Turning gravity into light

Title: Creating Electricity From Gravity - Smarter Every Day.

Duration: 8:25 minutes

Description:

Destin Sandlin from Smarter Every Day shows how gravity and human ingenuity can create electricity in even the most difficult of situations - including the middle of a rainforest.

[Animated sequence]

Scene starts in complete darkness.

Destin Sandlin

Hey it's me, Destin.

[Animated sequence]

Destin switches on a small light, which illuminates his face.

Destin Sandlin

Light-emitting diodes. Game changer right? Super-efficient power for the masses. Really cheap - really big deal but there's a problem. It only works if you have a power source. Last week I was in the Amazon rainforest and I had a headlamp and it didn't work because my batteries were dead.

[Animated sequence]

Destin takes out a headlamp to reveal the batteries inside.

Destin Sandlin

I was in the middle of the rainforest, you can't just go pick up batteries. This is the same story for billions of people. Let me explain.

[Animated sequence]

Destin turns off electric light. Room goes into darkness.

Destin Sandlin

For the 1.3 billion people who still don’t have steady access to electricity in the world, kerosene lamps or one of the most common forms of lighting in the home.

[Animated sequence]

Destin strikes a match and lights a kerosene lamp.

Destin Sandlin

This is a really big deal because kerosene lamps can be dangerous. Think about it.

[Animated sequence]

Family at table with a kerosene lamp providing light for a studying child.

Destin Sandlin

You've got an open flame in your home. You've got fumes; you've got burn hazards. There's a lot going on here that's bad.

There's a company in London that wants to change this in developing nations. They want to replace kerosene lamps with LEDs.

[Animated sequence]

Destin blows out the lamp.

Destin Sandlin

Let's go to London.

[Animated sequence]

Scene switches to the GravityLight office in London

Destin Sandlin

This is Jim Reeves, co-inventor of GravityLight.

Destin Sandlin

So it's a plastic gear box which drives a generator internally. There's no batteries and no power storage. You fill the bag with rocks, lift the weight and it drives the plastic gear chains inside, that runs through to a DC motor which is running backwards generating power and that creates our live, on demand, to run the LEDs.

Destin Sandlin

This device is incredibly simple to use. You simply tie it overhead and then hang a weight from it and boom you've got light.

Destin Sandlin

Jim let me inside the secret lair where they develop GravityLight.

Destin Sandlin

Well it’s a workshop; this is home. I get it man; this is what I like to do.

Destin Sandlin

OK, so this is the… this is the side under tension

Jim Reeves

That's right

Destin Sandlin

And so it's pulling the outside of the planetary gearset.

Jim Reeves

And the outside there, the annulus - or the ring gear – turns at about 2 RPM.

Destin Sandlin

Wait so this is the annulus?

Jim Reeves

This is the annulus part. It’s prototyped up out of several pieces but in the end it's going to be one moulding.

Jim Reeves

This is what it looks like when it's out. So this is an internal gear and it drives three planet gears which are these gears which are all the same, and that shares the torque because it's a plastic gearbox. You've got a torque limit that you can deliver before you damage the gears. These pinions are driven by the ring gear. Each planet takes the load across two teeth, so you get… you’re sharing the load across six teeth all in all. When you come to the centre here, you've got each of these driving an external…

Destin Sandlin

So you'll have three teeth in contact.

Jim Reeves

Precisely.

Destin Sandlin

And so you can cut that contact stress down by a factor of…

Jim Reeves

Down to a third.

Destin Sandlin

Yeah.

Jim Reeves

So we've shared it across six where it’s high torque. We've shared it across three where we get to a lower torque stage and then we get onto the final stage where this sun gear is going to drive the pulley wheel, and that's just a single gear. It has to be arranged very efficiently so we can't afford to lose any torque or loss of efficiency throughout the system, because by the time you get to here, there’s a very small amount of torque: it’s equivalent to hanging a few coins on a thread as to what's being pulled onto the shaft of the motor.

Destin Sandlin

Jim this is the engineering room?

Jim Reeves

That's right.

Destin Sandlin

All right and who’s this?

Jim Reeves

This is Rob Ford, our mechanical engineer.

Destin Sandlin

Nice to meet you.

Rob Ford

Pleasure.

Destin Sandlin

How are you, yeah? So what do we have here? This is your CAD model?

Destin Sandlin

The annulus, right?

Rob Ford

This is… exactly, yeah, this is the outside face of the annulus gear.

Destin Sandlin

So Jim showed me, on the inside of that we should have multiple teeth meshing, right? Let’s go in.

Rob Ford

Exactly.

