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Thin Film Could Soon Make Solar Glass and Facades a Practical Power Source

The possibilities for building-integrated photovoltaics are about to get much more interesting. Future buildings, even some in design today, could use a new, semi-transparent solar glass. Thin-film solar technologies may eventually make it practical for the entire building envelope to generate power.

A new technology makes it possible to manufacture windows that generate electricity and still allow 70 percent of the light to pass through. The developer of this technology, XsunX, calls it Power Glass. They are bringing their technology out of the lab this year, while they work on a solar cell that could be applied to a building's façade.

The transparency of Power Glass sets it apart from existing building-integrated photovoltaics (BIPV) products on aesthetics alone, and it could be considerably less expensive. Large-scale manufacturing techniques, combined with the use of thin-film photovoltaic materials, promise a lower cost on a per-watt or per-foot basis.

XsunX reel-to-reel cassette system allows high-volume production. Inside a sealed deposition chamber, solar cells are applied in a thin layer onto large rolls of supporting material. The process happens at 150 degrees C, low enough to use a plastic or polyester substrate.

Thin film offers diverse applications Power Glass is made using amorphous silicon, the non-crystalline form of silicon. What's different is that amorphous silicon can be deposited in a very thin film and remains flexible.

By comparison, the crystalline silicon used in conventional solar cells is a thousand times thicker, requiring more silicon. And crystalline silicon must be deposited on a rigid substrate that can withstand high manufacturing temperatures.

The applications of amorphous silicon thus far have been primarily in liquid-crystal displays and thin-film transistors; its photovoltaic applications have been limited by its relatively low power-producing efficiency compared to crystalline silicon.

The efficiency gap is closing, thanks to continued private development, and to research at the National Renewable Energy Laboratory. While the four percent conversion efficiency of Power Glass won't knock anyone's socks off, efficiency is not always the highest metric of effectiveness.

At the Power-Gen Renewable Energy conference I spoke with XsunX CEO Tom Djokovich, who offered a fresh perspective: "Maybe the opportunity is not in more efficient solar cells, but in more efficient use of solar cells," he suggests. "That's why BIPV is smart. It lets us use these vast, previously unused building surfaces. And we're not altering the aesthetics of the environment -- we simply wrap the building with an invisible capacity to produce energy."

Lawrence Gasman, principal analyst at NanoMarkets, writes: "Lower costs are likely to play a role in driving thin-film into the numerous markets already served by PV." However, he adds, marketers should not stress cost alone because, in the long run, "what will drive the thin-film PV market as much as anything else is its unique characteristics in terms of flexibility, weight and ability to integrate into other products."

Reel-to-reel reduces manufacturing cost
XsunX has exclusively licensed a reel-to-reel cassette system that it says allows high-volume production of thin films with low risk of contamination. Solar cells are applied in a thin layer -- about 0.2 microns thick -- onto large rolls of supporting material.

"This system provides our technology enough scalability and throughput to bring the price point down below two dollars per watt on power glass," Djokovich says.

The process happens at 150 degrees C, low enough to use a plastic or polyester substrate, but it requires extremely clean operating conditions.

"Roll to roll manufacturing suffers from various maladies," says Djokovich. "The innovation of our cassette system is that it allows you to place the scalability of roll to roll processing inside a vacuum deposition cluster tool."

In the sealed deposition chamber, multiple cassettes of film are processed simultaneously. The result is rolls of photovoltaic film.

Maybe the opportunity is not in more efficient solar cells, but in more efficient use of solar cells.
--XsunX CEO Tom Djokovich.

Alternative to mosaics
The flexible film is then applied, much like a low-e coating, to the surface of a multi-pane window. The film allows edge-to-edge coverage, making the entire window an active energy conversion area.

Architectural solar glass companies such as Scheuten Solar arrange opaque solar cells in glazing, separated by clear spaces, resulting in a visible mosaic or stripes. Power Glass looks more like tinted solar control glass, without a pattern. It blocks 30 percent of the incoming light, uniformly across the window opening.

Related articles:
"Solar Power Outside Promotes Collaboration Inside" Scheuten Solar Glass Case Study
"Solar Glass in a Nutshell"

Timing depends on licensees
XsunX has begun marketing its technology to potential licensees this year. Manufacturers will license the technology, and purchase the manufacturing equipment, from XsunX.

"We focus on the development of proprietary thin film solar cells and their manufacturing processes," explains Djokovich. "We sell technology, and the manufacturing processes are a delivery method that provides commercial scalability to our design."

A handful of product integrators have beta-tested sample films in concept Power Glass products for glazing applications. Tests like these help manufacturers build a business case for the new technology.

Once signed, licensees will take some time to integrate the reel-to-reel process into their plants. Look for the first commercial Power Glass products as early as 2007.

