Around the country, solar photovoltaic installations are sprouting on residences and commercial buildings. If Doug Neidich has his way, we’ll see many more of these, but of a different variety. Today, you mostly see conventional crystalline solar photovoltaic panels sandwiched in a rigid aluminum frame and mounted in a rack structure on the roof or a steel frame on the ground.
“Conventional photovoltaics are Model T technology. We gotta get more elegant,” Neidich said. As founder and president of Solarity in State College, Pa., he is pioneering a new form of thin-film photovoltaic based on nanotechnology, one that can be integrated with conventional building materials such as shingles, membrane roofs, and windows.
“You have to install conventional solar PVs after the fact now, after you’ve built the building,” Neidich said. “With nano, you integrate it into the design from the beginning. You can put the film anywhere you want.”
In explaining the solar trend, Peter Jansson, associate professor of electrical engineering at Bucknell University and a solar energy consultant, said solar energy use is increasing by 40 percent annually in the United States and achieving grid parity.
“System costs have radically declined over the last five years. All of a sudden, this is affordable by mainstream Americans,” Jansson said. With various incentives and tax credits, payback is typically five to 10 years but can go as low as two years.
In past years, solar power systems were mostly of the off-grid variety, with a battery for backup at night or when the sun didn’t shine. But now, the trend is toward grid-connected systems. With this, the electrical grid serves as a battery, and you pull power off the grid when you need more power than your solar system can generate, such as at night, and you send power to it when you generate an access. You can also have batteries as backup in case of an outage. This leads to the concept of net metering, which serves as an incentive to install a system that matches the power you use, a so-called net-zero system.
Although photovoltaic (PV) technology is mature, with commercial panels attaining over 20-percent conversion efficiency, opportunities remain to improve their performance and cost. Down the road, nanotechnology versions should come about that are lower in cost and higher in efficiency than conventional ones, resulting in a lower cost-per-watt ratio.
Lower cost comes by virtue of the fact that thin-film technology yields a thin, flexible final product that can be produced by an automated roll-to-roll process, similar to newspaper printing, versus the labor-intensive semiconductor fabrication methods required for crystalline panels.
To date, thin-film materials have mostly been packaged into conventional panels. This negates any significant weight savings because thin-film and crystalline modules use the same glass and framing construction. But Stephen Fonash, chief technology officer at Solarity, said, “With thin-film, the objective is to not need the big aluminum frame and have something that can be more easily integrated into roofing or siding.”
Greg Wilson, director of the National Center for Photovoltaics at the National Renewable Energy Laboratory, said, “When you ask what’s going to be the dominant technology, I really believe it’s going to depend on the application. There are going to be applications where the thin-films are best. The challenge for the thin-films is efficiency. They can’t get to the efficiency silicon has gotten, at least not yet.” This can make it difficult to get enough power for a building out of panels if available roof or ground space is limited.
Other hurdles remain for thin-film as well.
“Another problem is long-term reliability. Silicon has the best, most well understood degradation behavior over 30 years in the field. That’s a limit for thin-film, but one that could be solved with more research,” Wilson said. Without the sealed glass panels encasing them, thin-fllms are more susceptible to water intrusion. Conventional solar panels degrade over time as the adhesive layer between the glass cover and cell degrades from sunlight, causing them to lose about half a percent in performance a year. They typically last over 30 years and come with a 25-year warranty.
But on the plus side, Fonash said, “Thin-film solar cells will alleviate the problem of having them at an angle because the structure we’re working on accepts sunlight at a wider range of angles. They have the advantage of being lighter weight, more amenable to being integrated into building situations, and having a wider range of light acceptance.”
Solarity originated what’s known as the Light and Carrier Collection Management (LCCM) NanoCell Architecture for its thin-film design. For the absorber material, they use silicon, cadmium telluride, and copper indium gallium solenium (CIGS). Fonash predicted it will become readily available within five years with limited production coming in about a year and a half. They claim its efficiency will match or exceed that of crystalline panels.
The development of thin-film has led to a category known as building-integrated photovoltaics (BIPV). They blend with traditional roofing materials to form solar shingles, combining solar cells with slate, metal, fiber-cement, and even asphalt roofing. Hundreds of square feet of them together can generate enough electricity to power a whole house.
