When we talk about potential energy we usually think of water at the top of a waterfall or – far less beautiful but much more supportive of our energy paradigm – water behind a damm. The higher the water level, the higher the potential energy. It’s easy to figure out how much energy (kinetic) will be released once water is allowed to flow out of the bottom of the damm – usually to drive a turbine to make electricity: mass of the water (m) times the gravity (g) times the height (h) of the water (E=mgh or E=9.81m/s2 x gh).
A liter of water at the top of a tree (25 meters) without atmospheric friction:
E = 1kg x 9.81m/s2 x 25m
E = 245.25 Joules or (if one liter fell per second) 245 Watts.
Or better: A coffee mug sits on the edge of the counter and has a perfectly calculable potential energy: weight times height times gravity. The cup is bumped and falls off the edge; energy is released. The expended energy destroys the cup, or (if you’re lucky) work will have to be done to restore the potential energy: The cup needs to be picked up. I assume the glass splinters will have to be swept up as well (again, work) in order to work against the forces of entropy.
Looking at the world with the eyes of potential energy, there are enormous forces to be released. We’re all ready to fall off a cliff – we flatlanders just know that there’s an end/edge to the world out there to fall off of!
If I were to fall to the middle of the earth, my energy would be:
77kg (I knew you were curious!) x 6,800,000 meters x 9.81m/s2
= 5.14terrajoules
That is, if the earth (i.e. the earth’s gravity) were a point and gravity were the same all the way to the middle as "out here" (where all the earth is to one side of (below) me). Even if we were to get 2/3rds out of the fall (not talking on the level of efficiencies or friction yet, just gravitational forces) it’s still 3.4TJ.
Five of me would have to fall per second to get to the 16Terawatts needed to run the modern world. Not that much, is it!? Assuming, of course, that the middle of the earth would never get full of me. (Or is that "mes"?)
The problem is that we tend to consider potential energy only in the realm of gravity. The principle, however, can be applied to every sort of energy: Atoms have an enormous potential before we split them. Molecules have an enormous potential before they’re oxidized, while the air and oceans have an enormous potential due to pressure making the helium (lighter than "air") or gas bubbles rise.
In my opinion, however, the greatest – or at least most harvestable – potential lies in heat, the very thing we see now as Enemy Nr. 1 resulting from CO2 emissions.
Heat is seen in physics as the waste element of physical processes. Once dispersed, it’s dead.
The End.
Game over.
Maybe its last service will be bringing your environment up to a cosy 22°C before it radiates out into the night air. And then is gone forever.
Well..
Even on the coldest day in southern Germany this year at -15°C (in the night it was colder), there’s more than plenty of heat around. Water will freeze, but Ammonia e.g. will boil! In Kelvin (degrees C above absolute zero), that’s still plus 258°! There’s enough heat in one liter of ice at that temperature, for instance, to melt 4 liters or to boil 0.5 liters at their phase-change points.
Or the other way around:
16Terrajoules will take 15.000 kilograms (= liters when liquid) or 15m3 of this cold ice to reach absolute zero. Meaning, 15 cubic meters of water frozen (i.e. 15,000kg) and 15°C below Zero cold per second would be enough to power all of mankind’s present energy needs.
Well, how much steam changing its phase to liquid, all within a range of 1° ? Looking above at the fact that the heat would boil 0,5 liters, we see that steam has double the energy that we used above, meaning 7,500kg of steam (its "weight" after it turns to liquid) would power the world’s energy needs! If, of course, it could be converted 100%.
But, like I said, this is potential energy, so we don’t need to worry about such things as efficiencies, frictions, etc... Let’s stay in our ivory tower for now;-)
With this example, I’ve already demonstrated how much potential energy is in the warm (or cold) world around us. Besides, this type of potential energy is not so theoretical as a man standing on solid ground waiting to fall to the middle of the earth. We use it in everyday life all over the place – in our refrigerators, air conditioners and electric heat pumps. Only – of course these processes are energy eaters or "sinks" on the one side while providing a bit of useful energy (usually heat or cold) on the other.
With these theoretical thoughts in the back of my head, I’ve been working on a method (which I am in the process of patenting) to combine 2 different potential energies to evoke mechanical energy – which is directly convertable into electrical energy. Or think of it this way: like one hand washing the other, one potential is another energy’s kinetic and vice versa.
You’re more than welcome to check my math. And, yes, I’ll keep you posted!
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