I'm uninformed, "grid saturation" meaning what?

I'm not positive, but I might imagine that it's that the solar power generated by that particular grid either equals or exceeds the amount used by it. If there's multiple grids it could be that the residential area is nearly self sustaining during the day, and they don't have the capability to move that generation successfully to the other places that need it because the grid interchanges weren't built with that in mind.

That's exactly what it is. See presentation here: http://www.heco.com/vcmcontent/StaticFiles/pdf/LVM/LVMMECOPu...

It appears that there are neighborhoods in Hawaii where the PV generation capacity is approaching the max load of the circuit.

Can you simply disconnect from HECO and self-generate?

You could, but you would need to purchase and setup batteries.

The other option is to grid-tie, but agree not to sell any power back to them (which can be configured in the inverter). You would then use utility power when you don't have enough solar output to meet your needs.

Disclaimer: I have read WAY too much Home Power magazine over the last decade. I could design said system in about 20 minutes, part numbers and all. [http://www.homepower.com/]

For most home solar installations, this would dramatically skew the financial break-even for solar installation.