Mr Ewing made the comments at the International Tidal Energy Summit in London.
He described the Secretary of State's approach to energy policy as "inconsistent, incoherent and ineffectual" as the UK Government continues to "increase bills and weaken security of supply".
"Inconsistent, as the approach is to build new capacity at the lowest cost and let the market decide which technologies prevail, but skews incentives towards more gas and nuclear power," he said.
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"Incoherent, as it rules out support for proven, cheap technologies like onshore wind and solar.
"And it will be ineffectual - we urgently need to tackle the parlous state of affairs that has allowed the capacity margin to dwindle to one per cent, yet there are still delays to bringing on new capacity, including the development of renewables in Scotland."
Mr Ewing added energy capacity margins will continue to get worse when the Longannet power station, Scotland's largest power facility, closes early next year due to "unfair" transmission charges.
"The UK Government must change its course to provide more certainty for investment in new technologies and ensuring the next capacity market auction does more to bring new, clean power generation forward," he concluded.
(LM/CD)
