These are the ones that are used for inversion of green technology power generation methods such as solar cells, which generate direct current so that this can tie into the homes power grid.
This type of power inverter is called a grid-tie, or grid-inversion inverter.

However, the simplest use of all for a power inverter is through the addition of a simply 12 or 24 volt DC car battery. Many people will even leave their vehicle running while the inverter is attached, so that the battery continues to cycle. With this as an emergency or portable power supply the owner of the inverter can power simple electronics such as radios and televisions.
The amount of electronic equipment that can be run and the length of time they can be run, called run time, will vary on the voltage of the battery and the capacity of the inverter.