James Montgomery, News Editor, Photovoltaics World
January 17, 2012 | 7 Comments
New Hampshire, USA -- Researchers at MIT and Germany's RWTH Aachen U. have devised a new way to set up a concentrated solar power (CSP) project that both increases the system's efficiency and reduces the land footprint -- all thanks to inspiration from Mother Nature.
January 17, 2012 - Researchers at MIT and Germany's RWTH Aachen U. have devised a new way to set up a concentrated solar power (CSP) project that both increases the system's efficiency and reduces the land footprint -- all thanks to inspiration from Mother Nature.
The Andalucia, Spain "PS10" CSP install incorporates more than 600 heliostat mirrors tracking the sun through the day, all arranged radially around a central tower and staggered to align every other row -- but this also creates some unavoidable shadowing and blocking that reduces the light reflected to the tower. The team, led by MIT's Alexander Mitsos and postgrad Corey Noone and RWTH's Manuel Torrilhon, developed a computational model to evaluate the efficiency of heliostat layouts, dividing mirrors into sections and calculating the light reflectivity in each, and comparing to PS10's layout to determine overall efficiency. What they discovered, and reported in the journal Solar Energy, was that using their numerical optimization brought the fanned-out layers closer together, reducing the amount of land needed without affecting the mirrors' ability to reflect light.
They then compared the layout to the "Fermat spiral" pattern seen in, among other occurrences in nature, the florets of a sunflower, which are turned at a mathematical "golden angle" (roughly 137°) to each other. By rearranging a model of a CSP field to resemble this layout, they calculate a 20 percent smaller footprint than the PS10 field in Andalucia. And the spiral pattern reduces problematic shading and blocking, thus increasing the system's total efficiency, too.
From the paper abstract:
Specifically, this new heuristic is shown to improve the existing PS10 field by 0.36% points in efficiency while simultaneously reducing the land area by 15.8%. Moreover, the new pattern achieves a better trade-off between land area usage and efficiency, i.e., it can reduce the area requirement significantly for any desired efficiency. Finally, the improvement in area becomes more pronounced with an increased number of heliostats, when maximal efficiency is the objective.
Concentrated solar power has been somewhat overshadowed by plunging-cost solar PV, leading some developers to swap CSP plans to solar PV technology (roughly 3-GW worth over the past year or so). However, CSP has some tricks up its sleeve. Not only does it have a foothold in energy storage, but a recent NREL study suggests that having CSP/storage gives grids more flexibility to add other less-constant renewable energy sources in their portfolio. (This article goes into more detail about the pros/cons of each type of CSP technology.)