Google recently announced a million-dollar contest to reinvent the power inverter, the devices that turn the direct current coming from solar panels and batteries into alternating current you can use in your home to play Xbox and keep your beer cold. A smaller, more efficient inverter could help solar power finally go mainstream and save energy throughout our existing electricity grids. Here's a crash course on inverters and what it would take to win the prize.

Last month Google teamed up with the Institute of Electrical and Electronics Engineers to announce something called the Little Box Challenge: Build a power inverter that's size of a tablet, 95 percent efficient, and capable of powering a house, and the million bucks is yours. Today's inverters are 10 times bigger, about the size of a cooler. A smaller, denser inverter would force engineers to experiment with materials and circuit designs that the industry has been skittish to use, mostly because the current technology works well enough.