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« Nanofactory Proliferation | Main | Serious Stuff »

July 09, 2004


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One thing about the solar panel thing I haven't seen mentioned is walls. An apartment building 10 stories high might have as much as 10,000 sq meters on 1 outside wall if you say that the panels will be clear plastic and can be applied to windows. Then with indoor solar paint being able to recycle SOME of the energy, coupled with things such as low-power nano-computers, and Oled's or nanotube lightbulbs that consume a fraction of the energy their modern counterparts comsume, I think that power by solar alone may be ALMOST enough. Like Matt said above, other clean sources wont go anywhere. I live in Buffalo NY, and Niagara falls can produce 2.4 million kilowatts of power, and canada already is almost 70% dependent on hydro power.

Brett Bellmore

A tall building isolated among short buildings can take advantage of the sunlight landing on it's sides, to get more power than it's footprint would provide. A tall building among OTHER tall buildings will gain no such advantage, as it will be shaded on it's sides except when the sun is near the zenith.

It's worth doing, of course, as the side of the building will capture some of the light which comes down between the buildings, but you're still not going to get in total much more power than the area of the city lying flat would intercept.

If we were determined to be locally self sufficient for power, you'd kiss cities goodbye. I don't think we'll be that obsessive about it. If cities continue to exist, they'll just import power.

The real question is, would cities continue to exist? Cities are economic machines, after all: They exist because some things are more efficiently done if you collect a lot of people in a small area. Technology has been changing that, which is why we've got suburbs, and nanotechnology may be the death of cities. Not because it makes them impossible, but because it makes them uneconomic.

Chris Phoenix, CRN

Note that the energy use figure in my nanofactory paper is a pessimistic estimate for a very crude design. I don't know how much better it could get, but a factor of two improvement seems very likely, and a factor of ten is possible if some of the mechanosynthetic action can be reversible (which is likely in a mill system).

When thinking about places to put solar cells, don't forget about the cleared land under power lines. Random Googling: A 170-MW power line may have 30 meters of right-of-way. At 100 W/m^2, putting solar cells under 57 km of line will supply the line. A 760-MW 500-kV line may have a 50 meter right-of-way, needing 152 km.


Brett Bellmore

Out here we just plant crops under them.


So I gather from all this, none of us think that power will be too much of a concern in the near future. Am I right.?

If so, question, should the government regulate and distribute low cost solar panels. Or should current energy companies distribute them. My problem is maintainence, will they really need any, other than obvious things such as hail storms, hurricanes, tornados, in which case new ones all together would probably be needed.
Or should individuals be required to purchase them if they wish to, and again, if so should the government regulate costs.

Might solar panels be company or government property on private property, at least for those who cannot afford to purchase them...?

Brett Bellmore

What conceivable need would there be for the government to regulate and distribute these panels? Do you get shingles for your roof from a government agency?


This is an attempt to forcably ween people off of current non-renewable energy.

If it were up to the market-place, it might take 10-15 years to convince half the people in this country to go spend $5,000.00 (and thats when the price comes down)on a new roof, then install it.

I think things would go much quicker if such things as cost, and avialability were regulated.

I could just be impatient tho.

Tom Craver


Cities - there may be good reasons that they'll continue, even with the energy provision issue. If all or almost all jobs related to manufacturing and distribution of goods and energy go away, there may still be a need to work at design and service jobs (enforced by a nanoblock economy, or simply to get desired services from other people). Such work is easier to find in a city, and if one desires human service, there'd be a greater diversity available in a city.

If absolutely all requirement to work goes away we still might like living in a city simply for the concentrated variety and novelty it might offer. Likely there'd still be restaurants, clubs and other entertainments - run for the love of entertaining or as a way of gaining status. Possibly there'd be an informal economy of 'favors' - knowing the right people gets you into a popular place.

Perfect Virtual Reality might cut into that some - but I think most people will still find something desirable about actually being among other people - status, a little personal risk to you and those around you (even if it's only psychological - one can't just blink away when under stress).

