Optimal arrangement of solar array mirrors based on Fibonacci spirals.

In the Spanish region of Andalucía, there are several concentrated solar plants that from the air look amazingly like the floral heads of sunflowers. This is no artistic or random arrangement, but a highly practical one. The hundreds of heliostats, or mirrors, rotate with the sun to reflect concentrated sunlight toward a central tower, where water is heated to steam, which drives a turbine that produces electricity. However, having this many heliostats takes up a lot of space unless they are optimally arranged.Researcher Alexander Mitsos, the Rockwell International assistant professor of mechanical engineering, at the Massachusetts Institute of Technology, and colleagues who wanted to optimize the placement of heliostats. Early attempts to put spaces between the mirrors and staggered them resulted in some mirrors shading parts of others. They then used numerical optimization for the placement of the heliostats. They brought the fanned-out layout closer together, building a spiral-like pattern that reduced land by ten percent without affecting efficiency. At that point, they decided to look to nature to see if they could further optimize the pattern. The florets of a sunflower are arranged in a stunning spiral fashion; each floret is turned at a “golden angle” of about 137 degrees with respect to its neighbor. When the researchers twisted each mirror to be 137 degrees relative to its neighbor, their tests showed that the optimized layout took up 20 percent less space than the current layout of the PS10 solar plant in Spain, and even increased total efficiency.

Key Differentiators

The improved layout takes up 20% less land and is more efficient than the current design.

Biomimicry Story

The photo shows the Gemasolar plant, which is also in Andalucía. Although there’s no indication it has used the newly proposed layout, it appears like it is close to being optimized.Sources:Heliostat field optimization: A new computationally efficient model and biomimetic layout MIT research: A new sunflower-inspired pattern increases concentrated solar efficiency

Challenges Solved

Current concentrated solar plants take up a lot of room and are inefficient due to mutual shading by the mirrors.