MILANO, Dec 27 (Reuters) - Italian regional utility A2A said on Monday it had agreed to buy a majority stake in north-eastern peer Volta Green Energy, adding the deal would more than double its 300 megawatts (MW) of solar and wind assets. A2A said the binding accord for Trento-based Volta Green Energy brought in a pipeline of wind and photovoltaic projects with an expected installed capacity of around 800 MW, some of which were already under way or had been approved by local authorities.