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hwillis commented on Man wearing metallic necklace dies after being sucked into MRI machine   bbc.com/news/articles/cx2... · Posted by u/brudgers
theshrike79 · a month ago
People should try a magnet fishing magnet.

A fist-sized powerful magnet that's next to impossible to straight-up pull out of ANYTHING. You need to slide it carefully and NOT let your fingers get in between it and anything else.

Now imagine a magnet that's infinitely more powerful than that.

hwillis · a month ago
A good N52 neodymium magnet can be 1.5 tesla- MRIs are usually 1.5 tesla. The pull force is around the same too- a steel object will experience say 20g, and 100 lb fishing magnets are not hard to find.

The difference is the size. Even a large magnet only hits that 20g force over an inch or two. An MRI pulls at that force over a full foot or more; equivalent to dropping the object from 20'+. Worse, the MRI starts pulling at 5 or 10 feet away. Objects can experience a tremendous amount of uncontrolled acceleration in fractions of a second.

It's not like a black hole- unless you are trapped under something very large, the crushing force is substantial but not incredible. In fact inside the tube the gradient is actually smaller than the entrance of the tube- you are pulled in strongly, but once inside the tube you are pressed against the wall somewhat less forcefully. Instead it's like an invisible waterfall, and any metal will be swept away in it, fast enough to put holes in you.

hwillis commented on Preliminary report into Air India crash released   bbc.co.uk/news/live/cx20p... · Posted by u/cjr
testemailfordg2 · 2 months ago
Three things:- 1) Pilot clearly said I didn't do it. 2) Report talks about the second switch being turned off in a second. 3) Known advisory on switches getting flipped.

If you see these three together, it becomes easy to deduce that based on point 2, switch was not human induced as the actions required take more than a second. Next the third point, advisory was for this exact scenario which played out, though rare but still it shouldn't have been just an advisory, but more than that.

hwillis · 2 months ago
The switches are right next to each other and have a very short throw[1]- it would definitely be possible to do them in under a second and it looks possible to throw them together.

IMO that looks like a spot that would be pretty difficult to hit accidentally even if the ward failed. You'd have to push them down and the throttles are in the way.

Doesn't mean the switch couldn't have failed in some other way- eg the switch got stuck on the ward but was still able to activate with a half-throw, and spring pressure pushed it back into off during a bump. But switches generally only activate when fully thrown, and failing suddenly at the exact same time is not really what you would expect.

[1]: https://www.reddit.com/r/indianaviation/comments/1lxra3g/b78...

hwillis commented on Poland's clean energy usage overtakes coal for first time   ft.com/content/ae920241-5... · Posted by u/stared
rich_sasha · 2 months ago
I find these discussions usually collapse into a sequence of shifting goals.

You quote, and I believe, 5x solar irradiation power difference between December, plus a second-order 10% power consumption difference. Doesn't this mean already a 5.5x difference - if X panels are sufficient in July, then 5.5X would be needed in December? And July itself probably already needs overprovisioning anyway - Polish summers are not guaranteed sunshine. If "July" is overprovisioned 1.5x and we add the 5x for December for a combined 7.5x overprovision, plus batteries, is it still cheaper than nuclear?

If nuclear gets dismissed as an expensive fantasy, well, at least it has been built and operated at massive scale. I am not aware of any large scale operating exports of solar energy from equatorial regions to Northern Europe, or similar distance.

hwillis · 2 months ago
You're massively misrepresenting what I'm saying. I am not dismissing nuclear or suggesting overbuilding solar by 5x. I am responding to someone who is dismissing solar now for the fantastical idea that nuclear is cheaper now. Nuclear is good. Nuclear should replace coal. Shutting down reactors that are not unsafe is ridiculous. We should build breeder reactors. Personally I think even many countries that have reactors should build more, and retrofit existing reactors to have much higher ramp rates a la French nuclear. Countries with no nuclear or hydro or geo base like Poland should definitely build nuclear plants.

But many countries have large amounts of nuclear- many enough to supply most nighttime power. And in almost all countries, solar is by far the best and cheapest immediate option, and those countries should be building as much solar as possible until the marginal return of nuclear or storage or infrastructure for imports are cheaper than just building more and more solar.

> I am not aware of any large scale operating exports of solar energy from equatorial regions to Northern Europe, or similar distance.

No country is even close to a solar oversupply, much less a 2x or 5x. If there is no margin, why would those projects exist?

hwillis commented on Poland's clean energy usage overtakes coal for first time   ft.com/content/ae920241-5... · Posted by u/stared
adrianN · 2 months ago
Most of Polands heating is probably not electric. But it’s not unreasonable to store months worth of power, many countries have gas reserves in that ballpark. You just have to replace natural gas with a synthetic fuel.
hwillis · 2 months ago
That's just not true, unless you mean resource reserves. Taiwan has the largest NG strategic reserve I know of (11 days) and the US has the largest petroleum reserve in the world at 19 days: https://en.wikipedia.org/wiki/Strategic_Petroleum_Reserve_(U...

Resource reserves are unextracted and not replenished. They are not the same as storage.

hwillis commented on Poland's clean energy usage overtakes coal for first time   ft.com/content/ae920241-5... · Posted by u/stared
sofixa · 2 months ago
> This is false. Power usage everywhere is highest when the sun is shining

While the biggest peak is around midday, the second biggest is in the evening (most people are home, cooking, watching TV/listening to music/playing video games/etc; or in restaurants, clubs, cinemas, etc) which, depending on location and time of year, can easily be after sunset (e.g. half the year in the Northern hemisphere for sure). You still need enough power to cover that, especially if it has been a cloudy/rainy day, or week, or month.

> Non-renewable plants are the ones that need buffer. Solar, wind, hydro etc can all be connected to a grid with zero instability- you just unplug them if nobody wants the power. Non-renewable plants have slow ramp speeds- they need the buffer in order to follow a changing load

And this is so easy and foolproof to do, just check out the Iberian power outage.

hwillis · 2 months ago
> You still need enough power to cover that, especially if it has been a cloudy/rainy day, or week, or month.

That's besides the point! The window of highest demand completely covers the window of solar. You can build a LOT of solar before storage starts becoming cheaper than just building more solar. You only need storage if it's ALL solar- you can have a majority of your power supplied by solar with hardly any storage! There this idea that if you overbuild solar that power will have nowhere to go, or something- you can just turn it off. You use backup power for the non-shining hours and you're totally fine.

> And this is so easy and foolproof to do, just check out the Iberian power outage.

In fact I did[1]. Page 117: "In fact, in most of the network nodes analyzed, there is no correlation between voltage stability and the amount of solar generation or the amount of coupled synchronous generation"

They had 2.3 seconds of inertia, more than the regulated 2 seconds. Power sloshing through interconnects caused plant ramp rates to be overwhelmed one-by-one, causing the cascading failure, because they had no buffering. If they were all solar or wind plants, the failure would not have happened!

[1]: https://media.licdn.com/dms/document/media/v2/D4D1FAQGcyyYYr...

hwillis commented on Poland's clean energy usage overtakes coal for first time   ft.com/content/ae920241-5... · Posted by u/stared
rich_sasha · 2 months ago
> > and the fact that cycles of power generation in most cases do not align with usage.

> This is false. Power usage everywhere is highest when the sun is shining.

This is kind of true but also not. In Poland, and in a lot of Europe, power usage is by far the highest in winter, day or night, for residential heating. That's also the time with little sun: days are short and the sky tends to be heavily overcast. Sunny weather is rare in winter.

hwillis · 2 months ago
Numbers: In poland the solar output in December is 1/5th of July output while demand is ~10% higher. Insolation drops off quickly at higher latitudes so it dominates much more strongly than heating demand even if heating were electrical.

At the global scale this would ideally balance out- more equatorial solar is cheaper in the winter since they don't need air conditioning, so you just send it up north. That's the only really feasible solution to seasonal variation in individual countries- it's totally unreasonable to store 3 months worth of power. Its also important to note that even with 2x or 3x oversupply, solar is cheaper than nuclear currently is.

[1]: https://re.jrc.ec.europa.eu/pvg_tools/en/#PVP [2]: https://www.pse.pl/web/pse-eng/data/polish-power-system-oper...

hwillis commented on Poland's clean energy usage overtakes coal for first time   ft.com/content/ae920241-5... · Posted by u/stared
MarcelOlsz · 2 months ago
How many days worth of coal burning does 90 days of billionaire jets travelling to Bezos wedding count as?
hwillis · 2 months ago
A 747 burns ~9 tonnes of kerosene per hour, creating ~29.6 tonnes CO2. The Monroe Power Plant produces 3400 MWe at ~1 kg CO2 per kWh, so ~3400 tonnes CO2 per hour.

It's a little complicated to weigh stratospheric emissions- the CO2 has a larger impact, and while the water droplets and contrails left by planes somewhat counteracts it (by reflecting incoming infrared) it's harder to compare intangibles like mercury emissions from coal. If you just say its all a wash, that plant is equivalent to 120 747s running full speed.

Private jets consume more like .9-1.5 tonnes per hour, so that's equivalent to ~900 billionaires. That's a bit less than half of them which is probably a lot more than were at the wedding. They also probably parked them instead of leaving them circling in the air.

If there were 90 billionaires who flew 12 hours each way in their private jets, then they probably released around 2.5 hours worth of Monroe Power Plant time over those 90 days- 8458 tonnes. Fun fact, the pilots and flight attendants probably used ~1000 tonnes of CO2 worth of energy etc and exhaled ~25 tonnes of CO2 in that time. 25 tonnes is small compared to the planes (>.3%), but in those 90 days the planes released just .11% as much as the coal plant.

