Almost 4 billion people around the world today live without reliable access to electricity, and about 1.1 billion have no access to electricity whatsoever. To cook meals and light homes, these people often resort to ad hoc energy solutions that provide only limited relief while presenting substantial drawbacks. Low-quality kerosene lamps common in remote, off-grid communities create air pollutants that damage human health and the environment. Further, the levelized cost of kerosene lighting can be two to five times more than more efficient energy sources. Worse yet are disposable single-cell batteries, with an energy cost between US$100 and US$200 per?kWh, nearly 1,000 times the price of electricity in the United States.