Kerosene lamps are made with garbage. They can be replaced in minutes if there's a problem. Fuel costs are high, yes, but capital costs and maintenance are low. Those matter.
To really make this a long term win, you need to make it indestructible and easy to repair with on-hand parts. I hope they can do that.
>We're doing this in our approach to distributing GravityLight
>We are partnering with local networks of people earning a living by selling products such as GravityLight, rather than disrupting local markets and jobs with free giveaways.
>We're doing this in our manufacturing strategy
>We aim to create jobs and skills in the regions where GravityLight will be sold, firstly by establishing an assembly line in Kenya.
And it looks like they've already run into robustness issues, but they weren't due to cheap plastic components, and it looks like they've modified the system to deal with them...
>GL01 had a protection mechanism that clearly indicated an overload with a red light, and helped reduce damage to the gear teeth by allowing it to run more swiftly, but this did not make it indestructible. An entirely novel way of protecting the system has been designed for GL02. It will allow an overloaded bag to descend to the ground in a safe and controlled manner, repeatedly.
>GL02 suspends the bag from a pulley, which reduces the strain on the cord and the gearing. This also decreases the loading on the drive system and permits a smaller gearbox ratio, which helps to improve efficiency.
That was the first thing I looked for. The materials, at least from this image, look plastic and very custom made. http://static1.squarespace.com/static/552aca94e4b0c75f5b87b0... If these parts get brittle and break/crack, how are they repaired?
Also I wonder if you could just do all this with a refitting of a rachet lever hoist or something similar.
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.
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 cases the use of a boat makes no sense, such as transporting to a land-locked location.
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.
"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.
This isn't a boat with oars. This is a boat where you're given some wooden spoons.
We need to stop dicking around with idealistic ideas involving electronics and design more efficient and safer uses of these existing cheap fuels for lighting and more importantly cooking and phone charging.
They are being used because they work for people in these situations.
Beyond the "no moving parts" (and maybe cheaper to make), I think you're just spilling a marketing blurb.
> 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.
Potential energy = m.g.h So, lifting a 10kg weight at the height of one meter gives approx. 98J
Incident solar power is 100W/m2 (best case). A square solar cell 10cm of side hence gets 1W (or 1J/s), after efficiency losses this is even less (which are present on the GravityLight as well). Between 0.5W and 5W seems common on sale websites
So, lifting the weight above (which takes 1s approximately) gets you as much energy as 36s of solar energy (of course, you can't recharge it at night)
Also consider the cost of the battery
Edited for wrong math
First, you’re mistaken about the robustness of batteries. Batteries tend to have a very short lifetime, measured in months to years, and they can typically only be recharged a few hundred times. Generators have longer lifetimes, measured in generations to centuries. Batteries are usually a lot cheaper than generators, so it might make sense, as you say, to just replace the batteries a few times. But how much does a 100mW generator cost? Amazon is selling an “X Factor” brand 3000mW generator along with accessories for US$17.56, so I suspect that the retail cost of a 100mW generator would be about US$1. (Little 1-watt brushless DC motors do cost about US$1 to US$3. I can’t find any 0.1-watt DC motors.) By comparison, the retail cost of an 800mAh AAA NiMH battery (3700 J, 1000 charges, thus lifetime about 3–5 years, Tenergy Centura brand) is about US$1.50 to US$2.
Second, it is incorrect to say, “A lifted weight stores a miniscule amount of energy compared to a battery,” except according to irrelevant figures of merit. Batteries do indeed have orders of magnitude higher energy density per kilogram and per liter, about 400kJ/kg and 1MJ/ℓ, while a bag of sand that has been lifted two meters only stores 20 J/kg and something like 20 J/ℓ. But those are not relevant figures of merit here. The target audience has tens of thousands of liters of available storage space, even in the worst slums, and can store tons of material, and the target application only needs to store 120 J. Reducing the weight of the stored energy from 6 kg and 6 ℓ down to 300mg and 0.12 mℓ (or, more realistically, 4g and 2mℓ, since you need to store more than 20' of energy) is not needed to replace a kerosene lamp; it provides you with a flashlight. Not to say that flashlights and solar lights aren’t useful, but if this is cheaper than a flashlight, maybe it’s useful anyway. Solar lights and rechargeable flashlights cost about US$6 to US$10 at retail today, which is a significant amount of money to a lot of people.
It’s true but irrelevant to say that lifting a weight by hand is not particularly thermodynamically efficient. It’s incorrect (but still irrelevant!) to say that solar lights are more thermodynamically efficient. Lifting weight is about 25% efficient, due to the inefficiency of your own muscles. (Generators are typically better than 90% thermodynamically efficient.) This is substantially more thermodynamically efficient than solar lights, which lose 85% of the sunlight on input and another 50% or so in the battery. If you can get the energy from somewhere else, rather than muscle power, then the weight is many times more thermodynamically efficient.
The efficiency question is irrelevant because we’re talking about 120 joules of energy for 20 minutes of light, which is an amount of energy that costs US$0.000003 if you have an actual power grid, or 0.03 grams of carbohydrate if you’re powering your 25%-efficient muscles (between one and two grains of rice). The only people who worry about conserving the energy in individual grains of rice are people currently experiencing a famine, mentally insane people, and commenters on Hacker News.
