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Anyone who has sweltered in a south-facing room during torrid summer days knows just how much solar power can stream through a window. As a matter of fact, many architects and designers treat windows only to reduce the sun’s heat and glare. For many years, scientists have worked on a window coating that could capture the sun’s heat (or keep it outside) while letting the sun’s gentle rays enter. They’ve finally done it.

Solar energy is by no means a new concept. However, when people think about solar energy they generally imagine oversized, dark checkerboards sitting in endless fields or installed on rooftops. Despite their enormous size and unattractive appearance, solar panels are increasing in popularity.

According to a recent Fortune magazine report, the number of American residential solar energy panels has been quickly growing and expanding across multiple states. The magazine ads that the number of solar roofs has increased 70 percent every year, going from 4 states with animated residential solar markets, to 10 states.

The ever-increasing popularity of solar energy systems has fueled intense research. The final result: see-through solar panels.

The Transparent Solar Panel: Somewhat of an Oxymoron

Scientifically, the term “transparent solar panel” or “see-through solar window” is something of an oxymoron. That’s because photovoltaic solar cells generate energy by absorbing sunlight (photons), and transforming it into electricity (electrons). A material that is considered “transparent”, by definition, enables all the light to pass through it and strike the back of the eye.

Many so-called ‘transparent solar cells’ in the past weren’t actually transparent because they only allowed a part of the light to pass through and they also casted a colorful shadow. These past efforts have yielded poor results because the energy production was low and the materials were highly colored, despite their transparent label.

“No one wants to sit behind colored glass. It makes for a very colorful environment, like working in a disco.”- Professor Richard Lunt of MSU’s College of Engineering

Although the sun has the largest potential of any renewable energy source in the world, our ability to exploit it has been limited. Until now, at least. At present, solar energy is harnessed mainly through the installation of photovoltaic panels on rooftops. These installations are, at best, 20% efficient at turning sunlight into electric energy.

While solar energy advocates have boosted the efficiency of photovoltaic panels, many scientists believe that to truly take advantage of the sun’s power, we must expand into the real-estate sector and make cells entirely see-through.

The Future of Solar Energy is Clear

Back in August 2014, researchers at the Michigan State University developed a 100% transparent solar concentrator that could transform any sheet of glass or window into a photovoltaic solar cell. Unlike other “transparent solar panels” announced before it, this one actually is transparent. The MIT startup is getting very close to bringing its new invention to the solar panels market.

This innovative solar cell can be installed on the windows of skyscrapers, residential homes, and arboretums.

“Researchers on the Michigan State Team believe that their TLSC technology could span from industrial applications to more manageable uses like consumer devices and handheld gadgets.” Source: Digital Trends

Of course, harvesting the sun’s invisible rays means forfeiting efficiency, so researchers are changing the way the cell absorbs energy instead of shrinking its components. Their new technology is capable of selectively absorbing only parts of the solar spectrum that the human eye cannot see while letting visible light pass through.

Invisible Spectrum Power

We learn about transparent solar power in elementary school. We are told that the sun transmits energy in the form of invisible infrared and ultraviolet light, as well as visible light. A technology that would only capture invisible light would, therefore, be considered transparent.

The secret to such a technology is organic chemistry. By using nature’s building blocks: carbon, hydrogen, oxygen, and a few other elements, scientists have been able to design a plethora of molecules that transport electrons (= carry electric current).

“The beauty of organic chemistry is there is a big variety of materials available. The sky’s the limit. You can design the material to look green to the eye, blue, any other color, or transparent.” – Source: Nikos Kopidakis, of the U.S. Department of Energy’s NREL (National Renewable Energy Laboratory).

Nikos Kopidakis also ads that there is a direct relation between the efficiency and transparency level of a glass sheet. However, their approach to transparent solar window technology has enabled them to achieve an efficiency of over 10%.

This filtering of sun light could also have a positive health effect because – the glass panels block UV light that causes skin cancer. This means that the solar cells are serving a double purpose.

How Photovoltaic Glass can Transform Windows into Solar Generators

Imagine a skyscraper made entirely of transparent solar cell glass. Manhattan is currently home to roughly 47 thousand buildings that have a total of 10.7 million windows. If only one percent of these windows (100,700 to be more exact) could generate electricity using transparent photovoltaics, the world would be a much better place.

At least two companies are preparing to sell solar glass window technology to window manufacturers promising that the upfront costs could be covered in one to two years. They say that only 2% of glass manufactured globally is used for solar panels, and 80% is used for building windows. This means that there is infinite market potential for transparent solar windows.

