A combined combustion oven and refrigerator that can also harness electricity from its vibrations is now undergoing field trials in the UK and Nepal. The versatile appliance has been developed over the past two years through a UK research collaboration led by the University of Nottingham. With its cheap production costs and variety of functions, the new generator could become an affordable and sustainable energy technology for communities in the developing world, say the project leaders.
Underpinning the electricity generator is a two-step energy conversion from heat to sound to electricity, which takes place inside a gas-filled pipe. A fire at one end of the pipe creates a temperature gradient, which triggers acoustic waves as gas moves from hot to cold regions — much like a singing kettle as the water reaches boiling point. These sound waves can then be harnessed by a linear alternator, which converts mechanical energy into electrical electricity in the reverse process to an electric motor.
What’s more, some of the pipe’s vibrations can also be passed into another thermoacoustic engine, which works in reverse to generate a cooling effect. Finally, the heat from the burning wood or other available biomass can also be used for cooking. The real innovation is that these three functions can be run simultaneously to provide the users with a combined stove, refrigerator and electricity generator.
Three-in-one
The SCORE (Stove for Cooking, Refrigeration and Electricity supply) project was launched two years ago with the aim of developing an affordable, versatile domestic appliance to address the energy needs of rural communities in Africa and Asia, where access to power is extremely limited. One advantage of the new generator is its efficiency, which is higher than that in thermocouples — another device that converts heat into electrical energy. “The best [thermocouples] I have seen are less than 5–7% efficient. Compare this with 15–20% for a thermoacoustic engine,” said project director Paul Riley.
Technical development of the appliance has been split between different institutions in the UK. Researchers at the University of Nottingham have been working to maximize the efficiency of the linear accelerator. “The current design is very exciting for me as it solves many of the problems we had with using loudspeakers as alternators,” said Chitta Saha, a member of the Nottingham team.
Researchers at City University London have been developing the stove design and working with the University of Manchester to hone the thermoacoustic engine. In addition, researchers at Queen Mary University of London are working on the heat transfer aspects of the device.
Putting it into action
Paul Riley told physicsworld.com that his team has already generated 8 W of electrical power by using a propane burner instead of biomass. “We have built the stove top unit using local materials and tested it in Nepal. The results look very encouraging — the science is progressing well and we have developed mathematical models that are being tested,” he said.
The SCORE team are aiming to create a generator weighing between 10 and 20 kg, at a cost of £20 per household, based on the production of a million units. The target is to generate an hour’s use per kilogram of fuel — which could be wood, dung or any other locally available biomass material. SCORE are now looking for sponsorship to fund further testing and Riley believes that the Indian sub-continent (particularly Nepal), sub-Saharan Africa and South America are regions that could benefit particularly from the new innovation.
Riley also told physicsworld.com that his team will also begin to explore other applications once they have proven the technology. “Examples could include waste heat recovery, CHP for domestic boilers and low-cost solar power,” he said.
