Thanks! I'm going to work thru what I now understand based on the example in my question.
If I understand this, that kit would cost ~$9000 * 0.70 (us fed tax credit) or $6300.
On average it would produce (depending on shade, etc. etc.) ~1050kwh per month.
On an average month, that would cover all my electrical usage, which at our prices would be about $100. I would still have to pay all the fees just to have basic service.
On peak usage months with 2000kwh usage, I would produce about $100 worth of electricity and pay for another $100, plus the fees for basic service.
On below average usage months (for example, 750kwh), I would run a surplus of 250kwh, which I could sell later to the utility company. Those sale terms and conditions can vary dramatically.
I recall from reading about this before that some utilities charge you on this formula :Usage - production = surplus or deficit. They would buy the surplus at the wholesale price and sell the deficit at the retail price. That's the best deal available.
Others charge you full usage * retail price and subtract production * wholesale price. That sucks for consumers and is great for utilities.
Did I get that right?