What will happen if the sun is concentrated by directing sunlight to mirrors that are facing each other? i know that mirrors absorb light and dont reflect 100% but will the efficiency increase due to the multiplication of the sunlight over the multitudes of reflections? if this can be done with arrays of micro heliostats with programmable motion controllers, the reflection of the sun can be tracked and the beams within the reflections also tracked to produce an enormous amount of heat.......wont it? Isnt it going to be more efficient than this: http://www.youtube.com/watch?v=LMWIgwvbrcM ?

  • $\begingroup$ im thinking nano mirrors and these mirrors can be in any part of a city tracking the sun and directing it to various locations. each nano mirror can move at a degree so small that the rays are similar to laser. but my main focus is the concentration of the mirrors by facing them at each other. $\endgroup$ Feb 18, 2016 at 12:41
  • 3
    $\begingroup$ You mean much like in XKCD What-If Fire From Moonlight? $\endgroup$
    – user
    Feb 18, 2016 at 14:17
  • $\begingroup$ How do you configure the geometry to have the mirrors be facing each other and get direct rays from the sun? $\endgroup$
    – Peter R
    Feb 18, 2016 at 17:35
  • $\begingroup$ ok lets say an insulated pipe is laid underground across a nation, and molten salt is inside it. and small generators that use steam turbines can be attached to various points from the pipe in each district. but thats by the way.... ok you asked about the matrix of the geometry....The top of the cube (or any other shape) matrix will be mirrors that reflect the sun to the mirrors facing each other and the top must not be a square shape and each mirror can be in any location , all that matters in that the rays are channeled to the matrix. this creates multiple rays in the matrix..to b contd $\endgroup$ Feb 18, 2016 at 18:37
  • $\begingroup$ then within the matrix, there will be some nano mirrors that track the reflections. remember that the mirrors on top are nano too so there will be many rays ....and due to the fact that the sun moves , the mirrors within the cube will be traacking the movement of the reflections based on the movement of the sun $\endgroup$ Feb 18, 2016 at 18:40

2 Answers 2


This is a variation on a theme which has been discussed many times. For example, see Strength of moonlight

The short answer is no; you cannot heat an object hotter than the temperature of the source. The advantage of multiple passes with mirrors is that you may be able to extract more energy on each pass of the light - this is often done inside the cavity of a laser, in order to extract the maximum energy from the pump beam.

But for sunlight you might do better by simply improving the absorption rate of your final collector.

  • $\begingroup$ peter if i bring two mirrors facing each other, and place the sun between them, will i get more heat than it was when it was only the sun? $\endgroup$ Feb 18, 2016 at 15:13
  • $\begingroup$ see the thing here, concentrated solar power plants reflect the sun and concentrate it on the molten salt absorber. but what if you first of all try to make the heat more before taking it to the absorber? $\endgroup$ Feb 18, 2016 at 15:17
  • $\begingroup$ i mean im not trying to make any surface hotter than the sun. im trying to make more heat come out from mirrors $\endgroup$ Feb 18, 2016 at 15:20
  • $\begingroup$ When you review the link, and it's references, you'll discover the thermodynamic principles and optical theorems involved. Mirrors can certainly cconcentrate light - curved mirrors are used to focus light to a small spot. What you are proposing seems to be a method to capture extra light in a limited space by making it repeatedly pass back and forth, at the speed of light. You could do the same with sound in an echo chamber an a loud speaker. But the engineering limit is the transfer efficiency, and how to get the light transformed into heat at the desired point. $\endgroup$ Feb 18, 2016 at 16:02
  • $\begingroup$ im talking about the mirror effect that creates multitudes of reflections when mirrors face each other in a cube.....FOR EXAMPLE like A ROOM WITH ALL ITS WALLS COVERED WITH MIRRORS. $\endgroup$ Feb 18, 2016 at 16:03

As far as your theory of the suns rays becoming "trapped"between two mirrors bouncing back and forth gaining in strength with each additional photon added to the already building super power beam, please don't even try that, it may get so hot in cuts the planet in half! Please look up the first law of thermodynamics Sir. Gosh, you're no Alfred Eisenstein are you?

No, I actually thought of very similar contraptions when I was a youngster in high school. The particle of light has a certain energy level and either it will be absorbed by the mirrors or it will forever bounce back and forth kind of building up as more sunlight gets added to the parallel mirrors. So what you are thinking is that the device will be able to act like a sun capacitor, building up to a great level and then releasing it at some object and incinerating it instantly! Forget your method because it has some difficulties. Just get a field of mirrors and concentrate the sun at a focal point of your choosing and watch them scatter like ants on the sidewalk from you and your magnifying lens. There are no bad ideas and no stupid questions! But does that mean there are no stupid answers? Obviously not!


Not the answer you're looking for? Browse other questions tagged or ask your own question.