Solar energy generation is growing at an incredible pace. It’s getting cheaper, with a growing number of federal and state grants, tax incentives, and financing programs making it easier for building owners to pencil it in. In California, it’s even mandatory for most new buildings to have rooftop solar arrays. But another solar technology is emerging that, though largely unproven, could be vastly cheaper and easier to install and effectively allow buildings to power themselves. Solar windows, which convert sunlight into energy in the same way as solar panels using transparent cells, were first invented in the last several years and are now being tested on properties worldwide. The nascent technology could transform a building’s energy efficiency and energy use. Companies in the space are betting big that they’ll do just that.
A big coup for the emerging industry happened recently when the outdoor apparel brand Patagonia tapped the solar window maker Next Energy Technologies to install the technology on the company’s headquarters building in Ventura, California. The partnership made a lot of sense. The clothing retailer has long been known for its commitment to environmentally-friendly practices and sustainability efforts, not just in how it manufactures its products but in its offices too. Patagonia’s headquarters complex, made up of nearly a dozen low-rise buildings, already has a large solar array above its parking lot that provides some of the energy it uses to power its office and shade for employee vehicles. To start, the retailer has installed 22 solar windows from Next Energy Technologies at a south-facing building within its campus. “We can figure out how it works and support its development,” said Vincent Stanley, Patagonia’s director of philosophy. “If it does work, the potential is enormous.”
The concept of windows generating energy through solar has been around since the 1980s when the first prototypes for the technology were developed. Most commercial solar windows produced since then were made from glass coated in amorphous silicon. The substance is related to the black silicon panels typically found on rooftops. But while the material can be made thin so that light can pass through it, it’s reportedly only around 5 percent efficient, meaning windows don’t produce electricity very well, and the cost per watt is high. But it wasn’t until the last few years that researchers discovered chemical compounds that can make much more efficient–and extremely thin–solar cells to be used in solar window applications.
By using perovskite microcells, researchers in South Korea last year were able to convert electricity at an efficiency rate of 20.1 percent (equal to typical rooftop solar panel averages) that can be used in colored solar windows. In similar research out of Australia, scientists produced cells from the same chemical compounds with a conversion efficiency of 15.5 percent that increase solar windows’ stability while allowing more sunlight to pass through.
In 2017, a tech startup called Physee installed solar windows at the headquarters of a Dutch bank in Eindhoven, a city in the southern part of the Netherlands. The company installed 323 square feet of the solar technology, which the company calls PowerWindows. It was described at the time as “the world’s first commercial, fully transparent solar-power-generating windows.” With the technology, bank employees could charge their cell phones by plugging them into the windows via USB ports. More projects were on the docket for Physee, including its largest one yet: a 19,000-square-foot installation at a newly-built residential building in Amsterdam. At the time, the company said it was working on new technology that would triple its current model’s efficiency.
There are a number of companies manufacturing and selling solar windows in the US at the moment. One of those firms is the Silicon Valley-based Ubiquitous Energy, which claimed to have installed the world’s “first truly transparent solar window facade” at its company headquarters in Redwood City, California, in early 2020. The following year, the company announced it had installed solar windows at a newly-built office building in Boulder, Colorado. The company’s trademarked design is a transparent photovoltaic coating called UE Power that they developed over a decade with the glass industry after first creating the technology at MIT. At the Boulder office building, electricity collected through the windows is then transmitted through discreet wiring built into the window frame to help power the building, which also has opaque solar panels mounted on the facade of the building. “We want every window to be electricity generating while remaining invisible to allow people to see clearly out to the world,” said Veeral Hardev, Vice President of Strategy at Ubiquitous Energy.
Ubiquitous, which has raised $75 million in 13 founding rounds, has installed its solar window technology at other kinds of properties as well, including an academic building on the Michigan State University campus and a sheet glass manufacturing facility in Ohio. Company leaders at Ubiquitous have said that installing their transparent panels costs up to 20 percent more than a regular window. However, the panels themselves can produce up to two-thirds of the energy that traditional solar panels do, and the electricity generated helps offset the cost.
For owners of office properties, these recent examples from solar window companies and Patagonia’s solar window trial at its headquarters will be important to watch. The company that provided Patagonia’s windows, Next, said in December that his firm hasn’t decided how much the windows will cost but expects that customers will be able to pay off the cost within one to five years if they take advantage of federal tax credits and electricity bill savings that will come as a result of the windows.
Solar windows are generally more expensive than traditional solar panels, and many on the market have a lower conversion efficiency. That makes them a harder sell to both homeowners and commercial property owners. However, as the push for renewable financing grows around the country, it should help alleviate the upfront costs of the technology. Jessica Bailey is the president & CEO of Nuveen Green Capital, which lends to commercial building owners to help finance energy efficiency upgrades. She told me recently that her firm is doing a lot of financing for rooftop solar and windows, and it’s an industry where she’s seeing a lot of innovation. “Solar has been a big piece of our business as building owners explore ways to integrate solar,” Bailey said.
The promise of solar windows is undeniably promising. If they work as intended and are installed at scale, it could drastically change how buildings are powered. There are big issues related to the cost of solar windows that tax credits, renewable financing programs, and electricity cost savings will help address, and more examples of major companies installing them could be a big boost for the burgeoning industry. But the biggest hurdle to the widespread use of solar windows is proving that they work as intended. As it’s still a nascent technology, it will take time to study and analyze how it has performed. Once concrete, indisputable evidence of solar windows doing just as they are promised emerges, a rush of new companies will likely enter the market and lead to more knowledge and adoption of solar windows. All the industry can do now is hope and wait.