The Challenges of Building-Integrated Photovoltaics

Travis Lowder, NREL
May 08, 2012 | 9 Comments

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.

Price

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:

Customer perception that these products should cost more because of their specialty function and their willingness to pay premiums for that function
Supply chain issues for products and services (e.g., difficulties in establishing distribution channels and hence getting product to market)
BIPV modules may include additional materials (e.g., adhesives and framing and flashing materials)
Additional labor costs deriving from specialized architectural design, engineering design, and installation, according to a Greentech Media report.
It is important to note that BIPV prices are variable by market and by application (i.e., structure-specific design of the module), and so pricing is something of a moving target.

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.

Performance

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.

Market Limitations

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.

9 Comments

PHILIP MCCRACKEN
May 15, 2012

Some people do not like the white roofing material I put on roof. Even though it keeps the roof very cool on hot days, some think there is no esthetic appear. But nobody in my area has tried it. Dark roofs do not make sense unless you are putting all that heat or other energy to use.

Gerry Wootton
May 11, 2012

The better part of Gold Coast's site is the more-or-less turnkey solar carport. The easy way to color cells is to just diddle the ARC deposition. Economy of scale should be able to level this. This direct approach trades of efficiency and coloration directly which does increas $/Wp. There are other ways to accomplish the same thing with lower insertion loss or even some gain. There are also ways to make the metal less visible while boosting efficiency.

A true clay tile replacement would use 3-D structure to more accurately mimic tile but would also increase the power density which would offset losses associated with coloration.

A commercial rooftop sawtooth sky-light should be a good synergistic product with south facing solar and north facing glass. Could be a self-flashing unit with built-in inverter. Quick install with plug-in. Think product not system component.

One thing we need is a BIPV interconnect standard for small to medium installations. For example, 12/2 wire with specially colored jacket and 230/240 VAC / 20 A gated plug and GFI receptacle (reverse feed load-center breakers already exist). Let's have a standard way of wiring up distributed generators. (DC is just wrong in architectural applications for many safety,cost and standardization reasons).

Mike Mrozek
May 10, 2012

www.GoldCoastSolar.com is a California company who sells colored solar panels which are equally efficient at 15%+. This will be the future of residential PV, its like if you had the choice of a color HDTV or a black and white TV which one would you prefer. The panels are pricer but the average installed residential solar is $6.96/watt. (http://www.californiasolarstatistics.ca.gov/)

The homeowner now has a choice, curb appeal vs. looking at a black hole on their roof for the next 25yrs.

Patrick O'Leary
May 10, 2012

Gerald R, you have a good point, but could you take it a step further? PV/Thermal would mount better. The addition of tubing to the solved issue of wiring should not impose too much. The building on which the panels are mounted need heat as well as electricity. Glass facade office buildings only need to have southern exposures modified.

Gerry Wootton
May 10, 2012

BIPV is a different animal than building mounted solar. The PV industry needs different thinking to approach the BIPV market properly. Also, as others have noted, there are other things one can do with solar such as direct lighting, water and space heating which, in an ideal implementation, can be synergistic. One existing simple application is the integration of PV in skylights where the PV serves also to attenuate direct light to a desirable level while only having a small effect on indirect light. Another is integration into louvered or moveable awnings. Some other obvious integrations include curtainwall HVAC and water heating.

One striking observation in my area is how fast and efficiently backyard fixed mount and tracking daisies go up in rural backyards. This typically involves trucking in factory built solar arrays and precast bases. Of course, you need a large yard to do it; however, there are many more aesthetic opportunities going unserviced. These would include solar garden sheds and green houses, cabanas, deck awnings, carport covers, etc. These all have the advantage of being separate from the house and typically purchased as a prefab kit or a finished unit. For one specific example, consider a pool shed incorporating water heating and solar power - small enough to fit on a truck but very functional and self contained, factory built and certified. Or consider your classic 8x10 greenhouse with solar powered LED grow lights and ventilation fans. There are lots of forms of BIPV of this sort that can be turnkey applications and which meet aesthetic goals.

