Anyone know how this is supposed to work. The part about "compressing and cooling the air" doesn't make any sense. The air wouldn't be compressed and it it was it would get warmer, until it wasn't compressed any more.
My guess is that it allows a relatively high level of ventilation but blocks the sun that would otherwise come in through the open window. So more or less the same effect as an awning.
It's the expansion of the compressed air that cools it. IANAME (I'm not a mechanical engineer) but thinking through the physics of it, you need a fairly strong airflow since the compression has to be adiabatic (air must be compressed quickly enough so it doesn't heat up), then once it expands, it cools.
Of course all of this still takes energy and I'm not motivated to do the math, but cooling a room by 5 deg C still takes the same amount of energy whether it's powered by wind or electricity.
>air must be compressed quickly enough so it doesn't heat up
The heating is inherent to the compression. Adiabatic means something else.
To make air based refrigeration work, you would have to compress the air and transfer the extra heat somewhere else. Then you would get cooling when you let the air expand again.
... which is all still moot as the air would not be compressed enough to matter in this case.
"Gravity light" will never be something more than a curious gadget.
If you lift a 20 kg weight by two meters, you gain a potential energy of 20 * 2 * 9.8 = 392J. Amazon seems to be selling "60W equivalent" LED lights which consume 8.5W. (I think that's about the realistic minimum for reading or cooking.)
Assuming 100% efficiency, you can power this LED light for 46 seconds.
So, according to the tech spec, it has 0.075 W output = 75 mW.
A single 1.5V AA alkaline battery can provide the same output (50 mA * 1.5V = 75 mW), and it can provide up to 2600 mAh, which equals 52 hours, or almost a month if you need the light on for two hours every day.
So a family can simply buy a (very small) LED light and a single rechargeable AA battery. They probably could find a shop to recharge the battery once every month, with minimal fee. Sounds much more reasonable than buying a 12.5kg pulley that needs to be reset every 20 minutes.
* The fact that I've never heard of these amazing "single AA battery powered lights" sweeping through African homes makes me doubt your claim that it's "sufficient for reading and other activities". (Many Africans have cell phones; many more should be able to afford an AA battery.)
The problem is that the cheapest source of lighting for many poor communities is hazardous biomass fuels like kerosene. And unfortunately good alternatives like solar may not be a viable option for everybody.
Sure there are many parts of Africa with good infrastructure, but just because you are living in Africa in the 21st century does not mean you are now surrounded by power lines!
The nearest power socket might be a few dozen or even hundreds of miles away. How are you going to get there and back? If you don't succeed in charging your battery today because of floods or storms, will you go without lighting?
And there is also cost and access to credit to account for. The GravityLight is targeting $5 price point, whereas a basic solar charging pack in Uganda costs approximately $150 USD on finance [1].
Compared to batteries, GravityLight has no operating costs. It also does not degrade over time, lose charge when it is unused, or unexpectedly stop working when the battery runs out. This might be an important consideration for some.
As for whether the device can produce adequate lighting. A candle or simple kerosene wick lamp will produce around 8 lumens of light output [2] compared with the 16 lumens of the GravityLight. So this is pretty good.
Each community has different needs and circumstances. Providing people with more alternatives to kerosene fuel will allow them to choose the solution that is right for them.
I'd seen the Q Drum before, and thought the simplicity and effectiveness were great. I had not see the gravity light, but I like it, too.
And I think you're right about solutions being obvious only in retrospect. The simple fact that I can understand a solution as soon as I see it doesn't mean I'll think of the solution as soon as I encounter the problem. Or ever.
In my coding, it's always easier to "see" the complex bad solution than the simple and elegant good solution.
I have found that, with sufficient experience, it is possible to get better at recognizing bad solutions more quickly. Although this is not quite the same as seeing the elegant solution right away!
My guess is that it allows a relatively high level of ventilation but blocks the sun that would otherwise come in through the open window. So more or less the same effect as an awning.