[achr2]

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 would require raising that weight well over 127 times.

[TrevorJ]

Hmm, that's actually pretty doable if coupled with pedal power (you'd either charge directly with a dynamo in this case or pump water to a higher elevation to store as potential energy). Back of the envelope math says you could do it quite easily in 15 minutes which isn't bad at all especially given the fact that you can't shove power into the battery anywhere near that fast.

Granted, this works much better with something like a light because LED's use so little power to run.

[jimrandomh]

Pedal-powered generators already exist. Using one to charge a battery is better than this gravity-energy-storage gimmick in every imaginable respect, but they still are not used much, because electricity is not scarce. (If you can afford to buy a gimmicky generator, you can afford to buy a real one instead and the real ones are cheaper and better.)

[TrevorJ]

That's pretty fair.

[pavel_lishin]

But this isn't for charging a phone; it's for having light, right now.

[Gravityloss]

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.

[jameshart]

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?

[Retric]

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.

[Gravityloss]

Ok, I confess to not reading the article, I was just reacting to the comment. That actually starts making a lot of sense.

[CyberDildonics]

You can use it to read and it is free.

[imaginenore]

It's not free. It's a very inefficient way of converting food to human energy to humans lifting weights that in turn power the lights.

If this is targeted at very poor people, food isn't cheap for them.

[Gravityloss]

If you think about the methods of farming worldwide etc, they also use a lot of human labor etc because there's not enough sophisticated industry to run everything on solar charged battery powered robot tractors... So you have to accept a local optimum.

Reading for half an hour per day could have large payoff, compared to reading very little ever, because it's too dark.

[CyberDildonics]

Neither is kerosene. Many people reply based on their gut feeling, but that doesn't mean it lines up with reality. A chocolate chip cookie has enough energy for a person to go jogging for 20 minutes. No one is going to starve to death by lifting a weight every 20 minutes for a few hours at night. They might be able to lift themselves out of poverty if they stop paying for kerosene and read (or learn to read) in the time that they aren't working, which is likely at night.

[kragen]

The energy involved here is between one and two grains of rice.

[achr2]

I get it, I am just saying that there are a lot of ways to make a single LED light shine, potential energy from a weight is likely the least sensical.

[bnegreve]

> potential energy from a weight is likely the least sensical.

potential energy is very easy to produce, keresene is not always available. I think this is the #1 benefit.

[lyschoening]

The key here is that this method does not require a battery. In practice though I am skeptical that this contraption would live much longer than a rechargeable battery combined with something more versatile such as a hand crank.

[makomk]

For comparison, that's in roughly the same ballpark as the amount of energy one of the tiny, cheap rechargable batteries in a dollar-store solar light can store. Potential energy just isn't all that viable.

[oh_sigh]

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

[datashaman]

what lifts them?

[oh_sigh]

A human does.

[userbinator]

Also assuming 100% efficiently, 196 joules is enough to run a 1W LED for 196 seconds (3:16), or a 0.1W LED for 1960 seconds (around 32:40.) Not very bright, but still somewhat useful for illumination.

[nine_k]

A kerosene lamp probably converts ~2-3% of its energy into the light; I don't think they use catalytic burners.

Dynamos and LEDs are reasonably efficient in comparison, and also not fire-prone.