| Silicon for Solar Panels David A. Dietzler, 2008 Molten silicate electrolysis will produce large qtys. oxygen, FeSi and ceramic blocks. Serial electrolysis might be done by adjusting voltage, current and temperature to produce iron, silicon, and FeSi separately, ceramic blocks and of course oxygen, as iron is deoxidized at lower energy than silicon. Still, the iron will be contaiminated with some silicon, the FeSi will be a mix of the two, and the silicon will be contaminated with some iron, chromium and manganese. The thing to do will be to take the brittle silicon ingots and crush them with steel jaw crushers cast on the Moon and ball mills made on the Moon to grind up the brittle silicon. |
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| Calculations amorphous Si 100 watts/m^2 100 km^2 SPS = 100 million m^2 = 10 GWe 1,000 SPS = 10TW (20% or global total energy demand in 2050) 100 km^2 = 100 million m^2 100,000,000 * 150 grams Si/m^2 = 15,000 tons Si per SPS 1000 SPS requires 15 million tons of silicon ---------------------------------------------------------------------------------------------- MEU (magma electrolysis unit) using 3MWe 5000 tons thruput per year with constant power from distant and local solar plants processes about 100 tons per week 100 tons/2 tons regolith per cubic meter = 50 m^3 5 x 5 x 2 meters or 17' x17' x7' = 50 m^3 If walls are one meter thick ceramic blocks and base is one half meter thick then walls are 48 m^3 if block density is 3 tons/m^3 than walls amass about 150 tons. Base is about 75 tons. Total mass = 225 tons round up to 250 tons one MEU produces about 1000 tons O2, 100+ tons Fe, 1000 tons Si and 2000+ tons ceramic blocks Thus, one MEU produces enough blocks to make 8 more in one year 1, 8, 64, 512 in four years See: Magma Process -------------------------------------------------------------------------------------------------------- 15 million tons Si/ 1000 tons per MEU = 15,000 MEUs to produce all Si in 1 yr. or 1000 MEUs operating for 15 years. or 500 MEUs operating for 30 years or 250 MEUs operating for 60 years ------------------------------------------------------------------------------------------------------------ IT IS POSSIBLE TO MAKE AS MANY MEUs TO PRODUCE THE SILICON THAT IS REQUIRED TO BUILD 1000 SPS RATED AT 10 GWe STARTING OFF WITH JUST ONE IN JUST A FOUR YEARS TIME. CONTINUED GROWTH OF MEUs CAN MAKE THE BLOCKS NEEDED FOR MANY OTHER FURNACES ALSO. 500 MEUS WILL MAKE 500,000 TONS Si/yr. AND ONE MILLION TONS OF BLOCKS FOR OTHER FURNACES. note that in the 5th year we would have enough ceramic blocks to build over 4000 MEUs. Extra blocks will be used for solar flux, Al, Mg, iron and steel furnaces. Along with cast basalt, regolith embankments, steel reinforcements, etc. |
| Note: A specific gravity of 3 for the ceramic blox from the MEUs is a guess. Future data may change things. It takes 13 MWhrs. to get one ton of oxygen. About one ton of Si, 700 kg of Fe, some mixed together as FeSi, and 2+ tons of ceramic blox result also. So magma electro. is very productive. Only half of the O2 in the regolith is tapped, the rest remains bound to Mg, Al and Ca. With a 3 MWe power source, and a 328 hour lunar dayspan, 984 MWhrs are generated, enough to make 75.7 tons of oxygen. Roughly the same amount of Si, 53 tons of Fe, some mixed into FeSi, and 150+ tons of ceramic. Times 13 lunations a year = 984 tons O2 984 tons Si, 690 tons Fe and 1950+ tons of ceramic. This is close to the earlier figures of 1000t O2, 1000t Si, 700t Fe and 2000t+ ceramix. The MEU does not run by night as I assumed above for simplicty. If we did have nightime power, we could double output or halve the number of MEUs. 500 of them could make all the Si we need for SPS in 15 years. So much for the fudge factor. Thruput would go up to 10,000 tons/yr. or 100 tons every 3.65 days. There would probably be downtimes for anode replacement if consumable anodes are used. This all looks plausible to me. I've just been trying to arrive at ballpark figures and it looks like we can produce the silicon needed for 10TW of SPS in a few decade's time. Production of ceramic blocks would double and MEUs could be constructed faster. Also, in the 5th year based on the fuged calculation of 100 tons thruput per week for 50 weeks per year (actually we can do better with constant power from solar farms 700 mile E and W of Frigoris Coast at 65 deg. N latitude) we could build over 4000 MEUs or come up with one million tons of blocks from 500 MEUs every year to build large DRI furnaces, flux furnaces, magnesium smelters, aluminum smelters, slag decarburization fluidized beds, open hearth furnaces, solar furnaces for cast and sintered basalt bricks, ceramic heat exchangers and perhaps other furnaces. Fluidized beds for H2 redux of ilmenite should be made of steel, and we'll have lots of blister steel after a few years and even nickel-cobalt supper alloys too for special apps. Five hundred MEUs would make 350,000 tons of iron per year. Some of that could be converted to blister steel. Looks like we'd have enough iron to make metal jackets around the ceramic MEU walls for extra strength or about 700 tons per MEU and that much would not be nec. so iron would be available for other purposes. And that's at a thruput of 5,000 tons per MEU per year. We can forsee exponential growth. How much power will we need? For 500 MEUs, 1500 MWe. We will need large numbers of volatiles miners, iron fines miners, drag lines or "slushers" and they will all have to be made of blister steel. And we could have 24,000 tons of blister steel in 10 years and I allowed no fudge factor in those calculations. We could build bigger MEUs and blister steel iron carburizing "boxes" and