Exclusive: Firms say added costs would mean they are unable to install enough turbines to meet green energy goals

Offshore windfarm companies may be exempted from new UK nature rules in an attempt to keep down the cost of renewable energy, the Guardian has learned.

The energy firms have said they would be unable to build the vast number of turbines required to meet the government’s green electricity goals if they have to meet new rules for nationally significant infrastructure projects (Nsips).

The energy secretary, Ed Miliband, is trying to find ways to reduce the cost of building offshore wind projects to avoid an increase in energy bills, according to sources in his department. Inflation and labour and materials costs are making it expensive to build the projects, while the grid upgrade required to carry the extra electricity is also adding to costs.

Under new planning rules from the Department for Environment, Food and Rural Affairs (Defra)expected to be brought in May, all Nsips such as nuclear power plants, airports and road schemes will have to enhance nature when new projects are built, or when existing infrastructure is expanded.