Pot boiler

4 min read

An all-in-one cooker, fridge and generator could have a huge impact on the lives of people in the world’s poorest communities. Siobhan Wagner reports.

Hill walking in Nepal is not the sort of research one would usually associate with an engineering project, but it was essential to Nottingham University's Paul Riley, who is part of an international effort to help developing countries meet their energy needs.

The £2m project, Stove for Cooking, Refrigeration and Electricity (SCORE) is led by Nottingham's School of Electrical and Electronic Engineering and will attempt to create an affordable, versatile domestic appliance — a wood-powered, all-in-one generator, cooker and fridge — to supply energy to rural communities in Africa and isolated mountain regions of Asia where access to power is limited.

SCORE involves three other UK universities — Manchester, Imperial College London and Queen Mary, University of London — a major US research centre, a multinational electrical goods manufacturer, an international charity and numerous universities in Asia and Africa.

The idea of the fact-finding mission to Nepal was to help Riley get a better grasp of how to design technology that meets both the practical and social needs of such areas.

Riley said: 'It is very easy for us in the West to say we've read the papers, we've seen the photographs, we know what it's all about over there. But I think unless you meet the people and experience it first-hand, it is difficult to make the right decisions.'

The basic model for the SCORE device is being drawn from thermoacoustic refrigeration technology developed by project collaborator Los Alamos National Laboratory in the US.

The research centre developed the technology to cool electronic components on NASA satellites. Riley said that although hi-tech, the technology is ideal for use in developing countries because there are few moving parts, making the device more reliable. The operation of the device, fuelled by burning biomass products such as wood or, potentially, animal dung, will rely on thermoacoustics — sound waves generated by the non-uniform heating of gas. An example of this is when hot glass vessels 'sing' as the glass is being blown. When harnessed, this phenomenon can create new energy conversion process possibilities.

While many communities in the developing world cook on open fires, thermoacoustic technology could provide a more efficient way of using wood as a fuel — with fewer pollutants.

The device will begin to work when fuel is burnt in the stove. The generated heat will warm up one end of an attached pipe, while another part of the pipe would be cooled by air passing over it. If the conditions are right, the pipe will oscillate at about 50Hz and a microphone-like device attached to one end of the pipe will turn the sound into electricity. The 'microphone', which is a linear alternator, works like a loudspeaker in reverse.

Although there is technology available to do this, it is expensive. So the challenge for the SCORE team will be to find a way to make the existing technology cheap enough to manufacture and distribute widely in the developing world. The group is reviewing whether it would be better to have the devices manufactured within local communities using indigenous materials or produced by low-cost manufacturing centres in areas such as the Philippines. The target selling price would be about £20.

Riley's trekking in Nepal taught him that transportation will account for much of the cost.

'I learned that we have to keep the weight of the stoves down because it costs a lot to carry them up and down the steep hills,' he said. 'It took us four hours to walk up to the village where we were based, but in some regions you have to walk 15 days. The cost to carry a load can be anything from 40-50p/kg, which is quite close to our target.'

To achieve this the device's components will have to be sourced in a cost-efficient way. It will also have few moving parts, making it more reliable.

The one moving part, the linear alternator, would be developed at Nottingham in conjunction with loudspeaker equipment specialist GP Acoustics. According to Riley, this will require close tolerances and high magnetic fields.

Other components may be easy to find within the local communities. prof Chris Lawn of Queen Mary College, who is leading the overall design for the SCORE device, said a cold heat exchanger could be fashioned out of an old car radiator. 'These are quite plentiful in many of these countries,' he said. A prototype of the stove, based on a radiator, is now being made.

The SCORE stove could replace traditional cooking pots in developing countries

Although the team hopes to come up with a working stove/refrigeration combination device, Lawn said it recognised that it might not be right for every household. 'We're not sure that all of the people would need a cooler as in some cases a village might just require one refrigerator to store medicine.'

However, Riley said his Nepal experience taught him that most households would see the value of having electricity provided by a generator.

'Many villagers use kerosene lights, and they spend about 67p a month on fuel,' he said. 'So if they could replace kerosene with electricity they wouldn't have to spend as much money.'

How exactly thermoacoustics would be used to light a home is another issue the team will be investigating. One way would be to use the 50Hz the device generates and convert it instantly into 240V for lighting. Another way would be to rectify the current and put it into a battery for later use.

'The disadvantage with batteries is they are expensive,' said Riley. 'But we could negotiate fairly large deals with battery manufacturers to get the price down, or we could find another way to store the energy.'

Asked whether villagers would have to burn more biomass than usual to generate power, Riley said that they would actually burn less.

He explained that most people in developing countries use open-fire stoves that only achieve seven to 10 per cent efficiency. The SCORE stove, he said, would have a better thermodynamic design.

'So even though we are taking some of the energy out for electricity, overall it will use less wood than is being used today,' he claimed.

The devices are scheduled for distribution in Africa and Asia in the next five years. If the technology is successful there, elements of it might appear in the developed world.

'There has been much interest from Canada, the US and Australia for generating electricity when camping,' said Riley.

'So in the future we might sell the devices at a premium price to the developed world and then cross-subsidise. In other words, if you buy the stove for £80 or £100, £30 of that will go to make a developing country stove.

'However, right now we are focusing on the developing world.'