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Heliogen targets 1500°C solar thermal

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Re: Heliogen targets 1500°C solar thermal

#21

Post by Beltiras »

ginko wrote: post #19
reportgunner wrote: post #9

Earlier quoted context omitted.

AFAIK the solar towers actually use molten salts to store the heat in tanks so they can keep going even overnight.

Not sure which salts would be used here, but I 1500C+ is pretty hot even for many salts. Sodium chloride boils a bit below that(1465C) for instance.

Molten salt towers don't heat above 800 iirc. If they were designed for storing more energy it would come from more mass. It goes without saying that the benefit of salt is reduced once it becomes gasified.

Re: Heliogen targets 1500°C solar thermal

#22

Post by new299 »

ReptileMan wrote: post #10
new299 wrote: post #2

Bill Gross, Heliogen’s current CEO previously founded eSolar. eSolar proposed using an array of Heliostaticly controlled mirrors to direct light toward a solar cell: https://en.wikipedia.org/wiki/ESolar So... that part of the eSolar approach is carrying over into Heliogen. Last time this was posted the “AI” component of the play was less clear... But with an array of mirrors, in particular being to generate heat in s…

What exactly do you need AI for except for buzzwording? It is not as if the sun/earth trajectory or rotation speed is random. You can precalc with ease at every point which is the best position for each mirror.

I would imagine that it’s not the suns location that is the primary concern, but where you are directing the light.

The light is being reflected and focused by mirrors. That light is being directly onto some volume of material. So, in this case, they want to get the material above some critical temperature (e.g. so it melts). I imagine that uniformly heating the whole volume may not be the best approach, or that you may be able to work with smaller volumes depending on your expected solar input etc.

So I can see a little more justification here than the case where solar cells are just being pointed at the sun.

Re: Heliogen targets 1500°C solar thermal

#23

Post by pjc50 »

ReptileMan wrote: post #10
new299 wrote: post #2

Bill Gross, Heliogen’s current CEO previously founded eSolar. eSolar proposed using an array of Heliostaticly controlled mirrors to direct light toward a solar cell: https://en.wikipedia.org/wiki/ESolar So... that part of the eSolar approach is carrying over into Heliogen. Last time this was posted the “AI” component of the play was less clear... But with an array of mirrors, in particular being to generate heat in s…

What exactly do you need AI for except for buzzwording? It is not as if the sun/earth trajectory or rotation speed is random. You can precalc with ease at every point which is the best position for each mirror.

The difficult problem is not knowing where the sun is but knowing where the ground is. Since all the panels are separate structures not on a single rigid slab, ground "settling" can tilt them fractionally in unpredictable ways.

It sounds like what they have is machine vision as a novel input into a conventional control loop. For one panel at a time, wiggle it about and look how the light spot changes. Find the local maximum for tightest spot. That's now "locked" in the PLL sense and should stay locked for days or weeks.

Re: Heliogen targets 1500°C solar thermal

#24

Post by ygra »

VBprogrammer wrote: post #18
BurnGpuBurn wrote: post #17

Earlier quoted context omitted.

I was just wondering how many birds this would fry, thanks for the article.

The problem is generally trivial compared to the number killed by domestic cats and glass windows.

For wind turbines at least there's a bit of a difference, as those kill larger birds than cats, in smaller numbers, but those birds also have smaller populations. So just looking at the numbers without knowing the birds and their total populations, makes things hard to compare or judge.

Re: Heliogen targets 1500°C solar thermal

#25

Post by ovi256 »

ReptileMan wrote: post #10
new299 wrote: post #2

Bill Gross, Heliogen’s current CEO previously founded eSolar. eSolar proposed using an array of Heliostaticly controlled mirrors to direct light toward a solar cell: https://en.wikipedia.org/wiki/ESolar So... that part of the eSolar approach is carrying over into Heliogen. Last time this was posted the “AI” component of the play was less clear... But with an array of mirrors, in particular being to generate heat in s…

What exactly do you need AI for except for buzzwording? It is not as if the sun/earth trajectory or rotation speed is random. You can precalc with ease at every point which is the best position for each mirror.

Yes, you can precalc, and then you need very precise actuators to move the mirror to that precalced position.

You also need precise surveying of the ground site to know its geometry. The precise actuators and surverying are expensive.

Their approach is using cheap actuators in a closed-loop system where a computer vision controller (using the four cameras on top of the tower) moves the mirrors until it gets it right. Cheap actuator slip and lag is terrible, but with the feedback of the closed-loop, it's doable.

This is an approach that's now allowing hobbyists to build cheaper motorised telescopes, robot arms and so on.

Re: Heliogen targets 1500°C solar thermal

#26

Post by ovi256 »

TeMPOraL wrote: post #13
viraptor wrote: post #11

Earlier quoted context omitted.

