October 3, 2010 | bfeldman | Data Centers, Professional Development, Sustainability

Upcoming St. Louis USGBC Presentation – Photovoltaics

I’ve been asked to speak at the October St. Louis USGBC Chapter meeting on photovolatics.  I’m part of a panel that includes Mike Steinbaum at McCormack Baron, Erin Noble with the Missouri Coalition for the Environment and Dane Glueck with StraightUp Solar.    The panel is moderated by Alan Ely with Ely Consulting Engineering LLC.

Mike is talking about some McCormack Baron solar projects.  Erin will be speaking about State and Federal incentives for PV.  Dane will be discussing solar site assesment and standard PV components and systems, and I’ll be speaking on lessons learned from the recently completed Emerson Data Center PV project.

One of the things I like about PV is that when there is daylight outside, the panels are producing electricity.  Unlike wind turbines (which have problems in this area due to lack of consistent breezes), PV works when the sun shines.  In July this summer the array at Emerson produced slightly over 14% of all the electricity used at the Data Center – not bad at all!

One of the things I’ll be discussing is the quirks in this particular project.  2 things come to mind.  First is how we ended up with a “triangular” array.  We began with a study of the site conditions, and discovered that due to the surrounding trees, the best place for the array was on the roof of the building.

site study pv

pv array diagramThe diagram above shows how the shape came about.  Basically, the building is not oriented north to south, but is skewed approximately 40 degrees off axis.  Since the PV functions best when aligned due south, and with a 10 degree slope for our latitude, we rotated the traditional rectangular array, cut off the “overhang” and created the shape shown.

The odd thing about this – you would think the angle at the bottom of the triangular array would be 90 degrees: it isn’t.  The other points on the triangle are column lines inside the building.  They are orthogonal with the structural grid.  But when you lift the back of the grid in the air, the angle at the bottom is less than 90 degrees.  Good thing we were working in Revit – we realized in the design phase that this was occurring, and shifted each panel slightly with the next.  The effect from the ground is not noticeable.

The other thing I’ll be addressing is the requirements of the panels and the attachment rails.  You need to plan in expansion into the rail system – basically the rails come in standard sizes.  The installer is trying to find the most economical sizes of rails to make the system work.  Where two rails join together, they need an expansion joint.  On an array like Emerson’s you need to watch where the expansion joints occur.  Our got slightly shifted towards the east side of the array – again not something you pick up on from the ground but something that caused a lot of discussion during the installation phase.

PV array as seen from below
PV array as seen from below

building from a distance

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