Orienting a Parabolic Mirror

Correction: I Think only need two motors and two axis of rotation.

• If the time is known
• If the date is known
• If the latitude is known

The rest could be done by using look-up tables and interpolation. So why not get a Personal Computer to do it?

Bingo. Most Solar PV generator arrays that utilize tracking just do it this way. The minor corrections for planetary drift are usually not even bothered with because the net effect is so minimal.

"So why not get a Personal Computer to do it?"

Yes a PC will do it, but a programmable logic circuit is just as capable, costs a lot less and can be put in a container that will fit in the palm of your hand.

I have a Sidereal Technology dual drive module that is many times more sophisticated that anything you need and it's barely the size of a paperback novel. It contains, among other things, a database of most known objects, something you would have little use for, except perhaps for identifying the Cartesian coordinates of the mirrors current location.

Furthermore, PLC's do not require anything more than a 9volt battery to drive the whole system.

... Great ideas Thanks

The position of the sun during any part of our yearly travel is easily predicted, with great precision, without any need for sensors. If it were not, we'd all be in very serious trouble!

I do have one H-Alpha band width telescope built for observing sun spots and other activity. I use a quiet conventional two axis drive: one a right ascension and the other a declination drive. Between the two, I don't have to adjust much in spite of the fact that these two drives are built to match the Sidereal Rate of the Earth's rotation, which is ever so slightly different.

Because the sun's rate of movement is slightly different, motors or gearing would have to be adjusted accordingly. Not a big issue

My suggestion is to contact those who track the sun as part of their experiments in astronomy, particularly astrophotographic experiments where precision tracking has to be far more accurate than that needed for heating a solar collector.

One very respected authority on subjects such as this is Mel Bartels. I suggest you Google his name and follow the leads as necessary until you find him.

Knowing Mel, his solution will be very affordable, very effective, very efficient and easy to make.

Good luck and stay cool!

Found him .... his home page is : http://www.bbastrodesigns.com/

jfmart, if you would, when you get your answer, please post it.

thanx

Brad

ps. I have a half formed idea using solar cells but it would still need started every day.

Dear coleague, it is not hard and I see You got most proper answers allready. Yet I know how to make Your project cheaper an not using any electricity. Since begining of Solar Power use, people were going first this way building Heliostats and using parabolic mirrors, but then have found better ways, like parabolic trough, oriented from east to west and facing Sun Trajectory which at noon could be looking little southward. If You add also Fresnell Lens instead plain glass cover, and if You could fill inside with CO2 to stimulate IR rays emisions containment (this would be a >>greenhouse<< effect harnesed), then I believe You would have very effective device for heating water. In fact, perhaps it would be better used to power some steam turbine and generate electricity, as temperature can be pretty high in focus of Fresnell Lenses, and they should be built to focus in form of line along your pipe, not to a dot as they are usually made......... They should have same effect as that magnifier that is used for reading 2-3 lines of text in a book by sliding it over page from top to bottom, or similar lenses they put over names associated with bell buttons to make them appear BIG. Got idea? Good! If really necesary, trough could be able to be rotated around that pipe to adjust for solar declination in different seasons (but that differ about 7% in course of year anyway) or could be pointed fixedly to path of Sun on Equinox, i.e. days when lenght of day and night are the same. That would make it less efficient in other times, but I think You would have enough heat as it is :-)) Actually, greatest problem would be to store captured heat and cool that pipe less it start melting, as some engineers have produced 1300 degrees of Celsis using one m2 Fresnell Lens, and melted copper coin with it......

What do You say of idea?

hi Henrik 14

have been reading your comment and loked up the frensel lense a question if you were to make a parabolic trough and place a frensell lense across the diameter and the length would n't that be about the focal point of the the trough and if so would the frensell lense melt because it is were made of plastic .I have pondered this idea for a long time as were we live the sun shines 95% of the time and in the summer it is not uncommen to experiance temperatures in excess of 48 degrees c and we are 50 steps away from the sea and can produce fresh water from this scource at about 80 degrees so driving a steam generator from the solar collector could be a viable project to not only power the electrical grid but also to produce fresh water.

peter.

