Barber completed his lap in 26 minutes and 41 seconds
Rob Barber set the fastest lap as electric bikes went out on the Isle of Man TT course for the first time.
Barber recorded an average speed of 84.81 mph on his Team Agni Pro-Class machine, which he will ride in Friday's first ever zero-emission TT race.
The electric bikes took to the course on Tuesday afternoon with speeds in excess of 100 mph being recorded.
Speaking after his lap Barber said: "It was an amazing experience, we had energy in reserve."
The Bury rider added: "People need to get behind this, they're not to replace petrol, they are an addition to it and I hope it is a big success."
In the Open class, which is for machines built within a £30,000 budget, one of the stars of this year's TT, Daniel Kneen, lapped at an average speed of 70.677mph, 10 of the 14 starters completed their lap.
Lap times from the first practice session
Rob Barber (Team Agni): 26 minutes 41 seconds
Thomas Montano (Mission Motors): 33:45
Thomas Shoenfelder (XXL): 34:07
Roy Richardson (Brammo/Bike ): 35:47
Mark Buckley (Brammo/Bike): 35:52
Paul Dobbs (HTBLAUVA - TGM): 41:53
Dan Kneen (ManTTx Racing): 32:01
Chris Petty (Barefoot Motors Racing): 33:35
Chris Heath (Electric Motorsport): 36:26
George Spence (Kingston University): 40:44