The energy supplier Ovo is plotting the sale of a stake in its software arm at a 'unicorn' valuation as part of efforts to strengthen the balance sheet of Britain's fourth-largest residential gas and electricity group.Sky News has learnt that Ovo, which has just under four million retail customers, has appointed Arma Partners, the investment bank, to explore options for Kaluza. It replicates a move by larger rival Octopus Energy - revealed by Sky News - to hire advisers to work on a demerger of its Kraken s ...