Hazardous kerosene lamps, still used in many developing countries, are a major expense for many of the world's estimated 1.5 billion families without electricity. Poor households typically spend at least 10 percent of their income on kerosene, as much as $36 billion a year worldwide, according to the World Bank. So far, efforts to use solar energy to power lights in developing nations have run up against cost and technical challenges. Attempts to use hydroelectric microgrids or repurpose old car batteries have also been problematic, says Joe Hale, president of the nonprofit Global Brightlight Foundation.
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