The campaigners spent 30 hours on the power station site
Six Greenpeace activists have been cleared of causing criminal damage during a protest over coal-fired power.
The activists were charged with causing £30,000 of damage after they scaled Kingsnorth power station in Hoo, Kent.
At Maidstone Crown Court Judge David Caddick said the jury had to examine whether protesters had a lawful excuse.
The defendants said the protest was lawful because it aimed to prevent damaging emissions. Energy firm E.ON said lives had been put at risk.
Five people who scaled the chimney - 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, 34, from New Zealand - were all charged with causing criminal damage.
'Gordon, bin it'
Tim Hewke, 48, from Ulcombe, Kent, accused by the prosecution of organising the protest from the ground, also faced the same charge.
Jurors heard how protesters painted the name "Gordon" on the 200m (650ft) chimney on 8 October last year, in a political protest against the redevelopment of the plant as a coal-burning unit.
They had planned to daub the words "Gordon, bin it" on the stack in a reference to Prime Minister Gordon Brown, but were threatened with a High Court injunction and arrested.
The campaigners painted the name "Gordon" on the chimney
After the hearing, E.ON spokeswoman Emily Highmore said the firm, which is planning to build a coal-fired unit at the plant, was "hugely disappointed".
She said: "We respect people's right to protest, but what Greenpeace did was hugely irresponsible. It put people's lives at risk and that is clearly completely unacceptable."
Ms Highmore called for an "open and honest debate" about the challenges of energy and climate change, but added: "That's a debate that shouldn't be taking place at the top of a chimney stack."
She added: "Our men and women who work at Kingsnorth have a right to go to work to do their lawful business and to do it safely, so we're very concerned indeed about today's outcome."
This is a huge blow for ministers and their plans for new coal-fired power stations
Outside the court, activist Mr Stewart said the verdict was "a tipping point for the climate change movement".
He said: "When 12 normal people say it is legitimate for a direct action group to shut down a coal-fired power station because of the harm it does to our planet then where does that leave government energy policy?"
Mr Stewart called for "clean technologies" to be used instead of coal.
And he said: "This is a huge blow for ministers and their plans for new coal-fired power stations."
There has been no government response to the verdict.
Activists scaled Kingsnorth power station in Hoo in a protest over a coal-fired power plant
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