Firewood

Wood burned whole, split or as chips for heat is the oldest and, worldwide, still the most widely used biomass fuel. The U.S. Energy Information Administration puts it plainly: people have used wood for cooking, heating and lighting for thousands of years, and wood was the main source of energy for the United States and the rest of the world until the mid-1800s, when coal overtook it. It remains the largest energy source in many lower-income countries today, gathered rather than mined or drilled, and it is the raw material pyrolysis turns into charcoal.