Yi Guo, senior mechanical engineering scientist at the National Renewable Energy Laboratory (NREL):   In my childhood in China’s Shanxi province, a hub for coal energy, most of my family worked in the coal industry. My town was heavily polluted. One of my grandfathers had chronic lung disease from working in coal mines for many years, and my other grandfather had a severe spine injury from a mining accident. Because of that, I wanted to go into clean energy so I could make a positive change in the world.