Sir, I have answered to Mr. DIKL in some regards as both focusing devices are not necesary. No, lenses would not melt because of low heat absorption rate when light is passing trough, and ceramic thermal isolation could prevent heat transfer where is not wanted. But for such high temperatures which could be produced, some heat resistant material would be neded, and in big systems even Wolfram pipes. If this system would be used as source of superheated steam used in multi stage turbines, then condensed water could be still hot enough to heat some basin with sea water and evaporating water could be collected and condensed by pasing glass pipes trough basin with sea water that would be used to replenish heated basin once that water level drop in it, thus preheating water also. Thus You could have two basins in stages, main lower and preparatory higher, and second one with access to sea water, that could pass trough filters to preclude sand or sea microorganisms to enter process. Acumulated salt could be removed from time to time, or supersaturated water could be passed onward to 3rd stage, to dry on open air, and salt so produced would also be valuable resource. If I have Your posibilities and financing available, I would use Pelton turbines to produce electricity and get water and salt as byproduct. Water could be then used to replenish eventuall loses in system of Solar heater, and heated basin could have glass reservoir for heating water for bathing or cooking I have some ideas for multistage Pelton turbines, but lack good design proofing CAE program, which I could write myself if I need not to fight for survival, and could hire Physicist to help with fluid simulations........

Wish I could earn some money on such advices :-))

Hi AussieViking,

The Fresnel Lens and the Parabolic Mirror do the same thing except that

In the lens, The light goes through it and is focused in a small point , while

in the mirror the light is reflected to a focal point . It does not make sense to use both in series ... You would only change the location of the focal point.

What can be done is to use both. The mirror and the Fresnel Lens in parallel focusing in the same point. Then you would have Two hot points combined.

What those devises do, is capture The light in a large area and direct it to a small point.

You can Melt metals with a 3 ft X 3 ft Fresnel lens or with a 3 ft DIA Parabolic mirror.

In this case, for my project, I don't need such high temperature in such a small point so what I will do is leave the mirror a little out of focus so that the light hits an area of about 1" X 1"

That would heat the pipe enough to produce steam that I need to move a Generator. By means of a Home made Tesla Turbine.

The boiler will be moving together with the Mirror fixed at the focal point.

Henrik14:

In reading your description, it seems that you have 2 focusing mechanisms that would conflict. The Fresnel lens would be focusing rays entering the trough to the top of the collector pipe and the rays would not reach the parabolic trough. The trough would be trying to focus parallel rays on the back of the pipe, but couldn't because the lens would prevent the parallel entry of rays required for effective focussing by the parabola.

Either the lens or the parabolic trough would provide essentially all of the focussing that could be achieved. I'm missing the benefit of using both. A clear film (glass? plastic?) across the trough could reduce heat loss, though.

Best regards.

DickL

You are right, of course! Actualy parabolic mirror would be more expensive and would cause some energy to be lost by absorption, but since Fresnel Lenses have >>grooves<< where there is no lens material, then trough this would pass cca 10% of the unfocused light. In addition to this, there would be some IR comming from heated pipe, but to capture this and get it back to the pipe, there would be enough to have another pipe with slit lenghtwise in which slit would fit smaller diameter pipe. This greater diameter pipe should be mirror polished from inside to reflect all IR back to the source. But that all may be just too much of complications for possible lose of energy, which would be significant only if we are considering superheated steam production. Same effect could be got by making ceramic isolator that would protect small pipe on surface where there would be no focused light from lenses. Whole construction would be lighter then with parabolic trough, and would not offer so much resistance to wind. too! So it all depend on budget of whole project, as m2 of fresnel lenses is cca. 250 US$, and if average roof would be 10 meters, that would take 2500 US $ just for lenses. On the other hand, since high temperatures are possible with such lenses, maybe much less lenses would be necesary, and if it is just for heating water..........

I just built an 8 ft mirrored parabolic dish and I am having the same issues. I have been looking to power hydrolic actuators with software but haven't had any luck. Please keep me informed and I'll do likewise if I find a cost effective solution. Accuracy is key for tracking, otherwise, output is minimal.

