Renewable energy will meet only 10% of the UK's power needs by 2020 - half the government's target - according to a report from a government-funded group.
Renewable targets were 'deliberately ambitious'
The Carbon Trust said official policies and high costs for wind, solar and other forms of renewable energy were hampering the sector's growth.
A Department of Trade and Industry spokesman said targets were "deliberately ambitious".
Last year renewables reached 4% of energy for the first time, he added.
However, the Carbon Trust said it was still possible renewables could meet almost 20% of energy needs by 2020, with offshore wind power looking a particular good prospect.
It called for greater support of renewable energy and renewable technologies.
"Renewable energy needs a better support framework in place to bring down costs," said trust chief executive Tom Delay.
"If we get the right framework in place we can reap the benefits of reduced carbon emissions and strengthened energy security."
The report said that if the UK gave wave energy better support it could develop an export industry worth up to £4bn a year by 2050.
The DTI spokesman said wind energy had shown the largest increase last year.
"There are now more than 1,500 wind turbines in 125 locations producing enough power for almost 900,000 homes. That is far from a failed policy."
He added: "The forthcoming Energy Review is focused on low carbon energy and will reinforce our strong support for renewables as vital to reducing our carbon emissions and diversifying our energy mix."
The Carbon Trust works with business and the public sector to reduce their carbon emissions.