# Could sound be considered a kind of renewable energy? [closed]

Is sound energy useful as a source for generating electricity? If so, could it be a renewable resource?

Sound could be considered a renewable resource if taken from a source that was created by continual physical processes - such as the sound of waves crashing against rocks.

Although those sound waves contain energy (which is the kinetic energy of moving/vibrating air particles), their energy density is very low. Therefore they are not useful for generating electricity. This answer from MIT school of engineering will give you some idea of their relative power:

What the human ear perceives as clanging cacophony — the roar of a train engine or the whine of a pneumatic drill—only translates to about a hundredth of a watt per square meter. In contrast, the amount of sunlight hitting a given spot on the earth is about 680 watts per meter squared

If we were to assume that ocean waves created the same quantity of energy as stated here for pneumatic drills and train engines, then to get a similar energy as 1 metre squared of solar panels, you would need 'sound panels' that equaled a total area of 62,000 metres (62 kilometres) squared. However, these sound panels would then have to be very close to the source of sound to be most efficient, as sound energy is not transferred through air efficiently at all. To solve this, lets say we made them 1 metre high. In this case, to equal the energy available to 1 metre squared solar panel in full light, you would need 1 metre high sound panels that stretched along 3,844kms of rocky coastline. You see, not very practical at all!

• Thanks for your answer. So if technology one day advanced to the point where we were installing large piezoelectric based materials into for example, subway stations, that could harvest the vibrations into useable energy. Would that then be classed as a renewable energy source? Very hard to get your head around I know Jan 22, 2016 at 11:40
• If the trains themselves got all of their power from other renewable resources, then maybe you could make this argument, but that's a bit philosophical - really you would be making use of an operating inefficiency / byproduct. Anyhow, if you were going to install piezoelectrics anywhere in a subway, it would be much better to put them under the feet of passengers, as they already do in (where else?) Japan - inhabitat.com/tokyo-subway-stations-get-piezoelectric-floors Jan 22, 2016 at 11:51
• @user104713 It rather depends on what definition of "renewable" you choose to use. But in your example, the collected sound wouldn't really be renewable unless the source of that sound was itself renewable. Jan 22, 2016 at 15:01

I think you might be a little confused.

The phrases 'renewable energy' and 'un-renewable energy' are used to refer to industrial sources of energy. These industrial sources include Wind, Solar, Wave, and Nuclear power, and traditional fossil fuels (coal, oil, natural gas etc.).

If a source of power is renewable, it is not depleted (used up) when utilised - for example, the wind doesn't run out just because you put a few turbines up.

These industrial sources are not forms of energy themselves - they produce energy (heat energy like in a nuclear reactor or kinetic energy like in wave and wind power), but "solar power" or "wind power" are not a forms of energy. They are sources. This link gives a good overview of the different forms of energy.

Sound energy is associated with the vibrations of matter (sound waves vibrate air particles - that's how you can hear), so is a form of kinetic energy (the energy all things have when they move). It is not an energy source, so it doesn't make sense to call it "non-renewable" or "renewable".

• This was some needless terminological nitpicking that didn't answer the core of the question. The actual question is rather: could you build a "sound power plant" that worked in a similar way as wind power plants, i.e. you put it in a noisy place and it generates electricity. And could this be considered renewable energy, the way wind power is considered renewable. (I think the answer is yes to both, but even loud noise in cities doesn't contain enough energy to make it economical). Jan 28, 2016 at 17:56
• Actually, when I first answered the question, it read: "Is sound a renewable energy? I've been searching the web for this answer and can't seem to find it anywhere. Can anyone help me? Is sound a renewable energy or non-renewable energy?" So when I first answered the question, I was addressing the apparent lack of understanding as to what the difference between an energy source and a form of energy was.
– Swin
Jan 29, 2016 at 17:16

I think there is a problem in your question, cause "sound" is a phenomena in the meaning of process. When we talk about renewable energy, we in fact generally discuss sources (E.g. sun, not EM waves).

Straightforward and basically there are two, mostly engineering problems:

• Sound is a mechanical wave of a very low energy compared to industrial processes scales.
• What is the "natural" source of such waves that could be used in the meaning of "mining, collecting etc."

Little for fun thermodynamics note: Usual aeroacoustical linear approximation says that acoustical flow is homentropic. That means no heat transfer and therefore no entropy increase. It's not the "renewability", but at least the sound does not feed the beast of entropy much. :-)