Ingenious PV Glass Window Hits Chicago

Pythagoras Solar makes a revolutionary solar-powered window – literally an insulated window with integrated photovoltaics – that has the ability to turn buildings into massive power producers. The company has been testing a pilot project on the south-facing windows of the 56th floor of Willis Tower, formerly known as Sears Tower. If the pilot goes well, Willis Tower could end up with a surface area of up to two megawatts of solar.

Pythagoras Solar claims to be the first company to offer a fully-integrated photovoltaic glass unit, or PVGU, that balances energy efficiency, high power density, and transparent design in a meaningful way.

In other words, the PVGU replaces insulated glass units and has both a low U-value and a low solar heat gain coefficient. At the same time, the solar-integrated window delivers the highest power density of any other building-integrated photovoltaic solution by generating up to four times more of electricity, according to the company. The PVGU also allows natural light and a certain level of transparency (see picture).

The first PVGU offerings have been designed specifically for vertical curtain wall and skylight applications. Future products may include roof tiles and spandrels, according to Pythagoras.

Pythagoras told Jetson Green in an email the PVGU is priced to deliver a 5-year return on investment – a calculation that includes energy efficiency and power generation gains. Specifically, the PVGU is about $125 per square foot in U.S.-based projects.

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17 Comments

I remember seeing this late last year (I think it was) online. It looks promising, but the thought of floor to ceiling glass 58 floors up kinda freaks me out. I was in Chicago a few years back when an unsecured scaffolding got loose in the wind and knocked a bunch of windows out of the Hancock.

This is an exciting product. Products that serve multiple functions are where it’s at regarding sustainability. I hope that PV becomes one of the standard upgrades that are available when purchasing windows.

I don’t see a building like the Willis tower (or really any major existing skyscraper) doing a retrofit with these windows. New installations make sense, but imagine the cost of replacing thousands of windows. The payback of five years might be the offest of these windows versus a standard window pane in a new installation, but in existing buildings, the cost of the glass is already included in the building and unless a tornado comes through and blows out all the glass (happening more often these days) a building owner would have a hard time justifying the millions it would cost to do this.

Eletruk, take a look at what the Willis Tower folks have done: replaced glass where it will get lots of sun. I’m guessing that, even in new construction, one would only choose to put this glass where it actually stands to see a fair amount of sun. It’s not likely that every side of a skyscraper will be a good candidate for solar activity.

This sounds great, but lets look a little closer. The angle of incidence of the sun to a verticle building side is related to the latitude. Chicago is at 42 degrees latitude. This is better than the equator where the sun is directly overhead. In Chicago, the sun is 48 degrees from perpendicular to the panel. This reduces the sunlight hitting the panel by 33 percent (67 percent of the possible light, if the panel was normal to the sun, is hitting the panel) We are losing 33 percent of the possible energy. If the panel is 12 percent efficient, this makes the equivilient efficiency around 8 percent. Don’t forget that optics are not 100 percent effecient. Last time I checked Chicago was not the sunniest location. Don’t forget the cost of the wire and electronics to get all of this converted to 110 or 240 volt ac power. How much energy did it take to make all of this and install it and how much will we get back over the life of the panel??

@reality check well obviously the numbers you show arent all that. But then again the PING idea is PINGING good especially when the oil is POLLUTING and NUCLEAR is unsafe. To think beautiful thoughts you gotta start inside. retrofitting internally would drop any costs significantly . id like at least one of these panels . and the more they can make the cheaper theyll get. peace

great idea…but am curious why the “daylight” lite is covered in pv. Yeah you get the view, but lose a lot of potential light along with the opportunity to turn off electric lights. How does energy generation compare to the lost daylight and electricity savings? Maybe its a wash, but I doubt it. From the picture, it looks quite dark on the inside of the window.

huh?: Exactly! Diffused Lighting! Someday, when you are old enough and actually get to work in an office building with genuine windows, you will notice the windows are commercial grade THICKer than your bedroom window. Do you understand now? Be Well.

More than diffuse lighting. Greatly reduced daylighting. Why are so defensive? I have a sample on my desk in a real grown up’s office, and there is no way I would spec this as “daylight” glazing. Everybody knows to spec high vt glazing up high. The real reason is that it looks great in the picture.

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