Renault are adamant that they can make up ground on Mercedes in 2015, but have admitted that they still have plenty of work to do.

The French engine supplier came under fire last season following reliability issues, which plagued Red Bull's defence of their world titles.

However, Renault Sport F1 managing director Cyril Abiteboul believes that the manufacturer are halfway to reducing the power deficit in their units.

"Our main objective in Barcelona, which was outlined and shared with our partners, was to accumulate as many kilometres as possible in order to continue improving reliability," he is quoted by Planet F1 as saying. "Without a single major issue for either team it's an area that we're completely satisfied with.

"Equally, the test validated a certain number of measures implemented since Jerez, which have proven conclusive. On a human level it's also been satisfying to see our technical staff working ever more closely with our partner teams. The results have been very positive."

The 2015 season starts at the Australian Grand Prix on March 15.