Brett Bellmore

Oh, I don't think cities would entirely disappear. I think that really big industrial citiies would shrink, and what would remain would be more like theme parks, tourist traps, and college towns.

Nanotech could make really fast and versitile mass transit systems practical, so I expect that the only people you'd find living full time in cities were the people who enjoyed them. And that's a definate minority.

Chris Phoenix, CRN

One reason for regulating solar power collection: Heat pollution. Solar panels are dark. A sufficient concentration of them could change the local climate. And enough of them used worldwide could change the global climate simply by changing the earth's albedo.

According to Freitas, we risk climate change at 10^15 watts, about 0.5% of insolation. http://www.nanomedicine.com/NMI/6.5.7.htm

This is only about 10^5 W per person. Americans already use more than 10^4. 10^5 W is only about 10x20 meters of solar panel (remember, collection efficiency doesn't count for this calculation).

How quickly could we get there? Well, you can have a very stiff structure (a 1-cm panel pressurized to 25 atm) for <30 g/m^2. The crude-nanofactory energy cost is 6 kWh/m^2, and assuming 200 W/m^2 24-hour collected average, that would take...a bit more than a day to pay back its construction cost. Starting with 1 kg or 33 m^2, you could bootstrap the energy cost of building 10^15 m^2 in about... 45 days.

The total mass required would be about... 3E10 tons of carbon, or about... 40 years of U.S. oil consumption. On the other hand, we can expect carbon extraction technologies to improve if there's a demand for carbon. (That's almost a tenth of atmospheric CO2, and it'd be costly to extract due to low concentration.)

On the other hand, a silica-based nanotechnology would be less strong but the raw material would be far more plentiful.

Anyway, the point is that within a few years we might have to start worrying about allocating heat pollution rights.


Brett Bellmore

Yes, that's true. Perhaps a system of heat ballance credits and debits, (Easy to track using satelites!) so that people could actually earn money by covering their land with surfaces which were light during the day, and radiated efficiently at night.

Design solar panels which are perhaps a bit less efficent, but have the same albedo as vegetation on one side, (Another selling point for Electric Grass!) but which flip over at night to become optimal radiators. Some cost in efficiency, but you earn those credits, too.

You'd have to ballance this out on a fairly local level, though. If everybody was earning heat credits in one state, and spending them in another, you'd get some amazing winds...

Planetary engineering does have some potential for improving the situation, though; Ultra-thin specral filters could eliminate incoming sunlight at frequencies which didn't drive solar panels or plant growth, reducing the incoming heat flux without much impacting the ecosystem.

And as thermal radiation rises as the 4th power of temperature, you don't have to spend too much of that energy you're taking in, to radiate it away more effectively, though. I suppose you could store solar energy during the day, and utilize it to run various energy consuming processes such as recycling reagents and manufacturing generic blocks, right in radiators at elevated temperatures.

Don Quixote

Waste heat: another good reason for diamondiod windmills.

Brett Bellmore

Ok, so maybe we WILL put all the heat debits in one state, and the heat credits in another, to keep the windmills running. LOL

Keep in mind that windmills are driven, ultimately, by sunlight. A very tiny fraction of the sunlight that hits the earth, at that. The energy potential of windmills is pretty puny compared to directly harnessing that solar energy. I suppose, though, that you could get a decent efficiency boost by coupling solar panels with a solar tower, and using the heat from those dark panels to drive the system, instead of just using dark paint.

Chris Phoenix, CRN

Let's see... at 600 K, to radiate 1E15 watts requires... 5.67E-8 W/m^2K^4... the back of my envelope is pretty smudgy, but I think it's 1E11 m^2. Which is orders of magnitude smaller than the solar cell area to acquire the energy. This seems reasonable.

But then the problems start. Don't forget that the atmosphere absorbs infrared. You'd have to put your radiator above most of the atmosphere.

For that matter, you'd probably have to put your power generation above most of the atmosphere! If it's 60% efficient (pretty darn good for either solar cells or thermal cycles), then 2/3 of the usable power output (40% of the total) will come out as heat.

