Technology bulletin 969

Engineered glass tempering halts the spread of cracks

Researchers at Pennsylvania State University have developed a way to temper glass that could stop little cracks from becoming big ones. The technique also would allow for stronger, clearer windows, computer screens, and car windshields. Normal tempering uses heat or chemicals to strengthen glass. However, the method makes it difficult to predict at what point glass will break. And it produces a material where a single, unstable crack can shatter without warning. With the Penn State tempering technique, surface cracks would appear in the glass as a warning before more dangerous structural cracks occur. The researchers created the internal compressed layers by subjecting the glass to chemical processing, where potassium substituted for sodium, but then exchanged some of the potassium near the surface back to sodium. This resulted in glass with an untempered surface, and with a tempered, compressed layer below. "Unlike untreated glass or conventionally tempered glass where a crack progresses rapidly to catastrophic failure, small cracks begin to form in the untempered layer and then are arrested by the compressed layer," says David J. Green, professor of ceramic science and engineering at Penn State. E-mail [email protected].

'Bells and whistles' assist drivers to park safety

Parallel parking can be a difficult maneuver, especially when the space is small or a driver's vision is impaired. Valeo Sylvania has integrated a new safety and assistance feature into the design of its rear lighting assemblies to make the task easier and safer. The ultrasonic parking assistant communicates with the driver by beeps; the interval between beeps becomes shorter and shorter the closer the car gets to the object behind it. The device begins signaling at about 7 ft from an approaching object; the beep interval disappears at 10 inches. "Incorporating the ultrasonic device into the rear lighting assembly has a couple of advantages to car makers," says Jean-Paul Charret, director of engineering, research and development. "It is cost effective because the electrical connection can be included in the wiring harness for the lights, which also reduces factory assembly time." Phone (812) 523-5200.

World record moves lower-cost solar energy a step closer

Researchers at the National Renewable Energy Laboratory (NREL) (Golden, CO) have taken another step toward reduced costs and increased competitiveness for solar energy. They set a new world record for thin-film solar cell efficiency. The measurement of 18.8% efficiency for the copper indium gallium diselenide (CIS) cell topped the previous record, also set at NREL, by more than 1%. A solar cell's efficiency is measured by the percentage of available sunlight converted by the photovoltaic cell into electricity. Thin-film photovoltaics use very thin layers of semiconductor material applied to a low-cost backing, such as glass or flexible plastic or stainless steel. CIS thin-film technology, in particular, has demonstrated outdoor reliability and stable conversion efficiencies over time. Thin films appear to provide a promising path to low-cost cells because less of the expensive semiconductor materials are needed to convert light into electricity. "As the scientists and researchers at the National Center for Photovoltaics push the envelope of solar-cell efficiency, we can begin to visualize the day when energy from the sun will be generating a significant portion of the country's electric power demand," says Director Larry Kazmerski. E-mail [email protected].

Flywheel extends battery life in power-supply systems

EPRI, the science and technology organization for the energy industry, and Constellation Energy Source Inc., a subsidiary of Baltimore Gas & Electric (BGE), have jointly installed a UL-approved flywheel energy storage device in an existing uninterruptible power supply (UPS) as part of an ongoing energy-storage project. Active Power's (Austin, TX) CS 200 CleanSource^TM flywheel energy storage system was selected for the project at Comcast Corp., a large domestic cable company. CleanSource flywheel products store energy in the form of a rotating steel wheel. They can replace or supplement lead-acid batteries of the UPS system installed throughout data center and industrial facilities to ride through power outages. Art Beasman, senior power quality representative for Constellation Energy Source, explains that the natural-gas engine generators at the project site have a longer response time to load changes. Therefore, the existing UPS system would switch to batteries while the natural-gas engine generator output stabilizes after large load changes. "Now, the flywheel supports the UPS load during generator startup and when large loads are cycled," he adds. "This saves the batteries for emergency backup." E-mail [email protected].