 The estimates of remaining non-renewable worldwide energy resources vary, with the remaining fossil fuels totaling an estimated 0.4  yottajoule (YJ) or 4 × 1023 joules, and the available nuclear fuel such as uranium exceeding 2.5 YJ.Fossil fuels range from 0.6 to 3 YJ if estimates of reserves of methane clathrates are accurate and become technically extractable.The total power flux from the sun intercepting the Earth is 5.5 YJ per year, though not all of this is available for human consumption.