HOUSEHOLDERS face a hike of more than GBP170 in annual electricity bills to cover the massive subsidies shelled out to power firms for shifting to green energy sources over the next decade, experts have claimed.  Leading economists attacked the "excessive" GBP15 billion UK-wide payouts and warned they would lead to growing public anger, during a conference on the economics of renewables organised by The Scotsman.  The cost of the subsidies would be split between domestic and business customers, with households likely to pick up about a third of the outlay, amounting to an extra GBP170 a year on their bills.  The Scottish Government is committed to generating enough power to meet all of Scotland's electricity needs from renewable sources such as wind farms by 2020.  But energy minister Fergus Ewing told the conference yesterday Scotland's power supplies would always come from a "balanced mix" of sources.  Dr John Constable, director of the Renewable Energy Foundation, said that subsidy levels for renewable energy would be about GBP8bn by 2020, with grid management costs of about