Sam

sbruel@yahoo.com

Look up my photo of the parabola which I am using for cooking, steam generation etc which can easily track the sun with a simple timer coupled to one stepper motor. You can find it in 'Constructing a thermal referigerator for home use with solar power in Sustainable Engineering forum discussion. If you have difficulty in locating the discussion let me have your email id and I will send all the details. It cost me about 200$

Chandu Krishnamurthi

I found some of the details but not all. I welcome any plans and details you could send my way. sbruel@yahoo.com

Thanks

Dear Chandu. Thank you very much for your reply. Could you paste here the link for:

"Constructing a thermal referigerator for home use with solar power in Sustainable Engineering forum discussion"

Thanks a million everyone,

If someone has already implemented a solution for this problem or has a completed design:

Could you share details .. if you can please paste them here?

It would be great if you could share instructions on how to replicate what you are making?

for example:

- what brand and model PLC ...

- What brand and model Motor

_ Your stand design

- How are you wiring the PLC to control the motor
_ The Code to program the PLC
_ How you program your PLC

... Please keep in mind that not everyone here is an electrical engineer =)

Hey! you said you wanted something cheap and practical?

Re-read my post about using an equatorial mount from an old telescope with a motorised drive. Mount you parabolic mirror on that, balance it up and the mirror will point towards the sun all day - plus the electric motor will be only battery powered.

None of this PC or PLC controlled multi-axis drive stuff!!

Thos equatorial mounts will easily take a load of 10s of kilos with their balancing counter weights, so the motor is tiny.

John.

Curious, but how does the mirror balance towards the sun exactly: it sounds like a great idea, I am just not familiar with telescopes.

Cheers

An equatorial mount is designed so that when it set up correctly, for the axis to be aligned with true North and with the latitude of where you are.... Then the only rotation necessary is the one which follows the sky / star / sun etc...

With all the counterbalancing set up huge weights can be driven to follow celestial objects using tiny motors.

see here - http://en.wikipedia.org/wiki/Equatorial_mount

John.

The counter balance is so that the motor does not have to work as hard to lift the whole load, This concept is used in may applications. For example in elevators. You have a counter weight that weighs the same as your elevator. Thus the motor does not need to provide torque to lift your load but rather just to move weight 1 against the counter-weight.

Thanks John !

I will give it a try on Ebay

Since I had a good working parabola with fixed focus and a tracker I wanted to assemble a thermal referigerator using the surplus thermal energy from the parabola to power the unit and I am working on the cooler presently incorporating some excellent suggestion and ideas for this from the CR4 forum contributors. Are you in need of a tracker for your parabola or details of the thermal referigerator ? The only link at present of my work is personal one to one contact. Regards. Chandu. ckusbd@gmail.com

Hi Chandu,

What type of cooler are you using? An absorption type? If you have a design could you provide me with a copy? I would like to use the same concept for Air Conditioning ...

Yes an Ammonia absorption type. Let me have your email id so I can keep you posted with details, design and other relavant information. I am not sure whether you can make an air conditioner as cooling cycle is slower than the compressor type. Chandu

Obviously, if cooling cycle is slower, all You need is enlarge cooling surface, no? Also, it would help to make hot fluid flow from upper part of cooling system to lower, againest flow of warmed air. Then also, I would use flow of warmed air moving up and put pipe with fluid to cool into bigger diameter pipe and wind it spiraly down, while making fins for cooling facing inward to enlarge cooling area, AND set them so they also form spiral paths from right to left turned, as warmed air would start climbing leaving small vacuum behind that would suck in air from outside and speed up circulation without use of ventilator(s). Since warmest air would meet warmest fluid comming from top down, there would be still temperature difference to take advantage of, and coolest air would met coolest fluid on bottom, but perhaps also with some temperature difference to take advantage of. I would also paint it all white, not black as is usuall for refrigerators, at least on outside so Sun rays would not heat cooling system additionaly. I have this idea long time, just no simulation program to test it, nor money to build prototype, but still I am sure it must work. I have used similar principle for cooling my computer cabinet, making spiral chimney that also make warm air to climb and make vortice because of spiral ducts, and that nicely suck air without need for a ventilator.........

