The Stirling cycle engine post reminded me of these solar furnaces. Under the right conditions they can produce a great deal of heat without much in the way of complicated machinery. A few generate enough heat to melt steel, and smaller versions can be used for cooking or heating water.
I don't know how feasible that really is, given that you still need workers to do the smelting part, and workers tend to not want to live in the desert, not to mention that the desert seems to actively be trying to kill your workforce. I seem to remember that Morocco and Algeria had big plans for a massive solar panel project in their respective parts of the Sahara, but I haven't heard about those projects in a while, so they might have gotten shelved in favour of something a little less ambitious.