Solar Today March 2013 : Page 19

SOLAR TODAY elevation (10,600-foot, or 3.23-kilometer) site, located near the highest point of the Greenland ice cap. Although the mass loss of the ice cap was recently established, much of the melting occurs closer to the periphery of the ice cap. Temperatures at Summit rarely rise above the freezing point, and thus the snow here accumu-lates permanently, at around 25 inches per year in the general area. Wind-driven snow is the more difficult problem. During winter windstorms, structures directly on the snow surface can be buried to the roof from a single wind event, often lasting days. All of the buildings on station have roof hatches to allow occupants to exit after the winds have subsided. Everything exposed to the elements at Summit, including the people who work there, must be extremely robust. The solar resource at high latitudes (particu-larly on an ice cap) can be quite good, but the physics is somewhat complicated. It has taken me nearly 20 years of working in polar environ-ments to learn how to turn conditions to our advantage. While the sun’s rays travel through a greater length of atmosphere due to the angle, relatively low water vapor offsets this disadvan-tage. When combined with a permanent, highly reflective snow surface, the summertime global irradiance is quite high. The extreme cold of high polar environments results in significantly higher voltages being pro-duced by PV. Recent technological advances in maximum power point tracking allow us to take advantage of the higher voltages, resulting in greater net power production per unit of PV collector surface. During summer in the high latitudes, the sun stays above the horizon for months — but it remains below the horizon for long periods in the winter. For most solar collectors, the greatest annual production usually results by setting PV panels at an angle near the latitude of the site and fac-ing the sun. But Summit’s environmental factors argue in favor of orienting the panels vertically. While the angle of incidence affects optimal harvest of direct solar gain, vertical orientation allows for capture and conversion of some light energy reflected from the snow surface. Vertical orientation also tends to reduce snow accumula-tion on the panel faces. Since snow-covered PV MARCH 2013 VOL. 27, NO. 2 ® NICK SALAVA Author Tracy Dahl provides sustainable tech-nology solutions to researchers working in the remote Arctic with support from the U.S. National Science Foundation (NSF). For more than 20 years, Dahl has developed remote power systems allowing scientists to run instruments and communications equipment far from established infrastructure. With CH2M HILL Polar Services, the primary research sup-port and logistics provider for the NSF’s arctic program, Dahl has learned, through trial and error, how to work with the polar environment to create reliable and rugged systems. Dahl is a NABCEP-certified PV installer. He lives and works off the grid in Southern Colorado, where he and wife Amy are often in the midst of developing sustainable technology solutions for professional and personal applications. Coming to a Site Near You? hough designed specifically for a high polar environment, solar engi-neers should consider whether “going vertical” makes sense for applications in more temperate climes. The structure packs a large amount of generating capacity into a small footprint, and the tilt-down design allows for fabrication without a crane. The same basic design could use one live PV facet facing south, substituting inexpensive structural pan-els on the other two sides. I imagine solar towers in front of public and professional buildings — basically anywhere someone wants to reduce energy costs and carbon foot-print while making a bold statement.  TRACY DAHL T Copyright © 2013 by the American Solar Energy Society Inc. All rights reserved. SOLAR TODAY M arch 2013 19

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