Still, I would reccommend to you all to study history of Solar energy devices as people were doing research and were inventing devices from end of 19th century, so why should You repeat all this work and do same costly mistakes? If You set parabolic trough from east to west, facing path of the Sun from sunrise to sunset, You avoid moving parts and save energy and maintenance cost, while heat concentration area is much greater than with just one parabolic mirror few foots in diameter........ That is most effective system known till this days, and our predecesors tried same things as You want to do. Only innowation I propose is use of Fresnell lenses instead, as I allready wrote in this thread....... Also, did You know that puting lens with focus on some thing and facing to opposite side from sun make thing cooler? It is still unexplained phenomena, and some have postulated >>cold rays<< based on this, but I think trick is in lens that make surface to cool optically much larger, therefore same quantity of thermal rays are spread wider while preventing smaller quantity of enwironment thermal rays to heat lens focus, thus promoting cooling....... Again, if I have good simulation program, I may have good ideas to test, including cooling system based on this that would spend no energy and have no moving parts.........

Unfortunately, I cannot find anybody who would invest money in my ideas :-((

Hi again Chandu,

What I need for my current project is a tracker for the parabola. Could you share your design?

I think it would be best to post it here so that others can look at it but if you prefer you can e-mail me at jfmart65@gmail.com.

Thanks and Best Regards

jfmart

PS If you can also share your design on the cooler that would be great!. (Thats for my next project)

Hello jfmart

Since my parabola is fixed focus and has the xyz axis rotation, my tracker design is as follows:

I have used a stepper motor with appropriate torque with a simple time controller to drive the parabola from east to west. The stepper motor and a timer are standard items used for various other application and one can pick it up with any local suppliers. Depending on the parabola you have and the axis of the rotation of it you have to couple it to the axis to follow the sun. The timer synchronises the parabola and the sun and you have a very low cost but very effective tracker. The coupling could be the only non standard item you may have to get done with any mechanically minded person. I got this idea from the car wind shield wiper mechanism and modified it to to my parabola.

With my 8ft parabolic dish, (once properly mounted) I am anticipating having more than enough hot water to partially heat my house and make all of my daily hot water.

But I was thinking why not take this superheated water to move a small turbine to produce some electricity and the hot water would just be a by product for heat, etc.

But, I haven't been able to find a small turbine anywhere, through any searches, and I don't know how to make one either. All I have found through my searches were industrial use turbines, nothing appropriate for small scale applications such as mine. I welcome any suggestions/data/resources.

Thanks

To take the suns energy and turn it to steam and then turn it to mechanical energy so you can turn it into electricity is not efficient in small systems. Since you are taking energy out of the system to drive the generator, you loose some of the heat needed for domestic hot water and heating the house in the process. There is a transfer loss at each transition. That robs you of efficiency.

Rather than complicate a system that is not yet even in a prototype stage, I urge you to keep things simple. I would start with a modest collector and a good sized storage tank. The bigger the storage tank, the greater the number of BTU's that can be captured in your system.

I know of one man who has a 50,000 gallon pool in his back yard. At the end of the summer swimming season, he covers it with a black plastic tarp. The tarp transfers the radiated heat into the water.

In most winters, the temperature differential between the air outside and the pool water, never gets to be less than 15 degrees he says. The amount of energy contained in 50,000 gallons of water, 15 degrees warmer than ambient heats his home for most of the winter. Rarely does he need to use supplemental heating to stay comfortable.

You might have better results building a large swimming pool and you;d have more fun in the bargain.

Another friend who lives in Vermont (where it gets very cold in the winter) has an all electric house powered by solar panels that energize lead acid batteries in his basement.

Every appliance in the house is either 12 or 24 volt DC including his refrigerator which also works on propane gas if needed.

He's experimented a lot over the years and concluded that trying to do too much with one source of energy is not a good idea. Spread your energy requirements around several different technologies. He suggests, that If you want electricity, generate it directly from modern wafers.

I do have a 20,000 gallon pool so i was already thinking that would be an excellent storage vessel. How does your friend transfer the heat from his pool into his house?

I understand to a point what you were saying about heat loss and producing electricity and of course this is just a prototype. But after I complete my 8ft dish, i will of course want to improve/modify my design so I am curious having a co-generation type setup ie: superheating water to power a turbine then using the hot water as a by-product to heat house or pool or hot water isn't a good idea?

Also I think I will explore the solar trackers from redrok.com, they seem affordable but i do not have the slightest clue how to use these in conjuction with hydrolic actuators (i think hydrolic would be necessary to keep the 8ft dish still in the wind).