Destin Sandlin

Got it. and so he said on an internal gear… is this right, Jim? On an internal gear you have more than two contact points for each gear mesh, right? Six teeth here, so you distribute that contact stress… OK, got it. So you're not gonna break a tooth off. Let's go further. Nice… OK, so now, because we're no longer doing an internal gear mesh on the planets we are doing an external gear, so three teeth in all sharing the load. OK, what's next? We just have a single contact point here, right?

Jim Reeves

That’s right.

Destin Sandlin

All right, but because torque is lower at this point, we have far less contact stress, so this thing’s gonna work for a really long time.

Jim Reeves

So the pulley wheel has got the rubber belt around it, which drives straight to the DC motor pulley…

Destin Sandlin

So that's the motor, there.

Jim Reeves

It’s really quiet.

Destin Sandlin

If you think about a traditional bulb, you actually have to heat up the tungsten filament to make it work, which requires an incredible amount of current. LEDs are way different. If you applied voltage to an LED it draws no current until it gets to a certain threshold. Then it starts to draw current and emit light. But the voltage gets to a point where it won't increase. It’s like it hits a wall. If you've ever powered up a motor, you know that the more voltage you apply, the faster it will turn. The generator is just the opposite though. If you limit the voltage, you can also limit the speed. That's exactly what the LED does. It hits a wall. Think about it. When you hook up the LED to the generator, eventually you run into that voltage wall and the generator won't turn any faster. That's the magic of GravityLight. The LED is not only super-efficient, it acts as a self-regulating escapement. If you hang 10 rocks on it, or if you hang 12 rocks on it, it's always going to fall at the same rate. This is how GravityLight can run for so long.

Jim Reeves

The gearbox will accelerate up until that voltage is reached where the LED will want to draw current. As soon as it starts to draw current, that then limits the speed at which that motor’s gonna drive. It sets the voltage, because the voltage stays pretty well constant - not entirely, but almost. So if you add more weight, you don't shorten the drop time, you're always running at the same voltage, but you produce more current, because current is directly related to torque. So you're increasing the torque through the gear train, driving that motor with more force although it’s at the same speed and that enables you to take more current.

Destin Sandlin

So it always drops at the same speed, but it might be brighter, but has to reach a threshold current in order to operate.

Jim Reeves

That's right, yeah.

Destin Sandlin

How is this not an issue for these people, because I can imagine this is much more expensive than that cup of kerosene they would buy.

Jim Reeves

It is as a one-off purchase, but if you if they can access a GravityLight then it would pay for itself within 10 to 12 weeks for the outlay, and then of course they’ve got free lighting after that time. We crowdfunded earlier this year to set up an assembly line in Kenya. One of the things that we want GravityLight to do, aside from just provide people with low-cost lighting, is also to provide livelihoods in the economy.

Destin Sandlin

So you’re not going to make them here in London?

Jim Reeves

No, absolutely not. So the most of the components will initially be manufactured in China, and then containers of those components will be shipped to Nairobi, and in Nairobi there will be an assembly line. That's where all the work opportunities are around GravityLight. It’s the process of putting it together as opposed to the process of manufacturing it. We did look to try and do manufacturing fully in Kenya, but at the moment a lot of the industries are still in their infancy out there, so they don't have high tolerance moulding capabilities and things like that - although there is moulding. So, over time we want to transition to making more and more of the product fully in country but we're starting out with a plan to have a local assembly line. We've partnered with an existing factory there, that are called Burn Cookstoves who make and sell low emissions cookstoves. So they're going to assemble GravityLight for us, provide employment, and then that means we've got a supply of spare parts and we've got expertise in country and we can then supply the distribution networks that already exist across Kenya.

The Shell funding is very unusual because it’s unrestricted funds which means that really, you can use them for whatever purpose is best appropriate for your project.

Destin Sandlin

Like coffee and sandwiches to keep you working around the clock?

Jim Reeves

Well though, we normally do those ourselves. But there's very few sources of funding which come unrestricted which lets you apply them as is the best way to enable your venture. An awful lot of the funding that comes, you have to jump through - you know - the normal hoops. You're going to be getting funds in for a very prescribed task. You’re then on a path once that’s defined. The Shell funding is for us to apply flexibly and to deliver the product.

Destin Sandlin

So in summary, it looks like we had a problem with an obvious solution, but there was a disconnect. The people that needed the solution didn't have the technology to pull off GravityLight, and the people who had the technology to pull off GravityLight didn't have the funding to make it happen. So kudos to Shell for seeing this gap and bridging it with their springboard funding to actually bring GravityLight to all the people that want it and need it. It's not done yet, obviously. They just created their engineering solution, now the next step is to try to make it happen. So if you're interested in learning more about this project I'll leave links in the video description: go check those out and learn more about how Shell is working to make the world literally a brighter place.

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