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GravityLight: Generate light with gravity

gravitylight.org

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Re: GravityLight: Generate light with gravity

#91

Post by prewett »

hanoz wrote: post #78
beardicus wrote: post #16

Earlier quoted context omitted.

> You need to lift a 10KG weight about 2 kilometres to get a teaspoon of kerosene's energy, so it's not a great replacement on that front This says nothing of light output. If you want light, and most of kerosene's output is heat, your energy calculation is not helpful. > and having 10KG weights dangling around at variable points between ceiling and floor sounds if anything even more of a liability than a lamp with a…

Okay, okay, you are right of course, the light efficiency is very different, although the heat may not be an altogether unwanted by-product in many cases. There are also more efficient ways of getting light from petroleum than sticking a wick in it. But if you do want the benefits of LEDs, there are better ways of getting the energy than lifting sacks to the ceiling. It's still 180 meters for a pair of AA rechargeabl…

I would say the hazards of this device sure beat the hazards of kerosene lamps (fire, mostly). [1] lists a series of accidents with kerosene lamps in a three year period in a small town. I think a horse kicking over a kerosene lantern started one of the big Chicago fires. There's even a possibility that a kerosene lamp caused a deadly fire in modern USA [2]. And I'm guessing that fire would be a serious problem in small, dense areas such as the slums (not intended pejoratively) in the third world nations that are likely to have the most use for this.

Solar plus battery might be better than this, but this looks like a whole lot better than a kerosene lamp.

[1] http://www.thelampworks.com/lw_lamp_accidents.htm

[2] http://www.chicoer.com/20120322/kerosene-lamp-may-have-cause...

Re: GravityLight: Generate light with gravity

#92

Post by Retric »

jameshart wrote: post #89
Gravityloss wrote: post #61

Earlier quoted context omitted.

1 watt of led light would require 1 Newton at 1 meters per second. Assuming 100 kg is the highest practicable mass, so that's 1000 Newtons -> 1/1000 m/s for each watt. Assuming a height of 2 meters, you could operate a very dim 2 watt led light for 17 minutes. I think that's not practical.

Or, using the numbers provided for this actual product which exists, rather than a spherical LED on a frictionless plane, we raise a 12kg mass 1.8m and get a 0.1W LED light for 20 minutes. Do you think THAT's practical?

0.1W LED light is as bright as one of those clip on book reading lights, they only look bright in pictures. It's not quite useless, but you can build a 0.1w for 12 hour solar light with a 12' cord for ~2$ making the whole thing a joke.

Re: GravityLight: Generate light with gravity

#93

Post by aplummer »

scott_s wrote: post #71
ris wrote: post #64

Earlier quoted context omitted.

"Don't both have their places?" It's more that this "invention" has been bouncing around for a while and gets an unwarranted amount of attention for the amount of energy it can provide. Weird to think, but solar isn't "sexy" in the same way.

"D'oh, we forgot to charge our solar light earlier today." "No worries, we'll just use the gravity light for now." That scenario seems reasonable to me. The point is not the amount of energy the technique provides. The point is the utility people get out of it. And I see a place for both; GravityLight and Solar Aid seem like great projects.

I think they would be good in a mine safe room or something, no need to ever replace batteries right. There are a bunch of cases you might not have a charged light.

Re: GravityLight: Generate light with gravity

#94

Post by shaneofalltrad »

kbenson wrote: post #62
ris wrote: post #58

I implore people to support something far more practical like http://www.solar-aid.org/ than this. Solar lights are many times more thermodynamically efficient, cheaper to make, smaller and much more robust (no moving parts!). This "lifting weights" thing is a silly gimmick. A lifted weight stores a miniscule amount of energy compared to a battery that's been charged by the sun.

Don't both have their places? There are benefits to having a power source that is a) not dependent on a resource that is not available at all times and b) does not require a charging period. It's sort of like people in the late 19th century saying you shouldn't support the development of automobiles, because boats are much more efficient way to move cargo. While true, it does nothing to address the fact that in some…

exactly boats are still used when an automobile can't. Just the same as in low light areas, gravity is your only option. Plus I think gravity is probably a cheaper solution to offer, as the weight can be used from local resources while a solar panel is an added cost.

Re: GravityLight: Generate light with gravity

#95

Post by userbinator »

It looks quite a bit more plausible than the specs in http://www.howtospotapsychopath.com/2008/03/03/stop-press-pi... , but based on my experience with things like shake/crank torches, the light output would have to be really low to last as long as they claim it does.

Re: GravityLight: Generate light with gravity

#97

Post by pazimzadeh »

jpeterson wrote: post #11

The basic idea here is actually a very old approach -- clocks have been powered this way for centuries. But it's very cool and refreshing to see a modern electrical spin on it.

It would be great if the gravity system was bidirectional, so that you could just flip it upside down instead of lifting the weight each time.

Re: GravityLight: Generate light with gravity

#98

Post by gus_massa »

daveloyall wrote: post #48
romaniv wrote: post #30

Earlier quoted context omitted.

I don't think it's a nitpick. I think this is a very important point. Is the hypothetical fuel more expensive than food?

I think your muscles are pretty energy efficient. The kinetic potential battery (the weight lifted against gravity) is also very efficient. Food is very energy dense. https://what-if.xkcd.com/128/ (sandwich vs battery) Uh, change of topic: isn't the caloric value of a food how much heat can be released by burning it (probably when it is dehydrated)? Plenty of energy stored in a sandwich, sure. But a car battery could…

From Wikipedia: https://en.wikipedia.org/wiki/Muscle#Efficiency

> The efficiency of human muscle has been measured (in the context of rowing and cycling) at 18% to 26%. The efficiency is defined as the ratio of mechanical work output to the total metabolic cost, as can be calculated from oxygen consumption.

Re: GravityLight: Generate light with gravity

#99

Post by oh_sigh »

achr2 wrote: post #27

Years ago there was a similar 'potential energy to electricity' buzz and I was initially quite excited. Then I did the math on how much energy is actually available (even at 100% efficiency) from such a scheme. Spoiler - it's minuscule. E = mass x 9.81 x height So a 10kg mass at 2 meters can (@ 100% efficiency) provide 196 joules of energy. A modern cell phone battery has about 25000 joules. To charge said phone woul…

You could theoretically have something like a 1000kg mass which was lifted through a series of pulleys...

Re: GravityLight: Generate light with gravity

#100

Post by [deleted] »

aplummer wrote: post #93
scott_s wrote: post #71

Earlier quoted context omitted.

"D'oh, we forgot to charge our solar light earlier today." "No worries, we'll just use the gravity light for now." That scenario seems reasonable to me. The point is not the amount of energy the technique provides. The point is the utility people get out of it. And I see a place for both; GravityLight and Solar Aid seem like great projects.

I think they would be good in a mine safe room or something, no need to ever replace batteries right. There are a bunch of cases you might not have a charged light.

[deleted]
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