After closing its household insulation program and phasing out its green loans scheme, the government will soon announce major changes to the RET, which was supposed to encourage new large-scale renewable projects but has led to billions of dollars of investment being put on hold.

The RET was supposed to ensure that 20 per cent of Australia's energy was sourced from renewables by 2020 by requiring big energy consumers to buy certificates on a new green energy market.

But the price of the certificates plummeted below the amount required for the financial viability of wind farms and other large-scale projects, partly because the government used the scheme to reward households installing rooftop solar panels after the cost of its $8000 solar rebate program blew out.

The range of federal and state subsidies for rooftop solar and solar hot water heaters also contributed to the market being flooded with cheap certificates from domestic technologies.

New wind-farm investments were put on hold, work was stopped on projects that had already started and wind turbine maker Keppel Prince Engineering warned it would have to sack 150 workers as soon as this week.

With the government determined to avoid another environmental program disaster and more politically damaging job losses, it is now actively considering several options to fix the problem with an announcement said to be ''imminent''.

One is to make the 20 per cent target applicable only to the large-scale plants, with certificates from domestic technologies added on top.

Another option that has considerable support in cabinet is to set up a separate market for certificates from domestic technologies, so the market won't again be blind-sided if state or local governments offer yet more subsidies to households.

AGL is one of the major companies with huge investment projects at risk. It is due to deliver its profit results today.

The Clean Energy Council says that without significant changes there will be no major renewable energy investment in Australia for at least seven years.

Any changes would have to pass the Senate, where the Greens have already proposed amendments and the Coalition has said it is willing to negotiate to fix the scheme.