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

New Breakthrough with Perovskite Solar Cells

pero

As you’re probably already aware, perovskite solar cells have the greatest potential of being the most prominent source of solar energy in the near future. They’re cheap to make and flexible enough to be applied to most any surface.

And now a team of researchers from the University of New South Wales (UNSW) in Sydney, Australia has made a breakthrough by creating the biggest perovskite solar cell so far, and setting a new efficiency record with it.

According to them, they have managed to achieve a 12.1 percent energy conversion efficiency rating for a 6.3 sq in (16 sq cm) perovskite solar cell. This cell is also about 10 times larger than any existing high-efficiency perovskite cell. The team also managed to achieve 18 percent efficiency for a 0.5 sq in (1.2 sq cm) single perovskite cell, as well as 11.5 percent for a 6.3 sq in (16 sq cm) four-cell perovskite mini-module. They are also confident that they can achieve a 24 percent efficiency within a year or so.

These cells get their name from the crystals they are made of, which are grown into a structure called perovskite. Due to their special characteristic, such as the smooth layers of perovskite with large crystal grain sizes, these cells can absorb more light than solar cells made of silicon. They are also much cheaper to produce.

Perovskite cells can also be created in different colors, or be transparent due to their chemical composition. This means that they can be used to cover virtually any surface, such as the sides or roofs of buildings, gadgets, cars and even windows.

One of the major downsides of perovskite solar cells is the fact that they are not very durable. However, the team believes that they can also improve their durability as they strive for even higher levels of efficiency.

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

Update on the commercial prospects of perovskite solar cells

National renewable energy laboratory NREL

In our worst Seinfeld impersonation voice we ask, “what’s the deal with perovskite solar cells?” The National Renewable Energy Labratory (NREL) answers us by noting that a strategy for producing stable and commercially available perovskite solar cells (PSCs) has been proposed by Kai Zhu and Keith Emery in collaboration with Nam-Gyu Park (Korea), Michael Grätzel (Switzerland), and Tsutomu Miyasaka (Japan).

Solar cells using a halide perovskite with an organic cation such as methylammonium and/or formamidinium have attracted attention because of their excellent photovoltaic performance. Over a period of just a few years, their power conversion efficiency has rocketed to greater than 22 percent.

What is PSC?

However, PSCs face challenges to commercialization. Specifically, they have the following needs that must be addressed for the eventual success of this promising technology: 1) long-term stability, 2) a manufacturing method that can produce reproducible, hysteresis-free, high-performance devices, and 3) reliable device characterization.

Nam-Gyu Park of Sungkyunkwan University initiated this joint effort to provide solutions to these needs, and the authors proposed a strategy-to move toward stable commercial PSCs-that includes the following:

• Developing a reproducible manufacturing method that takes into account managing grain boundaries and interfacial charge transport
• Using electroluminescence as an effective metric or tool for evaluating PSC quality
• Realizing the importance of the design of device structures with interface engineering to yield performance that is stable and hysteresis-free
• Recovering and utilizing the lead in PSCs to address environmental concerns
• Ensuring the advance of practical applications through reliable device characterization.

The report

Details of the strategy are found in the paper, “Towards Stable and Commercially Available Perovskite Solar Cells,” published in Nature Energy.

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. The work at NREL is supported by the U.S. Department of Energy SunShot Initiative.

 

— Solar Builder magazine

UCLA promotes advances in perovskite solar cell commercial viability

perovskite solar cell

Yang’s team has conquered the primary difficulty of perovskite by protecting it between two layers of metal oxide.

UCLA professor Yang Yang, member of the California NanoSystems Institute, is a renowned innovator of solar cell technology whose team in recent years has developed next-generation solar cells constructed of perovskite, which has a decent efficiency converting sunlight to electricity.

Despite this success, the delicate nature of perovskite — a very light, flexible, organic-inorganic hybrid material — stalled further development toward its commercialized use. When exposed to air, perovskite cells broke down and disintegrated within a few hours to few days. The cells deteriorated even faster when also exposed to moisture, mainly due to the hydroscopic nature of the perovskite.

RELATED: Report: Perovskite solar cells show potential with efficiency improvement, lowering costs

Now Yang’s team has conquered the primary difficulty of perovskite by protecting it between two layers of metal oxide. This is a significant advance toward stabilizing perovskite solar cells. Their new cell construction extends the cell’s effective life in air by more than 10 times, with only a marginal loss of efficiency converting sunlight to electricity.

The study was published online Oct. 12 in the journal Nature Nanotechnology. Postdoctoral scholar Jingbi You and graduate student Lei Meng from the Yang Lab were the lead authors on the paper.

“There has been much optimism about perovskite solar cell technology,” Meng said. In less than two years, the Yang team has advanced perovskite solar cell efficiency from less than 1 percent to close to 20 percent. “But its short lifespan was a limiting factor we have been trying to improve on since developing perovskite cells with high efficiency.”

RELATED: Details on 11 new MOSAIC solar technologies that will receive government funding   

Yang, who holds the Carol and Lawrence E. Tannas, Jr., Endowed Chair in Engineering at UCLA, said there are several factors that lead to quick deterioration in normally layered perovskite solar cells. The most significant, Yang said, was that the widely used top organic buffer layer has poor stability and can’t effectively protect the perovskite layer from moisture in the air, speeding cell degradation. The buffer layers are important to cell construction because electricity generated by the cell is extracted through them.

Meng said that in this study the team replaced those organic layers with metal oxide layers that sandwich the perovskite layer, protecting it from moisture. The difference was dramatic. The metal oxide cells lasted 60 days in open-air storage at room temperature, retaining 90 percent of their original solar conversion efficiency. “With this technique perfected we have significantly enhanced the stability.”

The next step for the Yang team is to make the metal oxide layers more condensed for better efficiency and seal the solar cell for even longer life with no loss of efficiency. Yang expects that this process can be scaled up to large production now that the main perovskite problem has been solved.

— Solar Builder magazine