One of the reasons I agree with Dan, is that even if the goal of a Solar Smelter isn't achieved, the ideas we come up with could end up being the solution for a different problem. History is full of experiments that failed in their original purpose which got re-purposed into useful products/techniques. Too often there is pressure to "get the right answer" when in fact, learning from our mistakes is often the greater reality. That's why I really appreciate it when posters give us updates on things they try even when their update says - I'll never try this again!
There are a host of technical challenges with solar forges, kilns, and smelters. But there are solid reasons for permaculturalists to be interested in such designs.