bigger steel cleaning/fluxing "boxes" also. see: magma process and blister steel The limiting factors will not be blister steel production once we have enough iron fines mining robots at work, but: 1) energy for the MEUs and other furnaces 2) time required for manufacturing and construction of all necessary things from furnaces to robots to machine tools to habitat 3) time required to mine 4) manpower 5) robot capabilities 6) time required to zone refine large masses of silicon for solar panel farm expansion Reference 1) Development of the Moon. Michael B. Duke et al. section 4.3.5.1 pg. 40 http://www.lpi.usra.edu/lunar_resources/developmentofmoon.pdf has data on energy, thruput and oxygen production. I did a little stochiometery to make estimates of other products from magma electrolysis also, see; http://www.highfrontier.org/Archive/Jt/Koelle% 20PILOT%20PRODUCTION%20at%20the%20MOONBASE%202015.pdf pg. 22 about magma electrolysis, power, amps, mass of MEU (a bit more than ref. 1) etc. |
| Power for MEUs To power 500 MEUs, 1500 MWe would be needed at 3MWe per MEU. Amorphous silicon cells generating 100w/m^2 would have an area of 15 million square meters or 3873 by 3873 meters. That's about 3.9 km by 3.9 km or 2.4 miles by 2.4 miles for those who are more familiar with english units. For those familiar with farms and ranches, that's 3690 acres. At 150 grams silicon per square meter, only 2250 tons of silicon will be needed. One MEU with a thruput of 5000 tons a year could make almost enough silicon to power 500 MEUs in a few years' time! Or two or three working for a year. Of course, sheet steel, Al or Mg backing plates are needed, Al or Al-Ca alloy wires and cables, thin glass coverings, mounting brackets, etc. Also Al and P dopants. Many other manufacturing jobs must be completed before we can embark on construction of large numbers of MEUs for silicon for SPSs. |
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| Silicon Processing, Mn & Cr By-Products
By Dave Dietzler 2008 1) Molten silicate electrolysis ==> impure Si ingots or slabs ==> drop jaw crusher ==> ball mill ==> vacuum distill powder ==> Mn and Cr remain, separate magnetically and/or electrostatically. Silicon after vacuum distillation ==> zone refining ==> doping ==> sprayed on melted regolith or sheet metal If vacuum distillation does not work we must use chlorine gas 2) Molten silicate electrolysis ==> impure Si ingots or slabs ==> drop jaw crusher ==> ball mill ==> hot chlorine gas treatment ==> SiCl4 gas evolves and evaporates at 57 C. MnCl2 and CrCl3 remain. Separate these salts magnetically and or electrostatically . Use fused salt electrolysis to remove chlorine and get Mn and Cr. SiCl4 ==> thermal decomposition at 850 C. ==> silicon zone refined ==> doping ==> spray on melted regolith or sheet metal One million tons of regolith would yield about 210,000 tons of silicon and 2000 tons each of chromium and manganese. Chrominum for stainless steel. Manganese for steel monorails. Manganese might also be used to reduce AlCl3 at 250 C. The MnCl2 that forms would be heated under low pressure to decompose it and recover chlorine and reuse the manganese also. Carbo-chlorination of Al2O3 would be done at 675-975 C. Reduction of AlCl3 by Mn is slow. This should be investigated as an alternative to electrolysis. Since solar panel output is DC an inverter, transformer, rectifier is needed to get voltage just right for electrolysis. Mn reduction just requires some electric furnaces. |
| The crushed silicon will then be purified by vacuum distillation or by chlorine gas treatment to produce SiCl4 gas that boils at 57 C. The SiCl4 will evaporate leaving other salts behind. It will be decomposed on hot metal wires at about 850 C. The silicon purified by vacuum distillation or by chlorine treatment will then be zone refined to ultra-high purity. In the low gravity and free high vacuum it may be possible to ZR larger rods and large qtys. of silicon more economically that on Earth. Silicon rods during zone refinning are held together by surface tension of the melt zone. The rods can't be too massive or they fall apart, but in low lunar G this will be less of a problem. |
We will need dopants for silicon solar panels. There is no boron to be had on the Moon, so we have to upport the boron or perhaps we can use aluminum for p-type material. Phosphorus might be toasted out of KREEP to get n-type material. We must have aluminum for doping solar panels and wiring, in addition to calcium for cables. Silicon will be evaporated in the vacuum and sprayed on aluminum sheets in two layers, one for p-type and one for n-type to make panels of amorphous silicon. This will not be the most efficient kind of solar panel, but that's mass production. Future manufacturing methods involving nanotech perhaps might produce more efficient solar panels for SPS and Moon base power. See: http://www.nanosolar.com A 70 ton magma unit with a thruput of 5000 tons/yr. using 3 MWe would make about 1000 tons of oxygen (1). It would also yield about 700 tons of iron since regolith is 14% iron, about 1000 tons of silicon since regolith is 21% Si, with some of that iron and silicon mixed in the form of ferrosilicon and over 2000 tons of ceramic blocks. 5000 - (1000t O2- 1000 Si - 700 Fe) = 2000+ tons of ceramic blocks. We must wonder what the exact properties of those blocks are. They are molten at 1300 to 1600 C. in the magma unit. Perhaps when they cool they harden and undergo crystalline structure changes that increase their melting and softening points, so that they are most excellent for furnace linings. Research remains to be done. |
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| Chip of silicon from an ingot |