Module Evolution: What big-time PV improvements will boost panel efficiency?

Light Bulb Illustration

The solar industry is forever in need of constant innovation and scientific breakthrough. Even now, with PV capacity reaching record highs, prices continuing to fall and efficiencies inching up, more innovation is needed. A lot more. (Not to mention whatever fallout is felt in the module market following the Section 201 trade remedy.)

At Intersolar North America in July, Martin Keller, director of the National Renewable Energy Laboratory (NREL), told attendees that if new materials and new production methods don’t hit the market, solar will never make the impact we all think possible as a distributed energy source.

“What are some new materials we can combine with new manufacturing technologies?” he asks. “If you are really serious about manufacturing on a global scale, we need new methods and new materials.”

If you are reading this, we assume you meet Keller’s “really serious” criteria and thus would like an update on some of those new methods and materials on the horizon. As far off as Keller made 2017 technology seem from where it needs to be, we think there are enough smart people working on stuff right now that this challenge will be met.

Silicon Successors

NREL is at the forefront of renewable research and pushing innovation, and scientists there have developed a new perovskite ink with a long processing window that allows the scalable production of perovskite thin films for high-efficiency solar cells. Keller was excited about it and pointed to a chart that showed a severe uptick in efficiency compared to today’s cells.

The catch is perovskite solar cells have yet to move beyond the laboratory. The crystalline structure of perovskites must be carefully grown upon a substrate, which is normally done by laboratory-scale spin coating — a technology that can’t be scaled to large-scale manufacturing at this time.

“It’s years out from production, but you can see the increase in efficiency is a very steep slope, and then combine that with new technologies like inks and spray ons,” Keller says.

Over at Penn State, researchers are testing a prototype of a new concentrating photovoltaic (CPV) system with embedded microtracking that can produce over 50 percent more energy per day than standard silicon solar cells. CPV focuses sunlight onto smaller but much more efficient solar cells, like those used on satellites, to enable overall efficiencies of 35 to 40 percent. Current CPV systems are large — the size of billboards — and have to rotate to track the sun during the day. These systems work well in open fields with abundant space and lots of direct sun.

“What we’re trying to do is create a high-efficiency CPV system in the form factor of a traditional silicon solar panel,” says Chris Giebink, a Charles K. Etner assistant professor of Electrical Engineering at Penn State.

To do this, the researchers embed tiny multi-junction solar cells, roughly half a millimeter square, into a sheet of glass that slides between a pair of plastic lenslet arrays. The whole arrangement is about 2 centimeters thick and tracking is done by sliding the sheet of solar cells laterally between the lenslet array while the panel remains fixed on the roof. An entire day’s worth of tracking requires about one centimeter of movement.

“Our goal in these recent experiments was to demonstrate the technical feasibility of such a system,” says Giebink. “We put together a prototype with a single microcell and a pair of lenses that concentrated sunlight more than 600 times, took it outdoors and had it automatically track the sun over the course of an entire day.”

The researchers report that the CPV system reached 30 percent efficiency, in contrast to the 17 percent efficiency of the silicon cell. All together over the entire day, the CPV system produced 54 percent more energy than the silicon and could have reached 73 percent if microcell heating from the intense sunlight were avoided.

But (there is always a but) Giebink noted that major challenges still lie ahead in scaling the system to larger areas and proving that it can operate reliably over the long term. Insert sad emoji here.

While we wait for those new markets to scale and develop, there are a bunch of intriguing options that could boost efficiencies and bridge the gap.

Production Disruption

Rayton Solar

Rayton Solar wants to supplant the very way we cut silicon in the first place — a technique that hasn’t changed much since its inception in the 1950s. Cutting silicon with a diamond saw leads to a significant amount of sawdust because the process wasn’t originally concerned with reducing waste for large-scale production.

“We developed a process using ion implantation to cut our very thin pieces of silicon, and there is zero sawdust in the process, so it allows us to increase the yield of the raw silicon and get a 60 percent reduction in the cost to make a solar panel,” says Rayton Solar CEO Andrew Yakub.

Phoenix Nuclear Labs (PNL) has signed a long-term agreement to be the exclusive supplier of high-current proton accelerators to Rayton Solar to produce low cost, high efficiency solar panels. Under the terms of the agreement, PNL will deliver the first system to Rayton at the end of 2017, followed by several additional units in 2018 and 2019.

