Well theoretically so that when you decide to, y'know, improve the grid in 50 years time, you can just add more wires instead of replacing everything?
The only entities that can make such long term investments are governments, via taxes, and not all governments at that. And such investment is usually reserved for either basic research or incentivizing production by mobilizing human capital (i.e the IRA in the US), not building excess capacity of questionable utility.
Whether it's worth it depends on interest rates, not on how long your investors live.
It's just that 50 years is a long time, so the savings from leaving the additional space would need to be quite big to be worth it today when discounted back.
In addition, you have lots of uncertainty: overbuilding the infrastructure in this way only takes care of exactly this one contingency, but there's plenty of other reasons why you might want to replace your pylons. Eg perhaps in 50 years we will have figured out how to send power without wires, or we will move to buried lines everywhere, or we will get our power as laser beams from orbital solar satellites, or we need new pylons in new places because settlement patterns have changed, etc.
We had near zero interest rates for years, but I didn't see any private investors making infrastructure investments that wouldn't possibly produce a return for 50 years.
> In addition, you have lots of uncertainty: overbuilding the infrastructure in this way only takes care of exactly this one contingency, but there's plenty of other reasons why you might want to replace your pylons.
Practically I think that's the real reason. Nobody has a crystal ball to to tell them what tech will be a good investment in 50 years. It's anyone's guess, and no interest rate will allow that kind of private investment.
We had short term near zero interest rates (and even below zero real interest rates), but that doesn't mean that long term interest were that low. See eg https://fred.stlouisfed.org/graph/?g=1jVdN or https://fred.stlouisfed.org/graph/?g=1jVe8 for the inflation adjusted one. Those are interest rates that the US government is paying on 30 year bonds. Private issuers typically pay more. (I picked 30 years, because that's the longest duration the US typically borrows at.)
> It's anyone's guess, and no interest rate will allow that kind of private investment.
If you can lock in a zero or negative interest rate now, it might still be a good investment.
In the real world, what lending entity is going to offer you financing at <= 0% for 30 years?
Just because 30 year Treasury yields fell below zero from 2020-2022 didn't mean I can get that kind of financing for a project.
You've summarily lost your mind if you think any sane utility CFO would greenlight deploying capex to the tune of billions in gross excess of requirements for the speculative option of expansion capacity at marginal cost several decades into the future. Also, good luck convincing rate payers that increased costs realized today is to speculatively reduce the utility company's cost of doing business long after they're dead.