The drive to find novel energy storage systems for all the “alternative” energy produced from wind-turbines and solar (photovoltaic) systems is fostering the most bizarre ideas.
Needless to say, government bureaucrats are just too happy to throw taxpayers’ funds at any idea that promises to fulfill the quest. One of the latest “grand schemes” involves hollow concrete balls sunk into the depths of the ocean, the deeper the better and the larger the better too.
So, what am I talking about, specifically? Of course, hollow concrete balls, the latest scheme in the quest to provide “free energy.”
As reported, the Fraunhofer Institute for Wind-Energy and Energy-System-Technology at Kassel, Germany, has successfully tested a small (~ 4 m or 15 ft. diameter-ball) pilot system in Lake Constance at a depth of approx. 100 m. “There is a great potential for the application of the technology … ” it says at the institute’s website.
Like many other “alternative” power-generating or energy-storage systems, as I surmise, this one will also be doomed to failure; just look at the Pelamis and Osmosis ideas of the past. Such systems may even work on a small pilot-size scale, but when it comes to scaling them up by factors from 10-, to 100-, or even to 1000-times from the size from the pilot project, all kinds of novel and often insurmountable problems arise. You can see that for yourself with an easy experiment:
Take a little (empty) soup can and push it under the surface of the water in your bathtub or nearby lake, no problem. Then try to do the same with an inverted, common 10-L-size plastic pail, quite difficult already. Now think of doing the same with a pail of the diameter about half the size of a football stadium. I think you are getting the picture.
If you are mathematically inclined, do a simple calculation of the displacement (i.e., flotation-force-counter-balancing) requirements for a ball of 30 m diameter.
Displacement of a 30-m Diameter-size Ball
The volume of a ball with a radius of 15 m is calculated as ~14,000 m^3. The weight of that volume of water is ~14,000 metric tons. Therefore, to keep a ball of that size (air-filled) at the bottom of the ocean, it needs to have a weight that’s at least equivalent to that of the displaced water. Anything less will lead to that ball rising to the surface and make it useless for the intended purpose. To put that into perspective: it would have a displacement (i.e., also weight) of about 1/3 to ½ the displacement of the USS Midway (picture nearby), the USA’s longest-serving aircraft carrier of the 20th century, plowing the seas from 1945 to 1992, now stationed at San Diego, CA, as a museum.
If you are aware of any ocean-going ships or barges that have cranes to heave that kind of load far overboard, kindly let me know.
However, the whole “energy-storage system” with such concrete balls has other inherent problems that only bureaucrats are unable to see or understand like, for example, the fact that compressed air dissolves in water.
Dissolution of Compressed Air in Water
Only those folks who have their own water supply system, whether drawing the water from a well, cistern, or nearby lake, would likely know about the problem with that. Such home water supply systems are widespread in rural areas, relatively simple and commonly entail a pump and a storage vessel for a few gallons of water. The air above the water inside the storage vessel gets compressed until the pump’s cut-out pressure setting stops the pump and provides a certain pressure to the water until enough water has been withdrawn to activate the pump again via its cut-in pressure sensor.
Depending on the temperature, pressure settings, water usage, and other specifics, variations can be expected between different set-ups but there is one problem common to all. After a while, the air volume inside the pressure gets smaller and smaller due to the air’s dissolution. As a consequence, the pump will run more frequently with steadily reduced cut-in to cut-out intervals despite unchanged settings. And the only way to solve that problem of the diminishing air volume in pressure tanks is to add more air, usually achieved by completely draining the water. For details on the solubility of pressurized air in water, consult The Engineering Toolbox or similar sources.
Now consider, if the dissolution of air is a common problem at the typical household water pressure of around ~100 PSI (~3 BAR), just imagine how it will influence systems with 50 to 100 times that pressure. The air buffer in the balls would certainly disappear in a hurry and, then, the pump removing the water would also have to create a vacuum where the air used to be.
No surprise then when I think that the concrete ball idea will be just another multi-million dollar (or Euro) failure as many other “green energy” ideas of the past—hollow minds foster hollow concrete balls.