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Question:

..but don’t have the space, funding, or expertise; comments please? I’ve crossposted this deliberately to get wide exposure. I wrote this up in 1968, and showed it around to some of my fathers friends, one of whom taught at Cal Tech. Unfortuantely who pays attention to a smart-ass 16year old? But none of them could find any gross technical flaws in it. Materials sicence, insulation, PV systems, control systems, etc. have improved a lot in the last 28 years, maybe somebody wants to take a crack at it? If so,let’s talk. Picture a pair of parabolic linear focus trough collectors each about 2 feet wide and adequately long (my 1968 design called for 15-20 feet each), with a connection at the far end making them into a "U" shape. Have the sun tracking system linked to a thermostat so the exit temperature of the fluid is limited to it’s safe thermmal operating area as it traverses the focus-located collection pipe (i.e. if it got too hot the tracking system would rotate the collectors a few degrees "off-sun"). I do not know materials science well enough to know what the best working fluid would be for a system designed to heat it to about 700 degrees F (about 370 C), perhaps a silicone based oil?  My 1968 design had a seperate parabolic dish reflector with the hot end of a stirling engine in the focal point. This engine would pump the oil whenever the sun was up. Today, you could use a PV powered pump, no batteries needed here since pumping wouldn’t be needed unless the sun was up. You could also have a situation where the collectors would not go "on-sun" unless the oil was flowing. The hot oil, is run to a heat storage unit, by now in the 650-700 degrees F range, depending on the quality of the insulation and the length of the run. My 1968 design had a finned stainless steel tube coiled in a U-shaped curve, with S-bends in the area that makes up the vertical parts of the U, suspended in a highly, highly insulated 6′x2′x1′ tub of lead. Yes, we are talking 12 cubic feet at about 700 pounds per cubic foot, over 8,400 pounds (over 7500kg). But think of the thermal mass. Lead melts at about 620 degrees F (about 320 C), so we can store a lot of heat. There may be more appropriate materials than lead today, but in 1968 it seemed to be the most cost-effective to me, also commonly available. But thermal mass is thermal mass – a bigger tank of high-temp oil could do the same job. The phase change of lead from solid to liquid is what holds the bulk of the heat. A second thermostat here calls for heat, the solar collector delivers it, and the rate is limited by the thermostat at the collector, the flow rate of the pump and the quality of the insulation on the piping. Heat recovery is accomplished with additional tubes suspended in the lead tank. My 1968 design called for a stirling engine here, with the hot end actually bolted to the side of the lead tank, and a collector on the pressurized side, set up to start the pump when the pressure dropped. Today, PV/battery powered pumps are probably more appropriate. One heat extraction tube feeds a fluid-to-air heat exchanger in a forced-air or graity-flow furnace arrangement for winter space heating. Or maybe a pipe system for radiant heat in the floor. Summertime cooling could be done with an ammonia-based absorption system. I do not know how they work, maybe the small scale I am discussing (i.e. a single residence) would make it ineficcient or impractical. Another heat extraction tube can feed a flash hot water heater. Another heat extraction tube feeds the kitchen; picture a flat spiral tube in place of each burner in a stove. An individual valve controls the oil flow for each "burner" – just like on a gas or electric stove – with decent insulation on the piping we are talking delivery temperature of over 600 degrees F, so there is no problem cooking food. A similar arrangement could be done for the oven – but you could put the tubes in the floor and walls of the chamber. Makes cleaning easy – no heating element in the way. My 1968 design included electrical generation via either a strling engine, or a mini steam engine with a low-temp oil, or even deionized water as the working fluid. Today, a PV system is more practical. My dad and I tried to patent this in 1969, but the idea got shot down by a patent attorney. "Too obvious". Comments?  Ideas?   Please email as well as posting –

Response:

Mike: Overall your thinking is right on line, especcially for that time. ||: Picture a pair of parabolic linear focus trough collectors each about ||: 2 feet wide and adequately long (my 1968 design called for 15-20 feet each), ||: with a connection at the far end making them into a "U" shape. Have the sun ||: tracking system linked to a thermostat so the exit temperature of the fluid ||: is limited to it’s safe thermmal operating area as it traverses the ||: focus-located collection pipe (i.e. if it got too hot the tracking system ||: would rotate the collectors a few degrees "off-sun"). 2*15ft = 30 sqft X 2 = 60 total square feet of reflective surface. Based on LUZ’s documented performance (peak) of 14 watts a square foot… You’d get  840 Watts thermal. 840 watts thermal * 0.7455 would give you 0.63 hp. 0.63 hp *  1.34 = 840 watts electric  (gee my math teacher would freak) assume 50% efficiency: 420 Watts electric. Not going to melt much lead, either thermal or electically.. In order to consider thermal storage, start thinking in troughs 16×20ft, and allot of them.. I do not know materials ||: science well enough to know what the best working fluid would be for a system ||: designed to heat it to about 700 degrees F (about 370 C), perhaps a silicone ||: based oil? LUZ used oil and their thermal lag was horrific. Their collectors would not start producing steam till 10:00 AM.. H20, as steam, would condense at night, forming droplets, that upon morning reheat would vaporize into steam in a few minutes. No thermal lag. No overnite storage, but their are more elegant ways of doing this. See: http://web.mit.edu/afs/athena/org/t/techreview/www/articles/july95/Sm… (make into one line..)  My 1968 design had a seperate parabolic dish reflector with the ||: hot end of a stirling engine in the focal point. This engine would pump the ||: oil whenever the sun was up. Today, you could use a PV powered pump, no ||: batteries needed here since pumping wouldn’t be needed unless the sun was ||: up. You could also have a situation where the collectors would not go "on-sun" ||: unless the oil was flowing. Let it allways be full "on-sun"… ||: The hot oil, is run to a heat storage unit, by now in the 650-700 degrees F ||: range, depending on the quality of the insulation and the length of the run. ||: My 1968 design had a finned stainless steel tube coiled in a U-shaped ||: curve, with S-bends in the area that makes up the vertical parts of the U, ||: suspended in a highly, highly insulated 6′x2′x1′ tub of lead. Yes, we are ||: talking 12 cubic feet at about 700 pounds per cubic foot, over 8,400 pounds ||: (over 7500kg). But think of the thermal mass. Lead melts at about 620 degrees ||: F (about 320 C), so we can store a lot of heat. There may be more appropriate ||: materials than lead today, but in 1968 it seemed to be the most cost-effective ||: to me, also commonly available. But thermal mass is thermal mass – a bigger ||: tank of high-temp oil could do the same job. Very prohetic observation for then. The high temp freaks melt various salts to store heat. The low temp gus use ordinary water under vacuum for thermal storage. See the site I ref’ed above, again.. ||: The phase change of lead from solid to liquid is what holds the bulk of the ||: heat. A second thermostat here calls for heat, the solar collector delivers ||: it, and the rate is limited by the thermostat at the collector, the flow ||: rate of the pump and the quality of the insulation on the piping. Yes.. ||: Heat recovery is accomplished with additional tubes suspended in the lead ||: tank. My 1968 design called for a stirling engine here, with the hot end ||: actually bolted to the side of the lead tank, and a collector on the ||: pressurized side, set up to start the pump when the pressure dropped. Today, ||: PV/battery powered pumps are probably more appropriate. Getting mixed reviews on Stirling efficiency, does not seem to be the "wonder engine" it’s cracked up to be. It’s obviously good for direct focus dishes, (like Cummins stuff) but these are high tech and expensive as heck, Cummins think’s mass-manufacture will bring their resulting electrical rates down. NOT. ||: One heat extraction tube feeds a fluid-to-air heat exchanger in a forced-air ||: or graity-flow furnace arrangement for winter space heating. Or maybe ||: a pipe system for radiant heat in the floor. Summertime cooling could be done ||: with an ammonia-based absorption system. I do not know how they work, maybe ||: the small scale I am discussing (i.e. a single residence) would make it ||: ineficcient or impractical. Yes, it would work particularly well for passive. That is if your in a moderate solar region. ||: Another heat extraction tube can feed a flash hot water heater. ||: Another heat extraction tube feeds the kitchen; picture a flat spiral tube in ||: place of each burner in a stove. An individual valve controls the oil flow for ||: each "burner" – just like on a gas or electric stove – with decent insulation ||: on the piping we are talking delivery temperature of over 600 degrees F, so ||: there is no problem cooking food. A similar arrangement could be done for the ||: oven – but you could put the tubes in the floor and walls of the chamber. ||: Makes cleaning easy – no heating element in the way. Yeah, right on, no reason not to, as long as your collector’s output is very close to this stove..insulated, etc.. Oil might be right for this application.. ||: My 1968 design included electrical generation via either a strling engine, or ||: a mini steam engine with a low-temp oil, or even deionized water as the ||: working fluid. Today, a PV system is more practical. ||: My dad and I tried to patent this in 1969, but the idea got shot down by a ||: patent attorney. "Too obvious". Not obvious to the general public, very obvious to solar folks (now).. See: http://web.mit.edu/afs/athena/org/t/techreview/www/articles/july95/Sm… and learn that what your talking about reached fruition in ~1913 with low-temp, evacuated water, So2, and the like ||: Comments?  Ideas?   ||: Please email as well as posting –

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