If you want to cool your generator on the ground, you can try... Carnot then says you have to use at least an equal amount of the usable power to pump the waste heat up a 2:1 gradient to 600K. Then you have to transfer that heat a dozen(?) miles straight up. Heat pipes won't work due to gravity. Ballistic phonons in diamond or buckytubes might, maybe. An endless chain of moving thermal mass might work, in theory.

So even if your refrigerator was perfectly efficient, you'd only get to use 16% of the power of a 60% efficient power source (10% of its total heat). To cool 10^15 watts of ground-usable power, you'd be generating or collecting 10^16 watts at least.

So, this would be a massive engineering task, and likely not worth doing in practice.


Brett Bellmore

Yeah, but if you've got machinery, such as mills for commonly used blocks, that can actually RUN at the elevated temperature, there's no energy cost, (Save perhaps from diminished efficiency.) from pumping the heat. Since electricity doesn't care much if it's crossing a heat gratient.

And while the atmosphere isn't perfectly transparent to infrared, it's not perfectly opague, either, or else it wouldn't get colder at night. In particular, it can be quite transparent over deserts, given the relatively dry atmosphere.

So I do think there's some possiblity of designing your energy usage to enhance thermal radiation, though it would of course be easier if not for that pesky atmosphere. It's not going to totally save the situation, but it's probably worth doing. Might be worth running a more detailed calculation based on the actual transmission profile of the atmosphere, and spectral distribution of heat radiation at given radiator temperatures.

Now, that solar tower I mentioned earlier could carry a lot of it's waste heat pretty high in the atmosphere, where it would be above much of the blocking moisture. Atmospheric plumes like that could be a major heat rejection enhancing technique.

Chris Phoenix, CRN

Solar cells on a solar tower... I like it! And you could put your radiator at the top of the tower.

But I don't know enough of the physics to know whether a solar tower will work better the higher it gets. I found one site that said it should be just 3.5 air column depths, and there'd be just a 30 degree difference between top and bottom.

So it may not be worth it over cheap solar cells--not to mention the climate change!


Brett Bellmore

The air itself is the radiator. It picks up the heat from the solar cells and any local industry, and carries it in a thermally powered plume into the upper atmosphere, much higher than the tower itself, where it's above most of the water vapor, and the air itself can radiate the infrared.

Chris Phoenix, CRN

Can you actually get convection through a seven-mile tower? And what effect will this have on climate? Solar cells get less efficient at higher temperatures, so you may not be able to dump their heat to the manufacturing-heated air stream.

Also, some nanomachine dissipative processes are proportional to kT. A computer running twice as hot will take (I'm guessing) 50% more energy.

Thanks for volunteering to do the study! It'd be nice to know whether we can beat the hypsithermal limit. Email me your first draft or outline for technical commentary. (I'm actually not joking; go for it!)


John B

Mike Deering's self-disassembling dome is a VERY good point. Nanotech doesn't need to make things to affect criminal actions - it simply needs to unmake them.

Nanotech could be the ultimate way to hide an inconvenient body, or gain entry throgh a physical barrier. It could be incredibly useful to get rid of evidence - apply a carbon-sequestering nanite to a titanium blade, and voila - no prints, no blood, no DNA. (Don't use it on a steel blade - you'll loose any surface carbon.)

-John B

Chris Phoenix, CRN

Disassembly-by-nanobot is not efficient. There are lots of easier chemical and mechanical ways to destroy something. I don't see nanotech having a big impact here.


Brett Bellmore

Honestly, criminals typically don't use the technology already available to them; Gloves to conceal finger prints, sticking a crime gun in a ziplock bag of Draino, you name it. Or, anyway, most of 'em don't. There ARE some smart criminals around, but almost all of them work in the drug trade and other victimless crimes, and could be gotten to go straight just by ending the war on drugs.

Brett Bellmore

I can do some research, and run some preliminary feasibility calculations, but such techniques wouldn't eliminate the limit, just stretch it a bit. You wanted to seriously blow a hole through it, you could build an air dike around an industrial park, and fill it with something that didn't block IR, though. It would be a mega engineering project, but might pay off.

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