The one thing in your comment that might be true and relevant is the statement that solar lights are cheaper to make, because we don’t know how much the final retail cost of these Gravitylight gizmos will be. However, it seems implausible that they are many times cheaper to make. It seems likely that the vast majority of the cost in either case will be non-electromechanical components like the plastic housing, the gear train, glass or plastic to protect the solar cells, marketing, and so on, so the two solutions are likely to be almost exactly equal in cost. One will be portable but need to be left out in the yard to charge; the other will be heavy and nonportable, but you’ll be able to charge it in the middle of the night.
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.
Granted, this works much better with something like a light because LED's use so little power to run.
If this is targeted at very poor people, food isn't cheap for them.
Reading for half an hour per day could have large payoff, compared to reading very little ever, because it's too dark.
potential energy is very easy to produce, keresene is not always available. I think this is the #1 benefit.
Dynamos and LEDs are reasonably efficient in comparison, and also not fire-prone.
A more efficient LED, a power output port, and continuous operation, but most notably: a pulley system!
Great how a simple machine can massively improve the impact of this product. Very cool.
In practice most of the laptops are charged like other laptops--- from national power grids. Those that aren't are charged from diesel generators and solar power.
- Human muscles get energy from food.
- Food is or gets its energy from plants.
- Plants get energy from the Sun.
- The Sun's energy comes from gravity-forced fusion.
So gravity :)
the FLRW model of cosmology, which has made numerous confirmed predictions teaches us that the big bang is a geometric property of space-time i.e. a consequence gravity, and particularly Einstein's field equation from general relativity.
It's interesting to put that in perspective: the pyramids were built out of solar energy by way of muscle. Skyscrapers are built out of solar energy mostly by way of diesel fuel.
No wonder we're seeing exponential growth with that injection of stored energy into society. The industrial revolution is a coal-powered nitro.
He explains the light of a fire is just the light of the Sun, it's just been stored in the wood
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 power a small spaceheater-like thing for... a while. There's a lot of potential for heat production in a car battery (even without BURNING it). Did Mr. Munroe get this one wrong?
> 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.
this is because if something is collapsing from gravity it will stop once some other force is pushing out harder.
this explains a lot of phenomena and is a key piece of understanding the modern theories of stellar phenomena, e.g. via the pauli exclusion principle, why neutron stars can form during a supernova (from the extra inward pressure combining with the gravitational collapse exceeding the degeneracy pressure of electrons in the plasma)... its also why beyond a critical mass the collapse doesn't stop at all and produces a black hole.
in any case energy is always conserved... but the ultimate place it is being extracted from to power a star is the gravitational field. everything else, e.g. the nuclear fusion, the light pressure from temperature etc. is a result of that energy being transferred into the star as it forms and continues to evolve.
Similarly, I think saying both 'the sun is powered by gravity', 'the sun is powered by hydrogen' and 'the sun is powered by fusion' is reasonable.
Edit: I was wrong. See below.
Are you sure it's not powered by a standard watch battery ?
The first thing that came to mind when I saw that it lasts 20 minutes would be to use it as a pomodoro timer. Code for 20 minutes, then be forced to take a break, stand up, lift the weight, etc. You get a micro-workout as a small bonus. Again, it's a novelty but sort of a cool one at that.
Rechargeable batteries can be reused, but still need to be replaced; this may prove lower maintenance, which means once you can get it, you are more secure with it with a less secure distribution system. In many of the places where people are without electricity in the world, that's potentially a significant benefit.
(Also, solar recharging in places that experience long periods of darkness, e.g., the arctic, may not be an ideal solution. There aren't any places that experience extended periods without gravity, at least not on Earth.)
For emergencies, I would prefer a mechanically powered flashlight with a supercapacitor over this thing.
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 naked flame
This seems like an incredibly contrived "problem". What's the liability? Somebody may bump into a somewhat heavy object that is moving downwards at a barely perceptible clip? Somebody may tweak their back lifting the weight? That seems lower risk than my housing burning down with me in it.
I genuinely don't think the hazards are at all contrived, and range from the grave if unlikely to the mild but virtually certain. You are surely going to knock your head on this massive hovering, albeit reasonably well lit, object on a regular basis, and it might not be as soft and rounded as the illustration. On the floor, in dark mode, you'll be tripping over it, which doesn't always end comically. Reasonable precautions not withstanding it's not impossible that it could crush or smother something beneath it even at its snail's pace, but more likely it could come down hard through overloading, wear or misuse. It's really not something I'd want in a family home.
It is a nice idea and obviously of the very best intentions but I'm afraid it's simply misguided and efforts would be far better directed towards battery plus solar. Sorry.
Solar plus battery might be better than this, but this looks like a whole lot better than a kerosene lamp.
A kerosene lamp has an efficiency of 0.1-1 lumens/watt, while a white LED has anything around 80-100 lumens/watt.
Fire stays where it's put? No. The problems with flames involve toxic gasses poisoning people and the occasional building on fire. That's really not consistent with the idea that "flame stays where its put"
This is some LEDs, a weight, some gears and an alternator. Is a solar panel and a battery going to come anywhere close in price?