About how to build solar water heater. It is more correct to call it a parabolic solar concentrator. Its main advantage is that the mirror reflects 90% of the solar energy, and its parabolic shape concentrates this energy at one point. This installation will work effectively in most regions of Russia, up to 65 degrees north latitude.
To assemble the collector, we need a few basic things: the antenna itself, the sun tracking system and the heat exchanger-collector.
parabolic antenna.
You can use any antenna - iron, plastic or fiberglass. The antenna must be panel type, not mesh. Antenna area and shape are important here. It must be remembered that the heating power = the surface area of the antenna. And that the power collected by an antenna with a diameter of 1.5 m will be 4 times less than the power collected by an antenna with a mirror area of 3 m.
You will also need a rotary mechanism for the antenna assembly. It can be ordered on Ebay or Aliexpress.
You will need a roll of aluminum foil or lavsan mirror film used for greenhouses. Glue with which the film will be glued to the parabola.
Copper tube with a diameter of 6 mm. Fittings, for connection hot water to the tank, to the pool, well, or where you will apply this design. The author purchased the rotary tracking mechanism on EBAY for $30.
Step 1 Modifying the antenna to focus solar radiation instead of radio waves.
It is only necessary to attach a Mylar mirror film or aluminum foil to the antenna mirror.
Such a film can be ordered on Aliexpress, if you don’t find it in stores
This is almost as easy to do as it sounds. It is only necessary to take into account that if the antenna, for example, has a diameter of 2.5 m, and the film is 1 m wide, then it is not necessary to cover the antenna with a film in two passes, folds and irregularities will form, which will worsen the focusing of solar energy. Cut it into small strips and fix it to the antenna with glue. Make sure the antenna is clean before sticking the film. If there are places where the paint is swollen, clean them with sandpaper. You need to smooth out all the irregularities. Please note that the LNB must be removed from its place, otherwise it may melt. After sticking the film and installing the antenna in place, do not put your hands or face near the head attachment point - you risk serious sunburn.
Step 2 tracking system.
As it was written above - the author bought a tracking system on Ebay. You can also look for rotary sun tracking systems. But I found a simple circuit with a penny price that tracks the position of the sun quite accurately.
Parts list:
(downloads: 428)
* U1/U2 - LM339
* Q1 - TIP42C
*Q2-TIP41C
*Q3-2N3906
*Q4-2N3904
* R1 - 1meg
* R2 - 1k
* R3 - 10k
* R4 - 10k
* R5 - 10k
* R6 - 4.7k
* R7 - 2.7k
* C1 - 10n ceramic
* M - DC motor up to 1A
* LEDs - 5mm 563nm
Video of the operation of the solar tracker according to the scheme from the archive
Itself can be made on the basis of the front hub of a VAZ car.
For those interested, the photo was taken from here:
Step 3 Creating a heat exchanger-collector
To make a heat exchanger, you will need a copper tube rolled into a ring and placed at the focus of our concentrator. But first we need to know the size of the focal point of the dish. To do this, you need to remove the LNB converter from the dish, leaving the converter mounts. Now you need to turn the plate in the sun, after fixing a piece of the board at the place where the converter is attached. Hold the board in this position for a while until smoke appears. This will take approximately 10-15 seconds. After that, unscrew the antenna from the sun, remove the board from the mount. All manipulations with the antenna, its turns, are carried out so that you do not accidentally stick your hand into the focus of the mirror - this is dangerous, you can get burned badly. Let it cool down. Measure the size of the burnt piece of wood - this will be the size of your heat exchanger.
The size of the focus point will determine how much copper tube you will need. The author needed 6 meters of pipe with a spot size of 13cm.
