Selling the Light of Day

Incentive programs and increased demand for building-integrated photovoltaic installations has pushed research and innovation at companies and universities.

9/6/2006 By Russell Fortmeyer

	Aspen’s Wagner Park Edge includes a glass-laminated photovoltaic installation as its sole power source (above and right). Photography: © Lone Pine pictures (top); Ajax Design (below)

The sun shines a little brighter in Aspen, Colorado. Since the city lies 7,945 feet above sea level, snow-covered mountains tend to reflect a dazzling light on clear winter days. While elevation certainly plays a role, the city expects its reliance on renewable resources like wind and hydroelectric—which accounts for 57 percent of its electricity production—to eliminate the dispersal of 42 million pounds of greenhouse gases from the atmosphere through 2010.

When the city selected Willis Pember, AIA, to design a public service and storage pavilion for its Wagner Park, the architect decided early on he would test the waters of Aspen’s 2000 commitment to adopt green building initiatives.

“The City of Aspen likes to believe it was the first city in Colorado to produce its own electricity,” Pember says. “So that myth was something we exploited to sell them on the idea of photovoltaics on the building.” His final design, the Wagner Park Edge, incorporates a 3-kilowatt thin-film photovoltaic array sandwiched between two layers of glass mounted to a structural canopy blanketing the building. The array supplies the pavilion’s needs while also contributing enough energy back into Aspen’s electrical grid to power a typical single-family home for the year.

Although photovoltaics on buildings remains a curiosity for many architects, most people involved in the photovoltaics (PV) industry think projects like the Wagner Park Edge will become the rule in the near future. While the market for PVs has exploded, building owners expecting to see quick returns on investment still find the technology disappointing. As such, the additional benefit of energy production often follows as a bonus to the use of PVs as a highly visible sustainable billboard or as a path to points in the U.S. Green Building Council’s LEED rating program.

Steven Strong, of Solar Design Associates in Cambridge, Massachusetts, has experienced a surge in his energy consulting business in the past few years, owing to what he considers solar power’s new “cool factor,” a desire for more secure sources of power, and, especially, higher energy costs throughout the world. “Traditional economic analysis no longer applies; it’s just that most people don’t understand that yet,” Strong says. “We’re never going to return to the 1960s and 1970s where we had infinite amounts of cheap energy.” Strong adds that the consideration of utility demand charges at peak periods of energy use, as well as the growing unreliability of the electrical grid, has led to an increased cost-effectiveness for PVs. “This is a glimpse of the future, and it’s not an aberration.”

The availability of subsidies, as either a tax credit or an energy rebate, still compels many a decision to incorporate PVs into a project. Solar consultants and researchers, however, argue for a larger view, positioning PVs as a significant component of an overall energy-efficiency design strategy. Behind the scenes, manufacturers and university and government research teams endeavor to develop new PV technology, seeking to find PV solutions that balance energy performance with aesthetic value—something lacking in many past solar installations. Since the PV industry shares silicon production with the semiconductor industry, all of this increased development occurs with the backdrop of a serious silicon supply shortage—though the industry considers it merely a hiccup. Regardless of the issues, the building PV industry in 2006 is positioning itself to expect rapid growth in demand and technology in the coming years.

Research drives the industry

Although solar research in European countries and Japan has contributed significantly to the development of those countries’ photovoltaic markets—the largest in the world owing to widespread government incentives—the U.S. funds a number of research projects through the Department of Energy to push PV technology in new directions. The U.S.’s National Renewable Energy Laboratory (NREL) in Golden, Colorado, coordinates many research efforts, acting as a clearinghouse of information and approaches to the development of PV technology, either through partnerships or its own projects.

Photovoltaic technology consists of four different typologies, which together account for nine different varieties of PV cells either in production or development (refer to the NREL chart for the best research cell efficiencies). The most common are single crystal and multicrystalline silicon cells, which the NREL estimates to represent more than 90 percent of the market. These cells, combined into modules, function as additional components to buildings: awnings, canopies, or rooftop arrays. Multijunction concentrators simply stack up these cells; a laboratory cell developed by Spectrolab and the NREL achieved an efficiency of 34 percent in direct sunlight, by far among the highest efficiencies recorded outside of purely theoretical models. Efficiency is measured as a ratio of the cell’s actual electrical energy output to the available sun energy incident on the device. Commercially available cells can achieve anything from 5 to nearly 20 percent.

click images to view them larger The National Renewable Energy Laboratory charts photovoltaic cell efficiencies for developments worldwide (left). Research and corporate development have led to a rash of new photovoltaic products, beginning with BP Solar’s conventional silicon cells (opposite, top left) and Shell Solar’s modules (opposite, bottom right). Newer technologies include thin-film photovoltaics, such as the organic cells in development at Georgia Tech (top middle); United Solar Ovonics’ Uni-Solar product that rolls onto a building’s roof (top right); and Kyocera Solar’s photovoltaic roof shingles that have caught on with residential home builders in California (near right). Graph: Courtesy The Nrel and the Mrs bulletin; Photography: Courtesy BP Solar (top left); Georgia Institute of Technology (top middle); united solar ovonics (top right); kyocera solar (bottom left); shell solar (bottom right)

Industry has also embraced other thin-film technologies. Shell Solar developed a copper indium diselenide (CuInSe2) module that achieved a 13.5 percent efficiency last year. Cadmium telluride (CdTe) thin-film cells, which achieve efficiencies around 15 percent in laboratories, are still in development and aren’t available commercially for large-scale use. A drawback of CdTe cells is the high toxicity of cadmium, which could pose environmental issues in the event of a fire.

