How does sound wave energy get converted into electricity and why is it less efficient than solar energy?



How does sound wave energy get converted into electricity and why is it less efficient than solar energy?

In: Physics

I hope I worded the question in the right way! I’m really fascinated by renewable energies and want to learn more about how / why some energy sources are easier to harness than others.

The microphone reflects *a lot* of the sound energy that hits it. Your simple microphone is like a tiny speaker in reverse where sound hits the diaphragm (little movable plate) and pushes a magnet in and out of a coil of wire. This little diaphragm is hard on the surface which means that a lot of the sound energy hits it and bounces off rather than being absorbed in pushing the magnet through the coil. There are little capacitor based ones but the magnet setup is easiest to understand as a reversed speaker.

Solar panels on the other hand are very absorbant of the frequencies they work with. Some percentage is reflected off the top glass layer but 90% of the light will pass through and then be absorbed down below. The efficiency of solar panels mostly comes down to the sun emitting light over a wide range of frequencies and our little solar panels only being able to absorb a small range of frequencies which is why the best case efficiency of a single junction solar panel is just 37% because that’s the bigger window we can make in the highest energy portion of the sun’s spectrum.

Another issue with capturing sound energy is that there just really isn’t all that much of it. If you were to stand 1 meter away from a jet engine its sound level is around 150 dB, but if you were to capture *all* the sound energy from that jet engine it’d be around 1000 W, a 150 dB sound only gives you 1000 W of energy to work with. You can get that much energy with about 5 m^2 of solar panels and you won’t have a giant turbofan engine screaming away in the background.

Microphones aren’t designed to capture energy but rather to capture the pattern of energy fluctuation as precisely as possible.

The most common dynamic microphones are basically just speakers in reverse, you make the diaphragm move which moves the coil within the force field of a permanent magnet which creates minute amounts of electricity.

Condenser microphones don’t produce energy at all but rather vary their electrical capacitance which can be used to determine the diaphragms movements and convert them to an electrical signal with the use of some extra circuitry.

Capturing sound energy isn’t inherently more inefficient or complicated than capturing solar energy though, in fact its much easier. We don’t do it though because its kinda pointless, the amount of energy in audible sound is so small that its not worth it.

If we scale things up and scale frequencies down, way down, wind is a sort of sound energy and there are plenty of efficient methods of capturing that.

I’ll add one other thing to what people are saying, there are materials that are “piezoelectric” which means that when you deform them by applying force to change their shape they wind up with a net electric field, and similarly if you apply an electric field to them they deform their shape. These materials are used to make small cheap speakers (mainly ones that just need to beep or buzz and not have a wide range of frequencies they accurately produce) or small cheap microphones.

So these can be used to generate electricity from sound, but it’s just not a lot of energy to be gathered from sound. They do have applications with more powerful and directed sources of mechanical strain, for example they’re used to generate sparks for some lighters or gas stoves when you push a little button the mechanical energy gets turned into electrical energy to make a spark.