Hacker News Reader

Comment by mlsu | Hacker News Reader

In the energy section, they talk about using nuclear fusion to power AI... but not solar. What a joke.

Technically solar power is just fusion power transmitted via photons across space. Maybe solar qualifies ;-)

Technically most sources of available energy on or near the planet are the output of fusion in some way, so this tracks.

Everything except geothermal and fission.

Unless you count where the fissionable elements came from, in which case you're only left with the portion of geothermal that's from gravity (residual heat from the earth compacting itself into a planet).

Tidal waves comes from earths rotation, so not fusion nor fission.

what set off the spinning?

Earth's spin comes from the parent molecular cloud which formed the Solar System (including any impacts during the protoplanetary phase.) And that ultimately from density fluctuations after Big Bang, and the way they led to coalescence of galaxies and galaxy clusters.

To be nitpicky, our uranium and thorium were made via r-process (rapid neutron capture), which is not the kind of fusion occurring in the Sun at present.

[1] https://en.wikipedia.org/wiki/R-process

How much land mass would need to be covered by solar panels to power this future AI infrastructure. Yes, I'm implying that solar would be impractical, but I'm also genuinely curious.

Your implication is misguided, solar is in fact the most practical way to add more electricity for most countries.

The US generated an additional 64Twh of solar in 2024 compared to 2023. To get the same amount from nuclear you would need to build 5 large reactors in one year.

As for land mass, we can re-use already spent land mass, like rooftops, parking lots, grazing farmland and such. Solar can also be placed on lakes.

So for the foreseeable future there is no actual need for new land to be dedicated to solar.

Since America is so in love with car infrastructure, just turning open parking lots into covered lots would be more than enough.

Just converting all Walmart parking to covered solar would meet almost half of all US electrical demand.

4,070,000,000,000 kWh US electric use in 2022

Using 330W panels it would require 8,447,488 panels (4,070,000,000,000 kWh / (330W * 4 hours/day * 365 days/year)) which is 164,726,016 sq ft at 19.5 sq ft per panel.

Walmart has 4,612 stores in the US, averaging 1,000 parking spaces per store, and 180 sq ft per parking space (does not include driving lanes, end caps, etc.) giving us 830,160,000 sq ft.

Also doesn't count continuing to put solar on roofs.

You divided kW by W, so off by 1000.

It's worth considering total lifecycle use of water (mining, production and operation) for nuclear and solar.

Solar: ~300-800 L/MWh [0]

Nuclear: ~3000 L/MWh [1]

0: https://iea-pvps.org/wp-content/uploads/2020/01/Water_Footpr...

1: https://www-pub.iaea.org/MTCD/Publications/PDF/P1569_web.pdf

That’s not really useful information. The nice thing about water is that it’s usually still water after it’s “used”.

The question how much is used for mining slurry or chemical baths.

Those 3000L/MWh might very well be more environmentally friendly than solar because most of it’s used for cooling.

Water we have plenty of. We can desalinate as much as we need to

Build subsurface wells and responsible brine dispersion infrastructure then come back and tell me we can desalinate as much as we need to.

If you put the brine back into the sea, and later put the waste water back into the same sea, doesn't it balance out? Also, the sea is pretty big.

Perhaps, but locally, the higher brine concentration will cause issues.

Yes, hence my use of the word "dispersion". Over a wide enough area, the brine shouldn't have a noticeable impact on sea life. But concentrated release can be really damaging.

Nuclear reactors regularly shut down because the water from the nearby river is already too hot.

https://www.euronews.com/2025/07/02/france-and-switzerland-s...

Yeah, but you need energy to desalinate so...

How does it compare to ~3000 L/MWh? I assume it's a rounding error.

edit: Desalination uses 4 kWh per cubic metre of water. That is, it would yield 250,000 L/MWh.

Even though I think solar is impractical as a primary source for various reasons, it doesn't take a lot.

David MacKay in "Sustainable Energy: Without the Hot Air" did a calculation circa 2010. To fulfill the world's energy needs back then, a 10 km^2 area in the Sahara desert would be sufficient. Even if you scaled that to 100 km^2, it's absolutely tiny on a global scale, and panels have only become more efficient since then.

The challenge of course is storage and distribution, but yeah, in terms of land area, it's not much.

