The centralized power tower is still being invested in:
More on trough systems:
close up view:
The heat exchanger:
Large arrays can be built to leverage abandoned cooling towers:
354 MW capacity located on 7 square km of desert in California
So thats about 50 MW per square km.
Expected unit capacities are a strong function of solar irradiance and adopted technology.
California is moving towards an agressive implementation of solar