January 11, 2012
Nature Inspires More Efficient Design For Capturing Solar Energy
A team of researchers from MIT and Aachen University in Germany have engineered a new kind of concentrated solar power (CSP) plant that allows for a greater yield of energy on a smaller area of land. And the progressive-thinking scientists say they got their inspiration for the design from was Mother Nature herself.
In the journal Solar Energy, the transatlantic team recently reported that by arranging the mirrors, or ℠heliostats´, of solar devices in spiral formations they can actually reduce its “footprint” by about 20 percent while simultaneously increasing the amount of energy produced.The design for the spiral, researchers say, was borrowed from the face of a sunflower and makes for a more compact structure that reduces the blockage of light by adjacent heliostats.
At traditional CSP sites like the large PS10 solar field located in the deserts of Andalucia, Spain, the sunlight-capturing mirrors are arranged much like seats in a cinema, staggered and aligned in neatly ordered rows. For years, however, scientists and solar engineers have recognized and wrestled with the problem of shadowing, whereby individual mirrors block the light going to their neighboring mirrors as the sun traces its course across the sky.
The collaboration between researchers at MIT and Aachen University was an attempt to solve just this problem
MIT´s Alexander Mitsos, previously a researcher at Aachen, teamed up with a handful of colleagues and former colleagues to attempt to optimize the pattern used in CSP´s and thereby boost the overall efficiency of heliostat layouts.
Before embarking on a new design, the research team first wanted to test the precise efficiency of existing designs, so they came up with was a dynamic model that divides each mirror into separate sections and calculates the amount of light each section reflects and blocks at any given moment.
The group tested the PS10 plant in Spain using their new model and found that the efficiency of the traditional CSP plant was significantly diminished every day on account of the shading and blocking that takes place with the staggered mirror layout.
Convinced that a new design could significantly improve efficiency, the team began experimenting with various theoretical heliostat designs. After much trial and error, their models indicated that a tighter, fanned-out layout with some spiral-like features could reduce the area needed for the panels by 10 percent without decreasing efficiency.
This discovery was an accomplishment in itself, but the team didn´t stop there.
Noting that the spiral is a commonly used mathematical design in various organisms, the team began seeking inspiration from nature. And it didn´t take long before they arrived at the sunflower.
The hundreds of tiny florets on the face of every sunflower form a pattern known as the Fermat spiral, one of nature´s many engineering designs that have fascinated naturalists and mathematicians since the ancient world. Each unit in a Fermat spiral–for instance the sunflower´s florets or the CSP´s heliostats–is turned at a 137.5 degree angle with respect to its neighboring unit. This angle has come to be known in geometry as the “golden angle”.
Using the golden angle as a guide for aligning their heliostats, the research team found that they could not only reduce the size of the area needed for CSP layouts; just is significant, they were also able to reduce the amount of shading and thus increase the efficiency of energy production in absolute terms.
The team, which has already patented the design, believes that the practical implications of their discovery will be huge, given that it significantly maximizes the two most critical factors in the production of solar energy: land and sunlight.
“Concentrated solar thermal energy needs huge areas. [“¦] 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,” said Mitsos.
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