Completely off-grid, self-sufficient homes are still rare. Although the idea of renewable energy is to avoid using non-renewable sources, in practical terms this is a net effect for most people: through the year, your systems will provide enough energy that it counterbalances the grid power used. This means that your home will stay grid-tied even though you generate your own power.

Grid-tied renewable electrical systems work by generating power when nature provides the opportunity and using it or banking it (with a utility company) for later use. When nature isn't being helpful, the system takes power from the grid.

That's the simple version... but how does it work in the real world?

If you're using power in your home and the sun is shining or the wind is blowing (or whatever produces your electricity is doing the necessary), the system pumps the electricity straight to your appliances. If the system produces more power than you need, then the extra bit gets pushed out onto the grid and is sent to your utility provider.

The utility company "banks" the extra energy by giving you a credit and sending your power to someone who needs it. If you turn on more appliances or the system stops providing enough energy (at night, on a day with no wind or whatever), you pull power in from the grid to cover the shortfall. This uses up your energy credit, much like using money from a bank account.

Over the period of a year (in most cases), the utility company keeps track of all the credits and debits, sending you a bill for your net use. Unfortunately, running a net-positive system (where you generate more energy than you use over the period) doesn't necessarily mean you'll get a rebate: most utility companies will just say "well done" and send you a bill for a zero amount, pocketing any extra power you provided as a sign of your generosity.

The exception to this depends on how you define net-zero. If you define it by power use, you may find yourself giving away power. If you define it by cost, you are less likely to be so generous: your systems will generate excess power during peak times to counter using more at off-peak times, with a net result of imbalanced power use but balanced cost. In other words, although you'll use more power than you send, you'll buy low, sell high and zero out the total.