Coal really truly sucks and it's unfair that I can't eat tuna without getting mad hatter disease.

hwillis commented on Poland's clean energy usage overtakes coal for first time   ft.com/content/ae920241-5... · Posted by u/stared
Xelbair · 2 months ago
Are they? Usually most analysis ignore costs of having a buffer in the system - either batteries or water reservoirs for pumped storage. That also inclides efficiency of storage, and the fact that cycles of power generation in most cases do not align with usage.

Initial cost per unit is low and they're faster to build - that's the reason of their proliferation - and in case of personal use, subsidiaries.

Compared to nuclear - which takes many political terms to build - politicians can reap benefits early. Because nuclear is superior by every metric except:

- high initial costs

- longer lead time

Not to mention less land required, which is another of ignored costs.

hwillis · 2 months ago
> and the fact that cycles of power generation in most cases do not align with usage.

This is false. Power usage everywhere is highest when the sun is shining. There are also very very few places where solar power ever causes the market to bottom out with any regularity. Note that there is no technical problem with this- you can always just disconnect renewables from the grid.

The phenomenon you are thinking of -the duck curve- refers to the power demand after subtracting solar. The daily peak consumption of power in many places is wider than solar generation, so if there is enough solar you end up getting new smaller peaks just after dawn and around sunset. This is minorly inconvenient for non-renewable sources, which prefer to have more predictable demands.

> Usually most analysis ignore costs of having a buffer in the system

Correctly! Non-renewable plants are the ones that need buffer. Solar, wind, hydro etc can all be connected to a grid with zero instability- you just unplug them if nobody wants the power. Non-renewable plants have slow ramp speeds- they need the buffer in order to follow a changing load.

> Not to mention less land required, which is another of ignored costs.

This is incorrect; I don't know of any analyses which don't include land and interconnection costs which are obviously substantial. If you mean more intangibly... that's very silly. The US Interstate system is 3.9 million miles of road, with 60' medians, 16' of shoulder, and 48' of lanes. 237,250 square kilometers. The "blue square"[1] is 10,000 square km. The amount of land we spend on parking lots absolutely dwarfs it.

> Because nuclear is superior by every metric

Nuclear has not gotten cheaper- why would it? It's a big clockwork. We are not better at building pipes than we were 80 years ago. Solar has and will continue to: plants get more productive, panels get thinner, efficiencies go up. There is no grounding principle that indicates nuclear can be cheaper, and it certainly is not in practice. Solar is far cheaper than coal by capacity much less kWh, and nuclear plants are more complex than coal. What indicates that a 500 MW nuclear plant should be cheaper than a 500 MW coal plant, not counting running costs?

> Are they?

Demonstrably yes, absent weird conspiracy theories. Renewable installations keep opening at much lower costs than traditional plants.

[1]: https://blogs.ucl.ac.uk/energy/2015/05/21/fact-checking-elon...

hwillis commented on Gridfinity: The modular, open-source grid storage system   gridfinity.xyz/... · Posted by u/nateb2022
kalev · 2 months ago
Took me a while before i understood it was to store physical items. For a second I was thinking some battery solution-like grid storage system. A few photos on the homepage would help a lot and make it much more clear for noobs like me.
hwillis · 2 months ago
Same, hah. The similarity between gridwall and powerwall in another comment also snagged me. "Perfboard" has also gotten me before- both are perforated board, but one is used for quick circuit boards and the other (more commonly called pegboard) is a wall-mounted modular hook system for storage.
hwillis commented on NASA's Voyager Found a 30k-50k Kelvin "Wall" at the Edge of Solar System   iflscience.com/nasas-voya... · Posted by u/world2vec
perihelions · 2 months ago
Nuclear power is very feasible in space. Perhaps you're overlooking that radiated power scales with the quartic of absolute temperature (T⁴); it's not difficult at all to radiate heat from a hot object, as it is for a room-temperature one.

(How hot? I won't quote a number, but space nuclear reactors are generally engineered around molten metals).

hwillis · 2 months ago
Yeah, fair to say its feasible. ROSA on the ISS produces 240 W/m^2 and weighs 4 kg/m^2.

The S6W reactor in the seawolf submarines run at ~300 C and produce 177 MW waste heat for 43 MWe. If the radiators are 12 kg/m^2 and reject 16x as much heat (call it 3600 W/m^2) then you can produce 875 watts of electricity per m^2 and 290 watts at the same weight as the solar panels. Water coolant at 300 C also needs to be pressurized to 2000+ PSI, which would require a much heavier radiator, and the weight of the reactor, shielding, turbines and coolant makes it very hard to believe it could ever be better than solar panels, but it isn't infeasible.

Plus, liquid metal reactors can run at ~600 C and reject 5x as much heat per unit area. They have their own problems: it would be extremely difficult to re-liquify a lead-bismuth mix if the reactor is ever shut off. I'm also not particularly convinced that radiators running at higher temperatures wouldn't be far heavier, but for a sufficiently large station it would be an obvious choice.

u/hwillis

KarmaCake day6342March 21, 2012View Original