That did strike me as weird. Although they say "advanced computer vision software" so maybe they do some workaround and take the position from a camera rather than pre-calculations? Can it be the case that a few thousandths of a degree matters here and that's beyond our generalised model?

I'd imagine that the "few thousandths of a degree" is something you'd get worse with AI than with a mathematical model. AI methods introduce noise; with an explicit model you can keep adding complexity directly, until it gets more accurate than your measuring system. I suspect that the "AI" they mention is mostly photogrammetry - being able to tell the position and orientation of your mirrors from a video stream - in…

>mostly photogrammetry - being able to tell the position and orientation of your mirrors from a video stream - in a feedback loop with motor controllers and temperature sensors.

This. Modern photogrammetry uses computer vision techniques like deep neural nets.

It's an amazing advancement.

Imagine this problem: having to place a ground vehicle like a wheeled robot at an arbitrary coordinate in a room. The mirror positioning problem can be reduced to this one. Traditionally, you'd do it by building a very nice wheeled robot with non-slip wheels, wheel rotation angle sensors, fraction of a degree stepper motors, all very nice to work with, precise, and expensive. You could even solve this in an open-loop system with good enough actuators.

Today, just stick a camera on the ceiling - or on the robot, if want a more challenging problem - and use CV to move a cheap RC car where you want.

The Terminator will jangle and jiggle, instead of being built like a precise Swiss watch. But you'll get ten of them for the same price!

Re: Heliogen targets 1500°C solar thermal

#27

Post by JshWright »

pjc50 wrote: post #23
ReptileMan wrote: post #10

Earlier quoted context omitted.

What exactly do you need AI for except for buzzwording? It is not as if the sun/earth trajectory or rotation speed is random. You can precalc with ease at every point which is the best position for each mirror.

The difficult problem is not knowing where the sun is but knowing where the ground is. Since all the panels are separate structures not on a single rigid slab, ground "settling" can tilt them fractionally in unpredictable ways. It sounds like what they have is machine vision as a novel input into a conventional control loop. For one panel at a time, wiggle it about and look how the light spot changes. Find the local…

From my comfy armchair, with zero experience in this field, it seems like you could use star tracking to very accurately predict the angle of the sun (since the sun is effectively fixed in position relative to the background stars over the timescales you'd care about). Spotting the target is a little harder, but the same measurement could be made by sticking some reflectors in known positions around the target.

I'm sure there are tons of considerations that aren't occurring to me (for instance, thermal expansion likely contributes substantially to making it a moving target (literally)), but I really don't see where "AI" comes into it...

Re: Heliogen targets 1500°C solar thermal

#28

Post by TeMPOraL »

ovi256 wrote: post #26
TeMPOraL wrote: post #13

Earlier quoted context omitted.

I'd imagine that the "few thousandths of a degree" is something you'd get worse with AI than with a mathematical model. AI methods introduce noise; with an explicit model you can keep adding complexity directly, until it gets more accurate than your measuring system. I suspect that the "AI" they mention is mostly photogrammetry - being able to tell the position and orientation of your mirrors from a video stream - in…

>mostly photogrammetry - being able to tell the position and orientation of your mirrors from a video stream - in a feedback loop with motor controllers and temperature sensors. This. Modern photogrammetry uses computer vision techniques like deep neural nets. It's an amazing advancement. Imagine this problem: having to place a ground vehicle like a wheeled robot at an arbitrary coordinate in a room. The mirror posit…

> This. Modern photogrammetry uses computer vision techniques like deep neural nets.

I'm surprised to hear that. What good do DNN do for photogrammetry? Aren't they too unreliable?

I only have university course-level exposure to this, most of it spent learning how to compute coordinate systems and transformation matrices from points on a set of pictures taken from different position. I guess DNNs could help with object isolation and labeling (identifying same objects on a set of pictures taken from different perspective)?

Re: Heliogen targets 1500°C solar thermal

#29

Post by VBprogrammer »

ygra wrote: post #24
VBprogrammer wrote: post #18

Earlier quoted context omitted.

The problem is generally trivial compared to the number killed by domestic cats and glass windows.

For wind turbines at least there's a bit of a difference, as those kill larger birds than cats, in smaller numbers, but those birds also have smaller populations. So just looking at the numbers without knowing the birds and their total populations, makes things hard to compare or judge.

Sure, thought needs to go into the location of these things; avoiding migration routes and habitats of endangered birds. Using scarecrows and possible trained predator birds (presuming these can be trained to avoid the danger zone!) etc.

Of course conventional industry doesn't get a free pass here either, treatment and storage ponds, climate change, habitat destruction etc.

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