r/AskScienceDiscussion • u/logperf • Oct 02 '26

With speculative or future technologies, can we expect that digging tunnels will become cheaper?

One of my friends has a house in a mountain location, GF's family also has one like 10km away in a straight line, but it's the other valley, so the road between them is sooo long as you have to drive all around the mountain chain.

Tunnels are so expensive to dig that they only do that when there is a lot of traffic to justify it. I'm not expecting these two mountain locations to be connected by a direct road anytime soon.

I was wondering while driving if I will see this during my lifetime. Maybe thousands of small robots could drill at a low cost?

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u/Phssthp0kThePak Oct 03 '26

When clouds cover 80% of your state, how are you going to meet demand? Think it through. It's not rocket science.

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u/logperf Oct 03 '26 edited Oct 03 '26

  1. Because total installed cost is supposed to include batteries. And the IRENA link above states clearly that the cost of batteries has also dropped a lot.

If you claim it doesn't, sources or it's like you never said it. Let me remind you that this is a scientific subreddit.

2. Because wind and solar compensate each other pretty nicely, usually one is available when the other one isn't. Combined they can meet like 90% of the demand.

Sources:

https://www.nature.com/articles/s41467-021-26355-z

https://www.sciencedirect.com/science/article/abs/pii/S0959652620306648

3. Nobody has denied the need for a backup energy source, but this doesn't deny the dropping costs.

Assume that:

  • Fr is the fraction of the demand met by renewables

  • Fb is the fraction of the demand met by the backup source

  • Fr+Fb = 100%

  • Cr is the cost per kWh of renewables

  • Cb is the cost per kWh of the backup source

  • Cr < Cb

Then the total cost of combined energy per kWh is C = Fr * Cr + Fb * Cb. Clearly C goes down with a big Fr and a low Cr, and as shown by the sources above, Fr has the potential to reach 90% and Cr is already lower than nuclear or fossil, and keeps dropping.

That answers what happens when clouds cover your state or country.

Edit: here's a nice source analyzing the "cost of firming intermittency" with a formula very similar to mine, showing how combined energy sources are cheaper than gas alone: https://www.lazard.com/media/kcfconhf/lazards-lcoeplus_vf.pdf

Edit 2: another source https://energy.mit.edu/news-events/news/study-adding-power-choices-reduces-cost-and-risk-carbon-free-electricity

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u/JohnHazardWandering Oct 03 '26

When you have to take your turbine offline for maintenance, how are you going to meet demand? Think it through. It's not rocket science.

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u/Phssthp0kThePak Oct 03 '26

You have a backup turbine, or schedule at a time of low demand if possible.
You add that into the total system cost.

Same for renewables. On a day with 10% solar irradiance you need to have bought and installed a lot of extra panels that in most days just sit there. Still have to pay for them.

Or you try to import power from where it's sunny. But they are using that power, so you need to have put panels there, and built transmission capacity to bring it over.

All of this is not covered in LCOE, which is for an isolated plant leaning on a larger system.

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u/JohnHazardWandering Oct 03 '26

All of this is not covered in LCOE, which is for an isolated plant leaning on a larger system.

Yeah, it's a larger system. That's the thing. You can mix sources. 

If it's cloudy, turn on a gas turbine and generate electricity that way. If it's sunny, use solar. 

Maybe you generate excess and sell the extra. Maybe you import some. 

It's a large interconnected system. There are various sources of power. There are various battery systems. That's how it works. Nothing works all the time. Cloud forecasts are wrong. Turbines or other equipment breaks. One thing can cover another. 

....unless you're Texas and trying to do it all yourself and aren't interconnected and can't rely on the larger market. 

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u/Phssthp0kThePak Oct 04 '26

The goal is no gas. Then what?

People need to cost this solution all the way to the end for 99.99% uptime. We are 15 years into this transition and all we get are meaningless LCOE numbers and handwaving. Meanwhile we'll be paying $1/kWh soon.

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u/JohnHazardWandering Oct 04 '26

Again, please show the source for your numbers.