A "Crinkle-Cut" Solar Array
A 33,000 panel, 8.1 megawatt solar array atop Pfenning Logistics in southern Germany is the largest rooftop photovoltaic array in Europe, covering an area of 110,000 square meters. By itself that might not seem like a big deal. What's interesting to me is that instead of the panels facing due south or a little southwest, as is usually the case for a fixed-mount array, these panels are arranged facing east and west in a "crinkle-cut" fashion.
There are many ways to maximize the production of a PV system. Dual-axis tracking gives the most energy production for a given panel, but two motors and controllers can be expensive, especially for a large array. Single-axis tracking is a reasonable compromise, as it tracks the sun on its daily journey across the sky. Usually the north/south orientation is facing south (in the northern hemisphere) with a tilt angle roughly equal to the location's latitude. The least expensive option is a fixed mount array with each panel tilted to the site's latitude, and facing due south for overall maximum production. Sometimes it faces a little west of south to improve afternoon performance, where there's often a peak demand caused by air-conditioning in the summer. In a fixed-mount due-south setup, peak production occurs at solar noon. Of course, all of these assumptions are based on direct sunlight. Since it's often cloudy in Germany, diffuse light is a major component of what actually reaches the solar panels. The "crinkle-cut" arrangement may favor locations with a lot of diffuse sunlight. In the PV world, every situation is unique. There isn't one "best" configuration for every site.
The Pfenning Logistics array, designed and installed by WIRSOL Group, will have two peak production times: mid-morning and mid-afternoon. A grid-tied system with this configuration could help smooth the supply of electricity over the course of the day, since its peak production times will be different than a south-facing array.
The array uses more solar panels than it would if it were facing due south, which increases the cost of the system. On the other hand, the extra panels will offset the lack of a tracking system. You can either pay for more panels or pay for a tracking system. PV panels have a life expectancy of 30 years and require little maintenance except for occasional cleaning. Tracking motors have shorter lives and require regular maintenance, so in the long run, using more panels on a fixed array might be the better option.
Although feed-in tariffs (also known as "net-metering") are decreasing in Europe, the decreasing cost of solar panels, coupled with the increasing cost of grid-electricity, makes such an endeavor worthwhile for businesses that use a lot of energy. WIRSOL claims that this array produces enough electricity to power more than 1800 homes.
MIT has experimented with "3D arrays" tilted up and down and found their production, for a given footprint, to be better than a traditional south-facing array. It would be interesting to compare two fixed-mounted arrays – one with panels facing due south and the other with panels in the east-west configuration – and see which produces more energy over the course of a year.
I smell a research project!
Image: WIRSOL Group
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Monty Bannerman
ArcStar Energy
646.402.5076
www.arcstarenergy.com
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