World Student Community for Sustainable Development

by Julian Randall

Julian Randall has done his PhD Thesis at the Swiss Fededal Institute of Technology in Lausanne. How can indoor electronic devices contribute to reduce the general enery consumption? Here is the abstract of his thesis.

The use of ambient energy systems (AES) for indoor applications is often limited to products of low power (microWatts, mW). This thesis defends the case that, under certain conditions, AES based on photovoltaic solar cells may be used for higher power devices (mW rating). Such devices, which are expected [Cha98], would allow fully autonomous sensor nodes which hold a number of advantages. One is that wiring, which may otherwise be the most capital expensive element of a sensor network installation, could be avoided. Alternatively, the sensor network battery maintenance could be prevented.

The motivation for the thesis is both financial and ecological, as two examples for the United States show: it has been estimated that a source energy saving of 55 billion US$ per annum, or the equivalent of 35 million metric tonnes of carbon emissions, could be made with building automation based on AES sensors [Sil01]. Another example supports the case that using AES to extend battery life would reduce toxic waste as batteries represent -less than one per cent of total municipal solid waste generated- but -accounted for nearly two-thirds of the lead, ninety percent of the mercury, and over half of the cadmium found in the waste [McM98]. A further motivation is the trend towards more energy efficient and comfortable builings reflected in the Swiss Minergie standard [AMI02]; the latter would be furthered by the use of building sensors. The main avenues of this engineering design research are:

1. power management: ensuring that the application and AES consume minimal energy
2. characterising the influence of the environment on the ambient energy available
3. technological selection: with respect the conversion of ambient energy into charge and the storage of this charge
4. design methodologies that should be applied during all design process phases

Following these avenues, the case of solar (photovoltaic) cells is considered. The main contributions are:

1. two forms of a phenomenological model of solar cell response under indoor radiant energy conditions
2. the validation of a) with extensive experimental results which are necessary to the engineering designer but were hitherto unavailable
3. a model for application functionality confidence with respect to charge storage device capacity
4. a characterisation of the radiant energy indoors that solar cell collect
5. a range of design guidelines and heuristics that provides the designer with a complement to existing product design methodologies for indoor AES Overall, this work identifies the technological barriers which at present hinder the further use of ambient energy sources. The results obtained, however prove that solutions can be found by following the proposed design guidelines; hence further achievements can be expected.

REFERENCES:

Cha98 Chandrakasan A., Amirtharajah R., Goodman J., Rabiner W. Trends in low power digital signal processing Circuits and Systems. ISCAS ’98. Proceedings of the 1998 IEEE International Symposium on , Volume: 4 , 31 May-3 Jun 1998 Page(s): 604 -607 vol.4

Sil01 DaSilva, J. L., Shamberger, J., Ammer, M. J., Guo, C., Li, S., Shah, R., Tuan, T., Sheets, M., Rabaey, J. M., Nicolic, B., Sangiovanni-Vincentelli, A. & Wright, P. (2001). Design methodology for PicoRadio networks. Design, Automation and Test in Europe. Conference and Exhibition. (314-323). München (D).

McM98 McMichael, F. C. & Henderson, C. (1998, February). Recyling batteries. IEEE Spectrum, 35-42.

AMI02 Verein MINERGIE (AMI) Association MINERGIE Minergie Standard. Register: 2 Reglement Stand: Juli 2002 HB2-2 from http://www.minergie.ch/download/sta… on 010503