Net metering uses the common meter that is installed in most homes, running forward when power is used from the grid, and running backward when power is put into the grid (which allows them to “net“ out their total energy use, putting excess energy into the grid when not needed, and using energy from the grid during peak hours, when you may not be able to produce enough immediately). Power companies can quickly purchase the power that is put back into the grid, as it is being produced. Double metering involves installing two meters: one measuring electricity consumed, the other measuring electricity created. Additionally, or in place of selling their renewable energy, sustainable home owners may choose to bank their excess energy by using it to charge batteries. This gives them the option to use the power later during less favorable power-generating times (i.e.: night-time, when there has been no wind, etc.), and to be completely independent of the electrical grid.