Alternative Energy Forums

Ok folks,

Here’s another idea. I would love to hear your thoughts on this.

Assuming price is no object...

Lets pretend you drive into a parking garage downtown. The garage is elevated about an extra 20 ft. Instead of pillars, the garage has giant screws that can compress the air below the garage. The compressed air is forced into a efficient fan grenerator - like a steam engine. As a 9 hour day passes, the structure slowly settles. The roof of the same garage is lined with solar panels. This separate power system stores energy to raise (the now much lighter structure) through the evening.The extremely low wattage motors could take all of 10 hrs to raise.

The energy generated by the pillar air pressure could either go back into the grid or recharge multiple electric cars on that platform.

I have drawn the idea, but I cannot post it here.

Michael Reeves

That’s an interesting idea. Just to make sure I understand it correctly - the added mass of the parked cars and the change in height will provide power. Would the solar cells really be necessary if the system is producing electricity? Doing a back of the envelope calculation using an average weight of 2500 lb, a structure that holds 200 cars, and the change in height of 20 ft that you proposed, I came up with about 14 MJ. If the process took place over a 8 hour span this would produce an average of about 470 W. So overall, you wouldn’t be gaining much especially given the cost and inefficiencies not taken into account. PV cells would be a much better option (though I’m not especially fond of those either). Novel idea though.

Yeti

There's a bigger issue yet! Even if we were to ignore all the loses due to friction in the mechanism (which will be huge) and in the electrical generating process (which will be moderate), you have the fundamental physics do deal with - that is, gravity is a conservative force which means that when objects (such as parking garages) move, any work done moving one way is taken back when moving the other way. What this means is, if you consider the system as a whole (garage, electrical generator, cars, etc.) the only net gain is due to the solar panels themselves. You would gain the same amount by simply hooking the panels to the grid. The primary issue is that the cars need to move up 20 feet when entering the parking garage and the amount of work used to raise the cars 20 feet is the maximum amount (remember the loses) that would be gained when the cars sink that same 20 feet back to ground level.

In general, no work can be gained from gravity. The only exception for us on earth would be (theoretically) from items which already have gravitational potential built into them - such as asteroids and comets which are far up in the gravitational field. If we could build a 'catch basket' which would collect the asteroid's energy (the high potential energy would be converted to kinetic energy as the asteroid moves closer to the earth) then there would be a gain. Otherwise, nothing is gained. But, keep on thinking - certainly there are alternative energy devices which have not been imagined yet.

ElectricMan

Electricman:

It looks to me like you err ...

The proposal is that the energy is extracted by the slow falling of the mass of the garage AUGMENTED BY the vehicles during the day; then the mass of the garage ALONE (ie: when all the vehicles have left at night) is raised back up to the higher level at night. Raising the lighter night-time mass up takes less energy than is theoretically extractable by dint of the slow fall of the heavier day-time mass.

So, in theory, it works. The theory is FINE - even novel, as Yeti says.

Some clever stuff would probably have to be done with hinged ramps and so on to get access to parking say for drivers who mistime their arrivals/departures, or has a daytime dental appointment ;-).

In that case, some of the work may also come from/go to the vehicles leaving/departing as driving up a ramp that was steeper than before will take more gas ;-)

However, as Yeti points out, with the # of cars & masses he gives the "prize" for what would be ... er ... significant, let's say, engineering effort, would be the generation of a ... massive ... huge ... er, 3.766 kWh of energy/up-down cycle - a theoretical maximum!!!

In addition of course, electricity is derived via the agency of gravity all the time - hydroelectricity. It's just that the Sun is kind enough to do all the heavy lifting for us.

Dennis Revell.

(Oct 15 2009 06:06 AM)Guest Wrote:  In addition of course, electricity is derived via the agency of gravity all the time - hydroelectricity. It's just that the Sun is kind enough to do all the heavy lifting for us.

^ well put.

I'm sorry, but gravity is not an energy source.

If your system were 100% efficient it still would not produce power. The power generated from the falling garage floor will be the exact same amount of energy it took to drive the cars to the raised 20' floor in the first place.