About the Inverter

1) Grid-tie inverters interface with a grid connection to receive and sell back power, using the grid like a battery bank, and will shut off the flow of electricity if the grid power goes down in order to protect electric company linemen.  Generally, these do not also use or charge batteries.  If you want both grid-tie and battery usage, you need a grid-capable off-grid inverter.  A purely off-grid inverter does not have the ability to interface with a grid connection and does not contain any of the safety features to allow safe connection.  Off-grid inverters only work with batteries, or without batteries they will only function so long as your power sources are producing enough voltage.

2) The size of the inverter will be dependent on the size of your loads.  Obviously you cannot use a 500W inverter to power 2000W of loads.  Generally inverters are rated for continuous and instantaneous loads.  This means they can start a motor which draws a high amount of power initially, but runs on a lower amount.

3) Lightning protection (sacrificial), over-voltage (surge) protection, and over-amperage (breaker/fuse) protection are recommended on both the supply and load sides.