How a sunflower & big data inspired solar plant design

Scientists, such as those in the biofuel field, have been turning to nature for ideas to advance research. Now solar can benefit from that, too. Researchers at the Massachusetts Institute of Technology saw ingenuity in the sunflower’s petal arrangement and came up with a design for solar power plants that minimize land use and increase energy output.
The MIT research, published in the journal Solar Energy, focuses on the placement of the mirrors  installed on the ground and radiating out from a central tower. The sunlight is reflected by the mirrors and concentrated on the tower that boils water or other liquids to produce steam; then the steam runs a turbine and generator and produces electricity.
This type of solar power plant technology is called concentrating solar thermal, and some of the best known companies in the space include BrightSource Energy in California, and Torresol Energy and Abengoa Solar, both in Spain. In fact, MIT scientists used Abengoa’s PS10 power plant in Seville to show how the design works.
The design of the mirrors and their placement are both critical for determining how efficient the power plant can be in converting sunlight into electricity. Efficiency is related to the temperature of the steam; you want to achieve higher temperatures to boost efficiency. To do so requires optics that can concentrate sunlight well and beam it without obstruction to the boiler atop the tower.
Reducing the land use without sacrificing power production is also a sought-after goal by power plant developers. The use of land and other resources such as water have been a sticking point for environmental and community groups who oppose some of the large-scale solar projects in the American southwest. BrightSource announced a new power plant design last August that aimed to use land more efficiently.

Big data and computer modeling

The MIT research involved computer modeling that hones in on the layout of the mirror to minimize shading or other issues that diminish the mirrors’ ability to concentrate and beam the light in precise angles. The model used these factors to calculate how the mirrors’ placement affected the power production of PS10 each day.
The researchers then looked for patterns that could improve the mirrors’ optical efficiency and settled on the spiral layout of the florets in the center of a sunflower. Each of the florets is oriented toward its neighbor in 137 degrees, and the spiraling pattern created by this layout  has shown to be an efficient way to pack in the seeds.
By borrowing the idea from the sunflower, the researchers came up with a layout that can reduce land use by 15.8 percent and improve the mirrors’ optical efficiency by 0.36 percentage point, said Alexander Mitsos, a professor in mechanical engineering and a co-author of the research paper.
“For the same number of heliostats we use less area and collect more light,” Mitsos said. He cautioned that the research results apply to the P10 project in Spain, so the improvements will vary in other locations.
The research team’s modeling also shows there are trade offs between land use and efficiency that developers can work with to optimize their power plant designs. For example, the land use reduction can go up to 20 percent without improving the mirrors’ efficiency. So if land use is a bigger issue, then a developer could forgo the efficiency increase in favor of a smaller project footprint.
Photo courtesy of Abengoa Solar and Robert Benner via Flickr