u/StreetVirtual3037

Overbuild renewables + gas backup for low renewable days. On overproducing days, electricity is dumped into making synthetic natural gas. Natural gas does not have the engineering challenges of hydrogen. The infrastructure and generating capacity for it is already mostly there. This would allow for carbon-neutral gas generation and energy/fuel independence. The round trip efficiency is pretty low with a single cycle gas turbine, maybe around 10%. I'm not sure how the economics pencil out but the energy independence and decarbonization seem like they could be worth a premium.

edit: Based on a more realistic 65,000TWh/year electricity for a fully electrified world, it's more like 5 years.

Based on 44GWh of electricity per ton of natural uranium, it would take 3.9 million tons of uranium to supply the world with 167,000TWh of electricity, which was the global energy demand in 2024. 8 million tons of uranium reserves would run out in 2.1 years. If you want to say there are more uranium reserves that are currently uneconomical, it would need to be a LOT more. Even with 10x more reserves it's only 21 years.

Breeder reactors are not currently relevant since none of them get the fuel efficiency needed for the more optimistic numbers that some propose. In any case, there's no point in promoting the construction of LWRs which don't have enough fuel to power the world sustainably.

I am interested if there's any issues with these numbers I came up with.

This link [1] says

>A 1 GW (electric) fusion plant will need about 100 kg deuterium and 3 tons of natural lithium to operate for a whole year, generating about 7 billion kWh.

2.33TWh per ton of lithium. World energy demand in 2024 was 167,000TWh. Estimated global lithium reserves are 37 million tons. This is enough for 516 years at 2024 levels. There are an estimated 230 billion tons of lithium in the oceans. This would be enough for 3.2 million years if it could all be extracted.

This link [2] says there is enough deuterium in the oceans to last the Earth 637 million years at 2021 total energy demand, if D-D fusion could be engineered.

We can compare this to nuclear fission:

Based on 44GWh per ton of natural uranium from this link [3]: At 2024 global energy demand, LWRs would run through 8 million tons of uranium reserves in 2.1 years. It would take around 1050 years for LWRs to burn all 4 billion tons of uranium in the world's oceans, assuming it could all be extracted.

If we grant breeder reactors with 180x fuel efficiency compared to LWRs, this is 378 years with 8 million tons mining reserves and 189,000 years with the ocean's uranium.

There is the theory that the ocean will be replenished with uranium from the Earth's crust from erosion with varying estimates for the rate. Depending on the rate of replenishment and how sustainable it is, this could allow for hundreds of millions to billions of years of energy at 2024 levels.

For fusion, if we grant exotic scifi concepts such as mining gas giants or 'star lifting' hydrogen and helium out of the sun to burn at our own pace, this could potentially allow for much more energy.

[1] https://world-nuclear.org/information-library/current-and-future-generation/nuclear-fusion-power

[2] https://www.scirp.org/journal/paperinformation?paperid=129784

[3] https://world-nuclear.org/information-library/nuclear-fuel-cycle/introduction/nuclear-fuel-cycle-overview