Concentrated Solar Power (CSP) plants, such as the Gemsolar and PS10 plants in Spain, use arrays of mirrors (or heliostats) to focus a large area of the Sun's rays onto a small area, where the concentrated light is converted to heat that is used to generate electricity. While CSP has gained popularity in recent years with numerous plants being built around the world, they require a large area to generate the amounts of electricity needed to make them economically viable. Taking inspiration from the sunflower, researchers have devised a more efficient design that would allow such plants to be constructed on a much smaller area.
Most current CSP plants see mirrors fanning out from one side or radiating out from a central tower in concentric circles with the rows staggered so that every second row is aligned. After running the dimensions of Spain's 11-megawatt PS10 plant - which uses a fanned-out layout - through a computational model, researchers from MIT and RWTH Aachen University in Germany found that there was significant blocking and shading of the heliostats each day.
By modifying the heliostat layout using numerical optimization to create a narrower layout, the model calculated that the amount of land required for the mirrors could be reduced by up to 10 percent without affecting their efficiency in reflecting light. After noticing that the resulting pattern had some spiral elements similar to patterns found in nature, the researchers (naturally) looked that way for inspiration.
One such naturally-occurring pattern is the Fermat spiral, which is found in the spiraling pattern of florets in daisies and - fittingly - sunflowers. The Fermat spiral has long fascinated mathematicians who have found that each sunflower floret is turned at a "golden angle" of about 137 degrees with respect to its neighbor.
By rearranging the mirrors in a sunflower-like spiral pattern with each mirror angled about 137 degrees relative to its neighbor, the researchers found they could reduce the footprint of the mirrors used in the PS10 layout by 20 percent while increasing the plant's potential energy generation. This is because the more compact sunflower-inspired layout minimizes the heliostat shading and blocking of neighboring mirrors.
MIT's Alexander Mitsos says laying heliostats out in such a spiral pattern could significantly cut the costs of CSP plants by reducing the amount of land and the number of heliostats required to generate an equivalent amount of energy.
"Concentrated solar thermal energy needs huge areas," says 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."