Williams technical director Sam Michael says the British squad is working flat-out to have its KERS ready to race as soon as possible. He admitted, however, there is not date scheduled for its debut yet.
Williams is the only team developing a flywheel KERS system, while its rivals have used battery-based units. Despite having it ready, some teams have decided against using it in all races.
Michael reckons that as the season progresses, KERS will be more important.
"As the rate of development slows, KERS will take on a greater significance," said Michael. "We're working flat-out to get it onto the FW31 as soon as possible, but I can't say when that will be at this stage. As soon as it's ready, it'll be on the car."
The Williams technical director, whose team has scored just 3.5 points in the first four races, acknowledged the first part of the season has been frustrated because of missed opportunities.
"It's been quite quick in the opening few races, but we haven't delivered in terms of points and that's been very frustrating," Michael said.
"Our rivals are catching up quickly and it will be difficult to maintain a development edge over them during the year, but that's our job and we'll keep pushing."
He added: We've made a few mistakes. In Australia we had a problem with a wheel nut, which cost Nico about 10 seconds, in Malaysia we didn't switch to intermediate tyres at the right time and in China we made the wrong strategic call with Nico when we brought him in during the first Safety Car period."