What next?
In January 2006 XsunX began developing a high-efficiency opaque solar cell with exciting potential to make the non-glass portions of buildings productive. It, too, is flexible, so it can be applied to contoured surfaces on a roof or façade.

The technology combines concepts from Power Glass and a nanocrystalline solar cell to make a two-sided solar cell. Stacking techniques like this have been the subject of research to increase power output by trapping more of the light spectrum.

Stacked solar cells were initially built as a string with one positive and one negative terminal, similar to a storage battery. And, as with batteries, degradation in one cell degrades the entire string. This is because of a requirement known as current matching: The cell with the lowest current limits the current of the complete unit.

The XsunX stacked cell will have four terminals, instead of two. Djokovich predicts this design will eliminate degradation by overcoming the need for current matching. He explains:

"We can have a solar cell on one side of an insulator working to its maximum potential, and a solar cell on the other side working to its maximum potential, and combined they provide significantly more power. Out the back we run two positive and two negative terminals. With that we eliminate a condition that's plaguing other thin film devices, the need for current matching."

The market for opaque photovoltaics overshadows that of solar glass. With this technology, XsunX is aiming squarely at that larger market. The company's researchers expect to achieve at least 12 percent conversion efficiency, if not 15 percent (comparable to today's silicon wafer technology), at a lower cost.

"This is a product that will go right after the crystalline wafer market and offer an alternative, a lower price point, and more diversity of applications," says Djokovich.

He sees the next BIPV opportunity in the form of roofing materials and facades, particularly in prefabricated construction.

"The trend is toward modular panel construction -- where entire façades of a building are prefabricated offsite -- and integrating these PV components into the façades at the factory level. Then when they're installed they're all part of an engineered, integrated structure."

This panacea of BIPV may be two steps closer to reality.


Could you please tell me how I can contact XsunX?


XsunX announced June 13 that improvements to the Company's new Golden, Colorado facility are on track. The Company plans to begin assembly and installation of its manufacturing system in the first week of July, 2006.

The company sells thin-film PV manufacturing systems, among other things; so what they will be installing is a system for manufacturing the systems they plan to sell.

What is the primary range of the wavelength of light that this thin film extracts out of the sunlight and what is its efficiency per m² as it passes through the glass?

Hi Dennis,

Since you presented the company, the shares lost more than 50% of the price. Can you explain me what's going on? Anyone dumping the price? Why's that? Lack of viability or what?

[posting delayed]

Producing power -VS- saving power efficiency. (Practicable-reasonable)

Is Powerglass efficiency with the primary range of the wavelength of light that XsnX thin film extracts out of the sunlight which is only 5% or less per sq m?

Powerglass is approximately 4% conversion efficiency at 70% transmissivity (transparency). Note: Transparency and conversion efficiency can be either increased (to 5%) or decreased based on the required specifications of the application.

Some tint glass could be as efficient with energy saving without the cost of extras set up: (wiring, converters, controls, special mounts, seals, overall added maintenance). All this adds extreme cost, which makes Powerglass a interesting concept, but very possibly unjustified for manufactures to add it into architectural glass as it is today, unless-XsnX R&D can bring the efficiency up to compete with some smart tint glass with already long proven efficiency in some standing buildings of today. Remember although it may have a tint color it does not have the capability to also work like the tint glass.

Visionaries, think about it. XsnX is only 5% efficient or less. Tint glass could be as effective.

My Opinion; fresh perspective.

I would like to know the efficiency of the thin film
cells and the cost of the panels and the requirements for a manufacturing license.

Thank you and I wait for your response

Dr. Miguel A. Moreno
Professor of Physics and Engineering
Chief Research Officer
Support Services of America Corporation

For Powerglass to fly economically it will have to not only “LOOK” like tinted glass it will have to “WORK” equally like conventional tinted glass PLUS produce electricity. In other words it will HAVE to compete with tinted glass which is a very successful energy conservation product. In fact all large glass walled buildings rely on tinted glass such as PPG’s Solarban products. The primary electrical energy cost of a large building is air conditioning (A/C) and Lighting and it is “more than just a bit”. If you use Powerglass to collect 4% to 5% of the solar energy as electricity instead of using conventional tinted glass the A/C and lighting load increases dramatically. The resulting increase in the annual energy consumption of a building would be huge unless Powerglass can equally do both.

It does not work like tinted glass. It was never intended to work like tinted glass. It is not for the same purposes of tinted glass”, what are you using it for? Powerglass might apply well for an unconditioned canopy but it is not a good trade-off for most unshaded windows.

Solarban 70XL glass, by PPG, is one of the highest performing glazing products on the market that enables a design team to maximize natural lighting opportunities while minimizing the required cooling equipment with a clear glass aesthetic. Independent studies indicate that Solarban 70XL glass has the potential to lower upfront HVAC equipment costs by up to 26 percent, IN ADDITION to an on-going annual energy savings of 3 to 5 percent.

