

Make Steam Without Boiling Water - Just Add Sunlight and Nanoparticles - SamuelKillin
http://www.popsci.com.au/science/energy/to-make-steam-without-boiling-water-just-add-sunlight-and-nanoparticles

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ndonnellan
The technology is interesting, but the title is misleading at best. The water
is still boiling, but only a small fraction of the volume needs to be at the
boiling point. The tidbit about "cheap and abundant source of steam" is
totally uncalled for. Unless you're changing the heat of vaporization of
water, you will always get the same amount of steam for the same amount of
energy input.

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pedalpete
I understood this as improving the efficiency of creating steam, though
unfortunately they didn't say how much more efficient it is.

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kevinconroy
This lead me to an interesting Google search around engine efficiency. I
always knew that engines are imperfect engine transfer devices, but I didn't
realize how much is lost.

Seems like in most scenarios you're getting _at best_ 40% energy efficiency in
gasoline engines and somewhere between 17% to 40% in steam engines.

Even at 17% efficiency using the sun to generate steam power seems to hold
lots of potential. The trick will be to get it working at scale and able to
produce a similar level of energy with the same or lower cost as existing
technologies. May be a while yet, but it's an exciting time to teach your kids
science as this is the kind of stuff that they'll probably see in mass later
in life.

Source: <http://en.wikipedia.org/wiki/Engine_efficiency>

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SamuelKillin
This is exactly how large scale solar thermal power stations work.

The most common ones use thousands of mirrors around a central tower. The sun
bounces off the mirrors and focuses at the top of the tower where there is a
tank of water. The water is heated, boils, turns to steam, which turns a steam
turbine.

Look up BrightSource Ivanpah

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hcarvalhoalves
Cool. So it basically improves water's efficiency to absorb energy in the form
of light.

Can the same idea be applied to improve water's efficiency to _exchange_ heat,
to make it cool easier? Then you can slap a turbine and have the perfect steam
generator.

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SamuelKillin
Cooling it isn't hard, when the steam hits the turbine it loses a lot of its
energy and will inevitably cool down and condense. Then you just pump it
around back into the chamber and re-steam it.

I work in the solar thermal industry - my company (<http://www.sunapse.co>)
builds software for solar thermal power plants. I can say with some authority
that this is legit and VERY promising tech.

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Someone
Care to explain in what respect it is promising?

the way I read this is that they put black particles that adsorb heat better
in the water. That makes this produce some steam fast. I do not see how this
would produce more steam than, say, a thin layer of water on top of a thin
black-painted sheet that is well-insulated from below (sun heats black sheet;
sheet heats water).

How is producing some steam rapidly an improvement?

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SamuelKillin
how long do you have? :)

So, them being 'black' isn't really the point. The point is the potential to
get steam from water at lower temperatures, in less time.

If you are dealing with A LOT of water (if you were to scale this to power-
plant scale), you are dealing with large 'thermal mass'. This means you need a
lot of heat over time to raise all the water to a high enough temperature to
create electricity.

If you run a power plant, you want flexibility. You want to switch on your
power plant fast, and then shut it down when you want, without cost. This lets
you speculate on the electricity market, and be more available if there is a
sudden spike in electricity demand. If you're dealing with large thermal mass,
you don't have this flexibility.

Also lots of advantages of lower cost - not needing heat exchangers etc but
I'll leave it there.

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ndonnellan
How exactly would you scale this direct absorption? Glass tubes? Under
pressure? Oops, now we're at the air-receiver dream. Never gonna happen. Also,
can you guarantee that particles don't get entrained in the steam flow? I'm
not sure Siemens is gonna warrantee that turbine. Sorry to be a pessimist, but
it's gonna take a while longer for tech like this to make sense to me.

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leot
The big win seems to be from eliminating much of the heat dissipation that
would otherwise normally occur if, e.g., you tried to use sunlight to boil
water when nanoparticles aren't involved.

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rmundo
I always wanted a steam-powered laptop. Bring on the brass and leather!

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hayksaakian
Pressure.

