Vehicles powered by hydrogen fuel cells are, in theory, pollution-free but their popularity has been compromised by the difficulty of generating hydrogen cheaply and plentifully.
Solar energy is lauded as an inexhaustible fuel source that is pollution and often noise free. The technology is also versatile.
太阳能被称为是取之不尽的能源，没有污染，通常也没有噪声，而且用途广泛。
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Magnesia chrome bricks must be replaced by chrome free basic bricks because of chrome pollution and for utilization of substituting fuel in cement kiln.