From the article by Bridgette Meinhold at inhabitat:
BrightSource is holding a competition to come up with designs for the solar towers and Zurich-based RAFAA Architectue & Design in collaboration with engineering consultant, Schlaich, Bergermann und Partner have submitted two different concepts. While conceptualizing the different options, RAFAA sought to achieve high performances and efficiencies in terms of structural integrity, material usage and sustainability. Option A is a constructed of modular precast concrete or slip-form parts that would be transported and then assembled on site. Inspiration for the design came from light waves wrapped into a helix to form a column with diamond holes cut into the towers for aesthetic and structural purposes.
This first option seems to answer to a set of parameters that BrightSource was seeking in their request for proposals, however RAFAA feels in the long run, lightweight steel would provide a better solution both economically and sustainably than concrete. Therefore, they also came up with Option B, a square tower with a twist in the middle constructed of prefabricated 40-ft long steel elements. RAFAA proposes that steel is more sustainable in the long run because it would create a smaller construction footprint causing less damage to the environment. The solar tower can always be dismantled and moved to a new location or sold to another company when it is time to upgrade or the material can be recycled at the end of its life whereas concrete cannot. Either way, in the end we’ll have some design-worthy towers supporting the new solar plants in the Mojave.