Protesters against the Adani coalmine dressed as Bill Shorten and Scott Morrison. A poll has found 40% of voters are unsure which party has the best energy policy. Photograph: Lukas Coch/EPA

Australians remain overwhelmingly confused about national energy policy, with a new poll showing about 40% of voters are unsure which party has the best approach to affordability, reliability and emissions reduction.

With climate and energy policy a key campaign issue in the lead-up to the 18 May election, a poll from the Australia Institute shows that while Labor is slightly preferred for each category over the Coalition, more than one in three voters is unsure about who is best placed to address the vexed policy area.

On the question of which party has the best plan to reduce carbon emissions, 40% of the 1,536 people polled last month thought Labor’s policy was better, compared with just 22% who chose the Coalition. But 38% of voters remained unsure – only slightly down from the 40% of people who answered the same when the poll was last conducted two years ago.

When asked which party was best placed to reduce electricity prices, 37% said they were unsure, 34% nominated Labor, and 29% said the Coalition. This was the biggest shift compared to the 2017 poll, when only 24% thought the Coalition policies were better for lowering electricity prices.

On reliability, there was only a slight difference between the two major parties, with 33% saying Labor was best placed to provide the most reliable energy compared to 30% backing the Coalition. Again, almost 40% of voters did not know.

Richie Merzian, the Australia Institute’s climate and energy program director, said that while Labor was ahead on each metric, the furious debate over energy policy over the past decade had still left a large section of the community unsure.

“Crucially, the large number of voters who ‘don’t know’ which party has the best policies for energy reliability, prices and emissions suggests there’s still a lot of voters up for grabs with a little over two weeks of electioneering to go.

“Federal politics has been consumed for many years now by heated debate between the government and opposition about energy policy, including playing a role in bringing down a prime minister – or several.

“Yet surprisingly, all this energy debate has resulted in very little change in views about which major party’s energy policy they favour, with large parts of the community still unsure.”

Merzian said that the confusion came despite its research also showing that the number of Australians concerned about climate change was increasing, and seven in 10 Australians wanted a plan to shift to renewable energy.

The polling found that while Coalition and Labor party voters were more likely to nominate their own party as best placed to deal with each element of energy policy, Coalition voters were also more likely to choose Labor when asked which party’s policy would do better at reducing emissions.

Just over 40% of Coalition voters thought their side of politics had the best policies for reducing emissions, but almost 20% said Labor’s policy was better.

Among the high number of voters saying they did not know or were not sure which party was best placed overall to address the “trilemma” of emissions reduction, cost, and reliablity, those most likely to say they were unsure were One Nation voters, followed by Greens supporters and then the major parties.

The poll was conducted online by Dynata, and was a nationally representative sample adjusted by gender, age, state and territory, and household income.