Big companies have been buying a lot of clean energy lately – 3.5 gigawatts of renewable capacity last year alone (a good chunk of all the capacity added*). These leaders, mostly consumer-facing brands like Google, Apple, Microsoft, Walmart, and IKEA, have been covering their roofs and filling giant fields with solar panels and wind turbines. To do this, they have mostly used power purchasing agreements (PPAs) to buy their clean power. Under this financing structure, the company contracts to buy kilowatts, not the turbines and panels. They put up almost no capital and usually lower their day-to-day energy costs.