Sam

Thank you moe,

The LED tracking is more complex but easier than what I was thinking of and had not the time to fill out the idea.

GA from

Brad

Yes--The MAN at RedRock is Duane Johnson, we have one of his two-axis devices

you are right.

or use several photosensitive resistors as sensor t o track the sun.

this task is not difficult.

Great information. I believe that the set up you are describing is a Sterling Engine ...

What is stering engine? is it meaning " this is a very spend money project"?

now show you a youtube

http://www.youtube.com/watch?v=NbuuGdpbMJE

http://www.youtube.com/watch?v=IKyBEPbIgzY

That was supposed to be writen >Stirling motor< or >Stirling engine<, but NO, what was described works on basicaly same principle, only there is no rotation of shaft as result. I just dont agree that same system could be used for UP/DOWN movement because difference in heating would be too small.... Perhaps for LEFT/RIGHT adjustment there should be plate vertically in the middle between cilinders, to make SHADE on cilinder turned from direction of Sun, thus making greater difference in heating/expansion and therefore geting stronger reaction of control system. Since dish would turn on side with more sunlight, at proper position both cilinders would be in sunshine as shaddow would be under plate or behind it, while with Sun on the East dish would turn leftward because shade would fall on right cilinder and with Sun on the West rightward since shade would fall on right cilinder...... Having that in mind, I would put two counterbalanced springs in equilibrium at noon, and so at the evening after sunset, dish would turn back to >>noon<< position, and in the morning dish would turn Eastward and wind up spring in opposite direction, which would then assist moving it back at Noon position when heat diminishes from left direction..... Or springs should be set to pull back in direction opposite from movement of heated side, so when action due to heating cease, dish would be pulled back to starting, >>noon<< position. Problem is just how to balance dish when BOTH cilinders are in Sunlight, because of simultaneous push from both cilinders......... I could envision joints on dish edges and hydraulic system croswise connected so left cilinder push right edge out and right cilinder push left edge out, and when both cilinders are in sunlight dish is pushed forward. This forward push could be used also to elevate dish, but this would not be usefull at sunrise and sunset, so perhaps cilinders should be fixed on east to west line, then both cilinders would push only at noon together and elevate the dish also.... Alternatively, same trick with shade plate could be used to elevate dish untill system finds balance, and that could be only if edge of plate is pointed sunward and make NO shade on either cilinder......

Well, I like idea, just pray tell me which fluid ought be used to give so much expansion, same as they use in Stirling machine? To enhance heating, Fresnel lenses could be used to concentrate light on cilinders, but then they would have to be turned to follow Sun if cilinders are fixed, but then, instead of joints, cilinders could be positioned on edge of dish........ Sorry, I am just IT Engineer, so I would have to experiment with mechanic movements to find workable solution, but then surely somebody has solved this problem and solution could be found on WEB.........

But, coupling of pipes are complicated to enable flow of heated water or steam to circulate, and so as I wrote before, people tried this over hundred years ago and find that parabolic trough is simple and effective solution.....

thanks but I still dont understand the words.

if the shaft cannt rotation, how the machine move?

I mean the four at least photo cells of resistors or such sensors arranged by a quadrangle in a box with a lense focus sun energy ( a lttle out of focus) in otder to get a balance lighting energy.

so that you can detect the track of the sun move. and control motor movement according to sphere coodinate. of cause two motor are enough.

another way is using a microchip which recording a track of sun in a year in every time. to control motors.

because of the parabolic surface has a focus. and its very easy to construct. and less money than structure a fersnel lens

Hi,

>>if the shaft cannt rotation, how the machine move?<<

Point is that in this case it is NOT machine, what moves is Your parabolic mirror. Fresnell lens size of 1 m2 cost about 270 US $, also focus in a dot, and could produce over 1200 degrees of Celsius temperature, enough to melt copper coin (at least this somebody described on his WEB pages), o there woulds be a problem with materiall in focus, but one can allways produce lower temperature by slightly defocusing focal point, i.e. making area on target 1 dm2 instead of 1cm2.....