So given this kind economic trade-off consideration, what will architects and engineers specify?


Tint decreases IR (heat), UV (as does glass, per se) - energy savings #1.

The touted EFFICIENCY TO COST gains on material are not equal to a RETURN ON INVESTMENT analysis. In California the Title 24 Energy code has a DOE developed energy code computer program that analyses the total energy cost of a project, which considers things like solar gain, reflection, angles of incidence and orientation. The overall cost of the product must include a trade-off between Standard PPG solar glass cost and the real cost of the PowerGlass including hidden costs such as wiring, controls, converters, special mounts, seals, maintenance and development funds which are difficult to obtain. (Opps), I forgot you pioneers are giving this part away for nothing. When is your payback, 1 year, 1 decade or a century? Architects and specifying engineers are just waiting for your glass so they can ask, have you ever been in the construction business?

Solar energy is an important part of the energy picture. Much has been accomplished over the last twenty years in passive solar building design and conservation features including cost effective solar space and water heating. PowerGlass is offering only a few percent of power conversion, which a few conservation measures could achieve more simply. What really upsets me is that some utopian dreamers are over hyping the jump from a low-grade energy source to see it as an equal replacement for high-grade power. We can’t compete with the other countries like China, Japan India etc. for example who teach their children real science and have done their homework.


Thin-Film Solar Cells]
Newly developed “see-through” thin-film solar cells have been installed on the curtain walls of Plant No. 2. Because the heat from solar radiation is moderated by the slight shading effect provided by these cells, the electric power load from air-conditioning can also be reduced. In addition, these cells have a structure in which a crystalline thin-film silicon solar cell is stacked on top of an amorphous silicon solar cell on the same glass substrate. This design makes it possible to effectively use light from a wider band of wavelengths, improving conversion efficiency to 11%, about 50% higher than Sharp’s conventional cells (7% conversion efficiency). The thickness of these new solar cells is about one one-hundredth of a typical crystalline solar cell, using an extremely small amount of silicon, and the fact that they allow sunlight to pass through gives them the potential to be used in application products offering outstanding design characteristics.



Nanosolar is on track to make solar electricity:
· cost-efficient for ubiquitous deployment
· mass-produced on a global scale
· available in many versatile forms.
Nanosolar has developed proprietary technology that makes it possible to simply roll-print solar cells that require only 1/100th as thick an absorber as a silicon-wafer cell (yet deliver similar performance and durability). Watch the CNN video.

IS-XsunX being left behind ?

Top awards product."Victory or superiority"

Because these newfangled rolls of foil are 200 times lighter than their silicon-based predecessors, they can even be attached to the sides of buildings. Best of all, the thin film will even work well on a cloudy day. Power companies must be trembling at this development, where a huge percentage of their customers might soon turn the tables, selling power back to them. —

(dead links removed)

It seems to me that the solution of the PowerGlass vs. Conventional Energy-Efficient window tinting would be an integration of the technologies. Forgive my ignorance on the subject, but why not put the PowerGlass film on the OUTSIDE of the glass, and the TINTING either beneath it, or on the INSIDE of the glass?

Could both be used to work together to get all the benefits of the energy-saving window tinting AFTER the light has passed through the power generating layer?

I realize it's not that simple; I'm just throwing that out as a solution consideration.


The concept of solar glass is not new. There are certain Chinese companies who experimented with it for years. There is debate for buildings using glass to generate electricity and as tint and insulation material. So far, the technology in China is still lagging for any photovoltaics to be economically viable, except for solar panels. Is XsunX on the verge of a breakthrough?

I will be replacing my South facing roof panels in my conservatory. Is it possible to integrate this product at the same time?

i am Akhtar from pakistan and have interest to make solar energy glass please advice me about solar glass matarial. can i make it himself? please response me as soon as posible.thank you.
your truly Akhtar. akhtarswati33-yahoo-com

Solar Illuminations (a ‘green’ corporation who has its headquarters in Florida) are likely to be offering solar powered glass panels in 2010. Basically they will look no different than a regular piece of glass and can be tinted various shades too. From inside and outside the building it looks like regular glass. However, the great feature is that the glass is actually a solar panel and will therefore create electricity. Imagine a tall building, fitted with hundreds of solar glass panels. Then, imagine one, two or three entire sides of the building using this solar glass. There is a huge potential to capture a large amounts of energy, hundreds of kilowatts! That energy can be used to supply power within the building, or put back into the grid and sold to the electric company, or a combination of the two. Amazing? Well, that is what Solar Illuminations is all about. They are taking solar energy one step further! Not only will this new, patented technology be available for new construction but also

This technology is interesting, it was actually first thought up and created a couple decades ago, however their was just to much power loss, and expense in the design until recent years. MIT has been creating their own form of this technology that seems very credible. It will be interesting to see how solar glass evolves in the next couple of years.