Thursday, June 30, 2011

Implementing Building Integrated Photovoltaics

The concept of Building Integrated Photovoltaics (or BIPV) has been around for a while.  The idea behind BIPV is that an effort is made by the solar panel company to supply panels that don't look like an ugly after thought when placed on the roof or the wall of a structure.  For a long time arrays have often sat, somewhat insect-like, on the skin of a building.

Despite laudable efforts in the past decade, the problem of thinking about solar panels in a truly integrated way persists.  In short, it has just been very difficult to incorporate a mass produced mechanistic object into the esthetic fabric of the domestic environment.  Much of this can be blamed on the cultural schism that often exists between the worlds of architecture and engineering.

I've heard it said that good architects start off "knowing very little about many things until they know nothing about everything."  Good engineers, by contrast, are suppose to "know a great deal about very little, until they know everything about nothing."

This is a basic difference between the two disciplines and photovoltaic solar panels were conceived by engineers with the initial specific goal of providing solar power.  This undertaking required a great deal of expertise and specialization.

In the world of architecture, on the other hand, every building element is commonly asked to have "stacked" functions.  In other words, one building element should perform many functions.  This is not always true, and one can argue that the world of architecture is becoming increasingly engineering oriented.   Buildings are increasingly populated with elements that perform discrete functions. Not too long ago a wood floor simply sat on floor joists and performed the "stacked" functions of structural element, insulation, moisture retarder and finished floor etc.  This way of stacking functions has an efficiency about it that is wholly different from the efficiency of the engineering world.  The engineered solution tends to introduce specialized elements that address the individual design challenges; plywood subfloors perform the structural task, a finished wood floor for esthetic and wear issues and to protect the subfloor from wear and tear, and a possible vapor retarder between or under these two elements if one is specifically concerned about moisture.

This subject of "general" versus "specialized" design approaches is an intriguing one.  The environmental design movement today is taking a decidedly "specialized" approach vis a vis the LEED rating system.  This "point" system  is very much an engineering approach to the business of environmental stewardship and it can be argued that this specialized way of addressing our environmental problems is exactly what got us into this environmental mess in the first place.  After all, some of the most wasteful design solutions are the ones that, while efficiently executing their specific task, are inefficient in the breadth of their capabilities.

This project was intended to take the solar panel to a level beyond the BIPV approach.  We didn't want the solar panel integrated with the building only in the sense that it "plays nice."  On this project we wanted the solar panels to actively contribute to other functions on the project, namely to provide shade and a modicum of shelter.

If a pool is an ingredient of a project, it can be an organic place to utilize solar in this way since it gets good sun exposure and can benefit from an elevated structure that also provides a modicum of shade.   One sees this being done with carports as well and this is the strategy we implemented here.

The two biggest construction challenges with this installation were the wire management and getting all the team members to realize - conceptually -  that we weren't just installing solar panels; we were installing a shade structure.  

It turns out it is typical to install solar panels wires in a leap-frogging daisy chain fashion utilizing the wire whip that comes with the individual solar panel from the factory.  This practice avoids introducing an extraneous wire at the end of the run to bring the circuit back to the beginning.  This extra wire also adds a little cost and reduces the efficiency by a very minor amount.  But if you are making a shade structure and not just a photovoltaic array, this cost is minuscule compared with the cost of an entirely discrete trellis element.  This is exactly what we were trying to accomplish.  For this reason, Solarworks installed an extra circuit-completing cable (in addition to the whips provided by the factory) to keep the wire pattern consistent.  This strategy was facilitated by the presence of tube steel trellis members that provided a concealed manner for routing the wires as well as the mounting mechanism for the panels themselves.  A big thank you to Mark Rechin at Total Concepts for coordinating the final effort to fine tune this wiring issue.

figure 2
Left to their own devices, and in the absence of some clearly articulated alternate objective, any solar panel installer is going to install solar panels with about a 20° tilt at this latitude to maximize productivity.

These panels were installed with a 1/2" drop across their 5' length.  The reason for the minor tilt is to simply get standing water and grime off the panel and to prevent this scum from hampering energy production.  This array had two parallel rows of solar panels along its length and we simply pitched them to either side of the main axis with the peak running lengthwise down the array's ridge (see figure 2 and 3). The solar panels need to be cleaned with a hose once a year to maintain reasonable efficiency. 

figure 3

On this project we pursued a strong connection between the grape fields and the pool site work. The solar "trellis" was an element that was striking in its similarity in both form and function to the stakes and metal wires that supported the grapes and aided in their harvest.  This idea of harvesting energy became a strong force in designing this solar trellis and we wanted to create a real harmony between the geometry of the grape fields and the pool terrace with its solar-harvesting shade element.  We had wanted to design a building that had an authentic connection and harmony with its environment and this seemed like a strong way to pursue this connection.  A shade structure that was not pitched, but virtually flat, would resonate strongly with the layered planer geometry of the project (e.g. the pool surface, the terrace and the fields themselves).  It is true that there was a minor loss in power production associated with this strategy but in a more macroscopic sense for the project we had also built a shade structure where we could have simply built a solar array .  This is the basic idea behind building integrated photovoltaics.

I was happy to hear this week that the eight kilowatt solar panel array is currently running a credit with the electric company for the entire Diaz facility.  

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