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Dust down those orbital power plans
The Australian Government has, for reasons that have much to do with
politics, and little to do with the environment, decided to throw $Au 10 billion into the bottomless pit that is renewable energy. Lest it all get turned into yet more solar panels and windfarms, I invite all comers to submit their plans for orbital power satellites. At least then we might get some technological advance for our money, even though I doubt we'd actually see any orbital power. Sylvia. |
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Dust down those orbital power plans
On Jul 12, 4:17 am, Sylvia Else wrote:
The Australian Government has, for reasons that have much to do with politics, and little to do with the environment, decided to throw $Au 10 billion into the bottomless pit that is renewable energy. Lest it all get turned into yet more solar panels and windfarms, I invite all comers to submit their plans for orbital power satellites. At least then we might get some technological advance for our money, even though I doubt we'd actually see any orbital power. Sylvia. Please let me know more, especially who to talk to. I am hkhenson on Skype or hkeithhenson at gmail dot com Keith |
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Dust down those orbital power plans
On 14/07/2011 10:14 AM, Keith Henson wrote:
On Jul 12, 4:17 am, Sylvia wrote: The Australian Government has, for reasons that have much to do with politics, and little to do with the environment, decided to throw $Au 10 billion into the bottomless pit that is renewable energy. Lest it all get turned into yet more solar panels and windfarms, I invite all comers to submit their plans for orbital power satellites. At least then we might get some technological advance for our money, even though I doubt we'd actually see any orbital power. Sylvia. Please let me know more, especially who to talk to. I am hkhenson on Skype or hkeithhenson at gmail dot com Keith It'll be a while. The government has made the announcement, and supposedly has the numbers in parliament, but the legislation won't be passed until later this year. A single by-election in the meantime could yet lead to the whole thing unravelling. Sylvia. |
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Dust down those orbital power plans
On 12/07/2011 9:17 PM, Sylvia Else wrote:
The Australian Government has, for reasons that have much to do with politics, and little to do with the environment, decided to throw $Au 10 billion into the bottomless pit that is renewable energy. Lest it all get turned into yet more solar panels and windfarms, I invite all comers to submit their plans for orbital power satellites. At least then we might get some technological advance for our money, even though I doubt we'd actually see any orbital power. Sylvia. Didn't we go through this a couple of days ago? |
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Dust down those orbital power plans
On Jul 12, 9:17 pm, Sylvia Else wrote:
The Australian Government has, for reasons that have much to do with politics, and little to do with the environment, decided to throw $Au 10 billion into the bottomless pit that is renewable energy. Lest it all get turned into yet more solar panels and windfarms, I invite all comers to submit their plans for orbital power satellites. At least then we might get some technological advance for our money, even though I doubt we'd actually see any orbital power. Sylvia. You could make a **** load of parabolic reflectors aimed at the hot part of a Stirling engine, these things are about 6m wide and produce about 10Kw A Spanish comp[any makes them. The main problem is the colour, all shiny and not a bit og brown or green on them :-) \ Julian |
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Dust down those orbital power plans
Bohica Bohica wrote:
On Jul 12, 9:17 pm, Sylvia Else wrote: The Australian Government has, for reasons that have much to do with politics, and little to do with the environment, decided to throw $Au 10 billion into the bottomless pit that is renewable energy. Lest it all get turned into yet more solar panels and windfarms, I invite all comers to submit their plans for orbital power satellites. At least then we might get some technological advance for our money, even though I doubt we'd actually see any orbital power. Sylvia. You could make a **** load of parabolic reflectors aimed at the hot part of a Stirling engine, these things are about 6m wide and produce about 10Kw A Spanish comp[any makes them. The main problem is the colour, all shiny and not a bit og brown or green on them :-) That's actually close to what the generating part of an orbital power sat should be - lots of mirrors feeding sunlight to a Brayton cycle gas turbine. Forget acres of solar cells, they are too heavy and too expensive and too fragile. A Brayton cycle engine in that size range is lighter than a Stirling engine, no regenerator needed. Not as efficient, but cheaper and lighter to launch. -- Peter Fairbrother |
