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 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.