Federal Industry Minister Ian Macfarlane has moved to reassure wind farm operators and other energy providers that their investments under the Renewable Energy Target (RET) are safe.

The RET aims to achieve a 20 per cent target of renewable energy by 2020.

There are two targets within the scheme, a large-scale RET covering projects like hydro, solar and wind farms, and a small-scale RET covering rooftop solar panels and solar hot water heaters.

A recent review into the RET by businessman Dick Warburton found there was a "strong case for winding back" financial support for small-scale energy systems.

It also found that support for larger renewable energy projects should be either closed to new companies or scaled back.

The report sparked widespread concern among renewable energy operators that the Government would cut funding to the scheme and endanger planned projects.

Existing investors have nothing to fear: Macfarlane

Mr Macfarlane said the Government would not be taking action that affected existing investments.

"The Government will not make changes that will impact those who have already made an investment - small or large - under the RET," he said in a speech in Sydney.

"This means that regardless of what decisions are made about the RET, nothing will change for those who have installed rooftop solar, and large-scale investments such as wind farms or hydro power stations will be protected."

The RET review concluded that significant falls in the cost of solar panels and an increase in power prices meant that "the small-scale renewable energy industry is becoming commercially viable".

Mr Macfarlane said the RET's original aim of encouraging households to embrace solar panels had succeeded, with nearly 2 million homes installing them.

"That's certainly been achieved in spades," he said.

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The review also found that the installation of other small-scale systems had far exceeded expectations, with output already above levels forecast for 2020.

But the solar industry and its supporters say the review is biased and scrapping the subsidies will mean thousands of job losses.

Solar Council chief executive John Grimes warned of the political cost to the Government.

He said if 8,000 people in the solar industry lost their jobs, then Government backbenchers should fear for their own fate at the next election.

The review also found that:

renewable energy generation has almost doubled under the RET

renewable energy generation has almost doubled under the RET the RET is exerting some downward pressure on wholesale electricity prices

the RET is exerting some downward pressure on wholesale electricity prices the RET has delivered a "modest level" of reductions in greenhouse emissions but is a "high-cost approach" to delivering that aim

the RET has delivered a "modest level" of reductions in greenhouse emissions but is a "high-cost approach" to delivering that aim the RET will cost $22 billion in cross-subsidies if it is not changed

"In the presence of lower-cost alternatives [to reducing emissions], the costs imposed by the RET are not justifiable," the report states.

The Renewable Energy Target was first announced by the Howard government in 1997 to encourage investment in electricity produced from sources like solar and wind. A scheme to achieve this was first introduced in 2001.

In 2010 the Rudd government expanded the RET scheme to mandate 20 per cent of all electricity would come from renewable sources by 2020.

Greens leader Christine Milne has described the Warburton report as being full of "climate-denier drivel".

The Government is expected to make a decision on the future of the RET in coming weeks.