I think it's possible, instead of a coiled tube, you can put a radiator from a car stove, there are quite small radiators. The radiator should be blackened for better heat absorption. If you decide to use a tube, you should try to bend it without kinks or kinks. Usually, for this, the tube is filled with sand, closed on both sides and bent on some mandrel of a suitable diameter. The author poured water into the pipe and put it in freezer, open ends up to prevent water from escaping. The ice in the tube will create pressure from the inside, which will avoid kinks. This will allow the pipe to be bent with a smaller bend radius. It must be folded along a cone - each turn should not be much larger diameter than the previous one. You can solder the turns of the collector together for a more rigid design. And don't forget to drain the water after you're done with the manifold so you don't get scalded by steam or hot water after putting it back in place.
Step 4 Putting it all together and trying it out.
Now you have a mirrored parabola, a solar tracking module placed in a waterproof container, or a plastic container, a complete collector. All that remains to be done is to install the collector in place and test it in operation. You can go further and improve the design by making something like a pan with insulation and putting it on the back of the collector. The tracking mechanism must track movement from east to west, i.e. turn during the day to follow the sun. And the seasonal positions of the star (up / down) can be adjusted manually once a week. You can, of course, add a tracking mechanism vertically - then you get practically automatic operation installation. If you are planning to use the water for pool heating or as hot water in the plumbing, you will need a pump that will pump the water through the manifold. If you heat a container of water, you need to take measures to avoid boiling water and explosion of the tank. You can do this using
The problem of using solar energy has occupied the best minds of mankind since ancient times. It was clear that the Sun is the most powerful source of free energy, but no one understood how to use this energy. If you believe the ancient writers Plutarch and Polybius, then the first person to practically use solar energy was Archimedes, who, with the help of some optical devices he invented, managed to collect Sun rays into a powerful beam and burn the Roman fleet.
In essence, the device invented by the great Greek was the first concentrator of solar radiation, which collected the sun's rays into one energy beam. And at the focus of this concentrator, the temperature could reach 300 ° C - 400 ° C, which is quite enough to ignite the wooden ships of the Roman fleet. One can only guess what kind of device Archimedes invented, although, according to modern ideas, he had only two options.
The very name of the device - a solar concentrator - speaks for itself. This device receives the sun's rays and collects them into a single energy beam. The simplest concentrator is familiar to everyone from childhood. This is an ordinary biconvex lens, which could burn various figures, inscriptions, even entire pictures, when the sun's rays were collected by such a lens into a small dot on wooden board, sheet of paper.
This lens belongs to the so-called refractor concentrators. In addition to convex lenses, Fresnel lenses and prisms also belong to this class of concentrators. Long-focus concentrators based on linear Fresnel lenses, despite their low cost, are practically used very little, since they have large sizes. Their use is justified where the dimensions of the concentrator are not critical.
Refractory solar concentrator
The prismatic concentrator of solar radiation is deprived of this shortcoming. Moreover, such a device is also capable of concentrating part of the diffuse radiation, which significantly increases the power of the light beam. The trihedral prism, on the basis of which such a concentrator is built, is both a radiation receiver and a source of an energy beam. In this case, the front face of the prism receives radiation, the back face reflects, and radiation is already emerging from the side face. The operation of such a device is based on the principle of total internal reflection of rays before they hit the side face of the prism.
Unlike refractor concentrators, reflex concentrators work on the principle of collecting reflected energy into an energy beam. sunlight. According to their design, they are divided into flat, parabolic and parabolic-cylindrical concentrators. If we talk about the effectiveness of each of these types, then the highest degree of concentration - up to 10,000 - is given by parabolic concentrators. But for the construction of solar heating systems, mainly flat or parabolic-cylindrical systems are used.
Parabolic (reflector) solar concentrators
Practical application of solar concentrators
Actually, the main task of any solar concentrator is to collect the radiation of the sun into a single energy beam. And you can use this energy in various ways. It is possible to heat water with free energy, and the amount of heated water will be determined by the size and design of the concentrator. Small parabolic devices can be used as solar oven for cooking food.
