Here anyway, the generation cost of electricity is about 5p per unit, but the retail cost to consumers is between 10 and 17p. In other words, the actual cost of the power is less than half of the total cost of getting it to the user. A large part of the rest is in maintaining the cables, transformers and so on necessary to get the power to you. The problem which thus arises with allowing PV owners to 'use the Grid as a storage battery' is if they are getting retail rates in both directions. That simply isn't financially viable for the Grid operators, because it leaves nothing in the kitty for equipment maintenance.
The end result is that in order to cover maintenance the operators have to up their charges to all consumers. Thus, the ethics of such an arrangement become extremely questionable. It means that the savings made by having PV are partly money purloined from other consumers. Plus that's only viable if PV owners are a minority. If say 90% of houses had PV, then the other 10% would have to pay maybe ten times as much for their electricity to cover the maintenance costs of the Grid.
(In reality the supply companies would just shut-up shop before that stage was reached, because there would be no viable business model for them.)
Some places only pay the wholesale rate for feed-in, and that is viable for the Grid operators but the PV owners then complain that it doesn't cover their costs
Yes that is how it works normally but the 3 to 6 cent feed in tariff actually works and the owner gets is investment back but at no profit meaning the amortization period is 25 to 30 years and that is actually just fine but owners do not understand this and waste money in Lithium storage batteries that are a significant net loss for the owner.
The thing is that electricity production needed to be centralized as you can not have each house burning coal to produce is own electricity and thus it was more reasonable to produce this somewhere outside the city limits and then transport that to the user.
Now that solar PV is less than coal it is clean and distributed the grid losses + infrastructure cost amortization and maintenance will not make it economical.
My guess grid operators only have a few years left until some of them will no longer be profitable but this will depend on availability of low cost storage and people education on the subject (maybe).
Same will be true for natural gas.
While my costs are 17.5 cent/kWh for electricity and 4.2 cent/kWh for heating this is already lower than grid electricity and natural gas but it is a DIY installation and labor may double this numbers.
The thing is that PV panels and storage will continue to drop so there will be a point where this DIY numbers that I get will be available to anyone (maybe almost anyone).
For a new construction this is already profitable as the connection to the two utilities may be as much as the solar equipment cost.
My goal was to build an off grid house that has as close to zero ongoing costs as possible and I sure got there with energy but some other cost are harder to control. Here is a short list with annual costs
House: $2500 (paid in advanced and only considered 30 years but should last much longer)
Energy (heating and electricity): $500 (paid in advance for 30 years)
Internet/phone : $667 (cost can increase even more than inflation)
Water / sanitation: $200 (paid in advance not quite done so is an approximation again 30 years amortization)
automobile insurance: $719 (cost can increase)
automobile amortization: $750 (used car and lucky almost no repairs excludes gasoline)
transportation fuel cost: $480 (about 6000km/year mostly highway)
There are other costs but this are related to utilities. The transportation costs are almost $2000 and I can not wait for self driving car services as that should be less (hoping way less).
This is maybe a bit out of the subject of this thread but it shows where energy costs are in relation with the other spending's and for most they are much more significant.