The Rayton process utilizes high current ion beams produced by the PNL technology to cleave thin layers of silicon with zero waste. The process uses 50-100 times less silicon than the traditional method. Because of this, Rayton can also use a higher quality silicon that is about 10 times as expensive.

“We are capable of making up to 100 times as many solar panels with the same amount of silicon that our competitors use to make just one panel,” Yakub says.

In a less radical direction, mono passivated emitter rear cells (PERC) have efficiency seekers excited, and advancements keep happening every day. Silicor Materials says that, in its first ever attempt, it has produced p-type mono PERC cells at approximately 20 percent efficiency, using 100 percent of its standard silicon feedstock. Silicor hopes its technology for manufacturing solar grade silicon provides the solar market with a simple solution to manufacturing the highest quality, highest efficiency solar cells of the future at a substantially lower cost than all other solar grade silicon manufacturing technologies on the market.

Sol Voltaics has taken a big step toward commercializing a new efficiency-boosting solar technology. Using its proprietary Aerotaxy process to manufacture PV nanowires, its SolFilm solution could boost solar module performance up to 50 percent at a low cost.

SolFilm consists of billions of gallium arsenide (GaAs) nanowires oriented facing the sun. The nanowires, each of which is a complete solar cell, convert high-energy sunlight directly into power. Gallium arsenide, previously seen in space and concentrated solar projects, has long held great potential for the mainstream solar industry, but its high fabrication costs have prevented economical fabrication of large solar panels.

Manufacturing nanowires with Aerotaxy dramatically reduces the required amount of GaAs and removes the need for a crystalline support wafer, significantly lowering material costs.

“The nanowires are grown such that the top and bottom of the wire have opposite doping profiles. This makes each nanowire a fully functional solar cell, with a pn junction along the length of the wire,” states Erik Smith, CEO of Sol Voltaics. “Whether used by module manufacturers as a single-junction, high-efficiency, low-cost solution or as a boosting technology, we believe SolFilm will usher in a new age of solar power efficiencies.”

Sol Voltaics just closed a record funding round of $21.3 million (following a $17 million investment last year). The new funding will be used to accelerate commercialization of the technology.

You Down with BIPV?

Forward Labs Solar Roof

This is the part of the modules section when we throw an obligatory mention to Tesla and its new, mysterious Solar Roof. Building-integrated PV tiles are not new, but like the cool kid who started wearing bell bottoms to school, Elon Musk has made them trendy again. Any casual conversation I have about the solar industry outside the office always leads to the layperson asking about Tesla’s Solar Roof. So, word is out.

The buzz for the industry is certainly a good thing, but those everyday homeowners might not get the best bang for their buck going with the Tesla Solar Roof. Online solar marketplace EnergySage ran numbers on comparative systems for a 3,000-sq-ft home in Southern California with a $200 monthly electric bill, as an example, and the results speak for themselves:

  • Standard PV system: $26,030; 13,000 kWh annual production
  • Tesla Solar Roof: $50,900; 10,000 kWh annual production

The real hook of the solar roof is how it replaces the roof itself. But if you add in a $20,000 cost for a roof replacement as EnergySage did (based on a Consumer Reports estimate of such a job for that house size), the non-solar roof is still a better value.

Put more simply, GTM Research determined that Tesla Solar Roofs produce about 6 watts per square foot, whereas a high-efficiency module would produce 19 watts per square foot. There is also a potential hang up with applying for ITC credits because not all of the shingles being installed will be solar shingles.

Anyway, we wouldn’t bet against Tesla making this concept happen as the costs become more competitive over time, but a bit more quietly, Palo Alto-based startup Forward Labs entered this space at the same time as Tesla, claiming to be 33 percent cheaper, more efficient and easier to install — 19 watts per square foot of energy density at about $3.25 per watt, installed in two to three days.

“The way we achieved such fantastic cost savings was fairly simple,” Zach Taylor, CEO and product architect of Forward Labs. “We use more affordable materials than our competitors and employ standard manufacturing processes. The roof’s installation process is simple and quick — we can install our system in half the time that other companies can. The benefit to homeowners is a return on their investment that cuts the usual solar payback time in half.”

