An example of harnessing gravitational potential energy is a hydroelectric power plant which converts the potential energy of water falls, dams and the like into electrical energy.

As far as harnessing the potential energy of a building sitting on the ground, I suppose if you caused the building to topple you could harness the energy of the falling portions of the building. Obviously ridiculous.

All practical examples of harnessing potential energy involve its conversion to kinetic energy.Hope this helps.

Yes, you can convert the potential energy of the skyscraper into useful work. But, to extract useful work from the potential energy, must reduce the potential energy, that is: you must reduce the height of the skyscraper. You must tear the skyscraper down to get its energy.

You should note that skyscrapers aren't free and that someone used a crane powered by electricity or diesel to lift the parts of the skyscraper to their current positions. You are guaranteed to get less energy out of this process than was put in to build the skyscraper. You will waste a lot of energy in the process of converting energy from diesel or the electric grid into the potential energy of the skyscraper and then back into electricity. This would be a terribly inefficient way to store energy.

However, as noted by another answer, this is essentially what we do with hydroelectric dams. We move water from a high altitude to a lower altitude and extract useful work that is converted into electrical energy. This energy is free in the sense that the sun evaporated water somewhere and it rained down on the high altitude reservoir. So hydroelectric power is, at its core, solar power, because the sun effectively pumps the water uphill and we extract energy as it moves downhill.

Using actual electrically powered pumps, you can pump water uphill to store energy. You can use the energy later by allowing it to flow downhill.

There is a company in Switzerland that is developing an Energy Vault, which is a building sized stack of heavy blocks with cranes extending out from a central pilar.

Each of these blocks can be lowered to the ground and the crane generates energy doing so.

Re-stacking the block requires using energy to take it back up. There are, of course, losses when comparing the energy it takes to raise the block compared to the energy generated when lowering it.

This is meant to be used as an energy storage device, to give a method of storing excess "green" energy so that overproduction is not wasted. Again, energy is wasted in this process, but that is true of any energy storage/conversion system.

Note that the stack of stones, when unmoving, generates zero energy. It is only when the stones are actually being lowered that energy generation is possible. The Potential Energy of an object is an ideal calculation of the Kinetic Energy that could be generated if the object was lowered a specific distance. If the object is unmoving, no energy is generated.

By convention, potential energy (which can be mechanical, gravitational, chemical, electromagnetic or nuclear) refers to energy stored in a field (electromagnetic field, gravitational field, gluon field etc.). This energy must be converted into kinetic energy in order to be "harnessed" or do work. For example, you can convert potential energy into:

• kinetic energy of an arrow, a pendulum or a pipe full of water


• heat energy (which at a molecular scale is just kinetic energy again)


• an electric current (moving electrons, so kinetic energy again)


• energetic neutrons and other products of fission or fusion (kinetic energy again)

So you can harness potential energy, but only indirectly.

The other answers give perfectly valid examples of e.g. a "grandfather's" clock, where you have to put in external energy from time to time - here, to lift the weight back up against gravity.

However, I feel that there is an additional aspect to the original question: The asker probably wants to stay completely passive and just harness the potential energy of the building, sitting on earth's surface, somehow.
To this, I say:

TL;DR: Theoretically possible, but practically meaningless.

First of all, let's look at the basic formulae:
As the OP stated, a building exerts pressure on the ground. Pressure equals Force divided by Area:
$$P=frac{F}{A}$$
So, to get the force a building exerts on the ground, we have to factor in Area.
No problem, the relevant area, the 'footprint' of the building certainly is known.

Now, what we want to get out of this is Energy. And Energy is Force times distance:
$$E=Fcdot s$$
And that's distance downwards (hereafter denoted by $h$), because that's the direction the force works and therefore that's where Energy is to be gained. The force is, of course, gravitational force, so we finally get:
$$E=F cdot h = m cdot g cdot h$$
Now, we've got everything we need. Drop a skyscraper (let's say $m = 200 000 t = 200 000 000 kg$) down, say, $10m$, in a controlled fashion(*) and you're looking at
$$E = m cdot g cdot h = 200 000 000kg cdot 9.81frac{m}{s^2} cdot 10m = 19 620 000 000J = 19.62GJ$$
that you could harvest.

However, as you might have suspected by now, this is a one-time-only-ever-fullstop-period-type of deal. You can get that energy exactly once (**) and then, never again. You have to put up at least the same $19,62GJ$ to lift the skyscraper back up and repeat the exercise, gaining nothing in the process.

And factor in the energy expenditure from digging the $10m$ hole in the first place, putting up some mechanism to drop the skyscraper in a controlled manner and harvest the energy, you're certainly looking at expenditures that greatly surpass anything that is to be gained.

So... it's probably not worth trying.

(*) just throwing it down would probably cause it to collapse and release additional energy originally expended while building the skyscraper, but all that energy would be pretty much non-harvestable...

(**) at least within our earth's lifetime

Simply No. If you could generate energy simply from the potential energy of the building, induced by gravity, without somehow permanently decreasing that energy, you would build some sort of perpetuum mobile.

If you would gain usable energy (like an electrical current) out of the potential energy of the building, without reducing the mass of the building and without altering the gravitational field, you would have created energy out of nothing, but energy is conserved.

Absolutely, yes. We actually do that, for example in an old-fashioned grandfather clock. They have big weights inside. You give the clock energy by raising the weights up, and then they go down slowly (due to gravity) and in a very precise way, to drive the clock.

In theory, you could fathom a building where you put a huuuuuuge spring between its base and earth, and after the building is complete, you raise it up with some pretty substantial external energy input (some hydraulic mechanism driven by whatever source you wish). Then, as the building presses down and slowly compresses the spring, you could use that movement to drive whatever generator you like.

This has only two practical problems: 1) if you're able to find the energy to lift the house in the first place, why would you need this complicated contraption at all and 2) obviously totally impractical for reasons of "The utility of buildings is typically that they remain stationary so people can use them consistently and for a long time - Aaron Stevens"...

We already do. Take a look at any hydropower plant in the world. The problem with trying to harness the potential energy of buildings is they would have to fall down. Being inside a building that's doing this would be disconcerting at best.