This is from the Maine PUC, other PUCs across the country do their own studies. Maine is on the high side, but all but one PUC that I'm aware of have calculated positive values.
That link is from 2015, so I suspect it's talking about benefits at very low penetration.
Clearly things become very different at very high penetration. I mean, if everyone is net metering, who is consuming the excess power? Who is paying for the power plants that these people use when not providing their own power? The economics would go all to hell.
I think we'll have to go to floating rates for bought power to solve that. If there really is no where for the power to go the price of power from solar should fall to zero or below. The economics of your night load plants/storage gets tricky then though because you're losing time when you would currently be making money to solar but they still need to exist to provide power during the night or when there's bad weather all day and you don't get much solar power.
https://www.utilitydive.com/news/maine-puc-study-values-sola...