Many countries now require double-pane glass in commercial building windows for energy efficiency. In between these panes there is usually a gas that helps to cut down on unwanted heat transfer. But these double-paned windows have also opened a market for photovoltaic glass technology that simultaneously delivers transparency and solar PV power generation while maintaining the insulating benefits of traditional insulating glass units (IGU). With nearly 85 million commercial buildings and single detached homes in the U.S. alone, according to the U.S. Energy Information Administration, the potential for such a solar window technology market is drawing the attention of some fairly new PV start-ups.
The BIPV Market
Solar power generating windows come under the growing, green building category of building-integrated photovoltaics (BIPV).
Normally, BIPV are less efficient than traditional rooftop PVs. But traditional PVs must be mounted on a rooftop as a separate, added-on construction step. BIPV enables the architecture, engineering and construction sectors to create buildings with higher energy efficiency, electric power self-generation and even aesthetics at the drawing board stage. This actually cuts out a whole layer of extra engineering and construction issues.
Until recently, “solar windows” were not see-through and were delegated to skylight applications. But the feasibility and scalability of the market potential of BIPV windows is a niche some companies have made their own as they advance the technology.
New Energy Technologies
In late June 2011, U.S.-based New Energy Technologies filed four new patent requests with the Patent and Trademark Office of the United States for its “SolarWindow” technology that is capable of generating electricity on see-through glass windows. With now a total of 10 patents, the company is advancing their “SolarWindow” into development which includes boosting conversion efficiency.
The company says its SolarWindow units are unique because they not only generate power from exposure to sunlight, but also from artificial fluorescent light found in office buildings.
Their first 1'X1' prototype used a process for spraying an electricity-generating coating directly onto glass at room temperature, eliminating the expensive high-temperature production methods normally used by silicon PV manufacturers. The company was also able to eliminate all metal from the PV cells and contacts as well as introduce a PV cell arrangement making the windows more transparent.
New Energy Technologies' current engineering efforts include developing a production process to scale up the technologies for commercial production.
Pythagoras Solar is a privately held Israeli solar architectural glass maker founded in 2007 with operations in the United States and China. Using mono-crystalline silicon cell technology from their Chinese partner, China Sunergy, Pythagoras has developed a PV window panel that generates 13 watts a square foot, which is as much power as an equal size solar roof panel, according to the company.
The clear Pythagorus windows allow daylight to enter the building as would a normal window. But it also uses mirrors to reflect the sunlight down onto a horizontally mounted PV cell at the bottom of the window.
Pythagoras has been testing their fully-integrated photovoltaic glass units in the south-facing windows of the 56th floor of Willis Tower, formerly known as Sears Tower in Chicago, since November 2010. If the project performs as expected Pythagoras could expand to the rest of the building, which has enough space to house the equivalent of a 10-acre solar power plant and produce an estimated 2 megawatts.
In June 2011, Pythagoras was selected as a winner in the GE ecomagination Challenge, an effort by U.S.-based General Electric Co. and several venture capital firms to locate and fund promising building energy innovations. Pythagoras was one of five companies given the $100,000 grant that were selected from nearly 5000 entrants based on originality, feasibility and potential impact.
According to Pythagoras, their future products may include roof tiles and spandrels.
Massachusetts-based Konarka Technologies, Inc. -with European headquarters in Nürnberg, Germany, an office in Japan and an R&D facility in Austria - has been developing a lightweight, flexible organic semi-transparent BIPV curtain wall. The company recently installed a prototype at their New Bedford, Massachusetts facility on both the south-facing and east-facing walls.
The company uses a “roll-to-roll” manufacturing process to fabricate custom sizes of their "Power Plastic.” The ability to create custom sizes is preferred by architects in new construction and allows integration the semi-transparent PV material into multiple walls.
Konarka’s "Power Plastic,” which has been verified by NREL to have an 8.3 percent conversion efficiency rate, are also available in a variety of colors and degrees of transparency. In fact, San Francisco began installing the material in the red roofs of the city’s bus stops in 2010 to power lights and Wifi routers.
Israel’s SolarOr was founded in 2007 to focus on the curtain wall and building façade segment in the BIPV market. Like Pythagorus, SolarOr’s technology uses prisms to reflect sunlight to tiny faceted mono-crystalline PV cells sandwiched between two panes of glass. Their design is much like a honeycomb, making the visual appearance and light reflection more complex than two-dimensional glass as well as producing 155 watts per square meter. According to the company, the honeycomb shape creates an illusion of geometrical patterns that can enhance a buildings façade both day and night.
BIPV Market Outlook
According to a January 2011 report by NanoMarkets, the BIPV industry will be worth $11.5 billion worldwide by 2016.
But now, BIPV is uniquely positioned to interconnect with expansion of the energy-efficient green building industry and the PV manufacturing industry. And since commercial buildings account for around 40 percent of all energy consumption, the BIPV market has the potential for being huge.
The BIPV market will likely begin with commercial applications, such as windows in office and high-rise buildings, and the move to the homeowner market to. For homeowners, replacing older window panes with active PV windows will not only increase real estate values, but help speed the advancement of Net Zero Energy Buildings.
The key challenges to market growth for BIPV products such as solar windows are cost and the development of a wider range of products specifically for building integration. The high initial cost for installing BIPV systems offers an opportunity to develop a greater symbiosis between the PV industry and the construction industry as local building codes get updated – such as the LEED certifications in the U.S.
As these boundaries between the BIPV and building products industries gradually fade, architects and building designers will become increasingly dependent on the PV industry. This integration of PV with the building industry also opens up new development opportunities for specialized PV building products from new start-ups while the industry is still young.