Solaria has invented layered glass windows that sandwich photovoltaic cells sliced into 2.5-millimeter strips. While not as transparent as the solar windows invented by the MIT start-up, Suvi Sharma, CEO of Solaria, promises that their PV layered windows are invisible to the human eye.

The company is already working on several pilot programs and large scale commercial projects in California & Europe to prove its products. Solaria uses window frame wiring to hide its connectors, which lead to a central power inverter.

What’s more, the technology can also be used with micro DC-to-AC power inverters to generate electricity for only one room with a solar window. Other options would be to distribute energy through a microgrid inverter to an entire floor, or to distribute energy through a central inverter to the entire building.

Image Credits: ComputerWorld.com

An added benefit to Solaria’s invention is the fact that the photovoltaic strips absorb the light that strikes the window, thus reducing the solar heat gain coefficient. In simpler words, these PV panels will have a positive effect on a construction’s internal air temperature, ultimately reducing air conditioning costs.

All of this sounds great, but what are the costs involved in using this new technology? According to the CEO, solar windows will be approximately 40% more expensive than conventional windows, but return-on-investment (ROI) will be achievable within a year from the initial installation.

“This technology is in very high demand because right now skyscrapers don’t have a good way of offsetting energy through renewable energy generation.”

Another ambitions company that has invented a unique transparent photovoltaic cell technology for buildings is SolarWindow Technologies. The company has invented organic photovoltaics that come in various colors and transparency levels. According to SolarWindow’s CEO, John Conklin, the ease-of-integration sets his technology apart from other competitors.

The organic photovoltaics are based on a PV film that can be adhered to traditional windows or integrated into the manufacturing process. The company has also taken into account the orientation of a building. In optimal conditions, SolarWindow’s invention could provide eight to ten percent of a skyscraper’s energy needs.

Image Source: SolarWindow Technologies

In addition to this, SolarWindow plans on offering a 25-year warranty to its technology. The company claims that its coatings can generate electricity even from artificial or shaded light, as opposed to traditional solar systems that only work with direct sunlight and require 10-12 acres of space to be efficient.

The company presented a working version of its technology to stakeholders and participants. Unfortunately, this form of paneling will only become available in the next four years.   

These three inventions may not have entered the market yet, but they represent a huge step forward from traditional solar panel technology that have a PV efficiency of 15-20%.

“When you’re looking at absorbing visible light and it’s transparent, it’s not as efficient as an opaque panel.” Source: John Conklin, SolarWindows CEO

It’s crucial to note that the three inventions mentioned above can be installed virtually anywhere, as opposed to solar panels which require a lot of open space, or can only be mounted on rooftops.

Furthermore, where solar window technology is concerned, transparency matters more than efficiency, because passive windows can be transformed into energy generating ones. In other words, solar glass window technology is all about utilizing perfectly good real estate to supply global energy demands.

How is this Technology Possible?

To understand how this technology was made possible, we have to take a closer look at previous inventions. Despite the fact that multiple attempts were made to create transparent solar panels, most of them were unsuccessful. That’s because the material used remained dark so it could not be used as a glass window material. Furthermore, electricity generation for these technologies was minimal.

MIT researchers managed to resolve this problem by developing a material that only absorbs invisible rays (e.g. infrared light). Once this light is absorbed, it is directed towards the edges of the panel where it is transformed into electricity. Scientist were able to clear the central area of the glass by concentrating the area of transformation into the edges of the window.

As a result, the energy output of the glass has been significantly improved, and power loss generated from the window’s transparency has been reduced.

The Future of Glass Solar Panels

There is already great interest in this emerging technology. In the past years, some of the most ambitious & innovative buildings in the world have incorporated photovoltaic technology into their designs. For example, The Dubai Frame, an impressive construction in the shape of a rectangle, uses 1200m2 20% transparent golden photovoltaic glass tiles to produce 38kWp.

But this is not all. Some of the world’s most influential companies are also incorporating clean materials into their buildings. Coca-Cola has integrated PV panels at several of its largest bottling sites, while many airports, stadiums, and universities are installing solar energy solutions to limit their environmental footprint. Lastly, Apple has decided to commit a large portion of its budget to install photovoltaic technology on its flagships.

Despite the fact that the technology is still not accessible to the public, and the cost of photovoltaic solar energy glass is high, the potential exists. A functional transparent solar panel demonstrates that this renewable form of energy can go beyond the world of construction: mobile devices could use this technology to recharge batteries, agricultural greenhouses could become self-sufficient, and electric cars could increase their energy output.

Image sources: depositphotos.com