An advertising campaign to spruik the federal government's energy policy reforms cost taxpayers more than $9.4 million, before the coalition dumped its signature plan.

Answers provided to the Senate reveal the money was spent on the "Powering Forward" advertising campaign last financial year, promoting the National Energy Guarantee plan as a way of making energy more reliable and sustainable.

The energy plan was central to August's leadership spill which saw Malcolm Turnbull knifed as prime minister, with the conservative faction of the Liberal Party concerned over legislating emissions targets.