All of these technologies generally depend on expensive raw materials and a relatively high manufacturing cost. The price of silicon rises and falls with demand in the semiconductor industry, which explains the current lag in supply for the PV industry. This lack of supply is a very real issue; United Solar’s Guha says his company is sold out of product for the rest of 2006. These considerations have motivated research development of organic photovoltaics, which could be synthesized with chemicals any number of ways and are significantly thinner than even thin-film silicon cells.

Dave Ginley, an NREL researcher, focuses on organic PV cells, which don’t integrate silicon—a material with a finite production supply—in their production. While Ginley finds organics’ infinite supply appealing, he thinks their true promise is the flexibility of their application. The bond structure of a conventional silicon molecule is a predictable crystalline structure, whereas organic molecules have a “hair” chain sprouting along the sides of their double-bonds. This hair can be tinkered with, in a way that adds or removes electrons, to develop a molecule with the exact properties you want. “This isn’t to say we know what those exact properties are,” Ginley says. “If we did, we’d be done, and we’re not.”

Organic PVs, though at least 10 years away from commercial application, offer the possibility of design considerations such as fabric structures and basically any surface that can withstand a printing process. Organic PVs also have the potential to lower costs, since a single metric ton of a petrochemical could supply all of the organic solar cells you would ever want to make. Where the thickness of silicon-based cells are measured in micrometers, organic PVs can be reduced to a few hundred nanometers, similar in production and use as plastics.

click images to view them larger Atelier Ten is working with Pelli Clarke Pelli Architects in New York on the design of the Business Instructional Facility at the University of Illinois in Champaign-Urbana (near right). Atelier Ten developed a sun path diagram (far right) to chart the sun’s angles of incidence across the building’s surface in order to gauge the effectiveness of installing 4,000 square feet of photovoltaics on a section of the roof (below). Photography: Courtesy Pelli Clarke Pelli Architects (top left)

Among the remaining challenges for organic PV researchers, hastening higher efficiencies is key to the technology’s success. Currently, efficiency hovers between 5 and 6 percent, while organic PV’s theoretical efficiency of 24 percent competes directly with silicon.

NREL’s Ginley thinks the greatest potential for organics lies in the organic LED (OLED) industry, which could easily adapt itself to become a producer of organic PV products. “The ultimate would be OLEDS and solar cells where you could have a skylight that would make power by day and then at night make light,” he says. Another advanced organic PV development has been spray-on technology, where PV cells are incorporated into a liquid that could be applied to a building surface. While the lifespan is short, Joop Schnoonman, director of the Delft Centre for Sustainable Energy in the Netherlands, has developed an aerosol spray-on PV cell using a mix of copper indium sulfide and titanium dioxide that has led to a longer lifespan and an approximate 5 percent efficiency. “We are trying to make a cheap production technology with cheap materials,” Schnoonman says, adding, “Any shape of surface could be sprayed.” Solar industry researchers and manufacturers view the flexible application of PVs to buildings as key to achieving widespread use in architecture.

Building-integrated photovoltaics take off

The limited product applications and the perception of PVs as an additional cost to a building, as well as the owner-driven demand that PVs have a “payback” associated with their installation, has led many solar consultants to push toward building-integrated photovoltaics. “In a first-class building, the cost of the facade is significant, so the cost of putting photovoltaics on it versus granite or another material may actually be less,” says Andrew Wilkinson, with Arup’s Newcastle office in England. He adds that the photovoltaic industry’s biggest challenge lies in producing panels and systems attractive enough for architects to want to incorporate them into their buildings. “The question we’re asking now is, if you’re given a free hand, what sort of module would you like,” Wilkinson says.

While traditional PV installations—rectangular modules mounted to secondary roof structures—continue in wide use, in the past few years, a rash of new options has hit the market to address the aesthetic issues of PV use. Photovoltaic shingles, meant to replace conventional asphalt or concrete roofing shingles, have wide application in the residential market. Many manufacturers offer this type of product.