Forward Labs uses a proprietary five-layer construction. A robust glass panel sits atop an optical layer, which cloaks the underlying black monocrystalline solar cells and enables eight possible color choices. These top layers are embedded over a galvanized metal form-factor that appears nearly identical to the non-solar portions of the roof.

“The colors of solar roofing products have always been muted or limited in choice for the sake of energy production,” says Reid Anthony, former CEO and president of precision optics company Kowa American. “Forward’s embedded optics have overcome these challenges, giving homeowners the freedom to have a solar roof in some of the most desired colors, without increasing the cost or sacrificing energy production. It’s a game-changer for both consumers and the solar industry.”

The solar roof not only weighs the same as a composite shingle roof, its sleek design also vents cool air under the solar cell layer, keeping operating temperatures down while maximizing cell efficiency.

“Although most of the technology has been developed in-house, we’re proud to have developed Forward’s panels with high-quality materials from LG, Valspar and other Fortune 500 companies,” says Taylor. “This will enable Forward to quickly establish a strong network of key supply chain partners.”

Tweaks on the Traditional

panasonic

Current technology still offers a ton of potential, especially with tweaks to traditional panel architecture. Here are four recent developments.

1. Maxim Technology, which we initially reported on to start the year in our Innovations Issue, is gaining momentum with its module optimization technology — a chip that is installed directly into the PV module instead of a diode. The installer can simply wire this system with a string inverter as they normally might and achieve full optimization, MPPT and rapid shutdown compliance.

The Maxim technology, over time, could change the value of high-efficiency modules too. Certain mono PERC modules, for example, are prone to hotspots, which can counteract their added efficiency value. Incorporating cell-level optimization would remove that issue.

2. The two leading thin-film solar manufacturers, First Solar and Solar Frontier, represent a combined manufacturing capacity of 4 GW. While they do not pose a short-term challenge to crystalline silicon players’ market dominance, ongoing innovations will ensure thin-film remains a significant player, according to Lux Research.

Of the two, First Solar is far bigger, with expertise in utility-scale systems and a new large-format module design that will help maintain its GW-scale presence in utility-scale systems, as deployment grows in emerging markets. Solar Frontier has gradually diversified its business away from its home market of Japan and is making steps toward a rooftop BIPV product.

First Solar’s further growth hinges on plant-wide adoption of its Series 6 module and achieving systems costs below $1 per watt. Solar Frontier’s future rests on its ability to move its success in the lab to commercial production, and a partnership with a storage provider to integrate a lithium-ion battery option with its residential systems.

3. In the add-on category there is PLANT PV’s new Silver-on-Aluminum paste. The goal here is providing a 1 percent increase in relative power output for c-Si solar cells via easy implementation with no added investment cost for cell producers. Silver-on-Aluminum paste provides cell manufacturers with the ability to print the paste directly onto dried aluminum film, allowing them to cover the entire back of the wafer with aluminum paste and obtain the beneficial passivation of a continuous aluminum back-surface field.

“For 20 years the industry has had to accept an efficiency loss from printing silver bus bars directly onto solar cells,” stated Craig Peters, CEO of PLANT PV. “Our Silver-on-Aluminum paste has been developed to directly address this problem and enable cell producers to eliminate these unnecessary efficiency losses in all conventional solar cells today.”

4. Incremental efficiency improvements continue from the traditional sources as well. Panasonic Corp. achieved a new leading output temperature coefficient for mass-produced silicon photovoltaic modules, at -0.258 percent /°C. This improves on the previous temperature coefficient by 0.032 points at the mass production level, highlighting the positive temperature characteristics of heterojunction solar cells and further improving Panasonic’s unique heterojunction technology.

Panasonic HIT modules, which boast an improved output temperature coefficient, will nearly halve the decline in the conversion efficiency, significantly increasing performance in high temperature settings.

Chris Crowell is managing editor of Solar Builder.

 

— Solar Builder magazine

Solar system costs continued to fall across all sectors in first quarter 2017 (utility leading)

solar system costs

The installed cost of solar power fell to record lows in the first quarter of 2017 because of the continuing decline in photovoltaic (PV) module and inverter prices, higher module efficiency, and lower labor costs, according to an analysis by the U.S. Department of Energy’s (DOE) National Renewable Energy Laboratory (NREL).

