57Views1Replies

Author Options:

How to harness the energy in snow Answered

I found a thread that asked this question previously on instructables but the author wanted to harness the kinetic energy of falling snow, and many of the criticisms involved the unpredictability of when snow will fall.

I am specifically curious if it is possible to create a machine to remove snow that uses the energy of the snow itself. Ideally, it would melt the snow and use the water or steam to power itself.

The things Canadian winters do to the mind...

Discussions

0
None
Jack A Lopez

4 months ago

Let me share with you, a back-of-an-envelope caclulation,

https://en.wikipedia.org/wiki/Back-of-the-envelope...

regarding the feasibility of melting snow with its own gravitational potential energy.

Suppose I have some mass m, of snow, on the roof of a tall building, of height h. The gravitational potential energy of that snow mass, is U=m*g*h.

https://en.wikipedia.org/wiki/Potential_energy#Pot...

The minimum energy Q needed to melt snow, can be calculated from its latent heat L for melting (or freezing) per unit mass; i.e. Q = m*L From the Wikipedia article for "Latent heat", I found the number L = 334 kJ/kg. A similar number, 333.55 kJ/kg, can be found in the Wiki article, "Properties of water"

https://en.wikipedia.org/wiki/Latent_heat

https://en.wikipedia.org/wiki/Properties_of_water


So now I can calculate the height of the building, just from the requirement, U>Q

U = m*g*h > Q = m*L

The m divides out, and I am left with

h > L/g

The bad news is the minimum h is really big! Using L=333550 J/kg, and g = 9.8 J/kg/m, gives L/g=34036 m = 34 km!

That's taller than the tallest structures this civilization has ever built, by a factor of about 50x.

https://en.wikipedia.org/wiki/List_of_tallest_stru...

The very tippy top of this building would be above most of the Earth's atmosphere, where no snow falls anyway.

Although this height is still about 10x lower than the lowest orbiting satellites, which are found at heights around 300 km above the Earth's surface.

https://en.wikipedia.org/wiki/Low_Earth_orbit

https://en.wikipedia.org/wiki/Orbital_decay


To me this says the idea, of using a snow mass's gravitational potential energy to melt itself, is impractical

0
None
shareefhadidJack A Lopez

Reply 4 months ago

Thank you so much for your thorough explanation.

I'm afraid I might have been unclear: I am not looking to melt snow using its gravitational force. I am interested in whether it is possible to build a machine that BY ALMOST ANY MEANS uses snow to power itself, and is used to remove snow (from, say, driveways). Almost like a vacuum or snowblower.

The only factor I can forsee, as an upper limit, is whether the output energy is greater than the input. It doesn't even matter if the output is insufficient to power the machine as a whole, even if it can be used to support a process that is otherwise powered by something else, like a battery. Just curious lol.

0
None
Yonatan24shareefhadid

Reply 3 months ago

Instead of letting the snow fall and then using it's energy to power something that'll push it away which is really innefficient, just buy an old Boeing engine and blow the snow away to a nearby city. But seriously, that would be quite inefficient!

0
None
Jack A Lopezshareefhadid

Reply 4 months ago

Well, I think if this napkin, er envelope calculation is telling us anything, it is telling us it would be a mistake to attack the snow by trying to melt it, or rather to melt it completely.

Just melting small parts of it might be useful.

As an example of what I mean by just melting a small part of it, I have a metal roof on my house, and when it snows, which is rare because I live at about 33 degrees North latitude, but it does snow here sometimes, and sometimes it is enough to actually pile up on the roof.

Anyway, I have noticed the way this piled up snow moves itself off my roof, is by moving in big chunks, which slide down the metal roof, which is inclined.

Moreover, I am guessing the reason why the snow moves this way, is because there is a very thin layer on the bottom, touching the metal roof, and that part melts, and becomes slippery. Then a big mass of snow, above that thin layer, sort of breaks loose, all in one big chunk, and slides down the incline of the roof.

So maybe that is a property of snow that can help you move big masses of it. I mean, if you can manage to get your snow to sort of cast itself into a big block, and moreover if you can get this big block to have a slippery layer on the bottom, and be on a smooth surface, then it will be pretty easy for you to move that big block somewhere, for as far as you have a smooth surface for it to ride on.