The UK has fallen to 14th on the list, after first dropping out of the top ten in September 2015.
For the first time Morocco is higher than the UK on the index. Australia, despite its strong anti-renewables lobby, and politically-troubled Brazil also remain above the UK.
In EY's previous report, released in May 2016, the UK was 13th on the list.
"Uncertainty caused by Brexit, the closure of the Department of Energy & Climate Change and the approval of Hinkley Point C all dealt a sizeable blow to the UK renewables sector," the report said.
The UK's position won't be helped following the support the government gave to extracting shale gas from a site in northern England, granted in early October.
"Some respite came when the Government approved 1.8GW Hornsea 2, which will be the world's largest offshore wind farm if completed as planned," the report added.
"Despite this progress on offshore wind, the UK's renewables sector faces an unknown future as the country negotiates its future relationship with the EU, and Prime Minister Theresa May's new administration comes to grips with a power sector in turmoil.
"For now the deepest and most easily deployable technologies of wind and solar seem to be absent from the Government's plans," EY said in its report.
The top five places to invest in renewable energy remains unchanged from EY's May report. The US leads from China, India, Chile and Germany.
The analysis firm said the US's position at the top of the rankings was at risk following November's presidential election.
Argentina continues to improve on its ranking. It was a new entry in EY's May report, placed immediately in 18th position. In EY's latest edition of the RECAI report, it improved to 16th.
"Argentina successfully completed a recent auction that saw bids for more than six times the capacity offered — not surprising given the Government's new focus on the power market," EY said. A second 400MW tender is planned for November.