Scientists revealed that 1.2% of the Sahara desert is sufficient to cover all of the energy needs of the world in solar energy.
The total world energy usage (coal+oil+hydroelectric+nuclear+renewable) was 13,000 Million Ton Oil Equivalent (13,000 MTOE). This translates to 17.3 Terawatts of continuous power during the year.
Now, if we cover an area of the Earth 335 kilometers by 335 kilometers with solar panels, even with moderate efficiencies achievable easily today, it will provide more than 17,4 TW power. This area is 43,000 square miles. The Great Saharan Desert in Africa is 3.6 million square miles and is prime for solar power (more than twelve hours per day).
That means 1.2% of the Sahara desert is sufficient to cover all of the energy needs of the world in solar energy. There is no way coal, oil, wind, geothermal or nuclear can compete with this. The cost of the project will be about five trillion dollars, one time cost at today's prices without any economy of scale savings. That is less than the bail-out cost of banks by Obama in the last recession. Easier to imagine the cost is 1/4 of US national debt, and equal to 10% of the world's one-year GDP.
So this cost is rather small compared to other spending in the world. There is no future in other energy forms. In twenty to thirty years solar will replace everything. There will still be the need for liquid fuels but likely it will be hydrogen produced by the electrolysis of water and that powered by solar. Then tankers and pipelines will haul that hydrogen around the world. One can also envision zirconium or titanium batteries that store large quantities of hydrogen.