Solar Panels: Not Just Big Rectangles on the Roof Anymore

In designing the 28th Street Apartments in South Los Angeles, architects at KoningEizenberg had several underlying missions: To restore an 80-year-old structure, to add a new residential wing, and to modernize the entire complex, making it more sustainable. In sunny L.A., adding solar energy was a no-brainer.

But where exactly to add that solar is becoming an increasingly difficult question. Part of this affordable housing project is an historic 1926 YMCA originally designed by Paul Williams, the first African American to be certified as an architect west of the Mississippi. The building is a gem, both aesthetically and culturally, and it was incredibly important to keep Williams' vision as intact as possible.

The architects were able to add some photovoltaics (PVs) as well as solar water heaters to the narrow roof of the new structure, but, when it came to the historic structure itself, they didn't want to crowd its roof with anachronistic panels. Further, it was important to keep some space as a roof garden for residents. As they looked for available real estate on the building, they realized the back of the building faced south and, at some times of the year, got far more exposure than the rooftop. The architects decided they would try to install their SunPower monocrystalline photovoltaic panels vertically, along the rear elevation.

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It wasn't easy proving that it could be done. There were only a few buildings that had set the precedent, none of which had been reviewed by the city of Los Angeles.

"We had quite a challenge trying to plan check the system, because most of the PV panels are not tested for vertical application installations," says KoningEizenberg architect Paul Miller. Some community members were worried the panels would get hot and possibly cause a fire hazard. But, as principal Julie Eizenberg notes, the panels are installed a few inches from the exterior wall and rather than transfer heat onto the building itself, they actually allow air to circulate between the wall and the panel, creating a shading and insulating element. It's a win-win situation.

The architects' solution for adding solar was minimally intrusive and poetically simple. But it also made me wonder why we aren't taking full advantage of all sides of our buildings to gather solar energy in innovative ways.

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Building-integrated photovoltaics, or BIPVs, are a tiny but growing section of the solar industry looking beyond the traditional panel. First came "solar shingles," that use copper indium gallium selenide solar cells, the lightweight and unobtrusive "thin film" solar technology that's the slender cousin to the wafer-like traditional silicon cell. Dow's Powerhouse shingles, for example, pretty much disappear when applied to a traditional asphalt roof. The thin film is also much more cost-effective when it comes to installation.

Another, newer approach to integrating solar cells into a building is the concept of solar windows, where layers of monocrystalline silicon cells are placed between two panes of glass. Visible light is diffused through the panels while the direct sunlight is collected in the photovoltaic strips, which also can prevent heat gain from the sun. A prototype of this technology by Pythagoras Solar called a photovoltaic glass unit, or PVGU, can be found in a handful of skyscrapers, including the Willis (Sears) Tower in Chicago.

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The only issue here is that the glass isn't completely transparent—it's more like the effect of looking through a window with Venetian blinds. Of course, you don't always need to see perfectly out a window, but perhaps the smarter application here are Pythagoras' skylights, which bring in natural light and collect solar energy without needing to look like a regular window at all. These are also extremely cost-efficient, especially when you consider that you're integrating it into the cost of the window.

Meanwhile, in Switzerland, a group of researchers at the École Polytechnique Fédérale de Lausanne (EPFL) developed a different concept: dye-sensitized solar cells derived from an earlier technology called Grätzel cells, invented in 1988 by Michael Grätzel and Brian O'Regan at the University of California at Berkeley. This low-cost solar cell is based on the same concept as photosynthesis, using a photo-electrochemical process to generate power.

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To demonstrate this new tech, the school commissioned artists Daniel Schlaepfer and Catherine Bolle to design a facade of 1,400 windows in various colors. These orange, green, and gold panels are currently being installed at the SwissTech convention center, scheduled for completion in 2014. At over 3,000 square feet, it will be the largest solar glass installation in the world. Of course, you could argue that they still do look like solar panels, just turned on their side and installed like a kind of decorative stained glass.

But paneled solar glass is just the beginning. A British company named Oxford Photovoltaics is upping the ante by printing a layer of solar cells (Meso-Superstructured Solar Cells or MSSC) directly onto transparent glass, which can then be tinted any color, cut to almost any size, and won't have any of the telltale lines from the other solar windows. Not to be outdone, the University of Sheffield and University of Cambridge claim they will soon be able to spray "solar paint" onto plastic surfaces.

Solar panels on the side of a building are innovative now, but eventually we could transform an entire wall into a semiconductor as easily as we could slap on a coat of paint.