NEC has succeeded in reducing the size of a prototype fuel cell for laptop use with but says it is unlikely to become commercially viable until 2007 - two years later than recent predictions - because of legal hurdles.

Direct methanol fuel cells (DMFC) mix methanol with air and water to produce electrical power and are viewed by many as a potential successor to lithium-ion and other batteries used in devices such as laptops and other portable electronics devices. Their by-products are heat and water.

NEC's new prototype has a power unit that is 20 percent smaller than the company's previous prototype and has an output density of 70 milliwatts per square centimeter, the company said. The new fuel cell also includes a control system that helps optimise power output. It will be officially unveiled tomorrow at World PC Expo in Tokyo.

A single 250 cubic-centimeter methanol fuel cartridge can provide enough power to run a notebook PC for 10 hours, said NEC. The prototype machine is based on a 1.1GHz Pentium M processor and has 256MB of memory, a 40GB hard disk drive, 12.1-inch color TFT screen and runs Windows XP Professional.

A picture of the prototype released by NEC showed that the fuel cell resembles a notebook computer dock. The entire PC sits on top of most of the fuel cell and just past the back of the computer the cell rises to the same height as the PC.

Several prototypes developed as part of the company's DMFC research have been show before and the company has previously said it planned to have a commercial product on the market in 2004. However, this has now been put back to around 2007.

While development of fuel cell technology is more or less at the point where it can be commercialised, a number of other issues have yet to be solved, said Diane Foley, a spokeswoman for NEC in Tokyo.

These include regulations regarding carriage and use of fuel cells on airplanes and other forms of public transport. NEC had been hoping that such legal hurdles would have been cleared by this year but it now expects this to happen around 2007, hence the delay, said Foley.

There are other issues that need to be solved including standardization of fuel cell cartridges and establishment of a sales network were new cartridges or fuel can be purchased.

Earlier this year the International Electrotechnical Commission (IEC) formed a working group to draw up standards to ensure compatibility between micro fuel-cells after prompting from Toshiba and other Japanese companies. The group will attempt to set a standard for compatibility between fuel cells and fuel cartridges and hopes to set common guidelines by 2007.

Other companies in the race include Hitachi and MTI Micro Fuel Cells.