Energy Reflecting Windshields Could Also Produce Electricity

The road to reducing CO2 emissions and fuel consumption takes many directions. In California, a state that’s often ahead of the curve in encouraging better environmental performance, the Air Resources Board has issued a regulation that requires new cars sold in the state to have windows that reflect or absorb the sun’s heat-producing rays. Beginning in 2012, vehicle windows must prevent 45 percent of the sun's total heat-producing energy from entering the interior and the windshield must reject at least 50 percent. In 2016 this increases to 60 percent.

Besides reducing air conditioning loads that increase fuel usage and CO2 emissions, the mandate will mean less time is needed to cool a hot interior to comfortable temperatures. It will also help prevent faded upholstery and cracked dashboards. The added cost for these new windows is estimated to average $70 for the 2012 standard and about $250 for the 2016 standard, with annual savings in gas of $16 and $20, respectively.

As with previous environmental edicts that have come out of California, expect to see other states adopting similar rules. But even if states don’t fall in line, most new vehicles sold throughout the U.S. will undoubtedly comply. Automakers usually produce the same vehicles for sale everywhere, not just for California. For the time being, at least, California’s proposal to ban dark heat absorbing colors, especially black, has been dropped.

Possible technologies that could help meet these upcoming requirements include adding chemicals to glass to absorb the sun's energy. Also, laminated glass coated with invisible microscopic specks of reflective metal could be used. The Air Resources Board mandate allows other technologies that also produce equivalent results. So why not use transparent solar arrays to generate electricity? Less heat needs to be absorbed or reflected when some of the sun’s energy is turned into electrical energy. The electricity could be used to power a vehicle’s air conditioning, thus further reducing fuel consumption.

As an example, New Energy Technologies has developed its SolarWindow that features transparent, organic photovoltaic cells that could be coated onto transparent glass. Claimed to be the smallest organic solar cells of their kind in the world, they can be used in either direct sunlight or artificial lighting, including fluorescent. Vehicle windows and windshields are another application if the full windshield visibility standard required by the Air Resources Board can be met.

Transparency is achieved by using conducting polymers. The ultra-thin film is just 1/1000th the thickness of a human hair. In testing, New Energy’s cells outperformed all of the conventional solar cell materials tested under normal fluorescent office lighting conditions, without the benefit of outside natural light from windows.