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Dust down those orbital power plans
On Jul 19, 5:48 am, Peter Fairbrother wrote:
Bohica Bohica wrote: On Jul 12, 9:17 pm, Sylvia Else wrote: The Australian Government has, for reasons that have much to do with politics, and little to do with the environment, decided to throw $Au 10 billion into the bottomless pit that is renewable energy. Lest it all get turned into yet more solar panels and windfarms, I invite all comers to submit their plans for orbital power satellites. At least then we might get some technological advance for our money, even though I doubt we'd actually see any orbital power. Sylvia. You could make a **** load of parabolic reflectors aimed at the hot part of a Stirling engine, these things are about 6m wide and produce about 10Kw A Spanish comp[any makes them. The main problem is the colour, all shiny and not a bit og brown or green on them :-) That's actually close to what the generating part of an orbital power sat should be - lots of mirrors feeding sunlight to a Brayton cycle gas turbine. Forget acres of solar cells, they are too heavy and too expensive and too fragile. And it would be hard to scale up to the number needed for 100 GW/year of new construction. A Brayton cycle engine in that size range is lighter than a Stirling engine, no regenerator needed. Not as efficient, but cheaper and lighter to launch. The turbines themselves are around 1/10th of a kg/kW. The concentrating reflectors, radiators and heat absorbers seem to make up the bulk of the satellite. I have offered a spreadsheet before to anyone interested. It's partly a refutation of an influential paper published in 1962 and never revisited as far as I can tell. What I did was very simple. In the radiation spread sheet, the first column is absolute temperature, column B is deg C. Col C is radiation per square meter at 0.95, D is at 0.1. E is how many square meters per kW based on C (both sides radiate). D isn't further used. Column E is the area to radiate on kW. F is the Carnot efficiency from 1400 K down to the radiation temperature, G is the 75% of F based on the typical real turbines. H is the square meters required to collect one kW out at 100% of Carnot efficiency based on 1.366kW/meter^2. I is how much area it would take to collect sunlight based on .75 of Carnot efficiency. I is the area it would take to radiate heat from ideal Carnot, K is the area for real (.75) of Carnot. L sums the areas for ideal Carnot cycle, M sums the radiator area plus collector area at the temperature required to get rid of the heat rejected by a real (75%) Carnot cycle. This doesn't take into account the reflector (concentrator) loss or the re-radiation loss from the working fluid heater, but I have reasons to think both will be small. Of course I could have expressed area as a function of the sum of the two areas computed from radiation and Carnot efficiency as a function of T and solved it analytically by setting the derivative to zero. I find spreadsheets give me more insight though. Assuming the radiator and collector mass per square meter is about the same, then you can see from the graph that the minimum occurs a bit above 100 deg C, which is far below the 370-650 deg C quoted in an old paper he http://contrails.iit.edu/DigitalColl...2article42.pdf I can't say for sure what the mass per unit area of radiation or collection are. I need to analyze a canvas tube (like an air mattress) radiator filled with low pressure gas and air float charcoal, Buckey balls or BeO. Assuming they are both around a kg/m^2, a kW should come in around 3.2 kg. Turbines and generators are around 0.1 kg/kW based on Boeing 777 engines. Transmitters have been analyzed at less than a kg/kW. So giving room for such parts as power conductors and the joint to the transmitter, it *might* come in at 5kg/kW. If anyone has some spare web space to hang a small xls file, I can send it to you. Keith -- Peter Fairbrother |
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Dust down those orbital power plans
Keith Henson wrote:
[...] Assuming the radiator and collector mass per square meter is about the same, then you can see from the graph that the minimum occurs a bit above 100 deg C, which is far below the 370-650 deg C quoted in an old paper he http://contrails.iit.edu/DigitalColl...2article42.pdf I'd use something like 1,000 K as Tl. High efficiency and high rate heat radiation in space is problematic unless the temp is high. Radiative heat dispersal is about 100 kW/m^2 for the low temp radiator. Incident radiation on the collector is 1.1 MW/m^2, the mirror (which weighs 0.005 kg/m^2 excluding support) concentrates sunlight from 1.33 kW/m^2 to 1.1 MW/m^2, approximately 820 times at 80% efficiency. Th is 1800 K, Carnot efficiency is 44%, assumed overall efficiency to local electricity