A group of 15 investors, including several private equity and infrastructure funds, have launched a legal challenge to Spain's decision to cut solar energy subsidies. Last August's decision to retrospectively reduce tariffs is estimated to have cost investors tens of millions of euros.

The group of investors, who include Impax Asset Management and private equity firms Hudson Clean Energy Partners and HgCapital, are appealing the decision under the Energy Charter Treaty, a multilateral investment treaty designed to protect cross-border energy investments.