The analysis by consultants Access Economics, on behalf of the Electrical Trades Union, found a national gross feed-in-tariff would be a far cheaper way to boost uptake of rooftop solar panels than existing policies.

The union's Victorian secretary Dean Mighell said twice as many solar units would have been installed if the $1 billion spent on rebates was funnelled into a premium subsidy.

A national tariff has been backed by retailer Woolworths and the Property Council of Australia.

The states have already introduced tariff schemes, although they vary in design. In Victoria, for example, the government opted for a net tariff that pays households for electricity fed into the grid only. A gross scheme pays a premium for energy whether it is fed into the grid or used at home.

The analysis found a national gross tariff could push rooftop solar power to a capacity of 1000 megawatts - roughly equivalent to the Latrobe Valley's Loy Yang B coal-fired power station - within 20 years. It would cost $4.47 billion and put solar photovoltaic units on 650,000 homes. The $1 billion spent on rebates over the 18-month period to June installed 67,452 rooftop solar units.

Climate Change Minister Penny Wong backed the government's rebate scheme over a national tariff.

A ministerial spokeswoman said: ''It takes longer for households to recoup the cost of their solar panels and other technologies through a feed-in tariff.''