The subsidy for solar power is to be cut in half for new installations from 12 December of this year, the government has said.
Solar panel makers and installers say the cut will cost thousands of jobs.
It also means consumers who register for the scheme after that date - even if they have already paid a deposit - will see their return halved.
The government has launched a fast-track consultation on the change, but says it reflects falling panel prices.
The new tariff of 21 pence, down from the current 43p, will take effect from 1 April and be paid to anyone who installed their solar system after 12 December.
Speaking in an emergency debate at the House of Commons, Climate Change Minister Gregory Barker said the government risked running out of money by next year.