Gerry Wootton
May 10, 2012

Some of the assumptions about BIPV are weak on the 'I' part. If truly integrated, the building and the building material would be synergistic - PV would not simply be an alternative skin for the building. Issues such as ventilation and wiring access would be taken care of just like issues oventilation for insulation pockets are taken care of. However, this is a market with a lot of inertia and it will take time for materials, methods and building codes to come in line.

Some interesting things I discovered when working the aesthetic issues of BIPV:
- for larger structures, glass curtain wall construction is popular and presents an avenue for BIPV i.e. integrate solar with glass decoration with the potential of being cheaper than building mounted PV installation.
- when PV is integrated into the surface finish, the need for penetrating seals and exposed wiring goes away; this should actually reduce the wiring class and cost of modules although there are no PV certification standards as yet for modules applied in this context (compare for example building integrated exterior lighting, perimeter security systems, etc).
- it is possible to colorize PV in ways that actually enhance efficiency.

Form factor and attachment are certainly important considerations. Standard building sheathing sheets come in standard sizes which meet certain dimensional conventions. PV's cost obsession results in modules that are sized to meet string length and cell count parameters only without regard to awkward this may be when integrating to standard framing dimensions.
Also, in BIPV applications, the efficiency of PV cells not the aperture efficiency should be the important consideration from the perspective of meeting aesthetic goals and the need to cover 100% of the area. At the very least, there needs to be identical passive sheathing and complementary trim components to go with. The notion of wallpapering the entire structure with low efficiency PV isn't the right solution.

Patrick O'Leary
May 10, 2012

Travis, The emphasis on PV is understandable, but Building Integration covers more than just PV. Dawn Solar has "In-Roof" SWH and Light Tube daylighting also fits into the structure.

Futura Solar has gone a little further than that. Our Sawtooth Solar Daylighter, for low profile commercial buildings, provides daylight on the factory floor, process solar thermal air (with incidental air handling) and still has room for PV, SWH or PV/Thermal on the absorber plate of the 2 pass air heater. This system revives sawtooth roofing with additional solar benefits, going beyond what Cambar tried in Chattanooga back in the Bush Administration. Sawtooth roofing is the best roofing technology we ever abandoned.

Robert Benson of DCM-A&E has termed the system 'elegant' and is ready to fabricate, install and commission. Solaris-Energy of the EU is just opening discussions to bring the Sawtooth to the EU. Sasa-Marinic is on the wrong side of this, it actually becomes more attractive to bundle benefits. I usually point out desk top printers, which now do several tasks that originally required several different machines.

Single benefit, add on systems are the dinosaurs, they cannot carry the weight of their cost. Multiple benefit systems are the future.

Travis Lowder
May 9, 2012

Hi sasa-marinic,

Thanks for your question. While solar system costs continue their rapid decline, markets are still defined by policy schemes. Premium BIPV incentives are making a strong economic case for integrated systems in select markets (mostly in Europe). However, overall solar system economics are dependent on energy production over the life of the system, and it appears that even with premium incentives some BIPV designs (e.g., vertical systems on building façades) may have low economic appeal.

The policy framework in Europe is currently the most favorable environment for future BIPV market growth.
In addition to the premium incentives offered by some of its member countries, the European Union has two directives in place which may function as BIPV demand drivers: 1) national commitments to meet the EU's 20% renewables x 2020 goals (2009/28/EC); and 2) energy performance in buildings (2002/91/EC). The latter may prove especially advantageous for BIPV deployment.

SASA MARINIC
May 8, 2012

Travis,

It seems to me that is unattractive from economy point of view to build integrated-PV on existing buildings. How do you see that?

Sasa

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Travis Lowder

Travis Lowder is an Energy Analyst with the National Renewable Energy Laboratory's Project Finance Team. His research encompasses the U.S. renewable energy project finance market and financial policy, PV project risk management, PV asset...