The campaigners spent 30 hours on the site
Five activists caused £30,000 worth of damage after painting a slogan on a power station chimney, a court heard.
The five, who all deny criminal damage, were protesting at redevelopment of the Kingsnorth coal-burning plant in Kent.
They planned to daub "Gordon, bin it" on the outside of the 200m (650ft) chimney in a direct statement to Gordon Brown, Maidstone Crown Court was told.
They only got as far as "Gordon" before being persuaded to come down after a threat of a High Court injunction.
The five activists who climbed the chimney, some of whom were Greenpeace volunteers, are Huw Williams, 41, of Nottingham; Ben Stewart, 34, of Lyminge, Kent; Kevin Drake, 44, of Westbury, Wiltshire; Will Rose, 29, of London and Emily Hall, 44, from New Zealand.
Tim Hewke, 48, from Ulcombe, Kent, who the prosecution said helped organise the 30-hour protest from the ground, is also charged with causing criminal damage.
John Price, prosecuting, said the defendants had arrived at the power station at about 0630 BST on the morning of 8 October.
Dressed in orange boilersuits and white hard hats bearing the Greenpeace logo, they headed straight for the huge chimney which dominates the site.
Armed with bags containing abseiling gear, the five scaled the chimney as Mr Hewke waited below to co-ordinate between the climbers and the police who had now arrived at the scene.
Mr Price told the court the protesters had planned to paint "Gordon, Bin It" in huge letters on the side of the chimney which he said was "an injunction to discontinue the development of Kingsnorth Power Station".
He added: "This was obviously intended as a protest against the redevelopment of Kingsnorth as it is a coal-burning power station."
The protesters only got as far as painting the name "Gordon", but Mr Price said the painting "was sufficient to cause damage to the external surface of the chimney", which was "a few pence short of £30,000".
The case, which is expected to last eight days, is continuing.