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New Photovoltaics Made with Titanium Foil
Memorize writes "A company called Daystartech has released a new type of photovoltaic cell which, unlike almost all the cells currently in use, does not silicon. This is based on a thin titanium film. Given the current shortage of solar-grade silicon, and all-time high oil prices, maybe titanium solar panels are here at the right time. The questions are, will they release it as a consumer solar product, and what will be the price per kilowatt hour?"
Food for thought: if your solar sail is using photon pressure, then by coating it in a photoelectric, you're halving its efficiency as a solar sail. Why? Well if your solar sail is a perfect reflector, then the photons bounce off and reverse direction, so the momentum change is twice the initial photon momentum (yes photons are massless but they do have momentum). If the sail is absorbing the photons for electricity, then they are not reflecting, so you merely absorb their momentum, making your forward impulse half what it would otherwise have been.
But, as we all know, solar sails work both by exploiting photon pressure, and solar wind (particles emitted by the sun), so the situation is maybe not that bad.
It costs a lot to do anything with titanium because the oxide forms quickly on any exposed surface and takes a lot of energy to break down.
Slicon?
The interesting thing here is that the fastest growing solar cell market is not silicon: it's organic solar cells. They're incredibly cheap, but currently inefficient. However, their efficiency has been growing dramatically. One company, nanosolar, claims to have achieved almost the efficiency of amorphous silicon cells. Their patent is rather interesting, and well worth a read.
I once listened to a Philip Glass record for an hour and a half before I realized it was skipping.
Monocrystalline silicon is incredibly expensive. Polycrystalline silicon (which has largely taken over in the solar cell market) is simply "very expensive". Silicon is common, but pure silicon crystals require clean-room conditions to grow.
Titanium isn't that rare. The ore isn't the primary cost component (like, say, gold). Instead, like aluminum, the main costs are in refining. Unlike aluminum, however, there is currently no continuous production process - only an expensive batch production process. Even the inventor of the process, William Kroll expected to have it be replaced within decades of its implementation in 1940; no suitable replacement was found, however.
Fortunately, it looks like there are some on the horizon. Most interestingly, it appears that electrolysis can be conducted directly on titanium oxide (this has huge potential applications for other hard-to-refine metals as well, and may allow for the creation of new alloys). There's also a aluminum-style molten-salt electrolysis process (FFC-Cambridge) in testing.
Titanium isn't inherently hard to work with, persay; you just need to be properly equipped to work with it and experienced with it. You have to use *very* pure argon in welding, and you have to keep the argon going for longer after you take the heat off. You also have to avoid working it with aluminum tools, which can alloy with the metal and weaken it. Etc.
There are some benefits, though. Impurities in titanium are very easy to spot, as they tend to discolor. Also, titanium is *very* fatigue resistant, and aircraft with titanium structural components have sometimes even been found to be stronger after being flown a few times than when they were built.
I once listened to a Philip Glass record for an hour and a half before I realized it was skipping.
I should also add that titanium is really just the backing. It's a great backing, given it's strength and condition-tolerances compared to its mass, but it's not what generates the power The cell itself is actually a copper-indium-gallium-diselenide cell - not that it's cheap, either ;)
I once listened to a Philip Glass record for an hour and a half before I realized it was skipping.
Yes, actually. This isn't just some sand scooped off a beach. Solar panel grade silicon comes from the leftovers after semiconductor grade silicon users have picked through their crystal wafers, which is why there is a shortage in the first place, since there is a narrow range of quality ("almost" good enough for semiconductors). As for titanium, my 30 year old encyclopeda says its one of the 10 most common metals on the planet. Titanium Oxide is cheaply produced and used liberally in paint.
Titanium is malleable when hot (meaning you can flatten it into foil). So producing titanium foil is probably not a difficult task, depending on how hot "hot" is. (Though the article mentions that the titanium foil used is thinner than household aluminum foil. The process looks like it would be easy anyway, but time consuming.)
As for your post on waste products, the most common smelting procedure in use works without catalyst or flux to produce pig-iron and Titanium Oxide, though this process is common because of its use in paint. This process was recently developed for producing metallic titanium, its outputs are salt (NaCl), titanium, and whatever impurities get washed into the liquid sodium stream and removed later.
If I have been able to see further than others, it is because I bought a pair of binoculars.
Also, titanium is *very* fatigue resistant, and aircraft with titanium structural components have sometimes even been found to be stronger after being flown a few times than when they were built.
The above refers to one aircraft in particular. The SR-71/A-12 was found to have a stronger airframe after flight. This is not really due to titanium itself, but rather the gentle heating and cooling that the aircraft underwent with each flight. It annealed the metal, thereby making it stronger and helping to eliminate the fatigue that is normally problematic in airplane structures.
Don't confuse photoelectrics with photovoltaics.
For example, Sandia Labs has a plant currently in operation that produces 5MW in 9 acres, by focusing light onto a tower that heats molten salt which drives turbines. It can produce energy 24 hours a day.
The United States' generating capacity a few years ago was 813 gigawatts, so at .55 MW per acre you'd need 1.4 million acres for all of the US's energy needs. That's about 2300 square miles or 6000 square kilometers, or about 1.5 Rhode Islands. We have many deserts that are larger than that.