Parabolic concentrator as a solar oven
You can use them for additional lighting of solar panels to increase the power output. And can be used as external source heat for Stirling engines. The parabolic concentrator provides a focus temperature of about 300°C - 400°C. If the focus of such a relatively small mirror put, for example, a stand for a kettle, a frying pan, you get a solar oven, on which you can cook food very quickly, boil water. A heater with a coolant placed at the focus will allow you to quickly heat up even running water, which can then be used in economic purposes e.g. shower, dishwashing.
The simplest scheme for heating water with a solar concentrator
If a Stirling engine of suitable power is placed at the focus of a parabolic mirror, then a small thermal power plant can be obtained. For example, Qnergy has developed and launched the QB-3500 Stirling engines, which are designed to work with solar concentrators. In fact, it would be more correct to call them generators of electric current based on Stirling engines. This unit produces electricity power of 3500 watts. The output of the inverter is a standard voltage of 220 volts 50 hertz. This is quite enough to provide electricity to a house for a family of 4, a dacha.
By the way, using the principle of operation of Stirling engines, many craftsmen make devices with their own hands that use rotational or reciprocating motion. For example, water pumps for summer cottages.
The main disadvantage of a parabolic concentrator is that it must be constantly oriented towards the sun. Industrial helium plants use special tracking systems that rotate mirrors or refractors to follow the movement of the sun, thereby ensuring reception and concentration maximum number solar energy. For individual use, it would hardly be advisable to use such tracking devices, since their cost can significantly exceed the cost of a simple reflector on a conventional tripod.
How to make your own solar concentrator
The easiest way to make a homemade solar concentrator is to use an old satellite dish. First you need to decide for what purposes this hub will be used, and then, based on this, select the installation site and prepare the base and fasteners accordingly. Thoroughly wash the antenna, dry it, stick a mirror film on the receiving side of the dish.
In order for the film to lie flat, without wrinkles and folds, it should be cut into strips no more than 3-5 centimeters wide. If you intend to use the concentrator as a solar oven, it is recommended to cut a hole in the center of the plate with a diameter of about 5 - 7 centimeters. Through this hole, a bracket with a support for dishes (burner) will be passed. This will ensure the immobility of the container with the cooked food when the reflector is turned to the sun.
If the plate is small in diameter, it is also recommended to cut the strips into pieces about 10 cm long. Stick each piece separately, carefully adjusting the joints. When the reflector is ready, it should be installed on the support. After that, it will be necessary to determine the focus point, since the optical focus point at the satellite dish does not always coincide with the position of the receiving head.
Homemade solar concentrator - oven
To determine the focal point, you need to arm yourself with dark glasses, a wooden plank and thick gloves. Then you need to direct the mirror directly at the sun, catch a sunbeam on the board and, bringing the board closer or further away from the mirror, find the point where this sunbeam will have minimum dimensions- a small dot. Gloves are needed in order to protect hands from burns if they accidentally fall into the beam area. Well, when the focus point is found, it remains only to fix it and mount the necessary equipment.
Options self-manufacturing there are many solar concentrators. In the same way, you can make a Stirling engine from improvised materials yourself. And you can use this engine for a variety of purposes. How much imagination, desire and patience is enough.
I have a simple Celestron PowerSeeker 127 EQ telescope, like this one in the photo above. My wife gave it to me for my birthday. It was a rather spontaneous gift like this: "I don't know what to give you, look at the store, let's go look." In principle, I was very pleased with such a gift, the thing is very interesting. However, while using it, I realized that I wanted more. This PowerSeeker 127EQ telescope has a number of significant design flaws that, due to inexperience, I simply did not know about. The main disadvantage is the spherical main mirror and the corrective lens for it. As a result, an overcomplicated optical design, inaccuracies in the fit of the corrective lens, which, moreover, is not of high quality. In general, the quality of the observed image with such a mirror diameter, I think, could be better.
