Tesla recently announced that it's completed Japan's largest commercial household virtual power plant. Or more specifically, the company has installed its 'Powerwall batteries' in over 300 homes on the island Miyako-jima-and they can be used to help power the country's grid.                  Virtual by name, real in function...  Power usage isn't the same hour-after-hour, day-after-day. So the grid's more strained at some times than others. And when it's strained, the solution is usually to draw extra power from gas and oil fired "peak power plants," since they're easier to crank up and down to meet demand.                                                                                                                                                                                                                                                                                                                                                                                                       But that's where virtual power plants come in. People with solar panels and batteries in their homes can sign up and get paid to send extra power back to the grid, giving it a boost in potential blackout situations. Tesla already has virtual power plants operating in California and Australia, and is working on getting one off the ground in Texas. In California, people with Powerwalls installed in their homes can get $2 for every kilowatt-hour fed back into the grid when it's under stress during emergencies or periods of high demand, The Verge reports. Statewide emergency prices typically average $0.26/kWh.                                                                                                                                                                                                                                                                                                                                                                                      Tesla's virtual power plant in California has its first emergency response event earlier this month, which was seemingly successful.