This is definitely an engineering project that has an optimum size - both from an economical and efficiency standpoint. There are also other factors that can place upper or lower limits on machines or structures. An example is the height of skyscrapers being limited by lift technology and design. The Twin Towers for example were limited to 80 floors because of the large number of lifts required to service the floors. A new lift design system enable the buildings to reach 110 floors. They also had to make very light but strong metal truss flooring covered with 100mm concrete slabs.
I have had some experience with scale up in engineering projects and the difficulty of scaling up depends on what you are scaling. Mixing efficiency for example is a classic problem. If you mix two fluids in a test rube by shaking it with your hands, that mixing efficiency cannot be replicated on a large scale. There have been many failed engineering projects that were purely based upon laboratory scale results with no pilot or demonstration plants built in between the full scale production plant. Often, poor mass or heat transfer on scale up makes the full scale plant totally inefficient.
As I said my main engineering concerns with the initial proposal was the 1km high central concrete tower - nothing to compare this structure to. The original design was scaled back to tower heights comparable to already existing concrete structures around the world, so should present any problems from a structural or construction point of view.
The dimensions of the pilot plant constructed in Manzanares, Spain in the 1980s are Tower Height = 194m, Tower diameter = 10m, Collector Diameter = 240m.
Having said that, a working demonstration plant that is perhaps 5 to 10 times as large as the Manzanares plant and is near identical in design with the proposed full scale plant would have been great to generate efficiency data and identify any other problems. Also great for promoting the concept to potential nations or corporations who want to pursue it as a renewable and clean power source.
(incidentally, I know of small scale plants that produce minute quantities of product - either chemical or pharmaceutical products - and the entire plant can fit into a small room, and produces about 20 kg of product per year. But at $950,000/kg the returns can be pretty good. The most expensive material that I know of is anti matter coming in at over 50 trillion dollars per gram - whatever you do don't let it come into contact with anything - anything at all)
