such a thing as grid-interactive vs. grid-tie?

Gordon, way to go! In my opinion all PV should be installed as a means to reduce your dependant load on the grid and to grow until you no longer need them. Soon the electric barons will be the same as today's oil barons!
 But do consider using batteries for storage and supply to your inverter. Sacrifice a couple hundred Watts for now and purchase some batteries. Also use a charge controller. You can use small, cheaper ones in parallel or make an investment for the future with a larger one. Diversion loads can be made or purchased when using the larger controllers.
 One other thing, panels should be installed in the location that gets the most sun over the entire day and year. Sometimes the roof is not always the best spot, for this and other reasons.
 Good luck and I'm sure the folks here will help you in getting just what you need.

Gordon,

For two or more power sources to share the same load they have to be in phase. That is what grid-tie does. The best thing to do is find a small load that you can transfer to your inverter, and once you are happy with how that works then keep adding new loads until you are getting the optimum amount of power out of your inverter.

I use simple 3-way light switches with one pole connected into my main distribution panel and the other pole into a second distribution panel that is my inverter's output (mounted next to my main distribution panel on the wall). The third pole on the switch is then connected to the load (re-routed from the main distribution panel). This allows me to easily change (one load per switch!) between grid and inverter. UP for solar and DOWN for grid.

The description may sound confusing but it is really quite simple, and after a year I only need to take a glance up at the sky on any given day to know which switches I am going to throw.

If you are not going to connect your inverter to the grid then you will need a system that includes batteries.