A £10m drive to add wind turbines to public sites and to promote renewable energy is being funded by cuts to other green projects, it has been claimed.
The scheme will promote renewal energy on public sites
The Partnership for Renewables scheme will work with private firms to put the turbines on sites such as hospitals.
But the Lib Dems and the Energy Saving Trust say money from insulation and double-glazing schemes will pay for it.
The Department of Environment, Food and Rural Affairs (Defra) said the sum was never allocated to a specific project.
At the Labour conference, Environment Secretary David Miliband promised £10m to help fund projects such as wind power.
Mr Miliband said similar schemes on local authority land were being held back, because public and private investors were not working together.
But a spokesman for the government-funded Energy Saving Trust said it was disappointed to discover it was not an extra £10m, but part of money already announced in the budget.
"On three separate occasions, the government outlined that the £20m would be spent on energy efficiency programmes directed at the home owner," he said.
"But it would appear that £10m of it is now being reallocated to the Partnership for Renewables."
He added: "Whilst we recognise that local authorities have a potential role in promoting large renewable energy, it is proven that the biggest impact they can have is through promoting energy efficiency in the home.
"This is the most effective hierarchy. Make homes energy efficient first and then look to renewable energy."
BBC environment correspondent Sarah Mukherjee said industry experts had gone even further in their criticism of the cuts.
They claim there is little point putting wind farms up in hospitals when they are providing energy that will be wasted in badly-insulated buildings, our correspondent said.
Liberal Democrat energy spokesman David Howarth accused the government of "robbing Peter to pay Paul".
He added: "This is outrageous. Both energy efficiency and greater use of renewables are crucial to combating climate change."
A Defra spokeswoman said the money had not previously been allocated to any specific scheme.
She added: "Energy efficiency is an integral element of the UK's strong domestic programme to tackle climate change.
"Around 10 million British households have benefited from energy saving measures as part of the first phase of the Energy Efficiency Commitment, which will help to reduce fuel bills."