BIPV: Making Solar Sexy
While many an energy geek would tell you that solar is sexy, even when awkwardly jutting off a roofline, not everyone would agree. Installations like the one to the right cause architects to quitely weep and neighbors to loudly curse. Since no one should have to choose between tears and cursing and energy efficiency, Building Integrated Photovoltaics (BIPV) came to the rescue, allowing a happy intersection of aesthetics and energy production.
Consumers seem to agree, with a recent report projecting that the Building Integrated Photovoltaic market will quadruple by 2017, which isn't too shabby. You may be wondering what exactly BIPV is. And for those of you in the know, you might be wondering if this is really where solar spending should be going.
First things first. BIPV refers to photovoltaic materials that are integrated into the envelope of the building--curtain walls, roofs, and building facades. It's not the more traditional roof mounted system that most people are familiar with. In BIPV, typically a PV panel is replacing a building component, rather than attaching to one.
It is the fact that it replaces a component that makes it tricky. When panels are roof mounted, there is control over which way it faces and the angle it's installed at, both of which are carefully considered in order to maximize the amount of energy produced by the panels. With BIPV, the ability to mount the panels to maximize energy production is seriously restricted, which can hamper efficiency.
If you're weighing traditional roof mounted PV panels vs. BIPV, what is going to be less expensive to install? There are several factors that affect the initial cost of installation: PV materials, labor, and the savings from the building materials that BIPV replaces. The graphic below shows an example of how these different factors play out for BIPV that is replacing roofing shingles. With the different tradeoffs, overall it was less expensive per watt to install the BIPV system. This will vary depending on where the BIPV is going and you'll need to run costs for each specific installation.
(From a National Renewable Energy Laboratory report on installed rooftop system prices)
Space and Efficiency
In the above example, one thing to note is that a larger BIPV system was installed compared to a PV system. This is because BIPV systems are less efficient than their rack-mounted counterparts, primarily due to the different material that is used. Another factor is heat. Rack-mounted systems have airflow on both sides. BIPV systems, especially in the case where they replace shingles, lack airflow on the underside which causes them to be hotter. High heat causes PV to be less efficient. The NREL study took this into account when assessing cost differences, but if space is at a premium and there is a target amount of energy that your project needs to generate, it's worth keeping in mind.
There are a number of neighborhoods and Homeowners Associations that either don't allow or restrict PV installations for aesthetic reasons. BIPV provides a way to install solar without running afoul of restrictions. For corporations, BIPV, especially when incorporated as windows and curtain walls, provides a visible way to highlight their committment to sustainability.
Is it worth it?
Whether it's worth it to install BIPV depends on your goals. For many people a traditional roof mounted system is the easiest and quickest way to start producing energy on site. For existing buildings, it's often the only way without making significant changes to the shell of the building. For new construction, cost, efficiency, space, and aesthetics must all be considered. If local regulations prohibit roof-mounted systems, then BIPV is probably the only option that will be acceptable.