>> Set me the MINIMUM possible spec that you would find useful >> and I'll see whether I can make a realistically realizable >> proposal for it. >> This is an *absolute minimum* spec real device, not a toy, >> that would be borderline acceptable as a demonstrator that >> Stirling had its place. > Ok, this I can deal with... Apparently not :-) Read the above again. Your unit is about 2 generations on from there. What I had in mind and was trying to explain the specs of was something that *some* people would buy now because it met a need effectively, and that produced power at an exorbitant cost by normal standards but which would be cost effective if extended to the millions per month category BUT which showed that Stirling had real promise. ie something which looked as impractical to Joe average as eg the early innovator Segway purchases. Or Benz's 2nd car. or the first Motorola flip cellphones ($US3000 when introduced)(people bought them) Or ... . ie NOT a toy per se and undeniably useful, but not liable to be in any way competitive with grid power at this stage. I don't think that this is an unrealistic target to demonstrate viability as some people will buy such and they serve as harbingers of the halcyon years to come :-). Something which produces around 1 kW is a big energy converter by these standards. Once you have the technology sorted that would be run of the mill, BUT for small workshop & prototype production the torques and stresses involved at those power levels make turning out something like that an extreme challenge. If you asked most people to make a diesel motor from absolute scratch based on those requirements there would be major problems in doing so. And that's simply trying to emulate known technology. Also, I'd rather *start* with eg an LPG energy source. This is because it is a well known, consistent, readily and accurately variable and scaleable and available energy source to deal with which eliminates developing that aspect of the design. Getting eg 1 kW or even 100 W of consistent solar energy input is a challenge in its own right which distracts from the main development AND even measuring energy input adds to the fun. Once you have it running on LPG you can extend it to solar, cow dung, gasified garbage and more. > Lets make it easy for you: No need for you to justify fuel costs, > let's use > solar power and limit operation to when the sun is high in the sky. > I'll pay > for the concentration of the sunlight into several hundred 'F heat. Far too hard :-). And too cold as well. What I said was serious but it had to be seriously limited in power output and general expectation. This is not an attempt to back down from the original intention, just pointing out that it wasn't a suggestion that one start by making a grid power air-conditioning driver replacement. (And for that you are probably better off driving eg an absorption refrigerator directly and eliminating the middle stages). I'll give here the most basic of straw men specs for you or others to knock down and modify. Hot end temperature: Mentioned first as it impacts the whole design, how easy it will be to convert to other fuels, reliability, materials, more. 300 degrees C- excellent. 400 C - OK. 500 C - pretty marginal. 600 C - really too high. Cold end temperature: Around and up to 100 degrees C coolant temperature. ie hot or just boiling water is the aim. Actual cold end will necessarily be slightly to somewhat above this BUT not too much higher as efficiency is impacted by this. Aim is to use the hot water as the other (and larger quantity) output after electrical power. Fuel: LPG or Propane initially. Reasons as above. Power output: Up to 100 Watt electrical constantly as required. More is good if readily achieved. Electrical efficiency: 10% electrical compared to the thermal power achievable in a representatively good burner using the same input gas flow. ie if you can get 1 kW thermal output from the gas in the reference burner you can get 100 Watt electrical power from the Stirling energy converter. Higher is good if achievable reliably. Balance of power: Good concept. Remaining gas energy to be converted to thermal, mainly as boiling or near boiling water. Output water to be potable and usable for domestic purposes. ie so far, this looks like a 1 kW LPG water heater that produces 100 W electricity and slightly less thermal output as a consequence. Size: Smaller than a bread basket. Much smaller is good. Mass: Average woman can carry it from the car to the picnic table without too much difficulty (without water inside). Lighter better. Much lighter much better. Selling cost in small run production: $US1000. Less is better. Much less is much much better. $US100 target in zillions but not any time soon. Reliability: Reliable :-). TBD, but essentially "just goes" for a period of time consistent with consumer expectations based on other vaguely comparable equipment. 10,000 hours to full overhaul would be a commendable and probably too high target. (By comparison the average automobile engine probably lasts 2000 - 4000 hours, many much less. Noise: Distressingly quiet compared to alternatives. Running in your RV in a trailer park it wont disturb the neighbours. I could sleep with it running in the RV. My wife couldn't. ie it's not totally silent but it's quiet enough that some people would hardly notice it. SO: This is horrendously expensive and incapable compared to existing alternatives. It won't run a sensible air conditioning unit. It won't run power tools etc directly. It will maybe run a TV or a single PC. Power cost is substantial wrt grid power. eg even if it had a lifetime of 10,000 hours operating cost per unit of electricity would be ($1000/10,000hours) / 0.1 kW = $1 / kWh !!!! BUT that's ignoring the thermal output. Adding thermal output brings that to 10 cents / kWH. That's just for capital cost without fuel costs. Fuel costs depend on burner efficiency and fuel cost/kg but are probably in the $US0.10 - 0.20 / kWh range. Wood chips, solar, rice husks or cow dung may cost differently depending where you are. . What this will do is run a laptop or two. It will charge a 12v battery at about 7 amps and indirectly operate battery powered power tools. Use for anything whose main aim is to make heat or even light would be less useful than alternatives. But it will run specialist equipment that demands electrical power rather than thermal or optical. This is probably mainly electronic or electrical items. Where there is a specialist requirement for such there could be a place for it. For example, it may be a Wifi link and supporting computer equipment in any number of places. Or a satellite terminal. Or a TV or radio. Or a weather station, or coms node or ... . There would have to be reasons why this should be used rather than a diesel or petrol genset. Or solar panels, or wind power, or water turbine, or Peltier or ... . There will be niches for each of these. Now, if they would only deregulate the supply of nuclear waste, cast 1 to 10 kW heat output hunks of it in LARGE blocks of concrete and bury these in everyone's back gardens then one of these units per home could prove very useful. With a 10 kW waste source and a 1 kW version of this converter James could even run his air conditioner. . Russell > Harbor Freight has a 40" by 60" parabolic reflector for $99. It will > hit > 350'F in open air. That is about 180'C or 453K. > http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=94171 A bit over 1 kW IN at full sun. Enough for the above unit if it worked rather better than per spec. Two would be better. Don't forget to cost the liquid sodium heat pipe to deliver the heat to the hot end :-). > should get you ~90F, ~30C, ~303K on the cold end or 150K delta. > (450-300)/300 = ~50% Alas it's (Th-Tc)/Th (not /Tc) = (450 - 300)/450 = 33% And that's Carnot efficiency. Real world efficiency is less to much less of that. 50% of Carnot is usually doing rather well. >>From what I can see of available, useful AC units, we are looking >>for about > 1KW while operating, or 700 KWh per year to cool a few rooms. Check > under You arguably want to look at using an ammonia (or other) absorption cooler heated directly by the sun. One Albert Einstein long ago patented a new improved version of such. > If it fails before it pays for itself, you have to fix it; > your dime. Almost nothing gets sold on that basis. Domestic anythings (including cars) get sold on a typically 12 month warranty and commercial tools etc often on far less. Few cars "pay for themselves" (quaint concept) within warranty and vanishingly few power tools. > Looking over your numbers below, this offer looks iffy. I'm sure a > good > solar collector can get you your 50% temperatures, but 1000 watts > out is > 2000 watts in and that is a pretty big collector, huh? Or no? At full sun you get about 1 kW/m^2 input to a panel. Working on half that out would be safe. You can get insolation tables for your location online. Where I am its about 8 kWh/m^2/day in summer and about 2.5 in winter. -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist