The West Australian government has made a massive backflip to abandon its decision to halve a solar tariff rate for residents, only four days after announcing it.

The plan to cut the rate from 40c per kilowatt hour to 20c for homes that funnel surplus power back into the grid was announced in the state budget on Thursday and was expected to save $51 million.

But, after an overwhelming backlash from households and from within the WA Liberal party, Premier Colin Barnett announced on Monday that state cabinet had agreed to reverse the decision.

"Quite simply, we got this decision wrong and we have to fix it," Mr Barnett said.

"We have listened, and we appreciate the commitment that many people have made to take up renewable energy, like solar power.

"We understand that this measure would have had an unfair impact on one section of the community and it has to be reversed."

Treasurer Troy Buswell had only moments earlier told journalists there was no chance the decision would be reversed.

The program, introduced in 2009, was such a success the Liberal government admitted in 2011 the take-up cap had been breached, costing it some $46 million more than planned.

The opposition was to hold a rally outside parliament, protesting against the move to halve the tariff, on Tuesday.

"Honestly, how bad is the Barnett government - complete, utter turmoil," WA Labor leader Mark McGowan tweeted.

The decision also brought on an internal backlash, with Southern River MLA Peter Abetz labelling the move unethical while maverick Hillarys MLA Rob Johnson threatened to cross the floor for the first time in his 20 year political career.

Mr Johnson said his constituents were irate after the government's annoucement last Thursday to ditch its original 40c deal.

"People feel they have been absolutely dudded by the government," he told ABC radio on Monday.

"And I can't help but agree with them."

Some 18 Liberal MPs had met over the weekend to discuss the matter and all had made comments of disgust, he said.

"We should never renege on a contract with the people. It is disgraceful that we should even contemplate that.

"People have been misled in general terms on many areas, but this one is a very serious one because it affects people and their ability to spend their money.

"I won't have a bar of it."

Political analyst Peter Kennedy said the decade-long tariff promise to 75,000 WA households that feed excess power into the grid could have sparked a voter backlash against the Liberal party at the September 7 federal election, potentially representing 150,000 voters.

Mr Buswell denied the reversal was embarrassing or that he'd been hung out to dry.

"I have a job to do in government ... protecting the finances of the state," he told reporters.

"It's not always going to mean that you're the most popular person in town."