Taxpayers are is paying companies for emissions reduction projects that may not need government help, a new analysis shows.

This means much of the $1.7 billion Direct Action program had been spent ineffectively and emissions reduced by less than anticipated, ANU climate economist Paul Burke says.

"Unfortunately, projects that would have gone ahead even without a subsidy - 'anyway' projects - have a cost advantage that makes them well placed to win the auctions," he said on Monday.