Last month, the polar vortex brought below-zero temperatures to the Midwest and Great Plains. Over 220 million Americans experienced below-freezing temperatures across the lower-48 states, and about 26 million people were living with temperatures at or below -20 degrees. Despite the large amount of wind power in the Midwest, coal and natural gas provided about 80 percent of the electricity needed to keep the power and heat on, according to the Midcontinent Independent System Operator, which manages that grid. However, utility companies in parts of the Upper Midwest had to ask customers to turn down their thermostats ... (full story)