I wrote recently that it’s impossible to predict the ROI associated with solar thermal (aka concentrated solar power or CSP).
What I was referring to was utility-scale CSP. Personally, I think the future will hold significant reductions in costs and improvements in effectiveness, making this technology quite workable at the multi-megawatt scale. It’s certainly not there now, but we need to keep in mind that it’s a fairly new technology, whose R&D lags PV and wind by several decades.
So what’s the ROI? It’s a function of many variables, starting with the rate of improvement discussed above, but even more important is the cost of competitive energy solutions. Think of all the things that could transpire during the time in which a CSP plant is contemplated, designed, permitted, built, grid-tied, and operational:
Wars and natural events could change (likely reduce) the availability of oil
News about the safety of fracking could change (likely increase) the price of natural gas
Fukushima-like disasters could cause a permanent moratorium on nuclear
Note, however, that most of this uncertainty militates in the direction of an investment in CSP, or some other form of clean energy. Its cost can only come down, while the price of energy, even in the absence of a large, unforeseeable event, is likely to rise as traditional sources are exhausted and the population of energy-consumers skyrockets over the coming decades.