Concentrating Solar Power (NOT photovoltaics) can provide both electricity and desalination.
Every year, each square kilometre of hot desert receives solar energy equivalent to 1.5 million barrels of oil. Multiplying by the area of deserts world-wide, this is nearly a thousand times the entire current energy consumption of the world.
The cost of collecting solar thermal energy equivalent to one barrel of oil is about US$50 right now (already less than the current world price) and is likely to come down to around US$20 in future.
An area of the Sahara of 254 km × 254 km would generate the equivalent of the entire current world demand for electricity.
Waste heat from electricity generation in a CSP plant can be used to create fresh water by desalination of sea water: a very useful by-product in arid regions.
A CSP plant in California has been supplying electricity to around 500,000 people since 1985.
A recent report from the American Solar Energy Society says that CSP plants in the south western states of the US "could provide nearly 7,000 GW of capacity, or about seven times the current total US electric capacity".
The technology is relatively simple and robust, and apart from the energy used in construction, is totally carbon-free. The fuel never runs out (unlike uranium, coal, gas)
see
www.trec-uk.org.uk for much more detail.