I like your thinking on that . I can't see why you couldn't do a calculation now although the battery technology doesn't really exist to be viable , regardless of cost .
I read somewhere that you need 6 to 9 times the wind/solar generating capacity as compared to fossil fuel because of the intermittent duty cycle of renewables . You could then maybe base the cost of storage on flow battery technology and pumped hydro as they lend themselves more to big , longer term storages .
Fossil fuel is destined to get more expensive as it gets harder to find and supply while renewables have the potential to go the opposite way . Renewable technology is becoming more competitive every day to the point that it won't be subsidised too much longer . Economies of scale suggests that things like solar panels and batteries will continue to get cheaper . If , as is suspected , solar panels become integrated into building surfaces and batteries become part of the structure , they could get really , really cheap .
The end result is that we could have an energy surplus although that would be a long way off .
In the meantime , the electricity grid is going to have to be upgraded which will offset some of the savings . The benefit is that a lot of the grid is already quite old so the cost of upgrade could be amortised over quite a long time .
Then there's the maintenance costs . New technologies tend to be more robust and reliable so at some point that would have a significant impact I imagine .
