DELEGaTES clashed on the subject of power bills, with one contributor claiming policies on renewable energy and climate change would continue to have a disproportionate impact on the most vulnerable in society.  However, Professor Tony Mackay's claim was rejected by both Fergus Ewing and David Wilson, director of energy and climate change in the Scottish Government. Wilson said additional costs to consumers were offset by the benefits, especially in terms of energy efficiency.  Mackay quoted a 2010 report by the Department for Energy and Climate Change which suggested the impact of renewable energy and climate change policies added 14 per cent to the costs of generation by 2010, but that this would rise to 26 per cent by 2015 and 33 per cent by 2020, raising the cost per megawatt hour by GBP40.  This meant renewable energy policies added about 5 per cent to domestic energy prices in 2010, predicted to rise to 19 per cent by 2020. There would be a greater impact on non-domestic users from these policies, Mackay added - up an average 26 per cent. But he said his biggest concern was the impact on the poorest communities in Scotland: "The impact will be greater for those on the lowest incomes, and as far as Scotland is concerned, that is a very serious issue."  Energy bills are alrea