The Spanish investor Asterion is the new owner of the German energy company Steag, with the purchase finalized on Friday, Steag GmbH said. The takeover of what was once Germany’s largest coal-fired power producer was announced in August. Asterion announced at the time that it wanted to develop Steag as a whole into a sustainable energy supplier. The price quoted for the takeover was €2.6 billion ($2.87 billion). Since 2011, the municipal utilities of the German cities of Dortmund, Duisburg, Bochum, Essen, Oberhausen and Dinslaken have owned various shares in the holding company Steag GmbH. The…