This concave mirror is made from expanded polystyrene and this reflective film at a cost of 25 cents per square meter, and it is several hundred times cheaper than these mirrors which focus solar radiation to convert it into heat and electricity, and such a radical reduction in the cost of similar mirrors makes their electricity cheaper than from solar panels, or thermal and nuclear power plants.
I have already made many mirrors from expanded polystyrene for this solar station which provided space heating of this house in the winter and heated the water of this pool in the summer during 8 years. But my solar station used similar polystyrene mirrors which formed a concave trough, while this video will show the solution to a more difficult problem when such a reflective film should form not a trough, but a dish.
Now I am showing another blogger’s attempt to solve this problem, although we see that he used polyurethane foam instead of the polystyrene. This is his mirror, and we understand that making a quality mirror is a difficult problem, but I was able to do it, and now I will show how my mirror focuses the solar radiation to this point, which will set fire to this piece of paper.
But before I got that good mirror, I made seven unsuccessful mirrors which helped me see my mistakes and the possibilities of correcting them. With the goal of seeing the problems and their solutions, let's look at my journey through seven unsuccessful mirrors to this successful mirror.
Now I will remind you how this unsuccessful mirror of that blogger was made. He used this hard surface with this hole, and now we see how he applies glue, but only along this circumference. After that, he put a reflective film and pressed it to that glue circumference. Then he used this pump which pumped air under the film through that hole, and therefore the air pressure gave the film the shape we needed. After that, he put a lot of polyurethane foam, but unfortunately, the hardening of the foam is accompanied by its unpredictable expansions which spoiled the desired shape of the mirror.
Many of you have already realized that the foam needs to harden on a solid surface, and that is why I used this satellite dish. Then I put down a reflective film, and stretched it out. I will put a lot of polyurethane foam here, and now we see how I did it.
This was my first unsuccessful mirror, and we see that it turned out noticeably better, although it is still very far from our wishes. Now we see that it is even trying to focus solar radiation, but it is obvious that I have to make the 2nd mirror with the addition of this circle of expanded polystyrene whose surface roughly matches the shape of that satellite dish.
The making of the 2nd mirror also began with the action that I placed a reflective film on the satellite dish, and then covered it with polyurethane foam, but now I have added that polystyrene circle with weights. Now we see that the 2nd mirror turned out better than the 1st, and it focuses noticeably better, because that polystyrene circle limited the expansion of the foam, and therefore it more evenly filled the space above that satellite dish. However, we can see that the surface of the 2nd mirror still has many defects, for example here, where the edges of the steps of the polystyrene circle are located. That is why I decided to remove these steps, and now I will show that the polystyrene circle for the 3rd mirror has a smooth surface, without the steps.
So, making the 3rd mirror starts with preparing this reflective film which is placed on that satellite dish and stretched. After that I applied polyurethane foam. Another difference between the 3rd mirror and the 2nd is that I tried to use as little foam as possible and increased the amount of those weights.
This is the result of that making, and we see that the surface of the 3rd mirror is still not ideal. Nevertheless, it already focuses solar radiation well here, and now this focus will try to set fire to this piece of paper. Unfortunately, the focus quality is not good enough to give the paper a fire, but it is enough to give it a smolder which burns a large hole in the paper.
That is why I have to make a fourth mirror where the foam was placed not on the reflective film, but on the polystyrene circle, like this, because it seemed to me that the upper surface of the foam hardened more smoothly. Now my fourth mirror will try to give fire to this piece of paper, and we can make sure that it solved this task very quickly.