While utility-scale solar costs have declined nearly 30 percent, residential- and commercial-scale solar system prices have lagged behind at 6 percent and 15 percent reductions, respectively, according to a new report, “The U.S. Solar Photovoltaic System Cost Benchmark: Q1 2017,” by NREL’s Ran Fu, David Feldman, Robert Margolis, Michael Woodhouse, and Kristen Ardani. The report shows that the levelized cost of electricity (LCOE) benchmarks without subsidies for the first quarter of 2017 fell to between 12.9 and 16.7 cents per kilowatt-hour (kWh) for residential systems, 9.2-12.0 cents a kWh for commercial systems, 5.0-6.6 cents a kWh for utility-scale fixed-tilt systems, and 4.4-6.1 cents a kWh for utility-scale one-axis tracking systems.

The report estimates that the total installed system cost, which is one of the primary inputs used to compute LCOE, has declined to $2.80 per direct current watts (Wdc) for residential systems, $1.85 Wdc for commercial, $1.03 Wdc for fixed-tilt utility-scale systems, and $1.11 Wdc for one-axis tracking utility-scale systems.

Compared to the first quarter of last year, and using 2017 dollars, the benchmarks fell by 6 percent for residential, 15 percent for commercial, and 29 percent for utility-scale systems.

“The rapid system capital cost decline of solar PV systems, driven by lower module prices and higher market competition this year, demonstrates the continuing economic competitiveness of solar PV in today’s energy investment portfolio,” said Ran Fu, lead author of the report.

Vote here for the 2017 Solar Builder Project of the Year

These results suggest that the DOE’s SunShot Initiative, which was launched in 2011 to make solar cost-competitive with other forms of energy, has met its 2020 cost target for utility-scale solar systems three years early. The industry is more than 85 percent of the way toward achieving the 2020 commercial-scale and residential-scale solar cost targets.

“Detailed cost modeling and benchmarking are critical for tracking the progress of PV systems toward cost-reduction goals. Because our bottom-up cost modeling method quantifies cost categories with a high degree of resolution, the results can also be used to evaluate early-stage investment opportunities and assess regional LCOE,” Fu said.

The report highlights the importance of reducing the non-hardware, or “soft,” costs of solar, as soft cost categories are demonstrated in the figure below. As the PV module price has reached a new low level, the proportion from soft costs—such as labor and overhead costs—has grown. In the first quarter of 2017, soft costs accounted for 68 percent of residential system costs, 59 percent for a commercial system, and 41 percent of a utility-scale system.

Approximately 13.7 gigawatts (GW) of new PV systems were installed in the U.S. last year, with the largest share coming from 10.2 GW in the utility-scale sector. Nearly 45 GW of solar is installed in the U.S., accounting for about 1 percent of the nation’s electricity supply.

All costs are adjusted for inflation. NREL has produced the annual benchmarks since 2010. The full technical report as well as a presentation about the new results and a data file for this work can be downloaded at:

— Solar Builder magazine

Three ways solar energy is being underrated (and why this needs to change)

solar power stats

The solar industry always seems to be on the defensive politically, needing to constantly prove its worth on the grid compared to other electricity generating technologies. This makes some sense, being the newest kid on the block and requiring changes to “the way things have always been done,” but more and more evidence is being produced that indicates the paradigm should be flipped. Here are three key points.

Solar is surpassing nuclear.

The latest issue of the U.S. Energy Information’s (EIA) “Electric Power Monthly” reveals that renewable energy sources remain in a statistical dead heat with nuclear power, with each providing roughly 20% of the total. During the six-month period (January – June), renewables surpassed nuclear power in three of those months (March, April, and May) while nuclear power took the lead in the other three. In total, according to EIA’s data, utility-scale renewables plus small-scale solar PV provided 20.05 percent of U.S. net electrical generation compared to 20.07% for nuclear power.

EIA has acknowledged the neck-in-neck status of nuclear power and renewables and stated as much in a news release it issued in early summer. However, the agency simultaneously stressed its view that “nuclear will generate more electricity than renewables for all of 2017.”

But as pointed out by the SUN DAY Campaign, a non-profit research and educational organization, and the Nuclear Information and Resource Service (NIRS), while renewables and nuclear are each likely to continue to provide roughly one-fifth of the nation’s electricity generation in the near-term, the trend line clearly favors a rapidly expanding market share by renewables compared to a stagnating, if not declining, one for nuclear power.
Electrical output by renewables during the first half of 2017 was 16.34 percent higher than for the same period in 2016 whereas nuclear output dropped by 3.27 percent. In the month of June alone, electrical generation by renewable sources was 27.15 percent greater than a year earlier whereas nuclear output dipped by 0.24 percent.

