If something gets in the way of the door--a person's foot or a roof panel that's hanging down--the electric motor that closes the train door has to work harder and produces more current.

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And this is with a lighter V8 engine taking the place of the V10, as well as a concerted effort to reduce weight with, for example, a carbon-fiber roof panel.

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Greg Johanson, president of Solar Electric Vehicles in Westlake Village, California, said his company makes a roof-mounted panel for a standard Prius that enables the car to travel up to 15 additional miles a day.

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The new Corvette, for instance, incorporates lightweight materials to a degree not seen on even the most exotic cars, including a carbon fiber hood and removable roof panel, and a carbon-reinforced aluminum frame.

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Most of the roof is a photo-chromatic glass panel that can go from nearly translucent to almost totally opaque when you hit the button.

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The upper flashing lights are integrated into the roof panel, eliminating the need for a bolted-on light bar that causes aerodynamic drag -- reducing fuel economy -- and can lead to rust.

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Sharp's residential energy solutions feature greater overall power generation thanks to panel configurations geared to roof shape and a power conditioner, as well as a lithium-ion storage battery that allows load levelling in which inexpensive night-time electricity is stored for use during the daytime.

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To that end, Nissan incorporated a glass roof, to let in daylight, and a high-resolution seven-inch flat panel monitor for watching videos, using the Internet, or controlling cabin temperature, lighting, etc.

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