The main advantage is that it looks like a roof; it doesn’t look like you have PVs on the roof. Shingles are typically plugged into each other. There are only a couple of cells per shingle, so you have to have 20 or 30 shingles together before you get the equivalent of a module. Jansson pointed to another disadvantage.
“It also has much less efficiency because it’s actually on the roof, and it’s very difficult to dissipate the heat. With photovoltaic materials, the hotter they get, the worse they perform. There’s no place to dissipate the heat because underneath one of these roofs you have insulation," Jansson said.
Nonetheless, Wilson said, “Integrating PV cells into roofing materials is a big interest because you’d like to share the cost of this PV with the roof. As time goes on, more and more PV products will be successfully integrated into the roof.” Major players Dow Solar and Certainteed now offer solar shingles.
Another form of roofing that can adapt to thin-film solar is the membrane variety seen on flat roofs, often made of bitumen. Lightweight and low profile, it requires no supporting framework, which can penetrate or damage an existing roof. The ICOSUNTM PVL module consists of a flexible, thin-film amorphous-silicon PV cell that follows the shape and form of the roof structure and has a self-adhesive underside that bonds to the roofing membrane. Each strip has a connector box at the end, and these are connected to each other through conduit.
Onyx Solar is an example of a company that makes photovoltaic glass for windows, floor tiles and building skins. They can integrate it with other construction materials and features such as ventilated facades, skylights, canopies, curtain walls and balconies. These use mono-crystalline and poly-crystalline technologies and have connections similar to conventional panels. They make photovoltaic glass with a variety of options including different colors, gradient, and patterns as well as double or triple-glazed products. Variance in photovoltaic efficiency and light penetration enables multiple options for architectural design.
The cells are sandwiched between two sheets of glass. Photovoltaic glass is not perfectly transparent but allows some of the available light through. In environments where too much heat gets in with light, the reduced transparency can also save on air-conditioning costs.
Whatever type of PV panel is used on a building, an inverter converts DC power generated by the panel to AC power for the grid, matching the sine wave of the building current. Some panel arrays have a single inverter, known as a string inverter, while in other systems, each panel has its own microinverter on the back of it. Each type has its advantages, said Justin Charles, vice president of Lenape Solar in Sunbury, Pa.
“From a technology standpoint, microinverters are the best thing out there, but string inverters are cheaper,” Charles said. Microinverters allow you to monitor the performance of each panel, and if one fails, you only lose the output of that one panel. But you can access a central inverter easier because it lives in a building, typically a garage, utility room, or shed.
“Almost all the modules commercially available have a male and female connector for the plus and minus connection out the back of the panel. So they’re all designed to be easily installed in the field by the electrical contractor,” Jansson said. Panels can be arranged in an array in series, parallel, or a combination of the two, each with tradeoffs. In series, if one panel is blocked or doesn’t work, they all don’t work. But series uses less wire. Parallel requires extensive wiring to handle all the current.
Grid-tied solar energy systems are set up so they shut off when there is a grid power outage, to protect people working on the grid. This is one advantage of an off-grid system.
The popularity of solar energy systems has created a new breed of tradesperson with multiple skills.
“It is very rare in our industry for an electrician to just do electrical work. The same people do the roof work that do the electrical work. Solar installers have specialized training in many different facets of construction,” Charles said. “On rare occasions, they might partner with someone to do some of the work if it is beyond their scope. On a particularly large system, I have seen other installers bring in commercial electricians to do the final connections because the voltage and amperage was higher than they were comfortable dealing with.”
“Probably the best profession to become a solar installer is your typical electrical contractor,” Jansson said. “If they want to learn how to become a solar installer, they would probably need the least amount of training beyond what they already have.” Many installers are certified through the North American Board of Certified Energy Practitioners (NABCEP), but it’s not always required.
This adds one more piece to the puzzle that paints a rosy picture for electrical contractors wanting to get into solar PV. With solar installations increasing and thin-film technology adding to the mix, opportunities for electricians should continue to grow well into the future.