Inside Clean Energy: What’s Hotter than Solar Panels? Solar Windows.

Researchers and startups are moving forward with plans for windows that generate electricity.

A student demonstrates the semi-transparent view through the solar cell. The new manufacturing process could enable meter-scale electricity-producing windows. Credit: Silvia Cardarelli, Electrical and Computer Engineering, University of Michigan
A student demonstrates the semi-transparent view through the solar cell. The new manufacturing process could enable meter-scale electricity-producing windows. Credit: Silvia Cardarelli, Electrical and Computer Engineering, University of Michigan

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The tantalizing idea behind solar windows is that the vertical surfaces on the outside of just about any building could unobtrusively generate electricity.

But first, researchers and companies need to figure out how to take this product from the lab to the factory.

Along those lines, University of Michigan researchers have published the results of their work on a process to manufacture windows that can be large—up to two meters by two meters—and efficient in terms of electricity production.

“You see a lot of these glass and steel buildings around which are just walls of windows,” said Stephen Forrest, an electrical engineering professor at Michigan and co-author of the study. “Why not turn that excess energy (from sunlight) into electricity to help power the home or the building?”


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Most solar panels use silicon as the material that receives solar energy, but solar windows need something different because silicon isn’t transparent. An alternative is to use dye-like compounds, similar on a molecular level to the dyes used in clothing.

Nearly all solar windows are semi-transparent, with a tint that can come in a variety of colors. From a distance, they may look like any tinted window, but up close you can see the clear lines separating the strips of solar material.

The Michigan team, whose work appeared this month in the journal Joule, has come up with a process of making solar cells from dye-like materials, which are connected to lines of metal so small they are invisible to the eye. The researchers designed the process to be able to work in a factory, as opposed to just in a lab.

The solar cell shown in the journal article is small enough to hold in your hand, but the process allows for construction on a much larger scale.

The window has an efficiency of 7 percent, which is the share of solar radiation that gets converted to electricity. This is less than the 10 percent that the team views as easily within reach with the technology, and also less than the 15 percent that is a starting point for most new silicon-based systems.

But developers of solar windows aren’t necessarily competing with the efficiency of silicon solar panels. While some buildings can have solar on their rooftops, a buyer of solar windows may be looking for the opportunity to generate electricity from windows, in addition to rooftop solar.

Like most emerging clean energy technologies, much of the work on solar windows is to increase efficiency and reduce costs to the point that the product makes sense to a prospective buyer.

Forrest and his colleagues have previously written that a solar window can be built and installed for about double the cost of a conventional window, and the income from generating electricity would pay for the difference in cost in two to six years, depending on factors like the level of sun exposure.

The University of Michigan is seeking a patent on the technology and also is looking for partners to take the next steps in producing and selling the windows.

Among the companies working in this space is NEXT Energy Technologies of California, which is developing its window product and building prototypes.

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NEXT has said its efforts are an important part of the transition to clean energy because commercial buildings account for 36 percent of U.S. electricity consumption. Windows are a big part of a building’s energy use, with energy loss that leads to greater demand for heating and cooling.

Another player is Ubiquitous Energy, also of California, which says it is developing a fully transparent solar window.

Forrest thinks that some of the initial interest in solar windows will come from homeowners, who also were early adopters of rooftop solar.

Looking at other potential users, he is especially excited about the potential for greenhouses.

“What does a greenhouse consist of?” he asked. “Well, it consists of windows. It’s all windows, all sides. Why shouldn’t those windows generate power? Not just a carbon neutral building, but a very, very carbon negative building.”

You can’t yet buy the window he’s developing, or the windows being worked on by the startups, but Forrest expects that solar windows will be on the market soon—like just a couple of years soon.

Other stories about the energy transition to take note of this week:

Joe Manchin, in a Reversal, Agrees to Climate and Tax Package: The spending proposal once known as Build Back Better has made a surprising comeback. Sen. Joe Manchin (D-W.Va.), said on Wednesday that he has agreed to vote for a revised version. His support may give Democrats enough votes to pass the measure in a party-line vote. Manchin is calling this the Inflation Reduction Act of 2022, and said in a statement that “Build Back Better is dead.” Since the bill’s text was not immediately available, it’s not clear how much of Build Back Better is in the new plan, but Senate Democrats said it will include about $370 billion for energy and climate spending, as Burgess Everett reports for Politico. This is a major reversal for Manchin, who has angered clean energy advocates with repeated rejections of versions of the Build Back Better proposal, only to continue negotiating.

US Clean Energy Installations Down 55% in Second Quarter: Development of U.S. clean energy projects fell in the second quarter as companies felt the effects of trade and legislative issues, according to American Clean Power, an industry group. The decrease in projects compared to that quarter in the prior-year shows the lingering problems obtaining parts and navigating tariffs, among other challenges, as Timothy Gardner reports for Reuters. “We have been warning about the storm of policy and economic headwinds the clean power industry is facing, and this is a step in the wrong direction,” said Heather Zichal, the association’s CEO.

Midwest Grid Operator Approves a Major Expansion of Interstate Power Lines: The Midcontinent Independent System Operator has given the OK to $10.3 billion in spending on interstate power lines, which will vastly expand the grid’s capability to connect to new wind and solar projects. MISO, which oversees the grid in a region that includes most of the Midwest, says the 18 projects will begin to come online starting in 2028, as Miranda Willson reports for E&E News. “Not only does MISO need this, but our nation needs this as a model for how to move forward in building out our transmission grid in response to industry needs, market forces and customer choices,” said Lauren Azar, a consultant at the Sustainable FERC Project, in a comment to the MISO board.

NextEra Plans to Shift Away From Chinese Solar Panels Within Two Years: NextEra Energy executives are expanding their plans to build solar energy projects and have a two-year plan to eliminate the use of solar components manufactured in China. The timing means that the company, the country’s largest renewable energy developer, will have found other sources for solar equipment by the time the Biden administration’s two-year moratorium on new tariffs expires, as Emma Penrod reports for Utility Dive. The company is betting that renewables “are going to continue to get cheaper and cheaper over time, and gas generation, which we primarily compete against, continues to get more expensive,” said John Ketchum, the CEO, in a conference call with analysts. “When I think about gas prices today, we think they’re going to remain elevated over a long period of time … and that is creating a ton of demand for renewables.”

Georgia Regulators Approve More Solar and Gas Power for Largest Utility: Georgia Power, the largest utility in the state, will increase its use of solar and natural gas power over the next five years under a plan approved by state regulators. And, regulators delayed a decision on whether to completely close the state’s largest coal-fired plant. The results were mixed for environmental advocates, who support the increase in renewable energy but had pushed officials to rein in Georgia Power’s request to build new gas-fired power plants, as Emily Jones reports for WABE. “They don’t need that much gas,” said Isabella Ariza of the Sierra Club. “They don’t need gas at all if they increase solar.”

Inside Clean Energy is ICN’s weekly bulletin of news and analysis about the energy transition. Send news tips and questions to