I thought that I need another telescope. This is a normal situation. They say that no matter what telescope an amateur has, he always dreams of the best. And then the question arises: buy or make yourself? The answer is not really obvious. Is it easier to buy, maybe even cheaper? Building it yourself in the absence of experience is a difficult technical task, it is not known whether it will work at all and it is not clear whether it will be cheaper than just buying it.
I entered the slippery path of independent telescope construction. Next, I’ll talk about my first steps in this direction, but I immediately warn you that don’t wait to read an article with a happy ending just yet. I am very far from it (if it happens at all).
So, you need to start with the study of theory.
In my opinion, there is nothing better than the book "Telescopes for Astronomy Lovers", L.L. Sikoruk, 1982. Despite the fact that the book is more than thirty years old, I have not seen a more detailed presentation “from and to”. There is also a book by M. S. Navashin "Amateur Astronomer's Telescope", 1979. Also useful.
In addition to these very useful books, of course, you can and should visit astroforums. for example, this one. Here you can ask a question and read who does what and how.
Last resort: youtube.com. It may seem strange, but telescopes around the world are built by so many people. Some even video blog and show the manufacturing process. Keywords for YouTube search: mirror grinding.
In general, I would say that the niche of amateur telescope construction in Russia seems to be completely empty (but this is not accurate). In Europe and America there are special shops that sell blanks for mirrors (mirror blanks), and grinding powders, and tools and kits for making mirrors (teleskope mirror kit).
We now, of course, are not in the 79th or 82nd year, but where can I get a blank for the telescope mirror? Or where to get sanding powder? I found several optical factories, but they seem to have absolutely no interest in private customers. Probably their main customer is the state represented by the military-industrial complex. I wanted to buy a blank mirror - a disk with a diameter of 200 millimeters - and I was told that it would cost about thirty thousand without postage. Perhaps there is a very high-quality optical glass, but I just don’t understand an amateur (without irony, I know that exceptional quality may be required somewhere).
To tell the truth for thirty thousand you can already finished large mirror buy somewhere in great China.
In general, I decided to do it from improvised materials, as Sikoruk advised to do in his book. The material at hand is display glass (but not tempered). I need to cut several discs out of 10mm thick glass and then glue them together liquid glass. In his book, Sikoruk writes and substantiates required thickness primary mirror depending on its diameter.
Epic one. Glass cutting
I went to the glazier and asked him to cut me rectangular pieces of 10 mm glass approximately 250x250 millimeters, but they must all be from one sheet in order to be sure of the same properties of all blanks.
Went to the store and bought a pair aluminum pans internal diameter 180 mm. This is exactly what I planned to make a telescope. To tell the truth, Sikoruk advises making the first telescope no more than 100 millimeters and gaining experience on it, but no, we are smart, we do 180 right away.
The pan was sawn and a load and two protruding bolts were screwed to the bottom.
This will be the cutter.
Next comes the long and painful process of manufacturing a machine for cutting a workpiece. Here the engine from the old one is useful washing machine, a pulley from it, some old gearbox, pieces of plywood, studs, nuts and other nonsense.
In general, it looks like this:
The pot lid is glued to the glass with silicone and the edges are rounded. It serves as a centering element for my cutter. The cutter, that is, half a pan, is put on top and is driven by a gearbox from the motor.
This thing works like this (my video):
While working under the edges of the cutter, you need to constantly add abrasive. I worked with the abrasive for five to seven minutes, the abrasive was worn out and mixed with crumbs of glass and aluminum. Rinse off the old abrasive and pour in a new one. I then got used to doing all this on the fly without turning off the engine. It worked, washed off and then poured a new abrasive with a spoon.
That's not very Good photo, but you can see how much the “cutter” plunged into the thickness of the glass:
I mined the abrasive in the same way as our distant ancestors did in the time of mammoths. I had a piece of the old grinding wheel. I crushed it with a hammer on an anvil.
The resulting pieces were still pounded with a hammer, the crumbs were collected in a jar - a coarse abrasive powder turned out. Of course, at this stage, such savagery is still acceptable, but then we will have to improve the culture of production.
