Solar-control glazing cools cabins—and EV range anxiety

  • 10-Aug-2011 11:38 EDT

Advanced solar-control glass can alleviate the A/C system’s workload and is about 10% lighter than similar-thickness tempered glass—both of which can contribute to better fuel economy/freight efficiency as well as increased range in electrified vehicles.

While materials are an obvious area to comb for weight cuts—and, thus, improved fuel economy or freight efficiency for commercial vehicles—perhaps a less obvious route is right in front of the driver’s face: the glass used for the vehicle’s windshield and other windows.

For electric (EVs) and hybrid-electric vehicles (HEVs), advanced solar-control glass can offer the added benefit of increasing range—and decreasing range anxiety—by reducing air-conditioning use, which frees more energy to propel the vehicle further, the Enhanced Protective Glass Automotive Association (EPGAA) points out.

The glass is designed to reduce the solar heat load in the vehicle, alleviating the A/C system’s workload to make the vehicle cabin comfortable. When equipped with advanced solar-control glazing, cabin temperatures at start-up can be up to 20°F (11°C) lower than vehicles without the technology, the industry group claims.

Temperature of the dashboard can be 26°F (14°C) cooler and the windshield itself as much as 36°F (20°C) cooler.

Battery core temperatures can also be lowered by using the technology, a factor that could help prolong the life span of EV/HEV battery packs. The group cites National Renewable Energy Laboratory (NREL) research that supports this claim. NREL tests revealed that a hybrid vehicle equipped with advanced solar-control glass from Southwall Technologies reduced core battery temperatures by up to 3.5°C (6.3°F) compared to a vehicle sans the glazing.

So, what is the end result of these figures? An up-to-30% improvement in range during high A/C-usage seasons for EVs fitted with solar-control glazing, says the EPGAA.

The group anticipates high take rates in EVs and HEVs, as well as in standard internal-combustion-engine (ICE) vehicles seeking to improve efficiency, emissions, and comfort. And the technology offers the same benefits for off-highway equipment and heavy-duty trucks and buses, according to Robert Vandal, Director of Advanced Product Development for Guardian Automotive.

“In fact, with the recent implementation of the ‘no-idle’ laws in most states in the U.S., the solar-control glazing is even more relevant for the heavy-duty trucks than ever before,” said Vandal. “In several off-highway/construction applications, the cabins tend to have much larger glass area and the use of solar-control glazing would offer a tremendous benefit for the comfort of the user and for the reduction in fuel consumption for the air-conditioning system.”

Advanced solar control glazing for the automotive market was first developed and adopted in the early 1990s, but performance of the products has “steadily improved with fairly rapid advancement in the last five years,” according to Matt Coda, Director of Business Development at Southwall Technologies.

Nano-scale structures of noble metals, typically silver, and/or inorganic oxides make up the solar-control glazing, said Mukesh Rustagi, Director, Strategic Product Management, Pittsburgh Glass Works (PGW), formerly called PPG Auto Glass.

“There are two main approaches to advanced solar-control glass: infrared absorbing and infrared reflective (IRR). In the case of IRR solar control, alternating very thin layers of noble metals and ceramics are either directly applied to the inner surfaces of laminated glass or to polymer layers subsequently built into laminated glass,” Rustagi explained. “These multilayer structures reflect strongly in the infrared spectrum while allowing visible light to pass through the glass.

“Absorbing solar-control technologies utilize finely dispersed particles contained within the adhesive used to laminate automotive glazing; these particles absorb the infrared light while allowing visible light to pass through.”

Examples of solar-control products currently on the market include Southwall Technologies’ XIR line, Sekisui’s SCF PVB (polyvinyl butyral), Solutia’s S series PVB, AGC’s IRIS and Coolverre, Guardian’s SilverGuard, and PGW’s Sungate and Sungate EP. Advanced solar-control glass is suitable for all windows in the vehicle, including the windshield, sunroof, rear, and sides.

Laminated glass is typically 10% lighter than a similar-thickness tempered glass, according to Aaron Pelfrey, Technical Service Supervisor for Sekisui America. Adding the solar control function does not add any measurable weight to the laminated glass.

Other benefits include enhanced intrusion resistance and sound reduction. The use of laminated glass in the side windows of vehicles has been shown to reduce the interior noise by as much as 3 dB, according to EPGAA.

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