More efficient Concentrated Solar Power plants inspired by sunflowers

In our article about solar power, we already wrote about concentrated solar power (CSP) power plants. In order to function, these plants need a lot of space and sunlight, and researchers at MIT collaborated with RWTH Aachen University in Germany to come up with a design that increases the amount of sunlight its mirrors collect, while reducing the amount of land needed for these systems.

An example of a CSP system is located in the desert region of Andalucia, Spain. Named PS10, the power plant has a 100-meter-high (328-foot-high) pillar surrounded by rows of giant mirrors which concentrate solar rays onto it. There are more than 600 of these half a tennis court sized mirrors, and they concentrate enough heat which is converted into electricity at the pillar to power 6,000 homes.

At PS10 and other CSP plants in the world, mirrors are arranged around the central tower in concentric circles, and the spacing between mirrors is staggered so that every other row is aligned. However, this pattern results in higher-than-necessary shadowing and blocking throughout the day, reducing the reflection of light from mirrors to the tower.

Alexander Mitsos, the Rockwell International Assistant Professor of Mechanical Engineering, and Corey Noone SM ‘11 collaborated with Manuel Torrilhon of RWTH Aachen, where Mitsos was a researcher prior to joining the MIT faculty, in order to develop a spiral pattern of the mirrors (helistats) similar to one found on the face of a sunflower.

“Concentrated solar thermal energy needs huge areas”, said Mitsos. “If we’re talking about going to 100 percent or even 10 percent renewables, we will need huge areas, so we better use them efficiently.”

Mitsos’ lab developed a computational model which divides each mirror into discrete sections and calculates the amount of light each section reflects at different parts of the day. They ran their simulation through a model of the PS10 plant in order to determine the plant’s overall efficiency. The group found that the CSP plant experiences a significant amount of shading and blocking each day despite the staggered layout of its mirrors.

Noone and Mitsos used numerical optimization to bring the fanned-out layout closer together and ended up with some spiral elements similar to layouts found in nature. They managed to reduce the amount of land the mirrors occupy by 10 percent while being able to maintain their e efficiency in light reflection.

In cooperation with Torrilhon, they went further in optimization by applying sunflower’s floret layout which resembles Fermat spiral – a spiraling pattern that appears in many natural objects. The researchers devised a spiral field with its heliostats rearranged to resemble a sunflower, with each mirror angled about 137 degrees relative to its neighbor. The numerically optimized layout takes up 20 percent less space than the PS10 layout, reduces shading and blocking, and increases total efficiency of the system.

For more information, read the results the researchers published in the journal Solar Energy: “Heliostat field optimization: A new computationally efficient model and biomimetic layout”.