As a result, one 180 mm disk from a 10 mm sheet on my machine is cut in about three to three and a half hours. I cut out four disks:
My wealth:
According to my plan, I will glue them in pairs with liquid glass, I will process the edges with epoxy, as Seakoruk advises, and I will have two 180 mm primary mirror blanks. Next, I will start sharpening them and probably ruin one. As for the second one, I hope it works.
I have already purchased a set of grinding powders for this mission:
But then another story begins. Need to sharpen. This is done in several stages: rough molding-peeling, grinding and then polishing. I'm honestly stuck at this point. Here are some illustrations from the book Telescopes for Astronomy Lovers:
Peeling:
Grinding:
Typical mistakes:
Unfortunately, despite the detailed explanations in Seakoruk's book and from other sources, I do not have an absolutely accurate idea of \u200b\u200bhow this should be done correctly. The problem is that you need to execute the parabola with very high accuracy: errors, bumps or pits on the primary mirror must be less than 1/8 of the wavelength of light. The accuracy of the parabola must be at least 0.05 µm.
Here is how Sikoruk writes in his book:
The process of figuration and shadow tests is difficult to divide into components - this is a single creative process, where decisive role often play not only knowledge, but also intuition. In general, this process is so interesting in itself that the author, for example, is often in no hurry to finish, trying to work this way and that, finding great pleasure in the process of figuring, although, no doubt, the view of a completely flat shadow picture is an amazing sight.In the process of polishing, according to J. Matthewson, "there is always an element of mysticism." This is partly due to the fact that the polishing process is largely insufficiently studied, but partly also to the fact that the master himself often wants a little mysticism, when figuration ceases to be just a technology, but becomes largely an art. It was not for nothing that D. D. Maksutov said that the optician prefers to "conjure" over the home-made resin of the polishing pad, not trusting the factory resin. (However, if you have the opportunity to purchase a factory polishing resin, you should do it). Often the success of a business is decided by a creative impulse, and in order to have more time for creativity, it is necessary to prevent the causes that clearly lead to trouble.
It turns out that apparently there are no clear methods by which you need to act in order to get a true parabola?
In fact, of course, the same book by Seekoruk tells how to control the shape of a mirror. To do this, you must first build a special "shadow device". However, with the help of this device, I think it is possible to detect zonal errors, but it is absolutely not clear how to modify the polishing pad so that zonal errors are corrected during further polishing.
I watched a lot of video demonstrations on YouTube: there is both shaping and grinding and the so-called "parabolization" with the magic stroke "W".
Here are some colorful videos:
Rough processing:
Mirror grinding: 200 f/5 fine grinding:
Still people build machines for machining mirrors:
From all this it turns out that everyone does as he thinks, but how to do it in such a way as to guarantee the result? There is something to think about here...
After quite some thought, I decided before sharpening I should try to make a software model of the entire grinding process. For some reason I thought it would be pretty easy to do. I thought that I would make a grinding machine, something like the one in the last video.
The mirror blank should rotate slowly at the bottom, and, for example, a steel peeling ring will move from above with reciprocating movements using a crank mechanism.
I decided that the program model could be very simple: you need to calculate the time spent by each point of the mirror blank under the surface of the peeling ring. You can try to read not the entire surface of the workpiece, but only one cut-radius.
This video is formed from snapshots of the virtual roughing process in my program:
I thought that by choosing the length of the stroke in the software model, the length of the arms of the crank mechanism (and its movement is far from a sinusoid), I would be able to tell exactly how to sharpen in order to reach the parabola.
Unfortunately, I must say that the further I delve into the problem, the more I understand that my virtual programming model does not work at all. I do not take into account too many parameters that affect the speed of glass grinding: for example, I do not take into account the speed of rubbing parts, but it is different in the center and along the edges. Then I do not yet take into account the pressure of the peeling ring on the workpiece, and this apparently needs to be done, since in the process of work the shape of the workpiece changes, which means that the distribution of friction forces over the surface of the workpiece also changes.
