solar know-how to greenhouses, though not to generate electricity. The company’s PAR coating is designed to boost greenhouse yields by transforming ultraviolet light, which plants can’t use, into visible light, which they can.
Meanwhile, researchers continue to attack the challenge of transparent solar cells.
Some interesting developments this year include a new silicon nanowire design aimed at improving solar conversion efficiency, and applying fullerenes (think carbon and Buckminster Fuller) to improve transparency.
Transparent Solar Windows The Built Environment
Ubiquitous Energy certainly has put MSU on the solar cell map. Another emerging area of interest in the solar field is floating solar panels, and MSU is all over that, too.
Last year a team of MSU researchers came up with a study indicating that the push for constructing new hydropower dams could be alleviated by using the surface of existing dams to install floating arrays of solar panels.
The common denominator with Lunt’s research is the use of the built environment to generate clean power, rather than destroying natural habitats for new construction.
The emphasis on using pre-developed sites for solar power also extends to farmland. Experts at MSU see a lot of potential in the newly emerged area of agrivoltaics, in which ground-mounted solar panels on farmland are raised several feet higher than the usual practice.
The raised solar panels allow room for grazing livestock or maintaining pollinator habitats. Raised solar panels can also yield regenerative agriculture benefits, by reducing evaporation and conserving water.
Evidence is mounting that yields for certain food crops can also improve due to the partial shade and regenerative benefits of solar panels.
If all goes according to plan, the sparkling green farmhouse of the future will sport rooftop solar panels and transparent solar Windows that gaze out upon acres of lush fields and solar panels, too.
By the way, if you’ve been hearing a lot about agrivoltaics recently, remember you heard it here first. CleanTechnica began covering the solar-plus-farming trend back in 2019, including an interesting twist in which solar panels could help rescue, not destroy, an entire industry.
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Photo (screenshot): Transparent solar Windows developed by a team of solar researchers at Michigan State University (video credit: MSU).
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