Panel of MPs say connection charges are hampering the transmission of Scottish renewables across the UK.
Watchdog Ofgem says the increase has been driven by a rise of more than 50% in energy costs over the last six months.
The proposed site off the coast of Shetland could produce 132 million tonnes of CO2 emissions, Oxfam Scotland said.
The figures were revealed in a new review of the offshore energy sector in the UK produced by experts at Aberdeen’s Robert Gordon University.
Friends of the Earth Scotland, the Existing Homes Alliance and the Living Rent campaign group joined forces.