When I wrote this article, I even thought to give here the entire source code of my program (C / C ++), however, what's the point if the program does not work?
At the moment I am engaged in a radical rewriting of my software and intends to still make a program model of the process of figuring the mirror. Perhaps, if I still succeed, I will publish my code.
Today we will look at how to create a homemade reflecting telescope. As you probably already know, in reflecting telescopes, the lens is represented by a mirror. It is quite difficult to make a home-made reflecting telescope, especially if you manually make mirrors for it, however, the undoubted advantage of a home-made reflecting telescope over the same home-made refractor telescope is its greater optical magnification compared to a refractor.
How to independently make a powerful reflector or refractor telescope with a magnification of 500 to 6000 times with your own hands at home, see detailed description here: http://remontavto-moto-velo.blogspot.ru/2018/04/500-6000.html
Amateur astronomers build home-made reflecting telescopes mainly according to Newton's system. It was Isaac Newton who first created a reflecting telescope around 1670. This allowed him to get rid of chromatic aberrations (they lead to a decrease in the clarity of the image, to the appearance of colored contours or stripes on it, which are not present on a real object) - the main drawback of the refracting telescopes that existed at that time.
The scheme of the "Newtonian" reflector looks like this:
In this scheme, mirror 1 is the lens, also called the main mirror. This mirror is parabolic or spherical. Mirror 2 is called a diagonal mirror - this mirror directs the beam of reflected rays through the eyepiece to the observer. The element marked with the number 3 is the ocular assembly.
The focus of the main mirror and the focus of the eyepiece inserted into the eyepiece tube must match. The focus of the primary mirror is defined as the apex of the cone of rays reflected by the mirror.
The diagonal mirror is made small size, it is flat and may have a rectangular or elliptical shape. A diagonal mirror is mounted on the optical axis of the main mirror (objective), at an angle of 45° to it.
An ordinary household flat mirror is not always suitable for use as a diagonal mirror in a homemade telescope - an optically more accurate surface is needed for a telescope. Therefore, as a diagonal mirror, you can use flat surface plano-concave or plano-convex optical lens, if this plane is first coated with a layer of silver or aluminum.
The dimensions of a flat diagonal mirror for a homemade telescope are determined from the graphical construction of the cone of rays that are reflected by the main mirror. With a rectangular or elliptical mirror, the sides or axes are related to each other as 1:1.4.
The objective and eyepiece of a self-made reflecting telescope are mounted mutually perpendicular in the telescope tube. To mount the main mirror of a homemade telescope, a frame, wooden or metal, is required.
To make a wooden frame for the main mirror of a home-made reflecting telescope, you can take a round or octagonal plank with a thickness of at least 10 mm and 15-20 mm more than the diameter of the main mirror. The main mirror is fixed on this plate with 4 pieces of a thick-walled rubber tube, put on screws. For better fixation, plastic washers can be placed under the screw heads (the mirror itself cannot be clamped with them).
The pipe of a homemade telescope is made from a piece metal pipe, from several layers of cardboard glued together. You can also make a metal-cardboard pipe.
Three layers of thick cardboard should be glued together with carpentry or casein glue, then insert the cardboard tube into the metal stiffening rings. They also make a bowl for the frame of the main mirror of a homemade telescope and a pipe cover from metal.
The length of the tube (tube) of a self-made reflecting telescope should be equal to the focal length of the main mirror, and the inner diameter of the tube should be 1.25 of the diameter of the main mirror. From the inside, the tube of a home-made reflecting telescope should be “blackened”, i.e. cover with matte black paper or paint with matte black paint.
The ocular assembly of a homemade reflecting telescope in the simplest version can be based, as they say, “on friction”: the movable inner tube moves along the stationary outer tube, providing the necessary focusing. The ocular assembly can also be threaded.
Before use, a home-made reflecting telescope must be installed on a special stand - a mount.
