The French manufacturer has had a troubled opening two days at Jerez, with its teams completing just 38 laps so far.
In contrast, Ferrari-powered teams have completed 138 laps, and Mercedes-powered cars a total of 248.
Renault's head of trackside operations Remi Taffin has revealed that the issue that hindered Red Bull and Toro Rosso relates to the energy stores on the cars.
Caterham has escaped these difficulties because the integration of its package is different.
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The problems are such that they require an overnight fix, with new spare parts being flown in to Jerez to help make modifications that will get Renault's cars back on track on Thursday.
"We know on our side we have one problem that we have clearly identified and we want to fix it," explained Taffin.
"We could not fix it for this morning, so we decided to do as much as we could on our side to make sure that, for tomorrow, and especially for Red Bull and Toro Rosso, that we are sure we can take to the track at 9am.
"We are confident that tomorrow morning we will have all three cars on track."
Taffin declined to elaborate on the specifics of the problem with the energy stores, but suggested it was the way that the batteries were interacting with the rest of the power unit that was causing troubles.
"You have to bear in mind that a power unit is made up of a lot of sub components, and it is not a matter of one of them not working," he said.
"It is clearly a problem of integration of all these systems.
"In particular, for this problem, we had to fix the problem through the energy store - but I am not going to go into detail due to the nature of the architecture of our system.
"We have clearly identified something that we would have to change.
"We have the parts, we have the people here, we have the means to do this, and we were prepared to do this.
"We did not want to do this when we came here, but that is what has happened and we are doing it."
Taffin added that the smoking issues spotted at Red Bull did not relate to the energy store problems.
WHAT IS THE ENERGY STORE?
The energy from the MGU-H (heat) and the MGU-K (kinetic) can be used immediately on the car, or used to charge the energy store for later use.
The energy that is stored in the batteries can propel the car with the MGU-K, or be used to accelerate the turbocharger with the MGU-H.
The power of 120 kW is twice as much as last year - yet its contribution to the car's performance is ten times as great.
In a Renault preview document sent out last week it warned that one of the biggest problems with the new energy stores was coping with the large electromagnetic forces.
It said: "The electromagnetic forces can impact the accuracy of sensors, which are particularly sensitive.
"Balancing the forces is like trying to carry a house of cards in a storm - a delicate and risky operation."
- Nature & Environment
- Toro Rosso