 THE Scottish National Party s energy policy could be either its trump card or its achilles heel. Perhaps the most eye-catching pledge in the last SNP manifesto was to generate 100% of Scotland s electricity from renewable sources by 2020. To achieve that ambitious target would require a massive ramping-up of wind, wave and tidal power in the next nine years, especially when low-carbon nuclear generation is due to be wound down. Of course, it does not mean that no oil, gas or coal will be burned in Scotland by the end of the decade. Rather, that it will be balanced by the amount of surplus renewable energy Scotland is able to export. at least, that is the theory.  With the opposition parties in disarray since the Holyrood elections, there has been remarkably little detailed scrutiny of the Nationalist dream of turning Scotland into the Saudi arabia of renewables. Politically, there is a reluctance to fall into the trap of appearing to be anti-Scottish for daring to question whether this grandiose ambition was anything more than pie in the sky. as a result, the Scottish Government has not been under any significant pressure to explain exactly how it would pull off this remarkable feat. and so two reports this week, both from respected sources, both questioning the viability of the Scottish renewables target, make interesting reading.  Yesterday the Institution of Mechanical Engineers claimed the SNP s energy policy could turn Scotland into a net importer of energy and increase fuel poverty. and rather than shrinking the country s carbon emissions, they could increase, especially if the wind does not blow and, without nuclear power, Scotland is forced to import power from non-renewable sources. The Herald has deployed a similar argument over several years and supports the retention of nuclear as part of the energy mix. The institution also claims around two-thirds of households are opposed to the closure and non-replacement of nuclear stations, if it means having to  