I expect fusion will outperform solar and is reasonably likely to be viable if there is an abundance of extremely superhuman AIs.
Notably, there is no hard physical reason why the payback time required for solar panels has to a year rather e.g. a day or two. For instance, there exist plants which can double this quickly (see e.g. duckweed) and the limits of technology could allow for much faster double times. So, I think your analysis holds true for current solar technology (which maybe relevant to part of this post), but certainly doesn’t hold in the limit of technology and it may or may not be applicable at various points in a takeoff depending on how quickly AIs can advance relevant tech.
I mostly agree with your thinking. If there are multiple superintelligent AIs then one of then will likely figure out a method of viable fusion with a short payback period.
On the payback time of solar, it probably can be reduced significantly. Since the efficiency of solar panels cannot be increased much more (Shockley-Queisser limit for single junction cells, thermodynamic limit for any solar panel), then the only way to reduce the payback period will be to reduce the amount of embodied energy in the panel. I expect that the embodied energy of solar panels will stop falling once they start being limited by their fragility. If a solar panel cannot survive a windstorm, then it cannot be useful on Earth.
Your mention of biological lifeforms with a faster doubling time sent me on a significant tangent. Biological lifeforms provide an alternative approach, though any quickly doubling lifeform needs to either use photosynthesis for energy or eat photosynthetic plants. I expect there to be two main challenges to this approach. First, for the lifeform to be useful to a superintelligence, it needs to be hypercompetitive relative to native Earth life. This means that it needs to be much better at photosynthesis or digesting plant material compared to native Earth life. Such traits would allow it to fulfill the second requirement while remaining a functional lifeform. Second, the superintelligence needs to be able to effectively control the lifeform and have it produce arbitrary biomolecules on demand. Otherwise, the lifeform is not very useful to the superintelligence. I believe the first challenge is almost certainly solvable since photosynthesis on Earth is at best 5% efficient. The second will be more difficult. If the weakness in an organism a superintelligence needs to use to produce arbitrary biomolecules is too easily exploited, a virus, bacteria or parasite will evolve to exploit it, causing the population of the shackled synthetic organism to crash. If the synthetic organism has been designed such that it cannot evolve, its predators will keep it in check. Contrastingly, if the organism’s weakness is not sufficiently embedded in the genome, then the synthetic organism will evolve to lose its weakness. Variants of the synthetic organism which will not produce arbitrary biomolecules on demand will outcompete those which will since producing arbitrary biomolecules costs energy.
I expect fusion will outperform solar and is reasonably likely to be viable if there is an abundance of extremely superhuman AIs.
Notably, there is no hard physical reason why the payback time required for solar panels has to a year rather e.g. a day or two. For instance, there exist plants which can double this quickly (see e.g. duckweed) and the limits of technology could allow for much faster double times. So, I think your analysis holds true for current solar technology (which maybe relevant to part of this post), but certainly doesn’t hold in the limit of technology and it may or may not be applicable at various points in a takeoff depending on how quickly AIs can advance relevant tech.
I mostly agree with your thinking. If there are multiple superintelligent AIs then one of then will likely figure out a method of viable fusion with a short payback period.
On the payback time of solar, it probably can be reduced significantly. Since the efficiency of solar panels cannot be increased much more (Shockley-Queisser limit for single junction cells, thermodynamic limit for any solar panel), then the only way to reduce the payback period will be to reduce the amount of embodied energy in the panel. I expect that the embodied energy of solar panels will stop falling once they start being limited by their fragility. If a solar panel cannot survive a windstorm, then it cannot be useful on Earth.
Your mention of biological lifeforms with a faster doubling time sent me on a significant tangent. Biological lifeforms provide an alternative approach, though any quickly doubling lifeform needs to either use photosynthesis for energy or eat photosynthetic plants. I expect there to be two main challenges to this approach. First, for the lifeform to be useful to a superintelligence, it needs to be hypercompetitive relative to native Earth life. This means that it needs to be much better at photosynthesis or digesting plant material compared to native Earth life. Such traits would allow it to fulfill the second requirement while remaining a functional lifeform. Second, the superintelligence needs to be able to effectively control the lifeform and have it produce arbitrary biomolecules on demand. Otherwise, the lifeform is not very useful to the superintelligence. I believe the first challenge is almost certainly solvable since photosynthesis on Earth is at best 5% efficient. The second will be more difficult. If the weakness in an organism a superintelligence needs to use to produce arbitrary biomolecules is too easily exploited, a virus, bacteria or parasite will evolve to exploit it, causing the population of the shackled synthetic organism to crash. If the synthetic organism has been designed such that it cannot evolve, its predators will keep it in check. Contrastingly, if the organism’s weakness is not sufficiently embedded in the genome, then the synthetic organism will evolve to lose its weakness. Variants of the synthetic organism which will not produce arbitrary biomolecules on demand will outcompete those which will since producing arbitrary biomolecules costs energy.