Realistically, you don't need a power generation mechanism to be able to handle the entire United States energy needs before you put it in production. You just need it to be cheap (and cheap after the costs of fighting NIMBY lawsuits are factored in).
Sandia's web site doesn't say what their cost per megawatt hour is, but they do say the entire facility is currently worth $120 million. Since this type of system uses nothing exotic, I would expect economies of scale to change the numbers quite a bit. Assuming a life of 30 years, they'd have to be able to reduce the cost by about a factor of 10 to be competitive with today's rates. It could happen.
IIRC, the problem with titanium is not so much that the raw material is expensive. The problem is not even so much that it oxidizes readily (aluminum does too). The problem is that it has a high melting point, and is very difficult to forge and to machine.
Pure Ti-metal has a hexagonal close packed microstructure (HCP). Most other metals have a cubic structure (either face centered cubic:FCC or body centered cubic:BCC). FCC and HCP have the same packing effficincy, but it is much easier to form and move dislocations in a lot of different directions in either FCC or BCC than for HCP. Dislocations are necessary for forging, and forging creates such a tangle of dislocations that it actually strengthens the material.
That is why Apple moved away from Ti for Powerbooks, IMHO. It impossible to economically bend the titanium to form the laptop shell without making the metal so thin that it is way to flexible. So the old Ti-Powerbooks had a Ti top and bottom, with Ti-painted plastic in between. This paint invariably started to flake, which led to lots of complaints. Apple wisely switched to an aircraft grade of aluminum, which can be sufficiently bent and machined to form the entire shell of the laptop, not just the top and bottom.
Anyway, that is the basics. IAAMSBTDNCMA (I am a materials scientist, but this does not constitute materials advice)
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Si02 + 2C = 2CO + Si
Once this silicon is produced, it is refined into super-pure semiconductor grade silicon, or more usually, into silicone rubber pre-cursors. I used to work in silicon smelting R&D and so I have some idea about what I'm talking about. (We built and ran the worlds largest direct current arc furnace during a series of pilot runs in the early 90's to research making lower cost silicon. That was before Russia opened up. After they did, they flooded the market with cheaper silicon, and there was no point trying to create lower cost silicon.) The biggest use of silicon is in making silicone rubber (but not so many boobs any more). The raw material for ultra-pure silicon is taken from the raw material (not so pure silicon) used for silicone production.
Anyway, smelting silicon creates large volumes of CO. CO (carbon monoxide) is highly flammable, on the order of natural gas, and usually burns off to C02 at the top of the furnace bed. (CO could be used as a fuel like natural gas, but it is so poisonous it is not really safe to do so.) Since coal and charcoal are used in the process, other carbon by-products are also released, mostly in gaseous form. E.g. like the stuff that makes up tars and such... a little nasty... but quite small relative to CO and CO2 since the high temperature tends to atomize them. However, some of the coal and charcoal does burn away in the upper part of the furnace (where it is relatively cooler) and before it gets a chance to react. As well as producing some not so nice gases, it is a very energy intensive process. Silicon is never found in elemental form in nature. It must be separated from SiO2, which requires a lot of power, which in turn needs to be produced at generating stations.
As far as silicon used in semi-conductors goes, I'm not sure if they use electrolysis to refine it to ultra-pure levels. Maybe in some sort of deposition process from a gasous phase, but I am just guessing from what I have read in general chemistry related articles. The details of that type of processing are usually very top secret so I am not sure who could or would comment on that. And I mean either industrial secrets and likely in a military sense as well (it is probably of strategic value).
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The metal itself has a high strength and hardness, but there are plenty of steels harder than it. The oxide layer is very hard, and as soon as you chip some away it forms again. A slightly harder compound, titanium nitride, is the gold coloured stuff you see plating the tips of cutting tools.
If the oxide is being used in these cells the process may be surprisingly cheap, since the hard bit is reducing the oxide to metal. If it's something else, there may be ways of making it cheaply from an ore - a mineral sand. If a vapour is being sprayed onto a substrate it might not cost a lot either.
I'm not a materials scientist anymore, but for a while when I was I used to teach engineering students how to break things under controlled circumstances - and find out why stuff broke under uncontrolled circimstances.
Something to think about: in order to be flammable you need concentrations of at least 5% CO in air (about the same as needed for natural gas). That's 50000 ppm. To put it in perspective if you were in a room with 800 - 1000 ppm CO for several hours, you would likely end up dead. If you walked into a room with 4000 to 5000 ppm CO, you might not even know what hit you as you hit the floor. It wouldn't be long before you died. So basically, if you used it for a fuel source, it would really suck if the pilot light went out. Maximum OSHA allowable limits in the workplace is 35 ppm. In the middle of typical rush hour traffic (I measured it with a portable meter): 50 ppm! Mind you in industry you are usually indoors where it can concentrate, and often there are very high levels behind it (our offgas lines had 75 to 80 % pure CO... even small leaks were dangerous... we had monitors and venting systems and escape air bottles everywhere).
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