is 29%. I can't say for sure what the mass per unit area of radiation or collection are. I need to analyze a canvas tube (like an air mattress) radiator filled with low pressure gas and air float charcoal, Buckey balls or BeO. Assuming they are both around a kg/m^2, a kW should come in around 3.2 kg. I do not understand that. Ignoring the mirror, which I think - actually, I don't know what you are doing - In my example design the single sided collector has a mass of 5 kg/m^2, the double sided radiator 1 kg/m^2. The gas contact areas are 15 times the collecting or radiating areas. The coefficients of convective heat transfer are 800 and 80 W/m^2 K (the gas in the high temperature one is at twelve times the pressure of the low temperature one). The temperature difference across each is 100 K - the collector surface is at 1900K, the radiator surface at 900 K. One m^2 of collector produces 400 kWe at the station, and needs 8 or 10 square meters of radiator, so 15 kg of collectors and radiators are needed to produce 400 kWe, or 0.0375 kg/kW. My numbers might be a little hard to achieve, though they are meant to be only medium-tech at best, so let's be very generous and say 150 grams per kW. That's still 20 times less. Turbines and generators are around 0.1 kg/kW based on Boeing 777 engines. Transmitters have been analyzed at less than a kg/kW. So giving room for such parts as power conductors and the joint to the transmitter, it *might* come in at 5kg/kW. If anyone has some spare web space to hang a small xls file, I can send it to you. Yes please. I seem to be missing something in your argument. Will put it up too. -- Peter Fairbrother Keith -- Peter Fairbrother |
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Dust down those orbital power plans
On Jul 21, 10:47 am, Peter Fairbrother wrote:
Keith Henson wrote: [...] Assuming the radiator and collector mass per square meter is about the same, then you can see from the graph that the minimum occurs a bit above 100 deg C, which is far below the 370-650 deg C quoted in an old paper he http://contrails.iit.edu/DigitalColl...2article42.pdf I'd use something like 1,000 K as Tl. High efficiency and high rate heat radiation in space is problematic unless the temp is high. Radiative heat dispersal is about 100 kW/m^2 for the low temp radiator. That's not what the minimum mass calculation show, at least for the assumption that collector surface and radiator surface have about the same mass per unit area. I am assuming about a kg/m^2 for both, taking into account the supporting structure. What you want is for the sum of mass for the collector and radiator per kW, and taking into consideration the Carnot efficiency to be at a minimum. Here is the graph. http://www.htyp.org/Space_radiator The minimum came out 130 C with not much penalty between 75 C and 200 C. Of course, there could be an error in the spread sheet. If you can find one, please let me know. Keith Incident radiation on the collector is 1.1 MW/m^2, the mirror (which weighs 0.005 kg/m^2 excluding support) concentrates sunlight from 1.33 kW/m^2 to 1.1 MW/m^2, approximately 820 times at 80% efficiency. Th is 1800 K, Carnot efficiency is 44%, assumed overall efficiency to local electricity is 29%. I can't say for sure what the mass per unit area of radiation or collection are. I need to analyze a canvas tube (like an air mattress) radiator filled with low pressure gas and air float charcoal, Buckey balls or BeO. Assuming they are both around a kg/m^2, a kW should come in around 3.2 kg. I do not understand that. Ignoring the mirror, which I think - actually, I don't know what you are doing - In my example design the single sided collector has a mass of 5 kg/m^2, the double sided radiator 1 kg/m^2. The gas contact areas are 15 times the collecting or radiating areas. The coefficients of convective heat transfer are 800 and 80 W/m^2 K (the gas in the high temperature one is at twelve times the pressure of the low temperature one). The temperature difference across each is 100 K - the collector surface is at 1900K, the radiator surface at 900 K. One m^2 of collector produces 400 kWe at the station, and needs 8 or 10 square meters of radiator, so 15 kg of collectors and radiators are needed to produce 400 kWe, or 0.0375 kg/kW. My numbers might be a little hard to achieve, though they are meant to be only medium-tech at best, so let's be very generous and say 150 grams per kW. That's still 20 times less. Turbines and generators are around 0.1 kg/kW based on Boeing 777 engines. Transmitters have been analyzed at less than a kg/kW. So giving room for such parts as power conductors and the joint to the transmitter, it *might* come in at 5kg/kW. If anyone has some spare web space to hang a small xls file, I can send it to you. Yes please. I seem to be missing something in your argument. Will put it up too. -- Peter Fairbrother Keith -- Peter Fairbrother |
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