The Government has been accused of "killing" jobs after two clean energy firms went into administration, hitting around 1,000 workers.
Home insulation firm the Mark Group and energy efficiency firm Climate Energy went into administration within hours of each other.
More than 900 jobs will be lost at Leicester-based Mark Group, which has cancelled all surveys and installations.
A skeleton staff has been retained by administrators.
Climate Energy, a provider of "energy efficiency solutions", posted a notice on its website saying it has gone into administration.
Greenpeace said Government policies were killing jobs.
Its UK chief scientist Dr Doug Parr said: "For all his rhetoric about building, it's not scaffolding George Osborne is bringing to Britain's clean energy sector but a wrecking ball.
"Evidence is growing that the Chancellor's policies are putting people out of jobs, damaging investment, and harming one of the country's most promising industries.
"This should be a wake-up call for David Cameron, who faces international embarrassment ahead of crucial climate talks. As Prime Minister, he has a duty to leave internal party politics aside and rein back a rogue Chancellor who's putting investment, jobs, and growth at risk."
Friends of the Earth energy campaigner Alasdair Cameron said: "These huge job losses are likely to be the first of many as Government attacks on efforts to build a low-carbon economy begin to bite.
"Government policy threatens over 20,000 UK solar jobs - with many more at risk in other green sectors.
"It seems the Treasury is happier to give sky-high subsidies to Chinese nuclear power than support British solar.
"The renewable energy industry around the world is booming and costs are falling rapidly but the UK government seems to be stuck in the wrong century."