NUCLEAR energy will be more expensive than most forms of renewable energy by 2020, according to the University of NSW energy expert Mark Diesendorf.

A paper by Dr Diesendorf, to be delivered at a solar industry conference in Canberra today, finds the cheapest renewable energy sources - including landfill gas, onshore wind, conventional geothermal and hydro - are already cost-competitive with conventional nuclear energy power plants.

By 2020 offshore wind farms, solar thermal and solar photovoltaic power are all projected to be less expensive than nuclear energy.

Dr Diesendorf, the deputy director of the Institute of Environmental Studies at the university, said the cost of building a nuclear power plant had risen rapidly since 2002, from $US2000 ($2075) per kilowatt hour of generation capacity installed to $US7400 per kilowatt this year.

The capital cost translates to US15¢ per kilowatt hour of electricity generated, which is projected to rise to about 20¢ per kilowatt hour over the next decade.

The figures do not include subsidies for nuclear energy such as loan guarantees, land acquired for buffer zones around reactors or decommissioning costs.

By comparison the study cites big falls in the capital cost of onshore wind power in 2009 - from $1900 per kilowatt to $1700 per kilowatt while the cost of solar photovoltaic power fell from $7000 per kilowatt to $5120.

Dr Diesendorf said longer lead times and higher borrowing costs made it harder for nuclear power to compete with renewables, even before factoring in waste disposal and nuclear proliferation.

Last week the federal government released relative cost projections for 2015 and 2030, compiled by the US Electric Power Research Institute.

While broadly consistent in estimating the cost of nuclear energy, the institute's figures were more optimistic about the potential competitiveness of carbon capture and storage and less optimistic about the potential of wind and solar.