I was curious about this number, so: 10 km^2 is 10mil square meters, Googling suggests that the theoretical maximum energy captured by a square meter of solar panel is well under 0.5 kW, so well under 12 kWh per day. Say 10 kWh for neatness. Then multiplying by 10mil gives 100mil kWh. More Googling suggests that 10 TWh is a comfortable lower bound for daily world energy usage, but 100mil kWh is 0.1 TWh.

So maybe 1000 km^2 is more like right order of magnitude. That's still tiny, about Hong Kong-sized. Even 100000 km^2 is about South Korea.

I'm guessing it was supposed to be (10 km)^2, not 10 km^2.

3,000-4,000 acres per GW of production capacity in the US Southwest. According to AI :)

Considering how little use there is for most of that land anyways, it seems like a good option to me.

Also AI training seems like the perfect fit for solar. Run it when the sun is shining. Inference is significantly less power hungry, so it can run base load 24/7.

> Also AI training seems like the perfect fit for solar. Run it when the sun is shining. Inference is significantly less power hungry, so it can run base load 24/7.

If you're talking about just not running your data center when the sun isn't out, that effectively triples the cost of the building+ hardware. It would require a hell of a carbon tax to make the economics of this make sense.

> Inference is significantly less power hungry, so it can run base load 24/7.

All major AI providers need to throttle usage because their GPU clusters are at capacity. There is absolutely no way inference is less power hungry when you have many thousands of users hammering your servers at all times.

Furthermore NVIDIAs 80% profit margin makes idling your biggest capital expense a huge ROI problem. Google and Apple should have a big advantage in this regard.

If the balance between capital outlay and running costs was more balanced - then optimising the running cost becomes a big line item on the accounts.

the sun is always shining.

>How much land mass would need to be covered by solar panels to power this future AI infrastructure

Probably zero agricultural if you mandate all rooftops to be solar. And all parking lots to be covered with solar roofs.

The joke is my hometown that put acres of solar on prime farmland.

Solar is great for rooftops of houses, it’s not really great to run a DC 24/7 without batteries.

it needs to be better connected over larger distances i guess. Some 'sunny' countries around the equator are working on it. laying gridlines to other less sunny places and trying to offer solar to reduce carbon taxes or whatever.

i know Saudi, Morocco and China are all massively dumping panels into their deserts, likely more places too. these are great places to put them as it has less impact on environment (less wildlife etc.) and it's pretty much always sunny during the daytime, so it's high efficient per m/2 comparted to colder more cloudy places.

Morocco already is connected for energy providing to Europe via Spain afaik, though i think that is currently not used yet, so they are in a good position to leverage that as power demands surge across EU datacenters trying to compete in AI :'D (absolutely no clue if they will actually go that route but it seems logical!)

Nothing stops the AI companies from using only energy from renewable sources, right?

Tariffs, regulatory quick sand, political pressure...

Are those really going to be bigger for renewables than for nuclear power?

Probably in this administration at least tariffs will be more of an obstacle for renewables.

Sure anyone can come up with hypothetical threats. What’s your concrete evidence to suggest this will happen?

https://www.cnn.com/2025/04/22/business/us-tariffs-southeast...

opening sentence in that article: "... a key step toward wrapping up a year-old trade case in which American manufacturers accused Chinese companies of flooding the market with unfairly cheap goods."

Nothing other than the fact that renewables won't be able to keep up if the AI demand keeps growing the way it has been

They just buy a contract from a power distribution company. They don't care where it comes from.

If you want the PD companies to have a different blend, then they need carrots and sticks.

Demand is too high, same goes for nuclear which takes too long to build.

Well yeah, AI power consumption doesn't match the solar production curve.

That's interesting - I would generally like to use something like Cluade Code heavily during work hours and sparsely otherwise. Plus I assume most LLM-for-knowledge-work-at-industrial-scale demand will be similar as these datacentres are built out.

I'll tell ya, it certainly doesn't match the nuclear fusion production curve!

America has a few time zones to move the peaks around in a little bit. The world has plenty. Luckily AI power consumption doesn't have to be located where the consumer is.

I mean, it could.

As we build out solar, daytime power will become cheaper than nighttime power.

Some people will eventually find it economical to time-shift their consumption to daytime hours, including saving any non-interactive computation for those hours, and shutting down unneeded compute at night.

[citation needed]

Reply on news.ycombinator.com