As the solar module manufacturing industry continues to mature, we’re seeing ongoing innovation that’s increasing the efficiency of solar PV, specifically the efficiency by which it converts solar radiation into electrons. That improving efficiency has implications for solar PV, likely serving to drop system costs and make distributed solar financially and logistically accessible to an even larger base of potential customers.
Though solar cell technologies vary widely, most fall into three categories: thin film, polycrystalline, and monocrystalline. In 2012, thin film’s market share was 11 percent compared to crystalline silicon’s (c-Si) 89 percent (poly and mono combined), according to GTM Research earlier this month.
Thin film solar panels, which tend to be lighter and cheaper than “traditional” solar panels made of silicon (though not most recently), can be composed of a variety of PV materials, including cadmium telluride, and have the lowest efficiency of the three categories, hovering around 12 percent for commercially produced modules. Historically, this lower efficiency has required larger areas of solar PV to achieve a given generation capacity, and so thin film has gained the most traction for land-based installations.
However, recent advances, including improving efficiencies and decreasing module and balance of system costs—as well as some desirable properties, such as resistance to efficiency degradation under hotter conditions (e.g. on top of a house in Arizona in summer)—have made thin film attractive for certain rooftop applications as well, primarily large commercial rooftops. Thin film companies have mostly struggled in recent times, but First Solar remains a significant market force, especially with utility-scale installations.
Polycrystalline silicon solar modules—familiar blue or black rectangular panels covered in glass—offer a step up in efficiency, in the realm of 15 percent. This better efficiency, coupled with mid-range price per module, makes them more attractive for modestly space-constrained applications, such as larger rooftops.
Monocrystalline silicon boasts the highest efficiency rates, in the realm of 18–20+ percent, and its performance doesn’t degrade as much as polycrystalline under warmer conditions, but also costs the most. This technology is the most popular for rooftops where available area is at a premium.
Newer technologies, such as multi-junction solar cells, are demonstrating even higher efficiencies, but they currently do so at significant added cost. Meanwhile, recent advances in identifying potential organic materials for printable photovoltaic cells for thin film applications are promising to make that technology especially cost-effective, even while boosting its efficiency.
The result is a general rule of thumb: as efficiency goes up, so does cost, while required surface area decreases. But a new trend may soon emerge: as researchers and manufacturers pioneer ever-higher levels of solar PV efficiency while simultaneously decreasing cost, we’ll be able to pack more solar generation capacity into a given area (appealing for homeowners with limited rooftop space) or downsize the area requirement for a given capacity, ultimately reducing the total number of required solar modules and overall physical system size.
Hardware costs for some of the best quality China-manufactured modules have already dropped by more than half in the last three years. Today, hardware costs comprise just 40 percent of the total cost of a rooftop solar PV system. (Balance of system costs now make up the majority of solar system costs, which is why RMI’s Simple BoS project is working to decrease those costs.) Yet, efficiency gains may help to cut that number further.
Innovations at the Threshold of Commercial Application
For some new technologies such as that of V3Solar, innovations are focused on a new style of solar module. In the interest of exploiting as much sun energy as possible, V3Solar employs a spinning, cone-shaped solar device instead of flat panels. Spinning allows energy collection using flashes of light instead of static glare, which avoids cooking the PV cells. And since PV cells lose some of their efficiency at higher temperatures, keeping the cells cooler suggests they will maintain better efficiency and last longer.
V3Solar’s principle is simple: concentrate a larger area of light onto a smaller area of PV cells. Since much of the cost is in the PV cells, and not in the significantly less expensive lensing that reflects the light, V3Solar hopes to boost solar efficiency while dropping the cost per Watt. The company claims its system can reach the low price of $0.42/Wp while achieving an efficiency rate of 24 percent.
In essence, V3 is attempting an end run around the thermal issue, which also plagues the super-efficient but very expensive multi-junction solar technologies that similarly rely on concentrated solar radiation to coax out maximum efficiency.V3Solar’s cones will not be commercially available for at least another year, but the company is anticipating multiple utility-scale installations of 10 MW and more. Whether solar project investors will be attracted to V3’s technology, particularly V3’s risk considerations of moving parts and long-term performance uncertainties, is as yet unknown.
One company that, like V3Solar, has developed a three-dimensional solar module design—but without V3’s moving parts—is Sphelar Power. Unlike conventional flat solar cells, Sphelar has developed micro spherical solar cells, like a bead, that can receive light from any direction. Combined with a hemi-spherical dome lens, the company’s Sphelar Dome promises to better harvest light early and late in the day when the angle of the sun’s rays is less than optimal for traditional flat panels. Sphelar claims such technologies improve efficiency, such as on cloudy days and in high-latitude regions.
Solar Research Innovation Breaking Promising Efficiency Ground
While solar incumbents such as monocrystalline manufacturer SunPower Corporation and thin film manufacturer First Solar and startups such as V3Solar push the commercial boundaries for solar PV efficiency, researchers are likewise pushing solar’s overall efficiencies into new realms.
For example, the U.S. Department of Energy’s National Renewable Energy Laboratory has achieved 44 percent efficiency. They did so by multiplying the power of the sun by almost 1000 and focusing it on multi-junction solar cells. A Princeton research team hopes to vault past 44 percent en route to potentially crossing the 50-percent efficiency threshold. Their technology uses a 30-nanometer-thick gold mesh that reduces the amount of light that is reflected and lost, thus acquiring more light in total.
The Niels Bohr Institute in Denmark has produced one of the most recent research breakthroughs in solar efficiency. Their work with nanowires—and uncovering some of the unique ways nanowires interact with incoming sunlight—promise to raise the ceiling, not just of commercial and research solar efficiency, but of solar’s theoretical maximum limit. Researchers at Stanford University have accomplished a similar potential breakthrough, though by vastly different means. They’ve developed the equivalent of a solar turbocharger, a way to harvest both light and heat and turn both into electricity, thus overcoming the heat-equals-solar-degradation problem plaguing much of conventional solar PV.
Efficiency’s Ripple Effect
These increases in solar PV efficiency are exciting purely as examples of technological innovation. But they also have a potential ripple effect that could help to lower both the hard costs of actual modules and the hard and soft balance of systems costs associated with a new solar PV installation. As modules become more efficient, fewer panels are needed to produce the same amount of energy. Fewer panels means a smaller physical system size, smaller racking system, a potential opportunity for decreased installation time, decreased roof or land area requirements, etc. Also, if these new module technologies are coupled with additional whole system design considerations, such as RMI is working on in the Simple BoS project with Georgia Tech Research Institute, the total savings could be exponential.
RMI is hard at work to reduce solar’s soft balance-of-system (BoS) costs, which represent the majority, and growing, portion of total solar install costs for residential and small commercial systems. Soft BoS costs absolutely must be driven down to make solar competitive with utility power in more locations and utility power pricing scenarios. Nevertheless, the aforementioned exciting developments in efficiency gains can provide a significant aid to overall cost competitiveness.
First Image courtesy of First Solar. Second Image courtesy Shutterstock.com