The coalition has vowed to scrap the controversial means test for the $8,000 solar panel rebate if it wins the next election.
But opposition climate change spokesman Greg Hunt has conceded the coalition is powerless to act until then.
The government has stripped away the rebate from households earning more than $100,000, sparking outrage among environmental groups and panic in the solar panel industry.
Treasurer Wayne Swan showed no sign Sunday of relenting on the means test.
Mr Hunt said he would ditch the means test when he had the chance.
"We have categorically said that we would return the rebate and we would make sure it was non-means tested," he told Sky News.
"That's a clear, precise position."
Mr Hunt urged the government to change its mind on the rebate.
"This decision is ... a very bad decision for the environment and (the government) should categorically reverse it," he said.
The coalition could not seek to reverse the decision in the short term because it had been taken outside the parliament.
The government had signed an executive order to bring in the means test. It had not been done by legislation or an administrative decision reviewable by the parliament - which the coalition could have sought to block.
"There's nothing that can be done now," Mr Hunt said.
The rebate was introduced to boost the take-up of domestic solar power, and to commercialise the technology, which is expensive.
Opposition leader Brendan Nelson described the means test as "economic and environmental madness."
"How do you means test an environmental footprint?" he told ABC Television.
"I think that Mr (Kevin) Rudd needs to seriously re-examine this measure."
Mr Swan defended the means test, saying the solar rebate program was full so it made sense to means-test it.
"This (rebate) program was fully subscribed, one way of actually making it work responsibly was to means-test it," he told Channel Ten.
Mr Swan pointed to the means test already in place for solar hot water heaters.
"The previous government was means-testing a hot water solar rebate, we're simply means-testing this rebate, there's nothing exceptional about that," he said.
Mr Swan said there was a record amount of money in the budget to tackle climate change.