Now let's take a closer look at how to grind a mirror:
If the focal length of the main mirror with a diameter of 100 mm is more than 700 mm, and with a diameter of 120 mm it is more than 900 mm, then it is better to make the mirror surface not parabolic, but spherical, which is much easier.
For the manufacture of such a spherical mirror, two disks are needed (with a diameter of 100 mm, a thickness of at least 8-10 mm, with a diameter of 120 mm, about 12-14 mm) of well-annealed glass, for example, mirror, display, porthole. If there is a thick mirror glass, you can cut the discs yourself with a tubular drill. It is bent from a strip of iron, steel or other not very soft metal. The wall thickness of the drill is 1-2 mm.
It is fixed on a wooden disk of the same diameter as the mirror. The discs are cut out by rotating a tubular drill on a machine built for this purpose or by hand. Under the edge of the drill, a slurry of abrasive (for example, emery powder) mixed with water is continuously greased.
Plano-convex condenser lenses for photographic enlargers can be used as blanks for mirrors by processing their flat surface. Such lenses with a diameter of up to 113 mm can be purchased at photo stores.
Discs are cut. Now they need to be polished. To do this, you will need grinding and polishing materials, as well as resin and rosin. Grind the mirror with abrasive powders - carborundum (silicon carbide), corundum or emery. Your work will need abrasives with grains different sizes. They usually differ in numbers: 40-20 (the coarsest), 12-10, b-4. Abrasive powders of different numbers can be obtained by crushing an abrasive (grinding) stone into small pieces. The resulting powder is sorted by sifting through fine sieves.
Grind discs on a machine. On a thick board - the base - a rotating round or six-, octagonal table is fixed. In its center, an axis rotating at the base is tightly fixed. The table can be supported by 3 steel balls “recessed” in the base. It is very convenient to work on such a machine: instead of walking around the table yourself, you can turn the machine table.
Start sanding with the coarsest abrasive. To grind a mirror of a spherical surface, lay one disc on top of the other. First, fix the lower disk in the center of the rotating table with 4 screws with pieces of a thick-walled rubber tube put on them. Then, lubricating the mating surfaces with a gruel of abrasive powder with water, move the upper disk away from you and towards you 1/4 - "/z of the radius. At the same time, both disks continuously turn in opposite directions. As a result, the surface of the upper disk becomes concave, and the lower - convex.
To speed up the process of rough grinding, ring grinding is used in modern amateur practice. As a ring, take a piece of thick-walled cast iron pipe. The diameter of the ring is about half the diameter of the mirror. Putting the future mirror in place of the grinder, grind it with a ring, smearing the slurry of abrasive with water. Make sure that the ring does not extend beyond the edge of the grinder. The ring and the machine table must rotate uniformly in opposite directions all the time. When grinding with a ring, a recess in the glass is obtained much faster than when grinding glass with glass. With further grinding, in addition to the glass grinder, grinders are used, the bases of which are made of the most different materials: metal, getinax, textolite, cast from a mixture of cement with sand or cement with alabaster. A tree impregnated with a water-repellent composition is also used. Squares of glass or plexiglass are glued onto the base of such a grinder. Special metal grinders are also used.
Their bases, having the form of a sphere, are machined into lathe. The use of the grinders described above allows us to limit ourselves to one glass disk - the future mirror.
When the recess approaches the specified value (for 100 mm mirrors - no more than 0.90 mm; for 120 mm mirrors - no more than 1.00 mm), go from coarse to fine grinding, using finer and finer grades of abrasive.
After finishing grinding with the finest abrasive, polish the surface of the mirror. On the lower disc - grinder, apply a layer of resin alloy with rosin 4-5 mm thick. Divide the layer with a network of grooves into squares - facets for better contact with the glass and circulation of the polishing agent.The principle of operation of the shadow device is as follows. In the center of the curvature O of the mirror being tested, place an artificial star - a point source of light (for example, make a small puncture in sheet foil and illuminate from behind with bright light), and at the point of intersection of the rays of light reflected from the mirror (the top of the cone O"), put the "Foucault knife" ( for example, a razor blade.) Place yourself behind the flashlight and look for the reflection of the star in the mirror.
