Energy prices, and thus savings, are certain to increase over that 30 years too. Quite likely at a rate exceeding inflation.
Solar is not going to have a similar impact on (say) Ireland in the next 30 years.
Probably the bigger impact is bad incentives for the people building the grid, who are often able to do what they like and get a guaranteed percentage return on top, which pushes them to spend more than they need to. This has been particularly pronounced in Australia I believe.
This might also be why utility companies have been furiously lobbying against rooftop solar subsidies and Barclays have downgraded US utility bonds.