BIPV comprises a group of solar PV technologies that are built into (instead of installed onto) the host structure and may actually replace some building materials (such as windows or roof shingles). BIPV's potential to seamlessly integrate into the building envelope holds aesthetic appeal for architects, builders, and real estate holders, and this has been one of its principal sources of attraction in its three-decade lifespan.
Today, BIPV only claims about a 1 percent share of total PV installations worldwide, but several analysts foresee good times ahead for this niche technology. Below is a summary of the challenges and barriers that may block or complicate the pathway to those good times unless they are addressed by the relevant stakeholders. These challenges can be classified into four categories: price, performance, codes and standards, and market limitations.
Aesthetics alone, however, will not propel BIPV beyond its niche in the PV market—there are economics to consider. BIPV systems generally carry a larger price tag than do flat panel systems, though the reasons for this are somewhat unclear, given the lack of BIPV market data available. The following list of factors can account for some of the price differential:
Despite reportedly higher prices, BIPV systems may offer an offset value in the construction process through, among other things, the replacement of traditional building materials and the dispensation of rack-mounting hardware. A recent NREL report on BIPV in the residential sector cautions, however, that "past market experiences suggest that realizing these cost-reductions can be very challenging." And without significant reductions in installed costs (~5 percent), BIPV's cost of energy comes up short of competitive with flat-panel PV.
There are some important performance variables to consider when calculating energy costs of a BIPV system. For starters, BIPV modules may experience higher operating temperatures because, unlike rack-mounted PV, they are flush with the building surface and do not permit airflow between module and host structure. Higher temperatures may degrade the semiconducting material of the module, which could decrease the conversion efficiency more quickly and precipitate early failure. Some PV materials — for example, amorphous silicon, which has a flexible form factor and hence a potentially greater integration potential — are more susceptible to thermally accelerated degradation than others. Also, PV materials with greater integration potential, such as thin films and flexible PV technologies, generally have lower efficiencies to begin with, and this may contribute to higher energy costs.
Finally, because BIPV modules typically contain less semiconducting material than traditional PV modules, a BIPV system will likely produce less electricity than a flat-panel system of the same size. And even though BIPV can increase the PV-suitable space of a building (i.e., more than just the roof is eligible for installation), the sub-optimal angle of irradiation on these non-horizontal surfaces, combined with the obstructions posed by surrounding buildings, create diminished returns on increased module deployment.
Codes and Standards
Because BIPV modules serve dual functions, they must hew to the codes and standards of two separate industries (PV and construction). Currently, PV modules (including BIPV) are subject to the qualification and design standards devised by the International Electrotechnical Commission and the Underwriters Laboratory. But BIPV may be required to meet additional criteria as a structural component, and this can act as a market handicap. For example, the International Code Council, whose pervasive International Building Codes have been adopted by all 50 states and Washington, D.C., has established criteria for BIPV as a roofing material that dictates its performance on stability, wind resistance, durability, and fire safety.
Even something as simple as measurement standards could complicate BIPV deployment. The construction industry employs square meter units, which denotes area, and the PV industry uses watt units, which measure electrical output. If this incongruence remains unresolved, it could create some headaches for installers in the building trade.
For now, BIPV keeps awkward toeholds in both the PV and construction industries, without an integrated set of standards and codes to carve out the middle ground. The establishment of this middle ground through a clear set of guidelines and expectations for the manufacturing and construction process will serve as a growth platform for the BIPV industry.
Unlike flat-panel PV, where module designs do not vary greatly from one application to another, BIPV manufacturers' products vary by façade type (e.g., roof shingles, windows, and awnings). This emphasis on custom-design segments the BIPV market and, in turn, hobbles the technology's path to scalability. The fact that BIPV does not compete in the utility-scale, ground-mount space (in other words, it is limited to residential and commercial building applications) further hinders its scalability. Without the kind of capital accumulation, economies of scale, and learning curve progress that comes from a manufacturing and deployment scale-up, BIPV may not realize the kinds of cost reductions that could facilitate its adoption.
This article was originally published on NREL Renewable Energy Project Finance and was republished with permission.