Kyocera Solar, a dominant Japanese company, has targeted the California market, which practically all solar consultants and manufacturers consider the third-largest market for PVs behind Japan and Germany, mainly owing to state government incentives. Kyocera offers the MyGen Meridian product, a polycrystalline silicon cell from Japan integrated into a product that seamlessly ties into concrete shingle roofs. Jesse Henson, based at Kyocera’s U.S. headquarters in Scottsdale, Arizona, said building-integrated PVs owe their cost-effectiveness in large part to their ability to take advantage of existing labor on a job site. “We also need a more streamlined utility connection protocol,” Henson says. “Now, each utility or municipality is different, so very few PV installers operate on a national level.”

click images to view them larger BP Solar worked with Sheppard Robson architects in England on the University of East Anglia’s Zuckerman Institute for Connective Environmental Research, which included a combination of single crystal and polycrystalline silicon cells laminated in glass to meet nearly a third of the building’s electrical demand. Photography: Courtesy BP Solar

Advising nonresidential clients to invest in a large-scale PV installation should be part of an overall energy-efficiency design strategy, according to Nico Kienzl, a building energy consultant in Atelier Ten’s New York office. “In most projects, it makes more sense to install an advanced lighting and control system, a better HVAC system, and a good building envelope, and then, if you have money to spare, you could install photovoltaics,” Kienzl says. However, placing a PV installation in atrium glass or on a canopy can signify a client’s commitment to sustainability, which Kienzl says often rightly overrides decisions based purely on payback. “The danger is that people will view PVs as a technology fix, when PVs alone are never going to get us there.”

Kienzl begins a PV design proposal by creating a sun path diagram for the building. This diagram helps explain where it makes the most sense to install PVs on a building by indicating shadows from neighboring structures and zones with the highest incidence of sunlight during various times of the year. This information guides Kienzl in recommending building surfaces for PV use, as well as the most appropriate angle for PVs if they are installed on canopies or awnings. Determining what surface to use on a building exterior can sometimes run aground of warranty issues, since an awning supplier and installer may not certify the product if a PV contractor has affixed modules to them. Kienzl says any PV installation is often, if not always, an intense collaborative effort between the PV manufacturer and the design team, though this doesn’t always need to occur during the initial construction of the building. “PVs are a great technology because the cells can always be added later,” Kienzl says, noting that while only 5 percent of his projects contain PV installations, the majority of his clients consider them for their buildings.

Economics of photovoltaics

Time and again, economic factors contribute to the decision for or against PVs. Kyocera’s Henson says the way utilities price electricity today ignores the externalities, such as environmental damage, of its true costs, which keeps PVs from becoming competitive with conventional energy-producing technologies. Nevertheless, Henson, like many in the PV industry, views this as a short-term problem in light of decreasing fossil-fuel supplies and increasing energy costs. The biggest market change, Henson says, occurred when governments created incentives for grid-connected PV installations, which helped shift the balance of demand for PVs away from their traditional market of off-grid applications for isolated buildings and infrastructure such as highway call boxes and signs.

Widespread government initiatives like those in Germany and Japan offering incentives for rooftop residential solar installations account for the key differences in the size of these markets compared with the U.S., and underscore the reason Japanese electronics firms dominate the PV cell production industry. PVs are now so standard in Japan, incentive programs have been phased out.

Ray Noble, with BP Solar in England, said government subsidies have helped spur development of rooftop and stand-alone installations, but haven’t significantly encouraged building-integrated PVs. “This is turning into a real mass-production industry, though, so that will push down prices,” Noble says, adding that he expects more oil companies to enter the business once PVs become directly competitive with nonrenewable energy sources. Noble also points out that since demand for silicon in the PV industry has eclipsed that of the semiconductor industry, which requires a higher grade of silicon, it’s likely PV-grade silicon will go into production and further reduce costs.

Noble says many European countries, like Germany and Spain, have developed building-integrated photovoltaic incentive programs to lessen the aesthetic consequences of conventionally mounted rooftop and stand-alone systems. In cities such as London and elsewhere, he says, lack of space practically necessitates building integration of PVs.

The Bush administration has proposed the Solar America initiative, which would infuse nearly $150 million (an increase of $65 million from last year’s budget) into research and production programs, but its adoption as policy has not been assured. While NREL’s Ginley thinks research funding levels fall short in the States, he sees smaller companies making huge strides thanks to a ready supply of investment capital. “In a sense, PV may very well be the next large area of technology,” Ginley says.

Gary Gerber, of Sun Light and Power in Berkeley, has been installing small residential rooftop PV modules since the 1970s, so he’s seen the industry rise and fall with the times. This year, Gerber says they’ve had so much demand for their systems, which rely on PV cells from Mitsubishi, they can’t always ensure the availability of product. Gerber, a board member of the California Solar Energy Industry Association, says the state’s market has risen again thanks to the California Solar Initiative, a state-funded program that will pump $3.2 billion in incentives for PV installations over the next 11 years. “In 10 years, I really don’t think we’re going to need incentives,” Gerber says. “People who don’t use solar by then will be an oddity.”