 German utility firm RWE npower renewables has withdrawn its backing for the world s largest  wave farm , throwing the future of the 4MW facility in doubt, the Sunday Herald can reveal.  RWE npower renewables s decision to abandon the project at Siadar Bay off the north coast of Isle of Lewis leaves Inverness firm Wavegen, developers of the world s first commercial-scale wave energy device the Limpet, seeking a new developer or owner of the projected  ?30 million Hebridean scheme.  a Wavegen statement confirmed that RWE would  not proceed  with Siadar, adding we are in discussion with a number of parties in order to seek an owner and investor in the plant ... work on the civil engineering solutions is ongoing .  The Siadar project was the first of its type to be approved in 2009 and was originally scheduled to open this year. The project has been allocated a conditional ?6m grant from the Scottish Government.  While npower s withdrawal is understood to be linked to an  internal review  by its heavily-indebted parent company based in Essen, senior marine energy sources see the setback as symptomatic of wider funding, commercialisation and grid-connection problems in the emerging marine power sector, where Scotland has strong claims to lead the world.  Recent setbacks include Edinburgh-based company Pelamis Wave Power s decision in May to cut around 20 jobs at its Leith manufacturing plant, blaming the  shift ... from the completion of a manufacturing focus to an operational phase . In april the Crown Estate reopened tendering for a wind and tidal development zone in the Pentland Firth when ?300m plans by Singapore s atlantis Resources foundered after Norway s Statkraft pulled out of the joint venture to deploy deep-water tidal turbines.  The costs of developing wave and tidal power remain formidable obstacles to the sector, which is not expected to deliver substantial power to the grid until an indeterminate date after 2020. Most projects require ?30-50m to take a paper concept to full scale. although there is a plethora of ingenious devices in development in Scotttish waters, where incentives are more generous than in the rest of the UK, even the first 5-10MW  arrays  will  require large capital grants and five renewables obligation certificates (ROCs    the tokens used to subsidise the production of renewable power) to be viable.  Niall Stuart, chief executive of trade group Scottish Renewables, said:  The decision on the Siadar project looks more like a refocusing of operations by R 