Ireland has emerged as one of a handful of smaller European countries not to commit to double public investment in green energy R&D by next year, under an international collaboration called Mission Innovation.
To date, 24 countries, including smaller European nations such as Austria and Denmark, as well as the EU itself, have signed up to the target.
Even larger countries often regarded as climate change laggards, such as Brazil, the US and Saudi Arabia, have committed to the target.
Ireland missed its EU carbon emissions target this week, and the Government may need to spend up to €150m on carbon credits, which pay companies or other countries to reduce their emissions instead. Opposition TDs rounded on Climate Action Minister Richard Bruton's department for not signing up to Mission Innovation.
Green Party leader Eamon Ryan said: "This is a prime example of how they are missing out on the economic opportunities that will come from the clean energy revolution. We have all the ingredients to become a leader, including public support for action, real expertise in the area and abundant renewable energy resources."
He added: "We are small enough to be agile in trialling new energy solutions and yet big enough to provide proof of concept. Not being part of Mission Innovation is sending a clear signal that we are not at the races."
Fianna Fáil's James Lawless added: "I can see no good reason for the Government not signing up to the initiative. Minister Bruton has stalled on the issue, and the Government aren't even close to meeting their own target of spending 2.5pc of GDP on R&D."
A spokesman for Mr Bruton's department said: "The benefits to Ireland from joining the Mission Innovation initiative are currently under consideration, in consultation with countries who have developed some experience of it to date.
"Ireland has strong connections with energy research and innovation, through participation in the EU Strategic Energy Technology Plan and other such programmes."