Hospitals, schools and prisons will be expected to generate some of their own energy if the Liberal Democrats win power in the Scottish election.
Nicol Stephen wants to see a "green energy revolution"
Lib Dem leader Nicol Stephen also said Scottish Executive buildings would be made carbon neutral by 2011.
Speaking the day after Labour leader Jack McConnell pledged to cut his short-haul flights by 50%, Mr Stephen also promised to reduce his flights.
The Scottish Greens accused Mr Stephen of "electoral gimmicks and games".
However, Mr Stephen said he took the need to reduce Scotland's carbon footprint "very seriously".
"I am committed to ending the use of flights from Edinburgh or Glasgow to London for executive business in all but the most exceptional circumstances," he said.
The deputy first minister added that the public sector would be tasked with becoming leaders in both energy efficiency and the green energy revolution.
"Hospitals, schools, prisons, offices, leisure centres - all can set an example by generating this energy on-site and going carbon neutral," he said.
"I want to see them generate at least a fifth of their own energy needs on-site by 2020."
Businesses or homes which offset the carbon emissions they produce, by planting trees for example, are described as being carbon neutral.
The pledges are to form part of the Lib Dem Scottish election manifesto.
Green MSP Shiona Baird said: "There are major problems which aren't being addressed by the piecemeal approach of the Labour/Lib Dem executive.
"Today we get another green promise - tomorrow it will be a climate-wrecking promise in the shape of bigger roads and bigger airports."
The SNP also criticised the coalition for showing "little commitment" to energy efficiency during its eight years in power.
SNP energy spokesman Richard Lochhead MSP said: "The executive first announced that they would produce an energy efficiency strategy in December 2004 yet we are still waiting for it.
"Labour and the Lib Dems have been sleeping on the job as global warming continues to get worse."