9. 太阳能

    今年10月，一辆太阳能汽车以56英里的平均时速在澳大利亚内地行驶了2,000英里。听起来很完美——太阳能不用花钱，也十分清洁——但有几点必须注意：这辆由荷兰人打造的车（见上图）只载了一名驾驶者，只能在白天行驶，还要用一个小型电池才能开动。这就是未来的汽车吗？恐怕不是。用以捕捉阳光并将其转换为电能的光伏电池生产成本十分高昂，同时这辆车所用的钛合金这类轻型金属也非常昂贵。不过，太阳能车如果白天能充电，可能可用来当通勤车，比如有一些现在已用作高尔夫车了。

    9. Solar

    In October, a car powered by the sun drove almost 2,000 miles across the Australian outback at an average speed of 56 miles per hour. Sounds perfect -- solar power is free and clean -- but there are a few caveats: The Dutch-engineered car (above) just carried a driver, travelled only during daylight hours, and used a small battery to get rolling. Is this the future? Probably not. The photovoltaic cells that capture the sunlight and convert it to electricity are expensive to produce, and the car is made from pricey lightweight materials like titanium composites. However, solar-powered vehicles might find limited use as commuter cars where they had an opportunity to recharge during the day, and some are used today as golf carts.