Ubiquitous Energy, a start-up specialised in solar energy development, is raising tens of millions of dollars to turn windows into surfaces that capture solar energy.  The Californian start-up recently announced that it had secured $30 million funding for the development of windows with integrated solar photovoltaic cells. Mass production of its panels could lead to a reduction in the carbon footprint in both the residential and office sectors responsible for 40% of world-wide emissions. 
Opportunity for Solar Power Generation
The new technology provides a huge opportunity for solar power generation around the world, and in addition, potentially makes the use and habitation of such considerable buildings more energy efficient.
Ubiquitous Energy’s CEO, Susan Stone said “We’ll be able to make floor to ceiling glass. [By doing this] we can turn skyscrapers into vertical solar farms.” 
Figure 1: Skyscrapers in Manhattan, New York. 
The United States has more than 650 skyscrapers, while China has more than 1,600.  These high-rise structures consume a considerable amount of energy to cool and provide electricity for the people who live and work in them. Ubiquitous asserts that its technology could cut energy expenditures of the 5 million tall towers in the US by 50%, and supposedly provide 50-times greater energy than rooftop solar (according to their models). 
The New Technology
Ubiquitous makes a coating for windows that uses semiconducting materials to convert sunlight into electricity. The coating is just nanometres thick and tiny wires connect the solar window to electrical systems where the energy is used. In order for the technology to be successful, the material needs to effectively absorb invisible infrared and ultraviolet light from the sun for electricity generation, while letting visible light pass through the window in order to light the building.  These transparent solar cells can be applied to existing windows and placed in between the panes of double-glazed windows.
There are limitations to overcome before the technology becomes commercially viable, such as extending the cell life to a considerable number of years. Compared to replacing non-transparent rooftop solar panels, the costs of replacing solar windows after they reach their end of life could be very high. In order to cover the entire facade of a high-rise building with solar-generating glass, it needs to last a long time, as replacement would be a big endeavour.  Undertaking economic feasibility studies on retrofitting existing buildings with their advanced windows is also something that Ubiquitous is working on. 
Whilst this new solar technology is by no means a technically viable option that could be implemented today or even in the next few years, it is possible that it could be a useful contributor to the renewable energy mix in the decades to come.
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