Hanover Trade Fair 2001, Germany.
The Department for Energy Technology at the Fraunhofer-Institute - cradle of MP3 and MIT's opposite number in Germany - has presented a solar solution for powering PDAs without the need to externally recharge the battery. They soon could apear on the mass market, as Casio, Siemens and others have their hands on the technology.

The problem facing tehcnologists is the shortage of space in the casing of a cellphone or PDA to allow integration of another power source like fuel or solar cells, Fraunhofer researchers told ZDNet. And it's a race against time: as mobile electronic devices shrink, at the same time they're becoming more powerful, continually forcing manufacturers of solar cells to raise the efficiency of their products. There are special types cells where energy efficiency has almost reached 25, but they are still too expensive for the mass market (See Cell Phone runs on alcohol ZDNet, Decmeber 31st 1998)

Researchers at the Fraunhofer Institute for Solar Energy Systems ISE in Freiburg, Germany, have now managed to find a workable combination of these hitherto conflicting factors. Their high-performance solar module (which will be shown in Hall 18 on the same fair ground where, some weeks ago CeBIT took place, from next week on) is integrated in the lid of a Casio palmtop, and makes the device completely autonomous of external electricity supply.

The prototype is a genuine innovation in this category of devices. "The decisive factor," emphasizes Dr. Christopher Hebling, head of the Micro-Energy Technology group at the ISE, "is that the device can run on solar power alone even under low lighting levels. At a normal workplace, you have only three percent of the energy of direct sun light. Even down to a level of one percent, the electrical voltage provided by our solar module remains virtually constant; in conventional cell types it would have long since broken down." The high output rating of over 35 milliamps per square centimeter in direct sunlight is attributable to the solar module's special design. Hebling explains: "The fourteen individual cells of single-crystal silicon overlap like roof tiles. They cover the busbar, where no electricity is actually generated. In this way, the cells make optimum use of the limited available space, and achieve an efficiency of more than twenty percent."

Till now producing solar cells with this level of efficiency has been prohibitively expensive. Solar cells are coated with an electrically passivating layer of silicon oxide or nitride. This non-conducting material needs to be removed at specific points to allow attachment of the electrical contacts - a hitherto costly multi-phase process. Fraunhofer researchers have arrived at a new solution: A special laser "zaps away" the coating from the designated contact points. This reduces the total number of process steps by eighty percent, making these solar cells a viable alternative to other sources of energy.

The Fraunhofer Department for Energy Technology has also presented another hot solution to power your device: the first functioning micro-gas cell for use in smartphones or PDAs. Four German companies and the Fraunhofer Department based in Plymouth, Michigan, have united in order to develop a series-ripe gas cell system. Like solar cells, fuel cells offer attractive advantages compared to rechargeable batteries: significantly higher storage capacity, long lifetime, flat and variable designs, and extremely low self-discharge.

German and international industry-giants are now demonstrating their innovation in Hall 7 of the fairground with a camcorder that Fraunhofer researchers have equipped with micro-gas cells. It has an output of ten watts, delivered through an 8 volt circuit and it is hardly larger than a matchbox. It consists of 16 bipolar disks. This solution is provided by combining a polymer membrane (PEM) fuel cell with a hydrogen storage unit. The separation of the energy converter (fuel cell) and the storage unit (a hydrogen reservoir) allows energy and power to be dimensioned independently of each other. While the size of the fuel cell remains constant, to achieve longer operating life you only need to enlarge hydride storage unit. Fraunhofer first demonstrated this with a laptop at the Hanover Trade Fair in 1998. Among the development-partners for this prototype were Siemens PC Systems (now Fujitsu Siemens) and Aventis.

The most innovative feature of the fuel cell system is the banded-structure of the membrane. The area is divided into individual cell domains. An integrated series connection over the membrane surface allows the sum of the individual voltages to be drawn at the endplates. To store hydrogen in the smallest possible volume, Fraunhofer uses the well known procedure of hydride formation -- one of the safest known methods. Even at low pressure, high storage densities can be achieved with special metal powders. In addition, this storage medium does not suffer at all from self-discharge and can be refilled with hydrogen many times.

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