An audit has found that EU-funded energy efficiency projects are not cost-effective in EU member states.
The projects examined by the Court of Auditors were in the Czech Republic, Italy and Lithuania. Those countries received the most EU funding for such projects in 2007-2013.
National authorities used the funds to refurbish buildings, but the spending would not be recouped for 50 years on average, the report said.
That time scale was "far too long".
In some cases the savings would not appear for up to 150 years. Such a delay would go beyond the expected lifetime of the buildings concerned.