A couple of weeks ago I expressed my frustration with a competition to design a new kind of toilet for the third world, and a winning entry that looked like a physics lab with a toilet on top. That was the Gates Foundation attempting to reinvent the toilet, and while it’s an incredible piece of technology, it’s not something that’s going to go in a mud hut.
If you start with the poor and the assumption that it will go in a mud hut, you can still create amazing technologies. For evidence of that look no further than Practical Action’s new stove. They started off developing a smokeless cooker that would use fuel wood more efficiently and prevent the smoke-related illnesses that plague many families in poor countries. Along the way they realised that the stove could generate electricity at the same time. Remarkably, the Score-Stove generates electricity from sound.
The stove has a pipe attached that becomes pressurised as it heats up, causing lots of tiny pieces of metal to vibrate. These vibrations are then captured by a speaker, which feeds into an alternator. It can generate 36 watts of power, and the inventors believe it can be refined up to 50 watts – enough to provide a clean light source or charge a phone. Apparently it makes a ferocious din inside the pipe, but users only hear a humming noise while using the stove.
The stove has been tested in labs and in homes in Kenya, Bangladesh and Nepal, with development teams at a number of British universities. It works, and it can be installed in a mud hut. The challenge now is to adapt the prototypes to ensure that they can be built using only locally available materials – the true test of an appropriate technology.
The Earthbound Report 
What an extraordinary idea. 50 watts is useful anywhere. I wonder if you can retrofit it to my woodburner…?
This sounds fantastic, but I’m very sceptical. If you think about what would need to be going into the speaker to produce the current, it doesn’t seem feasible. alternator efficiency is approx 50%. Let’s say the speaker captures 50% of the sound energy, and converts it to electricity at 70%. That means there’s about 200W of sound energy, which is a _lot_ (louder than the loudest rock concert)… where’s all this sound coming from, anyway? I wouldn’t want it in my kitchen!
You may be right – my grasp of electrics leaves a lot to be desired. It is a working prototype though, tested in labs and in the field though, so they must have found a way of improving either the alternator or the speaker.
The great thing about Practical Action is that, whatever their secret may be, it will be published and given away rather than trademarked. Once they’ve refined it and got it right, they’ll write up the plans so that other people can make them.
There’s a rather rough diagram of how it works on flickr:
Looks like a scam to me. We can probably expect that many snake-oil-merchants will be trying to sell us free energy machines in the coming years…
It’s not free energy, it’s a wood burner. And it’s been developed by a charity, so it’s not for sale. But suit yourself.
The stove uses the principles of thermo-acoustics. That is the heat generated that is not used for cooking is converted into sounds waves, which in turn move an electrical alternator to produce electricity. The conversion of heat into sound waves requires a number of elements which have to be produced with precision, and the conversion of sound waves into electricity requires a linear alternator designed for this particular machine.
Because of those two components, demand precision and high quality standards, the research group (four UK universities and Practical Action) believe the two components have to be mass produced in order to have cheap prices. The aim is to have both components for less than £50 or so, so that it can reach millions of poor people.
The other components (an efficient combustion chamber and accessories) can be produced locally. The scientific detail is a bit much to go into here, but we at Practical Action are in the process of putting together a video which goes into much more depth. I’ll post a link to this when we get it edited.
In terms of noise, it does produce quite a buzz, but it is hardly anything compared to the din inside the pipes, which is equivalent to a jet taking off!
What a remarkable idea! As someone living and working in Bangladesh with many friends and adopted family living in the mud huts to which the post refers, I think it is a wonderful idea. My Bangladeshi friends spend much of the evening cooking without any electricity and without light. A cooking stove they can use that also produces light so their children can actually study their school books is a fantastic idea. I hesitate to say revolutionary because one never knows which ideas will actually change the world but I would not be surprised if this invention came to have much greater importance than mere cheap clean energy.
Only generating 50 watts of electricity is not enough by this.You need to search little bit more for its use.What if we search other alternatives to convert sound energy into electrical energy?