We pay this in Germany not as a flat rate but indirectly by a very low price offered by the grid company.
$8 however seems quite high but I do not know the offered price and solar output in California.
They propose to pay customers $0.05 / generated kWh instead of the $0.20-$0.30/kWh that customers pay in California. So you would have to generate an excess 160 kWh /month to cover the $8 fee (per installed kW of capacity). Your non-solar neighbor who uses your 160kWh of generated electrons will pay the utility $32-$48 for them, while reaping the benefit of lowered stress on the grid.
According to an article about the legality of the fee linked elsewhere in this thread, customers can still opt out of NEM, and just waste the excess electricity generation.
That will essentially always be the right financial decision.
It would actually be less hostile towards solar installs if they simply paid $0 for excess energy, and didn’t introduce the fee.
If I was still in the Bay, I'd have a 280 ish bill to pay for the convenience of having solar, assuming i'm reading this right. Combine that with the payment of $300 for the solar system itself and i'm well above what my power bill was by a large margin.
All these rulings do is turn people away from trying to reduce carbon usage and make things more economically prohibitive.