Approaching or moving away from the mirror, ensure that the artificial star fills the entire surface of the mirror with its light. If we now slowly cross the top of the cone of rays with the “Foucault knife”, then the entire mirror will “extinguish” at the same time. This means that all the rays reflected from the mirror converge at one point. If the curvature of the mirror surface deviates from the specified one, then you will see a "shadow picture", which is used to judge the shape of the surface. Correct the surface of the mirror by further polishing, changing the nature of the movements of the mirror (strokes) or the shape of the polishing pad. The real deviations of the surface of the mirror you made from the sphere are measured in fractions of a micron.
The concave spherical surface of a polished mirror reflects only about 5% of the light falling on it. Therefore, it must be covered with a reflective layer of aluminum or silver. Aluminize the mirror only in special installation, and you can silver at home.
In a Newtonian reflecting telescope, a diagonal flat mirror deflects sideways the cone of rays reflected from the primary mirror. It is very difficult to make a good flat mirror yourself. Instead of this mirror, use a prism with total internal reflection from prism binoculars. With a main mirror with a diameter of 100-120 mm, the dimensions of the rectangular planes of the prism, located at an angle of 90 °, are between 20x20 mm and 25x25 mm.
As a flat diagonal mirror, you can also use the flat surface of a lens, the surface of a light filter from a camera, or any other optically accurate plane. Cover it with a layer of silver or aluminize.
A huge amount of free energy from the sun, water and wind, and much more that nature can give, people have been using for a long time. For some, this is a hobby, and someone cannot survive without devices that can extract energy “out of thin air”. For example, in African countries, solar panels have long become a saving companion for people, in arid villages solar-powered irrigation systems are being introduced, “solar” pumps are being installed on wells, etc.
In European countries, the sun does not shine so brightly, but the summer is quite hot, and it is a pity when the free energy of nature is wasted. Exist successful developments solar-powered ovens, but they use solid or prefabricated mirrors. Firstly, this is expensive, and secondly, it makes the structure heavier and therefore not always convenient in operation, for example, when a light weight of the finished concentrator is required.
An interesting model of a homemade parabolic solar concentrator was created by a talented inventor.
It does not require mirrors to make it, so it is very light and will not be a heavy load on a hike.
It takes very few things to create a homemade film-based solar concentrator. All of them are sold in any clothing market.
1. Self-adhesive mirror film. It has a smooth, shiny surface and is therefore an excellent material for the mirror part of a solar oven.
2. Chipboard sheet and a hardboard sheet of the same size.
3. Thin hose and sealant.
How to make a solar oven?
First, two rings are cut from a chipboard of the size you need with an electric jigsaw, which must be glued to each other. The photo and video show one ring, but the author indicates that he later added a second ring. According to him, one could have been limited to one, but the space had to be increased to form a sufficient concavity of the parabolic mirror. Otherwise, the focus of the beam will be too far away. Under the size of the ring, a circle is cut out of hardboard to form rear wall solar concentrator.
The ring should be glued to the hardboard. Be sure to coat everything well with sealant. The design must be completely sealed.
On the side, carefully so that there are even edges, make a small hole into which tightly insert a thin hose. For tightness, the connection of the hose and the ring can also be treated with a sealant.
Stretch a mirror film over the ring.
Evacuate the air from the installation case and thus form a spherical mirror. Bend the hose and clamp with a clothespin.
Do convenient stand for the finished concentrator. The energy of this installation is enough to melt an aluminum can.
Attention! Parabolic solar reflectors can be dangerous and can cause burns and eye damage if not handled carefully!
Watch the process of making a solar stove in the video.
Used material from the site zabatsay.ru. How to do solar battery – .