With parabolic miror You would have to find material with high reflectivity and low absorption to prevent loses of heat energy, whole construction must be stronger and so more expensive because You move boiler together with mirror and conecton with piped leading to Your instalations is complicated and therefore not cheap...... In regard to tracking device, You need to have just termometer which could be read by computer, so actuall temperature produced would be kept as high as possible in any conditions, and if computer is controling position of parabolic mirror or lens, it could also store data about optimall position and time and date, and use that data to drive your system next day, which would then need less corrections, and after one year it could just follow memorized optimall positions for each day, without any corections necesary......... Then, tracking system becomes superfluous and could be removed. Also, since data could be duplicated, they would be usefull for any new such system installed in same area in future! New system have just to be alligned to east and west according to data for day of instalation, and would work then same as originall system, no? Good thing with Fresnell lens is that they could orbit around target point (be it boiler directly or Wolfram ball on the stick that would be transfering heat into boiler) as long as target surface is dome (half ball) like so focal distance from lens remain constant. Then, You could accumulate heat using graphite ball and graphite stick leading into reservoir with salt that would melt and keep temperature even trough night, enabling You to get electricity or hot water or heating at will during 24 hours..... This is for more ambitious projects, of course :-))

You could produce electricity using Stirling machine toping into acumulated heat, and since it works on temperature difference one part have to be cooled, and that temperature could be used to preheat water or acumulate this into Your pool....Just use Your imagination and You will find many posibilities to recircle energy untill it is finaly spent. With salt reservoir of bigger capacity, it would be possible to acumulate same amount of energy on lower temperature, so energy collected in severall sunny days could also carry over trough day or two when it is cloudy weather and so on.....

Also, since lens would focus whole spectrum including IR without any absorption, it could produce some heat even on cloudy day because clouds reflect heat irradiated by earth surface back down, but dont take my word for it since it is just my theory, while in case of parabolic mirror it is also radiating IR it absorbed, so reflected IR would not be effective because back of mirror would radiate IR as much as front would absorb and some from absorption before........

Since fresnell lenses are much lighter, You could mount even 4, 5, or 9 lenses, in size of as many m2, but then You would need prisms (or mirrors, but then You have same problems as with parabolic mirror) to aim focused light ray on a slant, or You could use two or more level systems where each level higher than bottom would focus only partially on lower level, but this system is limited to surface of uppermost level of lenses while using at least one lens more.....

In any case, I wish You full sucess and lot of energy harvested!

hi henrik

there also appears to be a fresnall lens that reflects lite to a focal point rather than transmits lite to a focal piont these could be utilised to gether i think which would cover more area of a sphere such as a wolfram ball.i have never seen one of these how ever i believe they are made of carbide where would you start looking for one on a stick to buy i imagine one would have to be reasonably large to be usefull in a boiler aplication.also it appears that fresnell lens are reasonable cheap so why not buy a few of them and position them in a arc at the focal length around the ball in line wwith the mean arc of the sun then enclose the system and charge it with co2 which apparently intensifies the uv rays as mentioned in the discussion earlier why this happens i don't know but if you can get more energy buy doing it probably worth the effort.

aussiviking.

Honored sir, I also have found just recently Fresnel type reflector is used. You cannot put Fresnell nor any other lenses anywhere but in direction of sun as perpendicular to lens and focal point. I suggested a ball made from Wolfram because it could stand high temperatures, but ball need not to be big, it is enough that orbiting lens can keep focus on surface regardless if they face East in the morning, up at noon or on other side, West at sunset..... and everything in between while system reposition itself during the day. Unfortunately, it is not possible to use at same time reflector lens with ther lens overhead, because overhead lens make opticall shade underneath it, save for focal point. As I wrote before, one m2 Fresnel lens could have focus temperature in excess of 1200 degrees of Celsius, and wolfram is good heat conductor, so stick ending in spiral inside Your boiler could produce superheated steam, or heat large quantity of water to a boiling point, so Your main problem should be how to use this heat most efectively.........

If You would put an arc of Fresnell lenses that would follow trajectory of sun, then each lens would >>work<< only in time when line from focus point trough center of lens would be also direction of sun, while in other times focus point would be in shade. Your idea of arc is quite similar to what I suggested in the beginning: Hyperbolic trough laying East-West and getting sunlight all day long without moving parts, because it was fould over century ago that this is most efective way to collect heat from Sun. Afterward, You insisted on parabolic dish and tracking Sun mechanism, so I tried to help in that direction. But, if You have pool, then it would be enough to make walls black and it would also accumulate energy from Sun. I know black is not nice color for pool, but it absorbs most of energy.....

