Peter Atherton from Citigroup Global Markets told the
Economy, Energy and Tourism Committee
it was "pretty unlikely" Scotland would be able to get the investment needed to meet its renewables targets.
Mr Atherton was giving evidence on the Scottish government's renewable energy targets.
The Scottish government's target for 2011 was to meet 31% of the country's energy needs from renewables.
If consumption remains at the 2010 level, they will have accounted for 35% of electricity needs.
Energy Minister Fergus Ewing said "great progress" was being made towards the longer-term goal of meeting the equivalent of 100% of gross annual electricity demand from renewables by 2020.
Mr Atherton said Scotland would require £46bn of investment to meet its targets which would require all of the UK's investment in renewables which was "pretty unlikely".
He also said investing in renewable manufacturers would be a "terrible catastrophic investment" and the said the idea capital markets would double their exposure to renewables is "borderline fantasy".
Dr Maitland Mackie the chairman of Mackies told the committee there was "far too much negativity about wind farms" and investment in renewables had to be increased or "the world will come to an end".
Dr Mackie said 10,000 three Mega Watt Windmills could deliver all Scotland's electricity.
He later said Donald Trump, who gave evidence to the committee last month, was the "tremendous personification of arrogance and ignorance together on wind power".
Andrew Buglass from the Royal Bank of Scotland said his bank was the leading lender to the renewables sector last year and funding was available for "strong projects".
Mr Burglass did concede many banks struggled with investing in smaller renewable projects.
Paul Lewis from Scottish Enterprise said there would be enough finance to attain the renewable targets if the confidence in the markets was increased.