Archive for the ‘ SCORE ’ Category

Blue print for a simple, reliable and low cost heat driven thermoacoustic generators for rural areas producing 20-50W electric power.

Thermoacoustics is a conversion technology in which the compression, expansion and displacement of the working gas is driven by acoustic wave motion rather than by pistons, valves  and displacers. Using acoustic wave motion eliminates mechanical friction and wear and therefore drastically increase lifespan and minimize maintenance. Because of the lack of moving mechanical parts in the thermodynamic process the construction tolerances and material requirements are relaxed allowing for (potential) low production and investment costs. These properties makes thermoacoustics not only a second generation energy conversion technology but also a candidate for low cost, small scale conversion technology for rural and developing areas.

These opportunities were recognized in, for example, the Score project in England ( and by initiatives supported  by the  FACT Foundation in the Netherlands ( The aim of these projects, started a few years ago, is to develop low cost thermoacoustic devices generating electricity combined with wood stoves for cooking or heating water.  These projects also address the social and economic aspects involving charities and local communities. This type of devices could  contribute to improving local living conditions by the use of small scale air operated multi-purpose devices for preparing hot water, cooking and generating some electricity. It could also stimulate  labour related to local production installation and maintenance of these devices.

The document below describes the design approach and underlying physics of a pre-production version of a small scale near atmospheric air operated  thermoacoustic generator and provide a blueprint for the further (local) development and production of such generators in and for rural areas and developing countries.  To make this happen, background information and construction drawings are available from Aster as input for local projects, students, scientist and construction companies who will intend to do experimenting and furthering this technology.

Design and build of a 50W thermacoustic generator(2)

On the way to 50W electric output

Thermoacoustic electricity generation is still under development. The emphasis hereto is on  increasing power level and efficiency and in reducing the cost per Watt electric output power.

Early May, Aster together with the Nottingham Score team managed to get the demo2.2 Score thermoacoustic engine to produce 36 Watts electricity continuously, and 45 Watts peak. The working gas was air at an absolute pressure of nearly 200 kPa. A high power speaker was used as alternator. Its acoustic to electricity conversion efficiency is about 50% which means that the engine delivers 70-90 Watt net acoustic output power. Increasing the mean pressure up to 250 kPa and/or using a more efficient alternator will suffice to achieve the 50 Watt project target.

This result was obtained by modifying the acoustic circuitry toward a serial connection of two individual (acoustic) matched engine stages. This yield both a higher power density and a reduction of feedback tube length. The test set-up is shown below.

Score rig May7

The current (messy) shape of the tubing is for measuring purposes and for easy access. In a final version the tubing can be folded to fit into, or be part of, the wall of the stove.  Note the relatively short feedback tube length which allows for a higher frequency and proportionally higher electric output of the alternator.

First wood fired thermoacoustic generator

On November 23th 2010, the Score team and Aster successfully tested a wood fired thermoacoustic engine with integral alternator at City University London.

Aster in collaboration with Nottingham University developed and built a planar traveling wave 2-stage thermoacoustic engine. City University London designed and built the prototype wood stove, the two were successfully integrated and power was generated on the first run. Score also includes the University of Manchester, Queen Mary University of London and the charity Practical Action.

Score 21 nov prototype A131-300x223

Score (wood fire) A26-300x225

The aim of this test was to bring all together and to demonstrate;

  • The simple construction based on the idea of a finned or corrugated back plate
  • Ease of integrating the planar design with a stove
  • Heat transfer by convection rather than by radiation between stove and regenerator
  • The rapid increase of performance at increasing mean pressure
  • Feedback by near traveling waves in order to end up with the smallest possible feedback loop.

When pressurized to 0.5 barg (150 kPa) the highest electric output measured at 350 °C regenerator temperature difference was 23 W using a standard loudspeaker as linear alternator. The measured acoustic to electric conversion efficiency of this speaker however is only 35%. A better alternator of 60% efficiency is under construction by the Nottingham University. When available, this alternator in the same configuration raise electric output to nearly 40 W. Steady state running achieved 7.5 Watts to charge a 12v Battery with atmospheric pressure acoustics.

For more information about Score see:

The team