Yes, it would be good to fill some chamber beneath lens and around ball where sunlight would focus to prevent irradiation of produced IR rays, and since CO2 would prevent oxidation, perhaps there could be used bronze instead of Wolfram, and it could be rodinized black to absorb more heat...... Alternative to Wolfram is graphite ball on graphite stick. To prevent temperature loss, I would have ceramic half dome cover over this ball with hole just where lens focal point would be, and if possible fixed to lens so hole with focal point would move together with lens following the Sun. That ceramic cover would also preclude loss of accumulated heat by iradiation during the night. Hole need not be much bigger than area covered by focal point would be, and it could be just 1/2 cm2 or less if You are precise enough :-))

So size of ball need not be large: even rounded end of stick would do instead, what is important is surface of media transfering heat to water inside of boiler, so it would be best if it is spiral shape........ Just rounded stick cannot have cap like I described to minimize irradiation of heat back from focal point and heated ball...... In the end, perhaps ceramic shield is not necesary, and for just heating water in boiler even one lens would be massive overkill. Such high temperatures need different means of heat accumulation, and that would be one kind of salt that is neutral and melt at 768 degrees of Celsius. But having reservoir of such salt melted would keep temperature to last trough night and if it is used to produce lectricity, would enable generator to work all day long, 24 hours! But with electricity production, You have to have means to store it if it is produced more than is actually spent.... But having heat source could be used for heating other things like water directly, for heating of house and so on, without need to use electricity.

Cheap Fresnell lens means whole system would not be so expensive, and even one may be enough for all Your needs. But to gather enough energy even on days with less sunshine, perhaps one could use multiple lenses in stages or using prisms to offset naturaly paralel vectors of focal points of severall lenses because they cannot hit same focus.......... Prisms would have to be positioned on 1/2 or 2/3 of distance from lens o focal point to prevent heating of prism by concentrated light, too....

I still cannt understand what is the stirling machine?

would you please illustrate me more detail? I cannt fint it in dictionary

thank you for your wonderful explain.

But Im still vague, the first thread hope to get a plan to track sun for his parabola stove. I show him a photo electric tracking plan with serveral photo sensors, acccording to the sum of these sensors accepting sunlight to control motors. but why he reflect to this stirling engine?

Does he has another meaning?

even fresnel lens needs sun tracking equipment to keep focus well at any time.

fresnel in fact is a conves, only but very thinner than the convex.

it cuts no use parts to make as thin as possible. it still acts as a function of convex.

Sir, thread started one way and after realizing that there could be high temperature produced, originator got more ambitious and started thinking beyond mere water heating to electricity production. One of ways is to directly use heat to power Stirling machine, and this I suggested as posibility if heat is accumulated in molten salt reservoir, and since Stirling works on temperature difference, it would work better if one side is cooled by water, which would use this otherwise wasted heat. If water is circulating like in central heating system, then one need not spend any fuel to heat house, and since that person mentioned big swimming pool, this could also be used to store heat and reuse it...... I recommended Stirling engine since there is not required to produce steam and steam turbines to produce electricity, therefore minimizing losing of energy and cost of electricity produced...

The topic sidetracked from tracking to the sterling engine because someone mentioned that a parabolic mirror can be used to heat the hot side of a sterling engine.

Honored sir, if You just write >Stirling machine< in any search engine like Google, Yahoo, Mamma or others, You would get ton of informations, I promise You!

Below You have some of adreses with informations:

www.globalcooling.com/pdfs/general_history.pdf -

freeenergynews.com/Directory/StirlingEngine/

www.youtube.com/watch?v=bzsrqmJqld8

www.ent.ohiou.edu/~urieli/stirling/me422.html

www.freepatentsonline.com/4161866.html

www.grc.nasa.gov/WWW/tmsb/stirling/doc/codes.html

www.ingentaconnect.com/content/pep/jmes/1998/00000212/00000003/art00005 -

with hundreds more there also...........

Hello jfmart,

Check out this link.

http://en.wikipedia.org/wiki/Heliostat

In Spain ( Seville) there is a huge power plant based on this principle.

Cheers.