Australian Broadcasting Corporation: The Australian and United States governments have pledged to make solar energy cheaper in the next five years. The Federal Government is investing $50 million on joint solar power research projects with the US, to cut the cost of the technology to that of conventional power sources. The US secretary of state, Hillary Clinton, says solar energy should be more affordable by 2015. “We have a common goal of making solar energy competitive with conventional sources by the middle of this decade,…