IBM Japan has unveiled a new ThinkPad notebook computer that can automatically shift its power source from an AC adapter to a stored battery, the company announced yesterday.

The ThinkPad R31 includes a peak-shift-control program that allows electricity to be used evenly throughout on-peak and off-peak times.

Usually when a PC is connected to an AC adaptor it always uses power from the adapter. With the ThinkPad R31 users can set a time for the computer to switch its power source to an internal battery, which has been recharged during off-peak hours, said Yuko Takeuchi, a spokeswoman for IBM Japan.

The ThinkPad R31 is the first result of a project IBM Japan started last March with Kansai Electric Power, Tokyo Electric Power, Sanyo Electric and Matsushita Battery Industrial.

The purpose of the project was to decrease the volume of electricity used for PCs in offices at peak time, an IBM Japan statement said.

During the summer in Japan, many offices turn on air conditioners in the afternoon, causing dramatic increases in electricity consumption. Power companies have been looking for ways to avoid these peaks, according to the statement. Using stored battery power in the office during the day can ease electricity costs and protect the environment, the company said.

From July to September last year, IBM Japan and the power companies conducted a trial using the peak-shift-control program on their PCs. The trial showed that by charging the PC battery at night when demand is low and then using that stored power during the day, they were able to decrease carbon dioxide production by four percent to 16 percent, according to the statement.

IBM Japan also calculated that if the 1,200 notebook PCs in its Tokyo headquarters are equipped with the peak-shift-control program, it could save around £1,000 a year, the statement said.

Sanyo Electric and Matsushita Battery have been researching the effects on a battery of being repeatedly discharged and recharged, and will keep working on a longer-lasting battery, the statement said.