6 ms·
I suspect that the big problem with this concept (vs. the hydroelectric example) is going to be the amounts of energy involved. Let's suppose the shaft is 500m
by Tloewald 13y ago
I suspect that the big problem with this concept (vs. the hydroelectric example) is going to be the amounts of energy involved. Let's suppose the shaft is 500m deep and a 100kg battery -- potential energy is simply F * z, so F = 980N and z is 500, which gives you 490kJ. A wH is 3.6 kJ (you'll need ~10-20 of these to run an iPad for an hour). You're going to need a really big weight and a really big shaft.
This shouldn't be surprising -- with a fairly small motor and good gearing you could raise a remarkably large weight a remarkably long distance with relatively little energy.
Also note that with a hydroelectric dam, the storage mechanism also happens to be the power generation mechanism (dam + turbine) so you aren't incurring huge additional construction and maintenance costs relative to just building the power source, so even if you replaced the weights with a giant tank of water, the entire storage mechanism is extra capital investment and maintenance on top of the solar panels.
If the fundamental problem you're trying to solve is baseline power, it's probably more efficient to bring power in from somewhere the sun is shining (8000 miles away, say):
"As of 1980, the longest cost-effective distance for Direct Current transmission was determined to be 7,000 km (4,300 mi). For Alternating Current it was 4,000 km (2,500 mi), though all transmission lines in use today are substantially shorter than this." (Wikipedia)
- maxcan 13y agoYou only need a large shaft if you construct the weight out of some material other than the matter from a neutron star.
- Pxtl 13y agoYeah, the problem is simply practical - digging a shaft like that and keeping it from filling with water is expensive.
- joezydeco 13y agoYou're going to need a really big weight and a really big shaft. Which means you're going to need a motor with a lot of torque to lift that weight, which means a lot of input current from your power source, right? Or, if your input is small, then you need a lot of time.
- alextingle 13y agoOr gears.
- IgorPartola 13y agoWhich means time.
- Tloewald 13y agoHow do gears help? The potential energy capacity of the system is the weight (mass x gravity) multiplied by the altitude. Gears only impact the power input/output. Use gears on the way in and you can "charge" the battery with very little power (but it takes a long time). Use gears on the way out and you can discharge the battery very slowly, but get very little power out of it.
- pbhjpbhj 13y agoPump mercury [or a safer dense liquid]? If you still want a weight system then have a vessel as a weight and fill/empty it at the top/bottom of the drop and use a counterweight to return the vessel. Then you only need a small pump instead.
- sp332 13y agoA wH is 3.6 kJ (you'll need ~10-20 of these to run an iPad for an hour) I'm pretty sure a whole iPad battery only contains ~7 Wh (1,900 mAh * 3.7v) and it can run for 10 hours. Edit: OK I was looking at completely the wrong device for these numbers. Thanks miahi!
- miahi 13y agoiPad 2 had a 25Wh battery, 3rd gen has a 43 Wh battery (11500 mAh * 3.7V). An iPhone has a ~5Wh battery.
- andrewcooke 13y agoif an ipad has a 40Wh battery and can run for 10 hours then it consumes 4Wh per hour so runs at 4W or 4J/s. 100kg dropping 1m releases 1kJ so will supply an ipad for 1000/4 = 250s = 4min. so a 100kg weight needs to drop 15m to power an ipad for an hour. i don't completely understand the parent comment - what are "these"? but you do not need multiple weights and shafts to run an ipad for an hour. a single 100kg weight and a 15m shaft is sufficient.
- renekooi 13y ago"these" are the Wh's
- Tloewald 13y agoAlso chargers and transformers are not perfectly efficient. Chances are you aren't transmitting power from this gizmo to your house at USB voltage (horribly inefficient) so it's probably being sent at a higher voltage (110V seems the obvious option) which means converting it back down using an power brick, so the Wh capacity of the battery understates the power requirement for running the iPad by the inefficiency of the power brick.
- akira2501 13y agoThe less energy you use to lift the weight, the more time it takes to move that weight; if it takes you 10 times as long to generate the energy as it does to use it, then you're going to need massive generation capacity to get anything appreciable happening in a reasonable time frame.