Land estimate in more realistic round numbers than other soures will use:
World Power requirement: 20 TW
Average annual solar irradiance: 1200 watts per square meter
Average annual PV efficiency in hot, sandy, desert environment: - 3%
1200 * 3% = 40 watts per square meter.
40 Watts * x = 20 TW; x= 5e11 square meters = 500,000 sq km = 700 x 700 km (or 10 7x7 km facilities)
Sahara Desert is 10 million square km (9.4 million to be more precise) so this is 5% covering factor. More optimistic models get covering factors as low as 1% but so what,
its still potentially feasible.
The
Desertec Plan (800M Euros)
Production plus Transmission
100 GW of Exportable solar power by 2050
But by then the world, at current growth rate, will need about 10,000 GW