The Labour Party has questioned the logic of the government’s changes to solar support warning that it will curb large-scale PV growth without stimulating the commercial sector.

The government has opened a consultation on a proposal that would remove PV plants above 5MW in size from the renewable obligation (RO) and move them into the new contracts for difference (CfD) scheme. Solar was set to join the CfD in 2017. It will compete with onshore wind for support under the CfD mechanism with bidding to begin later this year. At the same time, it is seeking to boost the country’s nascent commercial rooftop sector.

In oral questions in parliament on Thursday, Labour’s Michael Connarty MP said the proposed changes would not work.

“The analysis is that the reduction of the renewables obligation for projects above 5MW will result in the loss of 30% of the planned build – 1.3 GW will disappear. The regression tariff on roof-mounted solar above 50 kW will probably not encourage people with large roofs to make the investment that the minister wants. That will damage the carbon promise that we made and people who want to use solar,” he said.

Climate change minister Greg Barker responded by reiterating the government’s desire to curb large ground-mounted PV project development.

“The hon. Gentleman is obviously a fan of indiscriminately building field-based solar. We have been very clear in our solar strategy that we want the focus for growth to be on roof-mounted systems and on-site generation,” said Barker.

“The fact is that all technologies will transfer from the renewables obligation to CfD, and solar is simply at the front of the queue.”

The UK has become Europe’s largest solar market overtaking Germany. The success of large-scale solar farms has driven this growth in the past two years. The government is now acting to slow that growth with changes the industry has called “unjust” and “needlessly damaging”.

Shadow DECC minister Julie Elliott asked whether Barker’s long-touted ambition for the UK to reach 20GW of installed solar capacity was still credible given the new changes.

“I have been very clear that we will reach my ambition of having 20GW of solar, which is absolutely credible, only if we drive down to zero subsidy,” said Barker.

“We will not get there if we are still relying on subsidy by the end of this decade. We are working with the industry to drive down the cost even further and eliminate subsidy altogether, with a focus on rooftop and on-site generation,” he said.