BMW Sauber will not run with KERS at this weekend's Spanish Grand Prix.
The team has decided not to run with the regenerative energy system because it is introducing a major aerodynamic upgrade in Barcelona and wants to concentrate on getting the best out of it.
BMW Sauber also plans to run without KERS in the Monaco Grand Prix, although this is largely because it is not expected to be an advantage at a low-speed track with no long straights.
It will be the first time that the team has run the aerodynamic package on a proper circuit, although some practical evaluations have been run.
"We will not have KERS in our two cars in Barcelona, because bringing in an aero update and running KERS does not work" said BMW boss Mario Theissen. "We will have KERS on our cars probably in Turkey again."
Theissen added that overall he was happy with the progress the team has made with KERS.
Nick Heidfeld has run it in all four races, finishing second in the Malaysian Grand Prix, but team-mate Robert Kubica only raced it once, in Bahrain, because of the weight distribution disadvantages he suffers as a taller and therefore heavier driver.
"As a technology our summary is very positive," said Theissen. "It worked without failures. The positive result of KERS so far was that it worked even in the monsoon of Malaysia.
"We did not use it constantly because of our car configuration. Given slick tyres and the weight distribution, you need a good weight on the front axle, whereas KERS is placed in the middle of the car and cause more weight there, or even in the back."
The weight disadvantage of drivers such as Kubica will be eased next season following the FIA's decision to increase the minimum weight of the car and driver by 15kg to 620kg.