In fact, almost all renewable energy sources are experiencing strong growth rates. Comparing the first six months of 2017 to the same period in 2016, utility-scale + small-scale solar has grown by 45.1 percent, hydropower by 16.1 percent, wind by 15.6 percent, and geothermal by 3.2 percent. Electrical generation by solar alone is now greater than that provided individually by biomass, geothermal, and oil (i.e., petroleum liquids + petroleum coke).

And on the capacity front, renewables long ago eclipsed nuclear power. For the first half of 2017, the Federal Energy Regulatory Commissions reports that renewables’ share of total U.S. available installed generating capacity is 19.70 percent compared to 8.98 percent for nuclear — i.e., more than double.

“Everyone loves a horse race,” noted Ken Bossong, Executive Director of the SUN DAY Campaign. “However, the smart money is now on renewables to soon leave nuclear power in the dust.”

“Nuclear power is in irreversible decline in the U.S., due to rising costs and failing economics of new and existing reactors, alike,” said Tim Judson, executive director of the Nuclear Information and Resource Service. “Last month’s cancellation of half the new reactors under construction in the U.S. means that gap is going to be wider than projected, and accelerating.”

Solar is more grid-friendly and economical long-term than natural gas.

We reported on this two weeks ago, but the Department of Energy conducted a big study on grid resilience and reliability, and while it couched some of the language, in our reading, natural gas did not look like a more appealing option for prudent political support.

The findings show that natural gas is a big reason that plants are being retired. It became so cheap, so fast that it quickly moved to the top of the generation list and displaced other sources. As a result, any volatility in natural gas price or supply leads to big issues: “Low natural gas prices are driving greater use of natural gas for electricity generation, which has made exposure to natural gas price risk related to availability a growing concern.”

And as the Rocky Mountain Institute stated:

Distributed energy resources can improve affordability, reliability, and resilience. The study summary suggests that states that retire baseload generators are “accepting increased risks that could affect the future affordability, reliability, and resilience of electricity delivery.” On the contrary, a growing body of evidence suggests that states and countries that replace old, costly fossil-fired generators with renewables, efficiency, demand response, and other distributed energy resources (DERs) have found that the opposite is true: that these resources can provide the same or better services at lower costs.

Solar capacity and adoption continue to beat estimates.

A new paper published in the Nature Energy journal, makes the a fairly significant observation (that probably should have been figured out by now):  solar energy has consistently outperformed the predictions made by assessment models going as far back as 1998.

The authors show that the International Energy Agency has repeatedly predicted growth rates for solar deployment that are anywhere from 16 to 30 percent lower than their actual rates end up being.

One reason these models have fallen short is how they fail to account for policies that have accelerated deployment, but the study notes that the costs of solar panels have also fallen faster than expected. Also the National Renewable Energy Laboratory (NREL) noted in its 2017 Annual Technology Baseline (ATB), that solar photovoltaic capital costs have declined and are projected to continue to decline.

So, why does this matter?

The researchers’ conclusion in the report illustrates why the current narrative for solar needs to be flipped to properly account for its current lofty status and future potential – because continuing to undersell it will leave us unprepared to make the right forward looking improvements to accommodate a new DER reality and to capitalize on its potential.

While it may seem like good news that solar is performing better than expected, underestimating its potential could pose some serious problems in the future, the researchers suggest — namely, that “decision-makers might treat [photovoltaics] too reluctantly,” they write in the paper. If policymakers are dismissive of solar’s future potential, they might fail to adequately prepare the grid for its continued expansion.

— Solar Builder magazine

Renewable energy project in Colorado draws interest from Department of Energy

The U.S. Department of Energy’s (DOE) National Renewable Energy Laboratory (NREL) is partnering with Panasonic Corporation and Xcel Energy to simulate and optimize the energy load profile of Peña Station NEXT, a planned 382-acre mixed-use development in Denver, Colo.

The project will employ the grid modeling capabilities of NREL’s Energy Systems Integration Facility (ESIF) while demonstrating URBANopt software, a buildings and district energy modeling tool currently under development at NREL. Through this project, NREL hopes to enable a cost-effective, scalable net-zero development infrastructure that has great potential for replication and adoption across the U.S. in future developments.

