Inverters come in many configurations and ratings.  Some do more than others and some are for one purpose only. 

Some Inverters for Off the Grid or emergency backup allow you to Grid-Tie (sell your power back) some due not.  Some inverters are meant for one thing only- selling power back or off-setting your energy consumption.

If you are planning for Off the Grid applications, plan wisely.  Of all the equipment needed for a renewable energy system, the inverter is the most important.

Get the best you can to start with.  I have seen people go cheap on the inverter and learn that they need to replace it after a short time with a higher rated and higher quality inverter. That is a waste of your money.

Off the Grid Inverter information

Grid Tie Inverter information.
Remember: You can not use a Grid-Tie inverter to charge batteries and run your household loads.