At present the grid is a once-way tree, from the trunk at the power plant to the branches of sub-stations, the limbs of neighborhood power lines and the leaves of individual home connections. With very few exceptions, power only flows one way in this tree.
When many end-customers can supply excess power back to the grid in coordination from the central dispatch control center of the grid’s operator, the grid becomes a matrix, or mesh, where sellers of power could be commanded as needed to supply power and the mesh would account for who is owed money and who is to be charged.
The sizing issues greatly change, for in the present structure, like with the internet service of an ISP, the capacity needs ‘roll up’ and aggregate from one layer upwards to the next. This is why power lines quickly get very large. A mesh would not need to have nearly the capacity at the upper levels as it does now.
But economically speaking, this is all blue sky for the simple reason that the customer always must pay the full cost of every facility the utility builds to provide his power. The power plant and the power distribution system must be paid for even if the customer base decides to buy so many power-selling hybrid cars that the power plant is not needed.