A couple of USGNN blogs last week offered different takes on the coming solar panel technology wave. From recent efforts to incorporate photovoltaic (PV) panels into curtainwall projects in the Middle East holding some promise, now’s the time for North America to be looking at this issue even more closely. Thinking (way) back to a solar design/energy efficiency class I had in college, I remember some things I learned then …
First, because curtainwalls are typically vertical, architects can face the building south – or at least the façade with the panels to be glazed into it. The other sides merit few, if any, panels, as the sun isn’t going to do much good on the north face, and the east and west faces see less than a half-day’s worth of sun. Common sense, right?
Second, shading in the overall building design has to be addressed. If not from surrounding buildings, then shading within the wall components may come into play. A leading manufacturer of solar panels in the Middle East explained it this way: If there’s any shading whatsoever on the panel, its efficiency falls off dramatically: A 25 percent shading pattern may drop the efficiency of the panels by 75 percent. Think also about the amount of glass with the PV-electrical generating capacity that might be in the glass bite alone. On a 5- by 10-inch lite, with a glass bite of ½-inch, 2.5 percent of the square footage of that lite is in the glazing pocket. It’s not a lot, but needs to be considered.
Third, the most efficient PV panels are mounted perpendicular to the sun’s rays. Because that angle changes minute-by-minute as the sun moves across the sky, there are challenges with capturing sufficient energy with fixed panels. And, since the solar incidence angle (the angle at which the sun strikes the panel) varies by latitude, optimum panel placement varies by geography. If the panel doesn’t move to follow the sun, the ideal angle would be 900 to the sun, facing south, at noon on March and September 21/22, the spring/fall equinox. At least twice a year, it’s getting the sun’s rays to hit it exactly right.
For curtainwall applications of PVs, that begs several questions:
1. What’s the efficiency drop for a panel that’s vertical as opposed to one that’s mounted at an angle? Vertically mounted panels will NEVER reach 100 percent efficiency.
2. Will architects start designing curtainwalls with angular panels to increase the power the panels can produce?
3. Or, are panels going to be mounted and devices incorporated to follow the sun across the sky, maximizing their output as compared to their cost?
There are numerous other issues to take into account, such as the role of generating electricity with PVs vis-a-vis saving energy through daylighting, engineering PV curtainwalls to be leak resistant in light of incorporated wiring and pipes, and which specific type of PV technology is best for a given curtainwall application.
The point is, there’s a lot of learning to be done up and down the glazing industry. Hopefully the solar panel manufacturers will start publishing articles in the glazing trade magazines and further educate those who have to install the work and eventually offer the building owners the warranties. Educating the architects is a great first step, but please don’t forget everyone who will buy and install it!
Those of us in the glazing industry are quick studies, if it’s the way the game’s going to be played. We’re hungry for info!
And speaking of games: Go Phillies (Yanks are up 3-1 as I write this)!!! And Eagles over Cowboys on Sunday. I support two NFL teams: the Eagles and anyone playing the Cowboys.