1) For net metering and other backfeeds you MUST use an APPROVED COMMERCIAL device to perform the intertie. You do NOT get to homebrew this.
Get an inverter with a backfeed capability or a companion backfeed adapter.
2) If you just want to switch some or all of your loads manually from line to local generation you need an on-line, off, on-local disconnect switch. In most places the electrical or fire codes will require this to be accessabe to the fire department at the corner of the building or farther out - where the main disconnet would be in a purely line-fed house - in order for firemen to turn off all the power in the house. (And you need a separate circuit for the well so they can leave THAT on, even if they really never use it.)
(I'm certain 1) will be true essentailly everywhere. Power companies don't want to cook their employees and don't trust their lives to hobbiests. You may find some jurisdictions where there's some relaxation on 2) - but AFAIK the "universal" electrical code goes with 2) and most jurisdictions in the US incorporate it by reference - though they may make local modifications or have local interpretations. Final authority is your local inspector - and if you do something off-code and have a fire you can count on your homeowners insurance company denying your claim.)
I dumped several hundred bux on a on-off-on switch for my house just to be able to go off-grid later.
