Halving costs need not be equivalent to doubling of economic capacity. It might just as well cause an order of magnitude or higher of increased capacity.
I would not be able to estimate those factors, but it's almost certainly incorrect to assume a linear relationship between cost and productive capacity.
Each halving in cost doubles the amount of storage you can apply to any one project for the same cost. 2 hour storage on a solar or wind farm costs around about £5 per MWh, levelized over the batteries lifetime. There is no way to get around that, as far as I can see.
Halving costs need not be equivalent to doubling of economic capacity. It might just as well cause an order of magnitude or higher of increased capacity.
I would not be able to estimate those factors, but it's almost certainly incorrect to assume a linear relationship between cost and productive capacity.