CEE April-June 2012

Removing roadblock induding those related to regulations and lack of incentives would go a long way towards efficiency enhancement in wind power generation. Courtesy: Renewable Watch, Feb.2012, P42. Solar NEW SUNFLOWER· INSPIRED PATIREN INCREASES CONCENTRATED SOLAR EFFICIENCY In the desert region of Andalusia, Spain, sits an oasis-like sight: a 100 metre high pillar surrounded by rows of giant mirrors rippling outward. More than 600 of these mirrors, each of the size of half a tennis court, track the sun throughout the day concentrating its rays on the central tower, where the sun's heat is converted to electricity- enough to power 6,000 homes. The sprawling site, named PS10, is among a handful of concentrated solar power (CSP) plants in the world. Now, researchers Noone and Mitsos from Massachusetts Institute of Technology (MIT), in collaboration with Manuel Torrilhon of RWTH Aachen. University in Germany, have come up with a design that reduces the amount of land required to build a CSP plant, while increasing the amount of sunlight its mirrors collect The researchers found that by rearranging the mirrors, or heliostats, in a pattern similar to the spirals on the face of a sunflower, they could reduce the pattern's 'footprint' by 20 per cent and increase its potential energy generation. The sunflower-inspired pattern allows for a more compact layout, and minimizes heliostat shading and blocking by neighbouring mirrors. The researchers published their results in the journal Solar Energy, and have recently filed for patent protection. Concentrated Solar Power (CSP) Plant Blocking a shadow Mitsos' lab developed a computational model to evaluate the efficiency of heliostat layouts. The model divides each mirror into discrete sections and calculates the amount of light each section reflects at any given moment The researchers tested the model on an existing commercial scale CSP plant The group found that the CSP plant experiences a significant amount of shading and blocking each day despite the staggered layout of its mirrors. Spiralling out To increase the plant's theoretical efficiency, Noone and Mitsos tinkered with the pattern of heliostats, using numerical optimisation to first bring the fanned-out layout closer together. This narrower layout, the model calculated, reduced the amount of land the mirrors took up by 10 per cent without affecting the mirrors' efficiency in reflecting light The resulting pattern had some spiral elements similar to layouts in nature. So the MIT team, working with Torrilhon, looked to nature for inspiration - specifically, to the sunflower. The florets of a sunflower are arranged in a spiralling pattern, known as a Fermat spiral, that appears in many natural objects and has long fascinated mathematicians - with each sunflower floret turned at a 'golden angle'- about 137 degrees - with respect to its neighbouring floret The researchers devised a spiral field with its heliostats rearranged to resemble a sunflower, with each mirror angled at about 137 degrees relative to its neighbour. The numerically optimized layout takes up 20 per cent less space than the PS10 layout The spiral pattern also reduced shading and blocking and increased total efficiency compared with PS1 O's radially staggered configuration. Arranging a CSP plant in such a spiral pattern could reduce the amount of land and the number of heliostats required to generate an equivalent amount of energy, which could result in significant cost savings. "Concentrated solar thermal energy needs huge areas," adds Mitsos, "if we're talking about going to 100 per cent or even 10 per cent renewables, we will need huge areas, so we better use them efficiently." Courtesy: Renewable Energy Akshay Urja, Vo/.5, Feb.2012, P46. 44