Pena station panasonic solar project

“The NREL partnership with Panasonic and Xcel Energy helps deliver on our shared vision for clean, affordable, and reliable energy systems at a pace and scale that matters for our society,” said Juan Torres, NREL’s associate laboratory director for energy systems integration. “As a national user facility, the Energy Systems Integration Facility at NREL is an ideal place for both Panasonic and Xcel Energy to analyze and optimize the project’s energy master plan before construction, in a way that benefits all involved.”

The project uses URBANopt to analyze the projected dynamic energy consumption of corporate office space, retail space, multifamily dwellings, a hotel, parking, and street lighting within the planned development. The data will then be integrated into Xcel Energy’s grid distribution modeling tools to create a cost-effective design framework that the utility and developer can use to integrate more distributed energy resources, such as solar photovoltaics or efficient building systems, and innovative rate structures into the development before it is constructed.

DOE prioritizes solar power plant performance with Power Factors funding

The partners are confident the project holds great promise beyond Peña Station NEXT’s borders. Xcel Energy will consider owning and operating the necessary infrastructure to achieve carbon neutrality, potentially expanding the offering to future communities in Colorado. Panasonic is similarly interested in how it might replicate and scale carbon-neutral districts and developments across its other current and future smart city engagements through Panasonic CityNOW. NREL will share its expertise and apply the lessons learned from this project to future developments.

NREL’s ESIF is a flexible and fully integrated lab space dedicated to testing residential and commercial smart energy technologies. It is a one-of-a-kind testing space that connects appliances, electric vehicles, a home, or even a community to an end-to-end energy ecosystem. By incorporating power generation, energy storage, and dynamic energy loads into the facility, researchers can simulate and optimize real-world conditions in a controlled laboratory environment.

NREL is the U.S. Department of Energy’s primary national laboratory for renewable energy and energy efficiency research and development. NREL is operated for the Energy Department by The Alliance for Sustainable Energy, LLC.

— Solar Builder magazine

NREL improves Perovskite thin-film solar cell production scalability

perovskite solar cell

Scientists at the U.S. Department of Energy’s (DOE) National Renewable Energy Laboratory (NREL) developed a new perovskite ink with a long processing window that allows the scalable production of perovskite thin films for high-efficiency solar cells.

Proven highly efficient at converting sunlight into electricity, perovskite solar cells have yet to move beyond the laboratory. The crystalline structure of perovskites must be carefully grown upon a substrate, which is normally done by laboratory-scale spin coating – a technology that can’t be scaled to large-scale manufacturing. The best devices fabricated using scalable deposition methods, which are suitable for future module production, still lag behind state-of-the-art spin-coated devices.

This research is supported by the DOE’s SunShot Initiative, a national effort to drive down the cost of solar electricity and support solar adoption.

Inside the breakthrough

To create a perovskite film, a coating of chemicals is deposited on a substrate and heated to fully crystalize the material. The various steps involved often overlap with each other and complicate the process. One extremely critical stage requires the addition of an antisolvent that extracts the precursor chemicals, and thus create crystals of good quality. The window for this step opens and closes within seconds, which is detrimental for manufacturing due to the precision required to make this time window.

NREL researchers were able to keep that window open as long as 8 minutes.

The formula for the precursor perovskite ink included a chlorine-containing methylammonium lead iodide precursor along with solvent tuning, coupled with an antisolvent, which could be deposited onto the substrate by either spin-coating or blade-coating methods. Both methods were tested and produced indistinguishable film morphology and device performance. Blade-coating is more attractive to manufacturers because it can easily be scaled up.

PV breakthrough: Thin-film solar cells can now be mapped in 3-D as they absorb photons

The researchers tested one precursor ink containing excess methylammonium iodide (MAI) and a second containing added methylammonium chloride (MACI). The MACI proved most effective in reducing the length of heat treatment the perovskites require, cutting the time to about a minute compared to 10 minutes for the MAI solution. The shorter time also should make the process more attractive to manufacturers.

Using blade-coated absorbers, NREL scientists made a four-cell perovskite module measuring about 12.6-square centimeters. Of that, 11.1-square centimeters were active in converting sunlight to energy and did so with a stabilized efficiency of 13.3 percent.

— Solar Builder magazine