Energy | 25. May 2010 | posted by Jan Oliver Löfken

Energy question of the week: Can laptops and iPads dispense with power sockets in the future?

'Mobile electricity' - that is, electricity available on the move - is the most valuable form of electrical power. This is why it is worthwhile equipping notebooks and laptops with expensive lithium-ion batteries that need to be recharged at regular intervals by plugging them into power sockets. The iPad, which looks set to spur the market for electronic reader devices, remains uninteresting without its batteries. However, solar cells and hand cranks are already able to generate standalone power for mobile devices. Will these devices be able to cope entirely on their own without power sockets someday?

Crank the handle for one minute and run the device for 20

The demand for batteries in portable electronic devices that do not need recharging from power sockets is so great that researchers have developed numerous ideas – and have turned some of these into reality. Small plug-in solar modules can assume the role of emergency power sources. Turning an external hand crank can charge the 'hundred dollar computer' being handed out as part of the 'One Laptop Per Child' project to children in developing countries, where reliable electricity supplies are often unavailable. A minute of cranking enables these devices to operate for twenty minutes.

The power of the human touch

These devices can be made even more independent of power sockets either by equipping them with more energy-efficient processors and more powerful batteries, or by enabling them to generate their own electrical power. One of a large number of exotic ideas for power generation comes from a team of Korean scientists. They obtain electrical power for a laptop or table PC through the action of fingertip pressure on the touchscreen monitor.

An operational prototype of a flexible touchscreen 'power plant' of this kind already exists. Thin coatings comprising just a single layer of carbon atoms – known as 'graphenes' – are an important component of these power generators. "Nanogenerators based on graphenes are suitable for standalone power supplies on flexible transparent devices," reports Dukhyun Choi from the research laboratory of the Samsung Corporation, together with his colleagues at Korea's Sungkyunkwan University in Suwon. The researchers place a large number of parallel nanorods made of zinc oxide between two extremely thin and transparent graphene layers. This crystalline compound can convert mechanical pressure into electrical voltage impulses using the 'piezoelectric' effect –the ability of certain materials to convert mechanical movements directly into electrical voltages.

To date, scientists have managed to increase what is still a low energy yield to approximately one microwatt per square centimetre. The researchers do, however, believe that this will be sufficient to supply the sensors on the surface of the touchscreen with a reliable source of electrical power. Indeed, thanks to their flexibility, it will even be possible to generate electrical current by rolling or folding action. This technology is not yet mature enough for robust applications such as installation in iPads and similar devices. The researchers have stated that they will need at least five more years of development before their first product is ready to go on the market. The researchers were also unable to say how often users need to press on their monitors to prevent their devices from running out of power altogether.

It appears unlikely that there is going to be any future for standalone mobile power generation in industrialised countries. This is due in part to the fact that there is still plenty of scope for improving the charge capacities of lithium-ion batteries. However, this technology is already indispensable in rural areas of developing countries.

Further information:

One Laptop per Child-Projekt

Trade publication about the touchscreen power plant: "Fully Rollable Transparent Nanogenerators Based on Graphene Electrodes", Dukhyun Choi et al., Advanced Materials, doi: 10.1002/adma.200903815

Top image: One Laptop Per Child (OLPC)

The DLR Energy question of the week in 'The future of energy' Year of Science

The Federal Ministry of Education and Research (BMBF) has given the Year of Science 2010 the motto 'The future of energy'. For this reason the science journalist Jan Oliver Löfken will this year answer a question on the subject of energy in his blog each week. Do you have a question about how our energy supply might look in the future? Or do you want to know, for example, how a wave power plant works and how it can efficiently generate electricity? Then send us your question by email. Science journalist Jan Oliver Löfken will investigate the answers and publish them each week in this blog.


About the author

Energy journalist Jan Oliver Löfken writes among other things, for the Technologie Review, Wissenschaft aktuell, Tagesspiegel, Berliner Zeitung and P.M. Magazin on issues involving energy research and industry. For DLR, he answered the Energy question of the week during the Year of Energy 2010. to authorpage