Imagine fusion technology developed such that the marginal price of an additional unit of energy was ten thousand times cheaper than it is currently.

Further suppose that we invented cheap, safe, lightweight batteries with effectively unlimited storage.

What impact would that have on technology and society?

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You might like this video (from 9:18) by Isaac Arthur that talks about that

Global warming accelerates due to waste heat. See Freitas, Global Hypsithermal Limit for some relevant estimates.

One thing would be migration towards indoor agriculture, freeing a lot of land for other uses

What's the huge advantage of indoor agriculture? I imagine planting a field is much cheaper than building a multistorey building, putting down soil on all of it, and planting each floor.

4Chinese Room2y
More efficient land use, can be co-located with consumers (less transportation/spoilage), easier to automate and keep the bugs out etc. Converting fields back into more natural ecosystems is good for environment preservation
1Chinese Room2y
Also, soil is not really necessary for growing plants

If you feel the need to do something in response to the advent of fusion power and high-capacity batteries, you might want to think about doing it sooner rather than later.

Fusion: I'm beginning to think this is nearer-term than most of us believe. Last September, Commonwealth Fusion Systems demonstrated a 20 Tesla superconducting magnet with a bore large enough for their tokamak.

  • It's a REBCO magnet (rare-earth boron copper oxide) which superconducts at nitrogen temperature, but they're going at 10-20K to have some running room for high field strength without quenching the magnet.
  • The volume of the tokamak scales as the inverse cube of the magnetic field. ITER runs about 9 Tesla, so at 20 Tesla CFS has more than a factor of 2 increase in field, hence 1/8th the volume. Tokamak costs scale roughly by volume, so there's potential cost savings of a factor of 8. (Potential, not yet demonstrated.)
  • Their reactor is a high-beta design, i.e., high plasma pressure. They're building a demonstrator reactor now, expected to have a Q (power out/power in) of about 11. Target completion date is in 2025, only 3 years from now. 140megawatts of power, delivered in 10 second bursts.
  • If the demo reactor works, they predict building full-scale commercially useful reactors by 2030.

High-Capacity Batteries: Lithium-ion batteries are wonderful for portable applications, but… they tend to degrade after a lot of discharge cycles, and in high-power, high-density situations they have thermal runaway problems. "Thermal runaway" is excessively polite language for "halt, catch fire, sometimes explode". The thermal management equipment and software are pretty gnarly.

Check out the liquid metal batteries from Ambri. They're basically a highly insulated box with 3 layers of molten antimony, calcium chloride, and molten calcium. Discharge it, and the Ca atoms give up a couple electrons, the ions migrate through the salt layer, and form CaSb at the other end. Charge it, and the reverse happens.

  • Yes, its molten metal. But about 1 charge/discharge cycle every day (say, when coupled to a solar array) is enough to keep it heated, given adequate insulation. Unlike lithium-ion, it likes to be hot.
  • The materials are cheap. Don Sadoway, an MIT prof who founded Ambri with one of his students, tells the same joke in every talk he gives (and I mean every talk!): "If you want it to be dirt cheap, make it out of dirt. Preferably local dirt, so nobody can cut off your supply." (He has a number of very engaging talks on YouTube.)
  • It appears to have no measurable degradation after hundreds of charge/discharge cycles. Obviously you can't form dendrites in liquid metal.
  • The round-trip efficiency (power out / power in) is about 80% (with the losses going to ohmic heating to keep the metals molten). Pumped hydro storage, for commercial comparison, is about 70% or so. So the efficiency is very much on point.
  • Ok, they're heavy. And full of molten metal. So they're not going in your car. But for power plant applications, that's just fine. Unlike lithium ion, they can't catch fire or explode, and when frozen at room temperature for shipping they're completely inert.
  • They'd be great for peak shaving: you have generation capacity for the average case, and use the batteries to store energy during low demand periods and supply energy during high demand periods.
  • They also couple ideally with solar arrays and wind farms, whose generation capacity is variable.

So there you go: 2 commercial interests in fusion and batteries, each with at least some chance of success. There are many others; it is very likely some of them will succeed within 10 years.

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An interesting question would be about qualitative changes, not just "I don't have to ever charge my phone or laptop or electric car". Military applications (handheld railgun! powered armor! electric fighter planes!) would definitely take off right away, sadly. Space exploration would change drastically if high specific impulse no longer costs a fortune per unit of thrust (single stage to Mars on ion engines! Powered landing, no more atmospheric breaking! No interstellar capabilities though, unless energy density is close to 100% rest mass, 100x that of fusion). One of the transformative changes would be similar to what happened in transition from wired to wireless communication: no power lines, no electric grids, no power distribution (and no power companies). Also, no oil/gas/coal burning, but that's not very transformative, just a bonus. Anyway, most applications we can't possibly imagine at this point. Closed-cycle breathing, with CO2->O2 conversion in exhaled air. Closed-cycle life support in general, actually. Imagination fails me. 

Well, finally, flying cars! Actually, not even cars, closed-cycle power armor and cheap propulsion would mean one can just fly wherever and whenever, no car necessary.