Flexible Solar Cells Could Let Buildings Generate Their Own Power

Imagine a high-rise, downtown office building doubling as a power plant. The image isn’t so farfetched and will probably be realized in the not-so-distant future, says Hannah Bürckstümmer, strategic marketing manager at Merck Group, a pharmaceutical, chemical and life sciences company in Darmstadt, Germany. Her company, like many others, is working to perfect flexible solar panels so they can be produced on a mass scale.

When they’re widely available in large lot sizes, the flexible solar cells can be affixed to buildings and other structures, turning them into mini power plant, supplying electricity to the building or banking energy to sell back to a local utility.

In fact, the solar technology can contribute to a sustainable future of buildings, Bürckstümmer says.

A developed country’s buildings consume about 40 percent of that nation’s total energy demand. A building designed along sustainable principles can produce all the power it needs by itself, she adds.

To get there, builders must first reduce the amount of energy the building needs, by using well-insulated walls or windows, for instance. Then, they can then turn to renewable energy sources to provide energy for electricity.

“The sun provides abundant energy to our roofs and facades,” Bürckstümmer says. “The potential to harvest this energy at our buildings' surfaces is enormous. Let’s take Europe as an example. If you use all the areas that have a nice orientation to the sun and that aren’t overly shaded, the power generated by photovoltaics would correspond to about 30 percent of our total energy demand.”

Flexible solar cells can help harvest that energy because they’re easy to affix to buildings, she adds.

The flexible cells are squares or rectangles, about the size of a hand, strung evenly across a thin substrate that can be rolled over and affixed to a surface, much the way butcher paper can be rolled the length of a countertop.

The long strips of cells are lightweight, bendable, and semi-transparent. Not only can they harvest the energy of the sun outdoors, they can also make use of indoor light, such as that emitted by LEDs.

Builders can take advantage of the cells’ low weight and its bendability.

“The first is important when thinking about buildings in warmer regions,” Bürckstümmer says. “There, the roofs are not designed to bear additionally heavy loads. They aren't designed for snow in winter, for instance, so heavy silicon solar cells can’t be used for light harvesting. But the lightweight solar foils are very well suited.

The bendability means the cells can also be with membrane architecture, like the sails of the Sydney Opera House, she added.  

The panels are a fit with many types of construction projects and are more aesthetically pleasing on buildings and other structures than the glass panels often used today, Bürckstümmer says. An art installation or a fountain in front of the building could also feature enough panels to provide power for a building comprised mainly of offices.

Traditional glass solar cells—the type most people think of when they consider solar installation—are installed as a second layer on top of the roof, which adds to installation costs. The flexible cells can be integrated with roof or wall construction. This saves on the installation costs as well as construction materials because two functions are combined into one element, she says.

When the cells are widely available, they can be printed in different shapes and designs to suit solar architects, planners, and building owners, needs, she says.

Merck is working on flexible solar panel technology that can be printed on flexible substrates via techniques that include continuous roll-to-roll processing on flexible substrates, which Bürckstümmer terms “a simple printing technique.”

The company’s technology mixes a polymer in repeating units, “like the pearls in a pearl chain,” and a carbon molecule. These two compounds are mixed and dissolved to become a type of ink.

“After printing, the resulting thin layer is the active layer, absorbing the energy of the sun,” she says. “You only need a layer thickness of 0.2 micrometers to absorb the energy of the sun and this is 100 times thinner than a human hair.”

But Merck’s flexible solar panels, like that of many other companies, remains experimental and isn’t mass manufactured.

While flexible solar cells are available today from some manufacturers—an Internet search will easily turn up manufacturers. But those flexible solar cells can only be purchased in rolls small enough to be affixed to a recreational vehicle or a boat.

Manufacturers haven’t yet found the perfect production method that will allow for many cells to be rolled across buildings and structures, says Kati Miettunen, project manager in the bioproducts and biosystems department at Aalto University in Finland, where researchers are looking at how the cells could best be manufactured on a large scale.

They need to be made through continuous roll-to-roll processing on flexible substrates, which can be tricky for the fragile electronics inside the cells. They can’t be damaged while they move quickly through the rolls, Miettunen says.

The cells must also be sealed, another challenge. If the cells aren’t fully closed to the elements, liquid electrolyte could leak out of the cell or impurities could seep in, greatly reducing the device’s life, Miettunen adds. For that reason, the material that covers the cells must also be flexible and able to move through the rolls. The industry continues to debate about the best material for this use.

The lifetime of these devices remain an issue, as do environmental concerns, another challenge to commercialization, say the researchers at Aalto University and the University of Montreal.

“Another prerequisite for commercialization is making the lifetime of devices adequate in relation to the energy embedded in the fabrication of the devices so that the solar cells won’t degrade before they have produced more energy than was used for making them,” says Jaana Vapaavuori, assistant professor of chemistry at the University of Montreal.

But Bürckstümmer is confident the days of mass production of these cells aren’t too far away. Once it comes, builders will find the panels of great use, she says.